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CHEMISTRY RESEARCH AND APPLICATIONS

ACTIVATED CARBON SYNTHESIS, PROPERTIES AND USES

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CHEMISTRY RESEARCH AND APPLICATIONS

ACTIVATED CARBON SYNTHESIS, PROPERTIES AND USES

MASON HSU AND

ERICH DAVIES EDITORS


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Library of Congress Cataloging-in-Publication Data Names: Hsu, Mason, editor. | Davies, Erich, editor. Title: Activated carbon: synthesis, properties and uses / Mason Hsu and Erich Davies, editors. Other titles: Activated carbon (2017) Description: Hauppauge, New York: Nova Science Publishers, Inc., [2017] | Series: Series chemistry research and applications | Includes bibliographical references and index. Identifiers: LCCN 2017032657 (print) | LCCN 2017035516 (ebook) | ISBN 9781536123494 H%RRN | ISBN 9781536123487 (hardcover) | ISBN 9781536123494 (ebook) Subjects: LCSH: Carbon, Activated. | Absorption. Classification: LCC TP245.C4 (ebook) | LCC TP245.C4 A355 2017 (print) | DDC 661/.0681--dc23 LC record available at https://lccn.loc.gov/2017032657

Published by Nova Science Publishers, Inc. † New York


CONTENTS Preface Chapter 1

Chapter 2

ix A Comparison among Activated Carbons Prepared from Different Precursors Maria do Carmo Rangel, Sirlene Barbosa Lima, Alvaro Marcelo Porcel Padilla, Márcia Souza Ramos, Sarah Maria Santana Borges and Carlos Augusto Pires Environmental Applications of Activated Carbons: Synthesis and Applications in Adsorption of Organic Contaminants G. Ovejero, M. A. Uguina, A. Rodriguez, J. A. Delgado, J. M. Gómez, E. Diez, V. I. Águeda, S. Álvarez and J. García


1

49

vi Chapter 3

Chapter 4

Chapter 5

Chapter 6

Chapter 7

Chapter 8

Contents Mercury Adsorption from Aqueous Solution Using Activated Carbons Ninfa Marisol Zúñiga-Muro, Adrián Bonilla-Petriciolet, Didilia Ileana Mendoza-Castillo, Hilda Elizabeth Reynel-Ávila and Radamés Trejo-Valencia Surface Properties and Preparation Condition Optimization of Amination Bamboo/Lignite AC Guojie Zhang, Yongfa Zhang, Fuai Tian, Guoqiang Li and Ying Xu107

77

107

Polymer-Waste-Derived Nanoporous Carbon for Removal of Methyl Orange and Bromophenol Blue from Aqueous Solutions B. Tsyntsarski, I. Stoycheva, B. Petrova, T. Budinova, N. Petrov, A. Sarbu and A. Radu

141

The Preparation and Application of Activated Carbon for Gas Adsorption A. R. Hidayu

165

Dielectric Properties of Zinc Chloride-Castor Residue Mixtures at Microwave Frequencies Muhammad Abbas Ahmad Zaini, Siti Hajar Sulaiman, You Kok Yeow and Mohd. Johari Kamaruddin Adsorbents from the Residue of Waste Tyre Pyrolysis via Metal Hydroxide Activation Constance Joe Ondi and Muhammad Abbas Ahmad Zaini


185

203

Contents Chapter 9

Activated Carbon: A Potential Applicant For Solid-State Hydrogen Storage Amandeep S. Oberoi, Baljit Singh, Muhammad Fairuz Remeli and Navdeep Singh

Index

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217

231



PREFACE Activated carbons have been found a large variety of applications in several fields, such as chromatography, medicine, gas storage and environmental protection, among others. Most of these applications requires tailored physical-chemistry properties, regarding purity, particles shape, mechanical resistance, homogeneity, surface composition, specific surface area and porosity. Because of their especial properties, activated carbons have attracted increasing attention for several years. As supports and catalysts, they have been used in several reactions both in gas and liquid phases, such as hydrogenation/dehydrogenation, oxidation/reduction, decomposition of hydrocarbons, halogenation and methanation, among others. This book reviews the applications, preparation, properties synthesis, and uses of activated carbon. Chapter 1 - Activated carbons have been used in several fields, such in chromatography, medicine, gas storage and environmental protection, among others. Most of these applications requires tailored physicalchemistry properties regarding purity, particles shape, mechanical resistance, homogeneity, surface composition, specific surface area and porosity. Among them, the specific surface area, porosity and the surface composition are by far the most important properties, in applications concerning catalysis and adsorption. All these properties largely depend on the preparation method as well as on the precursor and thus can be controlled


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Mason Hsu and Erich Davies

during preparation. Aiming to obtain activated carbons with tailored properties for adsorption and catalytic applications, samples prepared from different precursors were compared in this work. For all cases, residues from agricultural and industrial activities were used as precursors in order to preserve the environment by the transformation of solid wastes to high value materials, such as activated carbon. Samples were obtained from residues of sisal fibers, exhausted sulfonic resin (in a petrochemical industry) and from coconut mesocarp. In the samples preparation, biomass was pyrolyzed and then activated under steam flow. The pyrolysis of residues of sisal fibers was performed in a pilot plant of fast pyrolysis, while the other precursors were pyrolyzed in a laboratory oven. The precursors and the samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and specific surface area and porosity measurements. The solids showed micropores and macropores, the sample obtained from resin showing the highest micropores volume and then the highest specific surface area. After iron impregnation, these solids were able to adsorb and oxidize methylene blue, a model molecule for dyes. No simple relationship was found between specific surface area and adsorption capacity, showing that the kind of functional groups determines chemisorption. The catalyst with intermediate value of specific surface area (prepared from coconut) was the most efficient adsorbent and the worst catalyst in oxidation. On the other hand, the catalyst with the highest specific surface area (prepared from resin) was the least efficient as an adsorbent and the most active in oxidation of methylene blue, suggesting that different functional groups are involved in adsorption and in oxidation. This catalyst was able to remove all methylene blue from a model wastewater, by combining adsorption and oxidation, being the most active to treat wastewaters. Chapter 2 - The use of lignocellulosic wastes as precursors of carbon materials has become an interesting alternative in the adsorption of organic compounds, due to their resulting excellent textural and chemical properties, promoting the binding interactions between the adsorbate and the surface activated carbon. Considering that the structural differences of the precursors play an important role in the creation of the porosity of the


Preface

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carbon, it is crucial to select an adequate precursor. It has been reported that sawdust, peach stones, olive stones, rice husks, fruit pulps, plant wastes, etc., which are mainly composed of cellulose and lignin, are suitable precursors for the synthesis of activated carbons via chemical activation. Additionally, earlier studies have shown that chemical activation by impregnation with phosphoric acid at moderate temperatures leads to activated carbons with high surface area and a medium-high degree of mesoporosity. These materials appear as good adsorbents because of their excellent textural and physico-chemical properties. It is known that the surface functionalization can change the reactivity and selectivity of a carbon surface, which plays an important role in the adsorption. The application in adsorption of these activated carbons was studied. Adsorption, since it is a non-destructive tertiary process, has been revealed as one of the most advantageous physico-chemical techniques in wastewater treatment processes. In the research practice, it is very important to find a material showing high binding affinity toward the contaminant, and high selectivity and adsorption capacity properties. Commercial activated carbons possess most of these features, since they show a desirable affinity to hundreds of organic and inorganic compounds. Since the pore diffusion seems to be the controlling mechanism in activated carbon adsorption, the use of commercial adsorbents is usually associated with high expensive and environmental undesirable regeneration operations. In this chapter, lignocellulosic-derived activated carbons obtained from peach stones and rice husk, showing mesoporous and macroporous properties, have been synthesized. These activated carbons have been tested in the removal of organic contaminants (as pharmaceutical, dyes, etc.) from water. The aim of the chapter is to compare the behaviour of the adsorbents, regarding the adsorption capacity as well as the kinetic performance, through the development of equilibrium and dynamic adsorption tests. Additionally, desorption tests using different eluents will be accomplished, in order to determine the recovery efficiencies for the contaminants. Chapter 3 - This chapter analyzes and discusses the synthesis and application of activated carbons for mercury adsorption. Specifically, the synthesis conditions of different activated carbons applied in mercury


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removal are reviewed. Physicochemical properties and adsorption capacities of a number of adsorbents are compared including some options for adsorbent regeneration. Chapter 4 - This chapter used bamboo char and lignite as raw materials to prepare the new material of amination bamboo/lignite activated carbon through carbonization and activation. It also investigated the influences of the preparation conditions on the desulfurization performance of the new carbon material. BET and XPS were adopted to carry out the physical and chemical structural characterization of the newly prepared carbon material. BET and XPS indicated that the pore structure of bamboo/lignite activated carbon through ammonia activation was similar to that through steam activation and the activated carbons after both activations contained carbon groups of the same variety. The difference between ammonia activation and steam activation lies in the two new nitrogen-containing groups in the carbon material after the ammonia activation: para-pyridine or para-nitrile group and amine, amine, amide, imide and para-pyrrole. After the desulfuration through simulation flue gas, protonation para-pyridine nitrogen or amine salt occurred on the bamboo/lignite activated carbon and the content of the introduced nitrogen groups decreased. After the regeneration of desorption SO2 activated carbon, the content of para-pyridine increased and the contents of protonation para-pyridine and amine salt decreased. These results indicated that the activity of bamboo/lignite activated carbon was related to the para-pyridine group introduced by ammonia activation. Studies on the preparation of activation conditions showed that the sulfur capacity of bamboo/lignite activated carbon increased along with the increasing activator concentration. The sulfur capacity increased first and decreased later along with the increasing activation temperature; and it increased along with the extension of activation time. The optimal activation condition is 8.5-14.5% ammonia concentration, 850C-950C activation temperature and 120 min-150 min activation time. Chapter 5 - Polyolefin wax, an industrial by-product from polyethylene processing at low pressure, is used to obtain activated carbon by thermochemical treatment and subsequent hydro-pyrolysis. The structure and surface properties of the activated carbon obtained are characterized by


Preface

xiii

different methods - N2 adsorption, IR spectrometry, and surface oxygen groups content. The adsorption of methyl orange and bromophenol blue from aqueous solutions by thus synthesized activated carbon was studied in a batch adsorption system. Langmuir model is applied to investigate the adsorption process. The activated carbon obtained from polyolefin wax demonstrates high adsorption capacity towards dyes - 106 mg/g for bromоphenol blue and 269 mg/g for methyl orange, respectively. The effect of pH on the adsorption was investigated. The obtained results show that the synthetic activated carbon produced from polyolefin wax can be successfully used for the removal of dyes from water solutions. Chapter 6 - Activated carbon (AC) is a carbonaceous matter originated from wood, coal, peat and biomass sources. AC is a predominantly amorphous solid that has an extraordinary large internal surface area, pore volume and pore diameter. AC is also known as the most effective adsorbent and has been extensively used. Most of its chemical and physical properties (i.e., surface area, fast adsorption kinetics, adsorption capacities) can be designed and adjusted according to the required applications, either for gas adsorption or liquid adsorption. Besides, the adsorption on activated carbon appears to be the most common technique because of the simplicity of operation since the sorbent materials can be highly efficient, easy to handle and in some cases can be regenerated. Basically, the structure of AC containing pores that is classified according to IUPAC and divided into three groups; micropores (pore size < 2mm), mesopores (pore size 2nm-50nm) and macropores (pore size > 50 nm). Usually for gas-adsorbing carbons, the authors used the most pore volume in the micropore and macropore ranges, whereas liquid-phase adsorbing carbons have significant pore volume in the mesopore range. The most common precursor used to produce AC is organic materials that are rich in carbon. These precursors will be converted into ACs because of their hardness and high strength in which are due to its high lignin, high carbon content and low ash content of the materials. The most frequently used methods for the preparation of activated carbon is carbonization of the precursors at high temperature in an inert atmosphere followed by the activation process. The activation process is subdivided into physical and chemical activation. Physical activation process comprises


xiv


treatment of char obtained from carbonization with oxidizing gases, generally steam or carbon dioxide at high temperature (400-1000oC). The porous structure is created due to the elimination of volatile matter during pyrolysis while the carbon on char is removed during activation. As for chemical activation, a chemical agent typically an acid, strong base or a salt that is impregnated to the precursors prior to heat treatment in an inert atmosphere. The pores are developed by dehydration and oxidation reactions of chemicals. Activated carbons are commonly used in gas purification, decaffeination, gold purification, metal extraction, water purification, medicine, sewage treatment, air filters in gas masks and respirators, filters in compressed air and many other applications. In this chapter, the application of activated carbon will be focusing more on gas adsorption. Chapter 7 - The conversion of electromagnetic energy of microwave into heat is associated with the dielectric properties of the materials. This chapter presents the role of zinc chloride solution on the dielectric properties of castor residue mixtures for microwave-assisted activation. The dielectric properties were measured using a coaxial probe attached to the vector network analyzer. Results show that the dielectric properties of the solidelectrolyte mixtures varied with frequency, temperature and fraction of zinc chloride in the samples. The loss tangent of the samples increased with increasing temperature, while the presence of zinc chloride enhances the loss tangent but decreases the penetration depth. The variations in dielectric properties thus instigate the need for multiple tuning of operating frequencies to sustain the uniformity of microwave heating. Chapter 8 - The residue of waste tyre pyrolysis is a promising candidate of activated carbon. This chapter highlights the preparation of activated carbons from the pyrolysis residue by metals hydroxide activation. The resultant materials were characterized according to pH, yield, specific surface area and surface functional groups, and were used to remove Rhodamine B dye solution. Results show that the activation using potassium hydroxide is better than that using sodium hydroxide in terms of specific surface area developed and the removal capacity of Rhodamine B. The highest surface area was recorded as 71.2 m2/g that renders a 42.6 mg/g maximum capacity. The adsorption capacity is directly related to the specific


Preface

xv

surface area, and the adsorption data can be well represented by the Langmuir model. Chapter 9 - Beside commonly known applications of activated carbon in numerous fields, it has attracted considerable amount of research attention as a medium for solid-state hydrogen storage (also known as electrochemical hydrogen storage). Hydrogen in solid-state could be stored either by physical adsorption (or physisorption) or by forming chemical bonds (or chemisorption). Activated carbon offers large internal pore surface area and high porosity that favors both physisorption and chemisorption. Other advantages of using activated carbon for electrochemical hydrogen storage are different pore sizes - macropores, mesopores, micropores and ultramicropores, low atomic weight and easy availability. The present chapter reports on experimental investigation on different grades of activated carbons, made from coal, for their electrochemical hydrogen storage capacity. The fabrication process of activated carbon-based solid electrodes is explained. The steps involved in testing of the fabricated electrodes for their electrochemical hydrogen storage capacity are given. The obtained hydrogen storage capacity of certain activated carbon electrodes is found to be above 1 wt% which is comparable with commercially available metal hydride-based hydrogen storage canisters, lithium-ion and lithium polymer batteries. The results pave a way forward towards commercializing activated carbon-based hydrogen storage electrodes for polymer electrolyte membrane fuel cell or PEMFC, and battery applications.



In: Activated Carbon Editors: M. Hsu and E. Davies

ISBN: 978-1-53612-348-7 © 2017 Nova Science Publishers, Inc.

Chapter 1

A COMPARISON AMONG ACTIVATED CARBONS PREPARED FROM DIFFERENT PRECURSORS Maria do Carmo Rangel1,2,3,*, Sirlene Barbosa Lima1,2, Alvaro Marcelo Porcel Padilla2, Márcia Souza Ramos1, Sarah Maria Santana Borges1 and Carlos Augusto Pires2 1

Instituto de Química. Universidade Federal da Bahia, Salvador, Bahia, Brazil 2 Escola Politécnica. Universidade Federal da Bahia, Salvador, Bahia, Brazil 3 Instituto de Química, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil

ABSTRACT Activated carbons have been used in several fields, such in chromatography, medicine, gas storage and environmental protection,


2

M. do Carmo Rangel, S. Barbosa Lima, A. M. Porcel Padilla et al. among others. Most of these applications requires tailored physicalchemistry properties regarding purity, particles shape, mechanical resistance, homogeneity, surface composition, specific surface area and porosity. Among them, the specific surface area, porosity and the surface composition are by far the most important properties, in applications concerning catalysis and adsorption. All these properties largely depend on the preparation method as well as on the precursor and thus can be controlled during preparation. Aiming to obtain activated carbons with tailored properties for adsorption and catalytic applications, samples prepared from different precursors were compared in this work. For all cases, residues from agricultural and industrial activities were used as precursors in order to preserve the environment by the transformation of solid wastes to high value materials, such as activated carbon. Samples were obtained from residues of sisal fibers, exhausted sulfonic resin (in a petrochemical industry) and from coconut mesocarp. In the samples preparation, biomass was pyrolyzed and then activated under steam flow. The pyrolysis of residues of sisal fibers was performed in a pilot plant of fast pyrolysis, while the other precursors were pyrolyzed in a laboratory oven. The precursors and the samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and specific surface area and porosity measurements. The solids showed micropores and macropores, the sample obtained from resin showing the highest micropores volume and then the highest specific surface area. After iron impregnation, these solids were able to adsorb and oxidize methylene blue, a model molecule for dyes. No simple relationship was found between specific surface area and adsorption capacity, showing that the kind of functional groups determines chemisorption. The catalyst with intermediate value of specific surface area (prepared from coconut) was the most efficient adsorbent and the worst catalyst in oxidation. On the other hand, the catalyst with the highest specific surface area (prepared from resin) was the least efficient as an adsorbent and the most active in oxidation of methylene blue, suggesting that different functional groups are involved in adsorption and in oxidation. This catalyst was able to remove all methylene blue from a model wastewater, by combining adsorption and oxidation, being the most active to treat wastewaters.

1. INTRODUCTION 1.1. Properties and Applications of Activated Carbons Because of their especial properties, activated carbons have attracted increasing attention for several years, being efficient in a wide range of


A Comparison among Activated Carbons …

3

applications, including environmental protection, fine chemistry, food processing, nuclear and military industries, medicine and catalysis [1-7]. As supports and catalysts, they have been used in several reactions both in gas and liquid phases [8-12], such as hydrogenation/dehydrogenation, oxidation/reduction, decomposition of hydrocarbons, halogenation and methanation, among others [13-15]. From several studies on the catalytic performance of activated carbons, many authors [10, 16-18] have found that the activity and selectivity largely depend not only on the specific surface area but mostly on the chemical composition of surface and on the pore size distribution. The kind and amount of oxygenated groups on the surface, for instance, were found to be responsible for the activity and selectivity of activated carbon in ethylbenzene dehydrogenation with carbon dioxide [10], nitrogen oxides reduction [19], methane decomposition [20] and phenol and dyes removal form wastewater [21, 22]. In addition, the groups on the surface are able to improve the metal dispersion, resulting in more active and selective catalysts. Guillén et al. [23], for instance, prepared mesoporous activated carbons from chemical activation of lignin with phosphoric acid and found that the high dispersion of small palladium crystallites (around 5 nm) was related to oxygenated groups on catalyst surface, generated during the activation step. These catalysts were highly active and selective in Suzuki reaction and in hydrogenation of organic compounds with double bonds, such as 3-vinyl pyridine,1-phenylcyclohexene and 2,4-dinitrochlorobenzene and others. Besides the catalytic properties, the chemical properties of activated carbon are related to the kind and amount of the functional groups on surface, which contain heteroatoms, such as oxygen, hydrogen and sulfur, among others. Although the kind and concentration of heteroatoms depend on activated carbon preparation, oxygenated groups are the most common because of the chemical affinity between carbon and oxygen. These functional groups play an important role on the chemical properties such as pH, hydrophilicity, acidity and basicity of activated carbons, affecting the adsorptive efficiency [24-26].


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M. do Carmo Rangel, S. Barbosa Lima, A. M. Porcel Padilla et al.

Regarding the physical properties of activated carbons, the most important for catalytic applications are crystallinity, porosity and specific surface area [27]. These properties are closely related to the random arrangement of irregular layers of carbon, giving rise to the typical porosity (microporosity), responsible for adsorptive capacity. It has been found [2830] that the layers are small, kneaded, with several structural defects and connected to each other to create a three-dimensional structure, generating different porosities, densities and hardness. Activated carbons differ from graphite, which shows an organized structure with parallel hexagonal planar layers bounded by van der Waals forces [28, 31]. As a consequence of the arrangement of carbon layers, activated carbons can exhibit micropores, mesopores and macropores, depending on the preparation method. The porosity plays a fundamental role on adsorption and on catalysis of molecules of different sizes. The micropores are responsible for adsorption and catalysis of small molecules while mesopores and macropores can adsorb and catalyze molecules of higher molecular weight, such as dyes. Pores with different sizes are responsible for the high specific surface area of activated carbon, which can overcome 2500 m2 g-1, being associated to a pore volume of 1.5 cm3 g-1 [32]. Micropores often produce the highest values of specific surface areas (600-1900 m2 g-1) while mesopores and macropores produce lower values (20-70 and 0.5-2 m2 g-1, respectively). Commercial activated carbons often show specific surface areas between 800 and 1500 m2 g-1, but higher values can be obtained depending on the preparation method under controlled conditions.

1.2. Preparation of Activated Carbons Activated carbons can be prepared by different methods but all of them can be included in one of the two following categories: physical and chemical methods. The first one involves a physical (or thermal) activation that is often performed in two stages at high temperatures under inert atmosphere. The other method involves a chemical activation, which



5

consists of a step of impregnation of the starting material with a dehydrating agent, followed by heating at low temperatures. Regardless of the kind of activation, the starting material is first pretreated by rinsing, drying and milling and then activated, as shown in Figure 1. During pyrolysis, the precursor is decomposed at high temperatures releasing water, carbon monoxide and dioxide and organic compounds, including aliphatic acids, carbonyls and alcohols. As a result, the C/O and C/H ratios increase and the carbon structure (composed of cyclic and mainly hexagonal structures in a random arrangement) remains [29, 30, 33]. The microporosity of activated carbon is developed during this step, due to loss of volatiles and to the random arrangement of carbon layers. However, during this process, the micropores are often blocked by tar and other decomposition products. To restore the porosity of activated carbon, another step (activation) is performed to remove these undesirable compounds.

Figure 1. Steps of activated carbon preparation.

The activation process is the fundamental step for obtaining activated carbon with improved physical and amphoteric properties [30]. It consists in heating the solid coming from pyrolysis (carbonization) to promote secondary reactions thus increasing the specific surface area. For this purpose, the solid goes on gasification (physical activation) or on dehydration (chemical activation), as shown in Figure 1.


6


Figure 2. Steps of activated carbon preparation by chemical activation.

In chemical activation (Figure 2), the sample is impregnated with an activating agent and then carbonized. The activating agents improve the porosity of solid by dehydration and degradation reactions, under lower temperatures as compared to gasification [34]. Several compounds have been used as activating agents such as zinc chloride, hydrogen peroxide, sodium hydroxide, nitric acid, phosphoric acid, potassium sulfate, potassium carbonate, potassium hydroxide, iron chloride, calcium chloride and sulfuric acid, among others. The precursor to activating agent mass ratio should be carefully chosen since it affects the porosity of the final solid, especially the pore size [32]. Moreover, changes on the chemical surface are produced, modifying the hydrophilicity and improving the adsorptive efficiency of the solid. On the other hand, physical activation (Figure 3) involves the use of oxidizing gases, mainly carbon dioxide and steam, at temperatures (800 to 1000 ºC) higher than carbonization or pyrolysis. However, gasification is often performed at a lower range (600 to 800°C) to reduce operating costs [35]. During this process, the most reactive carbon atoms (the most unsaturated ones) are eliminated as carbon monoxide. This selective loss of carbon atoms modifies the microcrystalline carbon structure, leading to the creation of voids and resulting in a microporous material [36].



7

Figure 3. Steps of activated carbon preparation by physical activation.

Activated carbons can be prepared from several kinds of raw materials both from agriculture (wood and biomass) and polymers, among others [37, 38]. However, activated carbons for removing pollutants from wastewater have been mostly prepared from agricultural residues, especially those coming from wood residues, which have shown high adsorption capacity after activation, being able to remove pollutants of different molecular sizes [38]. In recent years, many different vegetal biomass residues, such as coconut husks, seeds and cakes from biodiesel production process have been studied as raw materials for the preparation of activated carbon [22]. Polymeric residues have also been used for producing activated carbon by pyrolysis at high temperatures, followed by heating under non-oxidative atmosphere. The obtained activated carbons showed high degree of purity, high electrical conductivity and high resistance to abrasion and compression [8, 37, 39, 40]. Regarding polymers as starting materials, styrene and divinylbenzene resins have been used to produce activated carbon with a wide variety of functional groups on the surface and with controlled porosity, specific surface area and average size of spherical particles. In these cases, spherical activated carbon with several sizes can be obtained. The most important advantage of spherical activated carbon over granular


8


or fiber-like is the low resistance to liquids and gases diffusion in fixed bed reactors, due to the homogeneous stacking in the bed [10, 21, 41]. Among the different biomasses often used to obtain activated carbon, Agave sisalana (sisal) [42-45] can show some advantages. Sisal is a typical plant of the semi-arid region, Brazil being the world largest producer (1.11x105 t per year) [46]. The sisal fiber, produced form scaling the leaf, is the only part commercially used. It also shows thermal stability (250°C), high impact strength, high resistance to tensile and flexural strength and moderate stiffness [47, 48]. These features make the sisal fiber an important raw material for the synthesis of polymers, polymer composites [49], nanocomposites [50], biomaterials for building [51, 52], adsorbents and catalytic supports [37, 41, 53], besides biocides [54] and products for biomedicine [55]. In addition to all these products, sisal can be used as biomass for energy purposes due to its chemical composition [56]. Although the preparation conditions affect the structure and properties of activated carbon, they are primarily determined by the precursor. Moreover, the yield and the easiness of activation strongly depend on the precursor material [57]. As the performance of activated carbon is related to the chemical characteristics and porous structure, the choice of the precursor is one of the most important steps in obtaining activated carbons with tailored properties.

1.3. Protecting the Environment by Using Activating Carbons Over the years, the fast industry growth has largely improved the quality of life worldwide providing new jobs and modern life conveniences. The expansion of industry is directly related to the population growth, which is expected to increase around 35% by 2050 [58]. However, industrial activities often lead to environmental problems, mainly related to emissions of several toxic compounds leading to water and soil contamination.



9

According to the UNESCO projections, the demand for water by industry activities may increase by 400% from 2000 to 2050 [59]. Moreover, the xpansion of textile industry is expected to increase the water consumption, making this sector one of the main producers of wastewaters [60]. The effluents coming from textile industry account for 20% of freshwater pollution [61] and the global concentration of dyes in the effluents of textile industry reach around 103 t per year [62]. The toxicity, mobility and concentration of pollutants in industrial wastewaters impose a negative impact on the hydric sources, on the biodiversity and on the human health [63]. Especially for textile industry, the compounds found in the effluents are frequently toxic and recalcitrant with high biological oxygen demand (BOD) and chemical oxygen demand (COD), strong color and high pH [64]. These dyes are resistant to conventional biodegradation and oxidation processes [65], demanding for hybrid treatments with different processes combined. Among the negative effects caused by pollutants in textile wastewater, color is the easiest to recognize, even in small concentrations ( ki,2 (equivalent to the lines slopes), suggesting that when the free diffusion access of the dye was reduced, by the additional blocking of some pores, the diffusion rate parameters decreased. The values of the diffusion coefficients are in the range from 2.6 to 5.6 x 10-6 cm2.h-1; these data are in agreement to those reported for the adsorption of methyl violet onto perlite, and for the removal of methyl violet and methylene blue onto sepiolite (Dogan et al., 2007). The adsorption equilibrium of the methylene blue uptake onto the activated carbon at different temperatures was studied. The adsorption isotherms at temperatures from 30 to 60ºC are depicted in Figure 4.4. It is clear that the acidic nature of the adsorbent favours the methylene blue adsorption, since electron donor-acceptor interactions are occurring between the aromatic ring and the oxygenated surface groups. As it was discussed above, the activated carbon surface at the working pH range is negatively charged due to deprotonated acidic groups, enhancing the methylene blue uptake. This behaviour has been found in the removal of methylene blue and phenol onto chemical-activated carbon from vetiver roots (Altenor et al., 2009).


Environmental Applications of Activated Carbons

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Figure 4.4. Adsorption isotherms of methylene blue onto ACPS adsorbent at different temperatures.

From the Figure 4.4, it can be observed that the adsorption capacity highly increased from 275.7 to 444.3 mg.g-1 when the temperature increased from 30 to 60ºC. Since generally adsorption processes are defined as exothermic nature, many examples of endothermic processes in aqueous phase adsorption are usually found in the literature. According to some authors, this behavior could be attributed to an increase in the mobility of the adsorbate, to a decrease in the diffusion pore resistances by other works or even it might be a consequence of the increase in the chemical interactions between the adsorbate and the surface functionalities of the adsorbent when the temperature increases (Mahmoodi et al., 2011).

5. ADSORPTION COLUMN STUDIES. BREAKTHROUGH CURVES Column adsorption studies have been carried out in order to study the behavior of the different tested adsorbents (activated carbon from peach stones and activated carbon from rice husk) in dynamic operation. The


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G. Ovejero, M. A. Uguina, A. Rodriguez et al.

breakthrough curves obtained for ibuprofen and tetracycline removal are shown in Figure 5.1. From the Figures it can be observed the strong influence of the textural properties on the slope of the breakthrough curves, and on the breakthrough and saturation time values.

Figure 5.1. Breakthrough curves of ibuprofen and tetracycline removal onto ACPS and ACRH adsorbents at inlet concentration = 10 mg.L-1, volumetric flow rate = 2.0 mL.min-1 and mass of adsorbent = 0.8 g.



67

Table 5.1. Breakthrough and saturation times, adsorption capacities, MTZ, FBU and removal percentage for ibuprofen and tetracycline adsorption onto the ACPS and ACRH adsorbents Ibuprofen Carbon ACPS ACRH Carbon ACPS ACRH Tetracycline Carbon ACPS ACRH Carbon ACPS ACRH

tb(h) 7.1 1.2 MTZ(cm) 6.6 7.4

ts(h) 137.2 137.4 FBU 0.18 0.07

qb(mg g-1) 9.9 1.7 Y(%) 92.4 97.2

qs(mg g-1) 55.0 22.7

tb(h) 24.1 18.9 MTZ(cm) 6.0 5.8

ts(h) 184.9 185.2 FBU 0.25 0.27

qb(mg g-1) 33.1 27.3 Y(%) 91.6 96.1

qs(mg g-1) 132.6 99.4

Mesoporous activated carbon from peach stones (ACPS), showed a steeper breakthrough curve’s profile and a total column saturation. The meso-macroporous solid (ACRH), led to the sharpest breakthrough curve, being the breakthrough time and the exhaustion point shorter, compared to ACPS carbon. Tetracycline breakthrough curves showed generally flatter profiles, compared to the ibuprofen removal. This can be attributed to the higher length of tetracycline molecule, since it was supposed that a steric hindrance effect was developed in the bed. However, a great saturation in the bed when the mesoporosity of the carbon was higher was observed too, commonly to the ibuprofen adsorption tests. The above comments about the removal of the studied contaminants are in agreement to the results showed in Table 5.1. The calculated experimental adsorption parameters are the breakthrough time (for C/C0 = 0.05), (tb, h), saturation time (ts, h), adsorption capacity at breakthrough time (qb, mg.g-1), adsorption capacity at saturation time (qs, mg.g-1), mass transfer zone length (MTZ, cm), fractional bed utilization (FBU) and adsorbate removal


68


percentage at breakthrough time (Y, %). Higher breakthrough times were obtained for tetracycline removal, leading to greater adsorption capacities, at breakthrough and saturation times, and higher removal efficiencies. Table 5.2. Regeneration parameters for ibuprofen removal onto ACPS and ACRH adsorbents Compound Ibuprofen

Elution Agent NaOH H2O

NaOH H2O

Adsorbent ACPS ACRH ACPS ACRH ACPS ACRH ACPS ACRH

tp (h) 0.6 0.6 2.9 0.6 CF 4.6 6.5 3.3 1.1

Cp (mg.L-1) 46.3 64.7 32.9 11.2 DE (%) 54.7 70.4 26.1 46.9

Table 5.3. Regeneration parameters for tetracycline removal onto ACPS and ACRH adsorbents Compound Tetracycline

Elution Agent NaOH H2O

NaOH H2O

Adsorbent ACPS ACRH ACPS ACRH ACPS ACRH ACPS ACRH

tp (h) 0.2 0.2 0.9 0.2 CF 24.6 26.5 0.4 0.7

Cp (mg.L-1) 245.7 265.0 4.3 7.2 DE (%) 41.7 26.5 31.3 21.9



69

40 35

25

-1

C (mg.L )

30

20 15

Ultrapure water

10

Ibuprofen

ACPS ACRH

5 0 0

5

10

15 20 Time (h)

25

30

Figure 5.2. Elution curves for ibuprofen desorption using NaOH solution and ultrapure water.

In this chapter, we have carried out desorption tests of ibuprofen and tetracycline in dynamic regime. Two elution agents were compared, a sodium hydroxide (NaOH(s)) solution at a saturated concentration and ultrapure water at room temperature, using the same volumetric flow rate used in the adsorption cycle. The obtained elution curves are depicted in Figures 5.2 and 5.3, for ibuprofen and tetracycline desorption, respectively. The regeneration parameters, e.g., time of the peak (tp, h), maximum concentration (Cp, mg.L-1), overall concentration factor (CF), and desorption efficiency, (E, %) for the studied systems are shown in Table 5.2 and 5.3.


70


For the studies of ibuprofen recovery, more favorable desorption efficiency values were obtained for NaOH eluent: 54.7% for ACPS material and 70.4% for the carbon obtained from rice husk (ACRH). Water resulted in a less efficient performance, since the more mesoporous carbon (synthesized from rice husk) led to the more promising results, with a desorption efficiency percentage (DE) of 46.9%.

Figure 5.3. Elution curves for tetracycline desorption using NaOH solution and ultrapure water.



71

CONCLUSION The adsorption behavior of ACPS and ACRH adsorbents on the removal of pharmaceuticals and a dye has been investigated in this chapter. It was found that the adsorption isotherms can be classified as S-type, indicating multilayer adsorption. Textural properties – a fill-pore mechanism – and the competition between the adsorbate and water molecules highly conditioned the ibuprofen removal onto the tested adsorbents, so the acidic carbon ACRH showed the highest ibuprofen adsorption capacity. In general, for tetracycline higher removal values were obtained. π-π EDA interactions and the formation of H-, -COOH and C=O bonds are involved in the adsorption of tetracycline. The activated carbon obtained from peach stones in an acid medium presented the highest tetracycline adsorption capacity. All the kinetic experimental data for the studied systems best fitted to the pseudo-second order model. Only for the adsorption of ibuprofen a correlation between k2 constant values and the mesoporosity percentage of the adsorbents could be established. Ibuprofen and tetracycline removal data could be adequately fitted to the Weber and Morris model. The electron donor-acceptor interactions between adsorbate and adsorbent surface lead to the excellent behavior in the removal of methylene blue from an aqueous solution. The process implicated in the adsorption of methylene blue from a solution is based on the electrostatic interactions between the oxygenated surface groups on the carbon structure and the charged surface of the dye in solution. The results of this study suggest that the laboratory made-activated carbon could be successfully applied for the removal of wastewaters from the textile industry. In the dynamic study, the experimental breakthrough curves obtained for ibuprofen and tetracycline removal are in agreement to the results from batch studies. A high influence of the textural properties of the materials on ibuprofen removal could be evidenced. Tetracycline breakthrough curves showed flatter profiles, due to possible steric hindrance effects. In the regeneration tests, desorption efficiencies using a NaOH solution as an elution agent were higher than those for ultrapure water. The recoveries


72


of ibuprofen were again highly conditioned by the textural properties of the adsorbent, since in the case of tetracycline, the more impact factor in the desorption efficiency was the chemical nature of the material.

ACKNOWLEDGMENTS The authors would like to thank the financial support of the Regional Government of Madrid provided through project REMTAVARES S2013/MAE-2716 and the European Social Fund. Also, this work has been supported by Ministerio de Economía y Competitividad, TRAGUANET Network CTM2014-53485-REDC and Contract REMEWATER CTQ201459011-R.

REFERENCES Abe, F.R., Mendonça, J.N., Moraes, L.A.B., de Oliveira, G.A.R., Gravato, C., Soares, A.M.V.M., de Oliveira, D.P., 2017. Toxicological and behavioral responses as a tool to assess the effects of natural and synthetic dyes on zebrafish early life. Chemosphere 178, 282-290. Ahmed, M. J., Theydan, S. K., 2012. Physical and chemical characteristics of activated carbon prepared by pyrolysis of chemically treated date stones and its ability to adsorb organics. Powder Technol. 229, 237-245. Altenor, S., Carene, B., Emmanuel, E., Lambert, J., Ehrhardt, J.J., Gaspard, S., 2009. Adsorption studies of methylene blue and phenol onto vetiver roots activated carbon prepared by chemical activation. J. Hazard. Mater. 165, 1029-1039. Amalraj, A., Pius, A., 2014. Removal of selected basic dyes using activated carbon from tannery wastes. Separ. Sci. Technol. 49, 90-100. Balakrishnan, V.K., Shirin, S., Aman, A.M., de Solla, S.R., MathieuDenoncourt, J., Langlois, V.S., 2017. Genotoxic and carcinogenic



73

products arising from reductive transformations of the azodye, Disperse Yellow 7. Chemosphere 146, 206-215. Chen, Z., Zhang, J., Fu, J., Wang, M., Wang, X., Han, R., Xu, Q., 2014. Adsorption of methylene blue onto poly(cyclotriphosphazene-co-4,4’sulfonyldiphenol) nanotubes: Kinetics, isotherm and thermodynamic analysis. J. Hazard. Mater. 273, 263-271. De Lima, R.O.A., Bazo, A.P., Salvadori, D.M.F., Rech, C.M., Oliveira, D.P., Umbuzeiro, G.A., 2007. Mutagenic and carcinogenic potential of a textile azo dye processing plant effluent that impacts a drinking water source. Mutat. Res. Genet. Toxicol. Environ. Mutagen. 626, 53-60. Dogan, M., Özdemir, Y., Alkan, M., 2007. Adsorption kinetics and mechanism of cationic methyl violet and methylene blue dyes onto sepiolite. Dyes Pigments 75, 701-713. Fanning, P.E., Vannice, M.A., 1993. A DRIFTS study of the formation of surface groups on carbon by oxidation. Carbon 31, 721-730. Giles, C.H., MacEwan, T.H., Nakhwa, S.N., Smith, D., 1960. Studies in adsorption. Part XI: A system of classification of solution adsorption isotherms, and its use in diagnosis of adsorption mechanism and in measurement of specific surface areas of solids. J. Chem. Soc. 39733993. Guo, Z., Zhang, A., Zhang, J., Liu, H., Kang, Y., Zhang C., 2017. An ammoniation-activation method to prepare activated carbon with enhanced porosity and functionality. Powder Technol. 309, 74-78. Helmy, A.K., De Bussetti, S.G., Ferreiro, E.A., 1983. Adsorption of quinolone from aqueous solutions by someclays and oxides. Clay. Clay Miner. 31, 29-36. Holm, J.V., Rugge, K., Bjerg, P.L., Christensen, T.H., 1995. Occurrence and distribution of pharmaceutical organic-compounds in the groundwater down gradient of a landfill (Grindsted, Denmark). Environ. Sci. Technol. 29, 1415-1420. Krishnan, R., Radhika, G.R., Jayalatha, T., Jacob, S., Rajeev, R., George, B.K., Anjali, B.R., 2017. Removal of perchlorate from drinking water using granular activated carbon modified by acidic functional group:


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Adsorption kinetics and equilibrium studies. Process Saf. Environ. 109, 158-171. Kwiatkowski, M., Kalderis, D., Diamadopoulos, E., 2017. Numerical analysis of the influence of the impregnation ratio on the microporous structure formation of activated carbons, prepared by chemical activation of waste biomass with phosphoric(V) acid. J. Phys. Chem. Solids 105, 81-86. Liu, D., Wu, S., Xu, H., Zhang, Q., Zhang, S., Shi, L., Yao, C., Liu, Y., Cheng, J., 2017. Distribution and bioaccumulation of endocrine disrupting chemicals in water, sediment and fishes in a shallow Chinese freshwater lake: Implications for ecological and human health risks. Ecotox. Environ. Safe.140, 222-229. Mahmoodi, N.M., Hayati, B., Arami, M., Lan, C., 2011. Adsorption of textile dyes on Pine Cone from colored wastewater: Kinetic, equilibrium and thermodynamic studies. Desalination 268, 117-125. Mahmoudi, K., Hamdi, N., Kriaa, A., Srasra, E., 2012. Adsorption of methyl orange using activated carbon prepared from lignin by ZnCl2 treatment. Russ. J. Phys. Chem. A 86, 1294-1300. Mullai, P., Yogeswari, M.K., Vishali, S., Namboodiri, M.M.T., Gebrewold, B.D., Rene, E.R., Pakshirajan, K., 2017. Aerobic treatment of effluents from textile industry. Current Developments Biotechnol. Bioeng. 3-34. Namasivayam, C., Sangeetha, D., 2006. Recycling of agricultural solidwaste, coir pith: Removal of anions, heavy metals, organics and dyes from water by adsorption onto ZnCl2 activated coir pith carbon. J. Hazard. Mater. 135, 449-452. Nethaji, S., Sivasamy, A., 2011. Adsorptive removal of an acid dye by lignocellulosic waste biomass activated carbon: Equilibrium and kinetic studies. Chemosphere 82, 1367-1372. Putra, E.K., Pranowo, R., Sunarso, J., Indraswati, N., Ismadji, S., 2009. Performance of activated carbon and bentonite for adsorption of amoxicillin from wastewater: mechanisms, isotherms and kinetics. Water Res. 43, 2419-2430.



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Rodríguez, A., García, J., Ovejero, G., Mestanza, M., 2009. Adsorption of anionic and cationic dyes on activated carbon from aqueous solutions: Equilibrium and kinetics. J. Hazard. Mater. 172, 1311-1320. Ternes, T.A., 1998. Occurrence of drugs in German sewage treatment plants and rivers. Water Res. 32, 245-3260. Tran, H.N., You, S.J., Chao, H.P., 2017. Fast and efficient adsorption of methylene green 5 on activated carbon prepared from new chemical activation method. J. Environ. Manag.188, 322-336. Weber Jr., W.J., Morris, J.C., 1963. Kinetics of adsorption on carbon from solution. J. Sanit. Eng. Div. Am. Soc. Civ. Eng. 89, 31-60. Yang, Y., Ok, Y.S., Kim, K.H., Kwon, E.E., Tsang, Y.F., 2017. Occurrences and removal of pharmaceuticals and personal care products (PPCPs) in drinking water and water/sewage treatment plants: A review. Sci. Total Environ. 696-697, 303-320.





Chapter 3

MERCURY ADSORPTION FROM AQUEOUS SOLUTION USING ACTIVATED CARBONS Ninfa Marisol Zúñiga-Muro1, Adrián Bonilla-Petriciolet1,*, Didilia Ileana Mendoza-Castillo1,2, Hilda Elizabeth Reynel-Ávila1,2 and Radamés Trejo-Valencia3 1

Instituto Tecnológico de Aguascalientes, Aguascalientes, Mexico 2 CONACYT, Cátedras Jóvenes Investigadores, Ciudad de Mexico, Mexico 3 Instituto Tecnológico de Minatitlán, Veracruz, Mexico

ABSTRACT This chapter analyzes and discusses the synthesis and application of activated carbons for mercury adsorption. Specifically, the synthesis conditions of different activated carbons applied in mercury removal are *

Corresponding Author: [email protected].


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N. M. Zúñiga-Muro, A. Bonilla-Petriciolet et al. reviewed. Physicochemical properties and adsorption capacities of a number of adsorbents are compared including some options for adsorbent regeneration.

Keywords: mercury, activated carbon, adsorption, water treatment

INTRODUCTION Mercury water pollution is an important environmental problem due to the toxicity of this heavy metal even at trace levels (Boening, 2000). Mercury can be accumulated in the human body and may cause irreversible damages such as neurological problems, inhibition of enzymatic activities, loss of sensation in extremities, vision and hearing loss among other human health abnormalities (Fitzgerald et al., 1991; Baeyens et al., 1996). The toxicity of mercury strongly depends on its redox state (Clarkson, 1992) and mercury species can be also converted into more toxic compounds in the environment (Zhang et al., 2007; Li et al., 2009). Therefore, Hg2+ ions are considered as priority water pollutants due to their persistence and bioaccumulation via food chain (Miretzkya et al., 2009). The main natural inputs of mercury to the environment are related to weathering of mercuriferous areas, volcanic eruptions and other biogenic emissions (Morel et al., 1998; Gautam et al., 2014). On the other hand, different industries such as pharmaceutical, textile, paint, paper, plastic, oil refining, rubber processing, coal burning and fertilizers contribute to mercury pollution in the aquatic environment (Zhang et al., 2007; Li et al., 2009). World Health Organization (WHO) has specified a maximum allowable concentration of mercury ion of 1 μg/L in the drinking water (WHO, 2011). Therefore, the mercury removal from aquatic systems has become an important issue for environmental protection and water sanitation. Several physicochemical treatment methods have been explored for the removal of Hg2+ from groundwater and wastewater and they include chemical precipitation, ion exchange, coagulation, electrodeposition,


Mercury Adsorption from Aqueous Solution …

79

solvent extraction, reverse osmosis, membrane filtration and adsorption (Hashim et al., 2011; Huang et al., 2015). Herein, it is convenient to highligth that the usage of an inexpensive and efficient method is important for the treatment of water polluted with Hg2+. Adsorption has been recognized as the most effective, practical, simple and economic method for mercury removal (Fu et al., 2011). To date, a wide variety of adsorbents has been employed for the removal of Hg2+ ions from water (Manohar et al., 2002; Asasian et al., 2015; Kyzas et al., 2015; Pérez-Quintanilla et al., 2016; AlOmar et al., 2017; Kokkinos et al., 2017). The selection of the proper adsorbent is a key aspect for the design of effective adsorption processes (Li et al., 2017). Carbon-based adsorbents have received considerable attention due to their high adsorption capacities and wide availability (Mohmood et al., 2013; Nasser et al., 2016). In particular, activated carbons have been extensively used for Hg2+ adsorption due to they have several functional groups, high surface areas and large pore volumes (Kumar, 2006; Anirudhan et al., 2011; Hadi et al., 2015a). Numerous studies have reported the Hg2+ removal from aqueous solutions using commercial activated carbons (Sharma et al., 2014). However, due to the high cost of these commercial adsorbents, various authors have analyzed alternative synthesis routes for activated carbon production using different precursors (Kadirvelu et al., 2004; Azargohar et al., 2013; Kazemi et al., 2016). The physicochemical properties of the activated carbon and its performance for Hg2+ adsorption depend on both the precursor and synthesis conditions employed. They are fundamental aspects to obtain effective adsorbents for Hg2+ removal (Cheung et al., 2001). Aditionally, the mercury adsorption in aqueous solution is highly dependent on the process conditions such as pH, temperature, metal concentration, process configuration, contact time between solution and adsorbent, adsorbent dosage and particle size. Changes in these parameters may significantly impact the Hg2+ removal efficiency of an adsorbent (Agarwal et al., 2010; Anitha et al., 2015). Therefore, a general knowledge of the effect of these parameters is critical in the design of cost-effective mercury adsorption processes.


80

N. M. Zúñiga-Muro, A. Bonilla-Petriciolet et al.

Based on these facts, this chapter reviews the state of the art of the application of activated carbons for Hg2+ adsorption. The synthesis conditions, physicochemical and adsorption properties of a number of activated carbons used for Hg2+ removal at batch conditions have been analyzed. The regeneration of some adsorbents is also discussed.

SYNTHESIS OF ACTIVATED CARBONS FOR THE REMOVAL OF MERCURY IN AQUEOUS SOLUTION As stated, commercial activated carbons have been widely used in mercury removal from groundwater and wastewaters. However, their use has been limited by the high cost (Di Natale et al., 2006). Therefore, research has been focused on the exploration of alternative low cost precursors for activated carbon production where the nature of feedstocks and the synthesis conditions determine the properties of the adsorbents. Different raw materials can be used for the preparation of mercury adsorbents and they include a variety of lignocellulosic biomasses and urban wastes (Babic et al., 2002; Zhang et al., 2005; Nabais et al., 2006; Silva et al., 2010). Textural properties and surface functional groups of activated carbons are the principal characteristics that should be enhanced by the synthesis route in order to improve the adsorption capacities (Hadi et al., 2015b). Physical and chemical activation techniques are the common approaches to develop the textural properties and to introduce certain functional groups onto the adsorbent surface (Macia-Agullo et al., 2004). A suitable synthesis procedure for processing a specific precursor may lead to develop the best textural properties and surface functional groups on the final adsorbent and, as a consequence, a high Hg2+ removal efficiency. Table 1 reports a survey of different synthesis routes used to prepare activated carbons for mercury adsorption. In general, different protocols have been reported in the literature and some of them will be discussed and analyzed in this chapter including the properties of adsorbents obtained. The review of these synthesis procedures can be used as a reference for future



81

studies on the preparation of adsorbents for mercury removal from aqueous solution. For example, Babic et al., (2002) prepared an activated carbon from viscose rayon cloth via physical and chemical activations. The precursor (i.e., cloth) was pyrolyzed and activated with carbon dioxide at 850ºC for 1 h. The chemical activaction was performed with mixtures of NH4Cl and ZnCl2 solutions. The specific surface area of this adsorbent was of 1125 m2/g, which was higher than those obtained in other studies (e.g., Silva et al., 2010). The total pore volume of this adsorbent was 0.42 cm3/g with an average pore radius of 0.7 nm that corresponded to a microporous structure. The pHPZC was 7, which indicated the presence of surface groups of low acidity (Babic et al., 1999). Zhang et al., (2005) reported the preparation and modification of activated carbon obtained from organic sewage sludge. For the synthesis, sewage sludge was impregnated with 3 M H2SO4, H3PO4 or 5 M ZnCl2 solution. The loaded samples were then pyrolyzed in a N2 atmosphere at 650°C for 60 min. Results indicated that the chemical activation dramatically improved the textural parameters of the adsorbents. For example, the BET surface areas of the carbons activated with H2SO4, H3PO4 and ZnCl2 increased from 137 m2/g to 408, 289 and 555 m2/g, respectively. Similar trends were obtained for the total pore volume of these adsorbents, while their average pore diameters were within 2.26 - 5.21 nm. The pHPZC of these activated carbons decreased and were lower than 4.9. In order to enhance the mercury adsorption from aqueous solution, several authors have studied the combination of chemical and physical activation techniques. For instance, Silva et al., (2010) tested the impact of the chemical activation using two procedures for preparing an activated carbon obtained from the physical activation of Eucalyptus camaldulensis Dehn wood.


82


Table 1. Synthesis conditions reported for the preparation of activated carbons for mercury removal from aqueous solution


Table 2. Overview of kinetic studies performed for the mercury adsorption with activated carbons Adsorbent

pH Temperature, Initial Contact °C concentration, time, h mg/L

Activated carbon from wood

25

Adsorbent Solution Stirring Kinetic models dosage, g volume, speed, and trends in L rpm adsorption data fitting

Up to 3

0.02

250

Author

Lloyd-Jones et al. (2004)

Activated carbon from sewage sludge

5

25

80

Up to 11

Pseudo-first order

Zhang et al. (2005)

Activated carbon from olive stones

2

25

20

5-24

0.5

0.1

200

Pseudo-first order

Wahby et al. (2011)

Activated carbon from sheep bone

3

25-65

80

0.5-6

0.1

0.025

150

Activated carbon from bituminous coal

7

30, 45, 60

200

0.08-48

1

1

200

Pseudo-second order

Asasian et al. (2015)

Activated carbon from waste tires

5

25-70

25

0.1-1

0.06

0.02

100

Pseudo-second order > Pseudofirst order

Saleh et al. (2017)

Dawlet et al. (2013)


Table 3. Overview of isotherm studies performed for the mercury adsorption with activated carbons Adsorbent

pH

Temperature, °C

Initial concentration, mg/L

Activated carbon derived from wood Activated carbon from waste tires

4, 6

0.01-0.10

5

25


7

30, 45, 60

Activated carbon from sheep bone

3

Activated carbon from sewage sludge Activated carbon from cloth

Contact time, h

Adsorbent dosage, g

Solutio n volume ,L

Isotherm models and trends for adsorption data fitting

Adsorption capacity, mg/g

Author

0.01

0.05

Langmuir

10 - 36

0.6

0.06

0.02

Langmuir > DubininRadushkevich > Freundlich

2 - 16

Lloyd-Jones et al. (2004) Saleh et al. (2017)

50-800

48

1

1

Freundlich > Langmuir

50 - 530


25

5-160

0.5-6

0.1

0.025

Freundlich > Langmuir

4 - 21

Dawlet et al. (2013)

5

25

120

7

0.01-1

0.1

Freundlich

10 - 150

2.5, 4, 6.5

20

15-1003

2

0.1

0.04

Zhang et al. (2005) Babic et al. (2002)


5 - 65

Table 4. Overview of desorption studies for the recovery of exhausted activated carbons used in mercury removal from aqueous solution Adsorbent

Cycles

Activated carbon from sewage sludge

Desorption conditions Solution

Initial concentration, M

HNO3

0.1

Adsorbent Solution dosage, g volume, L

Agitation speed, rpm

0.2


4

HNO3

2

0.1

0.05

Activated carbon from waste tires

3

HNO3

0.5

0.03

0.01

200

Temperature, °C

Time, h

Final adsorption efficiency, % (Capacity adsorption loss, mg/g)

Author

60

Sonicate for 0.5

73 (40.5)

Zhang et al. (2005)

30

4

58 - 96 (83.8 11.02)


24

95 (0.8)

Saleh et al. (2017)


86


This precursor was pyrolyzed at 500°C for 2 h. The pyrolyzed material was activated with water vapor at 880°C for 105 min. The activation yield was 47.3% and the elemental composition of the adsorbent was 88.9 carbon, 1.62 hydrogen, 0.05 oxygen and 9.43 nitrogen in wt.%. The specific surface area was 701 m2/g with a pore volume of 0.51 cm3/g. This adsorbent showed an acid group concentration of 1.08 mEq/g. Surface treatments with sulphur were assesed to improve mercury adsorption. Adsorbent samples were soaked with concentrated sulfuric acid and carbon disulfide. Elemental analysis of these adsorbents showed that the treatment with CS2 incorporated a higher sulfur quantity on the adsorbent surface than those obtained with H2SO4 treatment. Both treatments were favorable for the Hg2+ removal. However, the specific surface (582 m2/g) and pore volume (0.42 cm3/g) of the adsorbent treated with CS2 were lower than the other adsorbents. Overall, the H2SO4 treatment increased the quantity of acid and basic sites in contrast to the CS2 treatment. In addition, the pHPZC of the activated carbon with H2SO4 was 6.1, which was lower than that obtained for the other adsorbents impliying a different adsorption behavior depending on solution pH. Wahby et al., (2011) have studied the synthesis of activated carbon using olive stones. These authors showed that pre-oxidized carbons had more surface functional groups and better textural properties than those adsorbents obtained without this pretreatment. For the synthesis, the raw precursor was washed with decalcified water and treated with a 10 wt.% sulfuric acid aqueous solution for 4 h. Different adsorbent samples were obtained via pyrolysis under N2 flow (100 mL/min) at 400, 550, 700 and 850°C for 2 h. The pyrolysis yield ranged from 35 to 45%, which decreased with pyrolysis temperature. Some pyrolyzed samples were activated with CO2 (120 mL/min for 8 h) at 900°C, while other adsorbents were submitted to a pre-oxidation process with a flow of 100 mL/min of synthetic air (O2 20% diluited in N2) for 5 h at 250°C plus the activation stage with CO2. Results of temperatureprogrammed decomposition analysis showed that the pre-oxidation process increased the amount of oxygen-containing surface functional groups (e.g., carboxylic acid, lactones, carboxylic anhydrides, phenol, quinone), which are relevant for Hg2+ adsorption. All the adsorbents were microporous materials with a pore size 5.5. These authors reported that the metal removal (given in percent) was almost constant over the whole range of tested pH conditions and it ranged from 85 to 90%. Adsorption isotherms were obtained at final (equilibrium) pH of 2.5, 4 and 6.5 with Hg2+ initial concentrations ranging from 15 to 1000 mg/L. These authors did not fit the experimental isotherm data with any model. However, they reported an adsorption capacity up to 65 mg/g at pH 6.5. In the whole pH range, the surface of this adsorbent was positively charged because pH < pHPZC and authors concluded that metal hydroxide could precipitate on the adsorbent surface. These authors also analyzed the mercury distribution diagram and concluded that the precipitation of mercury hydroxide was the dominant adsorption mechanism but the electron transfer from the carbon surface to the precipitated Hg2+ cations could contribute to their surface anchoring. On the other hand, Lloyd-Jones et al., (2004) studied the Hg2+ adsorption using a wood-based granular activated carbon. Adsorption isotherms were obtained with initial concentrations of 0.05 - 0.50 mmol/L and pHs 4 and 6. They were reasonably fitted by the Langmuir model where the maximum monolayer adsorption capacity was calculated as 26.1 mg/g at pH 4 and 36.1 mg/g at pH 6. Authors concluded that this adsorbent had oxygen-containing surface functional groups, which tend to dissociate at pH 4. Consequently, they can interact with positively charged Hg2+ in solution. Hg2+ adsorption was enhanced with solution pH and this behavior was attributed to the higher dissociation of weakly acidic surface functional groups. Kinetic studies showed that 56% of mercury uptake was attained in the first 2 min of adsorption test. According to the results obtained in this study, the mechanism proposed for mercury removal was a physisorption of HgCl2 uncharged species, which could be coupled with a reduction reaction of Hg2+ to Hg+ and followed by precipitation of Hg2Cl2 on the surface and in the pores of the adsorbent. This removal mechanism was represented as:



91 (2)

In other study, Zhang et al., (2005) prepared various activated carbons from organic sewage sludge using H2SO4, H3PO4 and ZnCl2 as chemical activation reagents and applied these adsorbents for Hg2+ removal. Adsorption kinetics experiments were carried out using an initial concentration of 80 mg/L at pH 5 and 25°C. Results showed the traditional trend for adsorption rate where the metal uptake increased sharply at a short contact time and gradually slowed down approaching to the adsorption equilibrium. The times to attain the equilibrium were different according to the type of activated carbon and they ranged from 3 to 7 h. Kinetic data were fitted to the pseudo-first-order equation and Hg2+ adsorption capacities of these adsorbents ranged from 44.8 to 130 mg/g where the adsorbent obtained with ZnCl2 showed the best removal performance. According to the authors, the highest adsorption capacity of this activated carbon could be attributed to its best textural parameters, i.e., BET surface area of 555 m2/g and pore volume of 0.752 cm3/g. pH effect on Hg2+ adsorption was studied in the range of 1 - 12 using a solution concentration of 80 mg/L at 25°C for 7 h. Overall, the adsorption increased with pH increments and reached a plateau value at the range of 5 - 12. These adsorbents had a pHPZC within 4.12 - 5.38. It appears that electrostatic interactions played an important role for mercury adsorption at tested operating conditions. Additional adsorption experiments were performed varying the initial concentration and adsorbent dosage obtaining the wellknown trends for these operating variables. Adsorption isotherms were carried out with 120 mg/L Hg2+ solution and varying the adsorbent dosage from 0.01 to 1.0 g at pH 5, 25°C and an equilibrium time of 7 h. These experimental data were fitted to Freundlich isotherm. Finally, Hg2+ desorption from these activated carbons was tested to understand the adsorption mechanism and elucidate the feasibility of recovering both the adsorbents and Hg2+. Desorption was performed with 0.1 M HNO3 solutions and the mixture adsorbent-eluent was sonicated for 30 min at 60°C. The recoveries for these adsorbents ranged from 63.5 to 81.6%. These results


92


indicated that the removal of Hg2+ from water using this type of activated carbons was mainly via physisorption. Silva et al., (2010) analyzed the batch mercury adsorption using an activated carbon made from Eucalyptus wood with and without a chemical treatment using H2SO4 and CS2. For the experiments, a solution of 40 mg/L of Hg2+ was mixed with different amounts of the adsorbents. Adsorption experiments were performed at 25 and 45°C; and pH 3, 7 and 10. The highest mercury adsorption was obtained with H2SO4 modified adsorbent (~98%) and the lowest with the raw activated carbon (~80%) at 25°C and pH 7. These results were in agreement with the content of acid and basic groups on the adsorbent surfaces where the activated carbon treated with H2SO4 had the major concentration. Experimental data were modeled using the Freundlich isotherm equation. Temperature did not influence the adsorption capacity of the three adsorbents. On the other hand, pH had a minor impact on the adsorption process. H2SO4-modified adsorbent showed the highest adsorption capacity at pH 3 (~100%). The authors concluded that this behavior can be explained via the analysis of the net surface charge of the adsorbent and the charge of the mercury species in solution. pHPZC of this adsorbent was 6.1 and, at solution pH 3, the net charge of the solid surface was positive. At this pH, the dominant species in solution are HgCl 2 and HgCl3-. Then, electrostatic attraction forces between the adsorbent surface and the negative charged species enhanced the adsorption. For removal tests at pH 7, the net charge of the surface is close to zero. In this case, the adsorbent capacity decreased due to the absence of favorable electrostatic interactions. For the adsorption studies at pH 10, the net charge of the adsorbent is negative and the main species in solution were mercuy anions causing an electrostatic repulsion and, consequently, there was a reduction in the metal uptake. A similar behavior was observed for the other adsorbents. Wahby et al., (2011) studied the Hg2+ affinity for certain functional groups of activated carbons obtained from olive stones with and without a pre-oxidation treatment. Hg2+ adsorption experiments were carried out at pH 2 and 25°C in a batch reactor. Removal tests indicated that the Hg2+ adsorption capacity of pre-oxidized adsorbents (~2.76 - 2.88 mg/g) was



93

higher than that obtained for the non pre-oxidized samples (~2.64 - 2.72 mg/g). Authors concluded that the presence of oxygen surface groups on the activated carbons was beneficial for mercury adsorption due the adsorbent was more hydrophilic allowing a better accessibility of the Hg2+ cations in the aqueous solution to the carbon surface. The activated carbon pyrolyzed at 850°C exhibited the maximum mercury removal, while the adsorbent obtained at 700°C showed the lowest mercury uptake. On the other hand, kinetic experiments indicated that the Hg2+ removal efficiency of all activated carbons increased sharply at short contact times and slowed down towards the equilibrium. This behavior was attributed to the saturation of the active sites by the metal cation. Kinetic data were fitted by the pseudo-firstorder equation and the adsorption kinetic rates of the non pre-oxidized carbons were slower than those obtained for the pre-oxidized ones. For preoxidized activated carbons, the time required to attain the equilibrium was different and depended on the pyrolysis temperature used in adsorbent synthesis. Equilibrium was attained at 2 h for adsorbents obtained at pyrolysis temperatures of 400 and 550°C, and at 4 h for samples obtained from 700 and 850°C. However, these last adsorbents showed the maximum adsorption capacity for Hg2+. This behavior could be attributed to the textural properties (surface area, porosity and pore size distribution) that may impose restrictions to the diffusion of mercury species through the inner adsorbent structure. This finding suggests that, in addition to a proper surface chemistry, an ideal mercury adsorbent should also exhibit a welldeveloped porous structure. Finally, these authors proposed that the mercury adsorption could be represented by the next reaction:

(3) This removal mechanism could also involve electrostatic interactions between the positively charged surface and the mercury anionic species:

(4)


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Dawlet et al., (2013) have used a chemical activated sheep bone charcoal for Hg2+ adsorption from water. The authors studied the removal of Hg2+ on this adsorbent as a function of solution temperature, which varied from 25 to 65°C and with an initial Hg2+ concentration of 80 mg/L, adsorbent dosage of 0.1 g, stirring speed of 150 rpm and pH 3. In this case, the adsorption efficacy decreased with the temperature and it ranged from 8 to 3.5 mg/g. This decrement in adsorption performance indicated an exothermic process. For this adsorbent, the optimum temperature was selected as 25°C for mercury adsorption. Also, a kinetic study was carried out at the same conditions but varying the contact time from 0.5 to 6 h. Mercury adsorption capacity increased with the time until reaching the equilibrium condition. pH effect on Hg2+ adsorption was studied at the range of 1 - 11. At pH < 2, hydrogen ions competed with mercury species, while metal ions could precipitate at pH > 7. The adsorption decreased with increments of pH where the maximum adsorption (~8 mg/g) was observed at pH 3.0 and decreased to 5 mg/g at pH 9. These results confirmed that mercury adsorption was highly pH dependent. Adsorption isotherm was obtained with metal concentrations ranging from 5 to 160 mg/L and it was fitted to Langmuir and Freundlich models. In particular, the Freundlich isotherm model showed the best correlation results. Recently, Asasian et al., (2015) reported the Hg2+ adsorption using a bituminous coal-based adsorbent and three activated carbons sulfurized with dimethyl disulfide, elemental sulfur and disulfur dioxide. These adsorbents were studied with a series of kinetic experiments under the following conditions: initial concentration of 200 mg/L, adsorbent dosage of 1 g/L, initial pH of 7, agitation speed of 200 rpm and temperatures of 30, 45, and 60ºC, respectively. The kinetic mercury adsorption was fitted by the pseudosecond-order model for all the adsorbents at tested temperatures. Adsorption capacities of sulfurized activated carbons were smaller than raw activated carbon at early contact times due to this last adsorbent had a higher specific surface area and pore volume. Note that the first stage of adsorption kinetics is usually dominated by the physisorption mechanism. After 60 min of contact time, the adsorption capacities of sulfurized adsorbents were higher than those of raw activated carbon. This behavior was attributed to the



95

contribution of sulfur functionalities in mercury uptake via chemisorption, complex formation or other chemical interactions. In general, the adsorption capacity increased with the temperature and the mercury uptakes of activated carbon obtained with dimethyl disulfide were higher than other tested adsorbents regardless of the operating conditions. The maximum adsorption capacity of this adsorbent was 218.2 mg/g at 60ºC. Equilibrium tests were performed using initial concentrations of 50 - 800 mg/L for 48 h at 30, 45 and 60°C. These Hg2+ adsorption experiments showed a direct relationship between the metal uptake and initial concentration of the metal ion present in the solution, and an inverse relationship between the removal percentage and initial metal concentration (Hadi et al., 2015a). Herein, it is convenient to remark that the removal percentage is not a proper metric to reflect the adsorbent efficacy at various initial concentrations and adsorbent dosages. Indeed, the adsorption capacity takes into account the adsorbent dosage and it is an intensive variable to quantify the adsorption effectiveness at different operating conditions. Several authors have reported 100% Hg2+ removal at different adsorption conditions (e.g., Mohan et al., 2001; Rao et al., 2009; Wahi et al., 2009). But, when the initial concentration and adsorbent amount are taken into consideration, the adsorption capacity calculated can be very small in some cases. Therefore, the report of mercury removal percentage is highly discouraged due to misleading results (Hadi et al., 2015b). Asasian et al., (2015) also fitted the equilibrium experimental data with Langmuir and Freundlich isotherm models. Freundlich adsorption model showed the best fit. SEM-EDX analysis of the sulfurized samples after mercury adsorption confirmed that there was a direct correlation between the amount of sulfur on the surface of activated carbons and the amount of mercury adsorbed. FTIR results showed that the main sulfur functionalities of modified adsorbents were the organic (thiophenic) and oxidized forms. However, the organic forms of sulfur including sulfide and disulfide were detected in the structure of the activated carbon treated with dimethyl disulfide. It is clear that the types of sulfur-containing groups present in the adsorbents have an important role to determine their mercury adsorption capacities. These authors evaluated the presence of unreacted elemental sulfur in the adsorbents structures and results confirmed no


96


elemental sulfur in the structure of the samples sulfurized at high temperatures. These findings suggested that the higher mercury adsorption capacity of activated carbon modified with dimethyl disulfide may be the consequence of the higher affinity of unreacted sulfur, sulfide and disulfide groups toward mercury ions compared to the thiophenic and/or oxidized forms. The leaching of sulfur compounds into water after contact with this adsorbent was evaluated. Results showed that this adsorbent can release sulfur species, which was considered as one of its disadvantages. XPS analysis of these activated carbons after mercury adsorption was also performed. It confirmed the presence of Hg-O and Hg-Cl bonds for raw adsorbent and the existence of Hg-S, Hg-Cl and Hg-O interactions for modified adsorbents. These authors believed that this finding was an evidence of the involvement of sulfur-containing groups in the adsorption of mercury ions via chemical reactions. With respect to adsorption thermodynamics, the activation parameters of mercury adsorption on sulfurized activated carbons (18.21 - 33.05 kJ/mol) were higher than those for raw adsorbent (12.31 kJ/mol). The values obtained for ΔG0 indicated the spontaneity of the adsorption processes (11.36 to -2.18 kJ/mol). The positive values of ΔH0 (19.78 - 38.21 kJ/mol) indicated an endothermic adsorption. Calculated values of ΔS0 (72.48 147.51 J/mol·K) suggested an increment in the randomness at the solidsolution interface during the adsorption. Finally, the efficiency of HCl, HNO3, KCl, KBr and KI for desorption of mercury from these activated carbons was compared. The experiments were carried out using an extractant concentration of 2 M for 24 h. None of the extractants were able to desorb mercury completely from the surfaces of the saturated adsorbents. These desorption studies verified the strength of the bonds formed between mercury and the active sites of these activated carbons. The weaker desorption capability was found for acidic extractants specifically HCl. The potassium halides, and in particular KI, showed the best performance. Desorption performance of potassium halides was better for the regeneration of raw adsorbent than modified activated carbons. The potassium halides desorbed mercury via the exchange of K+ ions with metal cations previously adsorbed by oxygenated and sulfur-containing groups on the surfaces of



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these adsorbents. Based on the HSAB theory (Pearson, 1963), potassium is a hard acid and mercury a soft one. In contrast, the oxygen- and sulfurcontaining sites on the surfaces of these activated carbons can be classified as hard and soft bases, respectively. So, it is expected that the interaction between K+ ions (hard acid) and oxygen groups (hard base) occurs easier than that between K+ ions and sulfur-containing groups. The opposite behavior is observed in the case of acidic extractants. In this case, the desorption mechanism was pH dependent. This implies that the mercury adsorption capacity of an adsorbent was enhanced by pH increasing, while the efficiency of acidic solutions for desorption of mercury was higher. Therefore, the acidification of solution was more beneficial for mercury desorption from the sulfurized activated carbons compared to raw adsorbent. The performance of raw and sulfurized activated carbons in four consecutive adsorption-desorption cycles was compared. The results indicated that the use of acidic and/or potassium halide solutions alone was not enough for the recovery of inactive sulfur sites. Therefore, authors suggested the addition of a reactivation step prior to each adsorption cycle to insert new sulfurcontaining groups or activate the old functionalities in the activated carbon. Finally, Saleh et al., (2017) reported mercury adsorption studies using a polyethylenimine-modified activated carbon derived from waste tires. These authors proposed a 2-level factorial experimental design to understand the impact of operating parameters on adsorption performance. These parameters were the contact time (10 - 60 min), adsorbent mass (30 - 90 mg), pH (3 - 7), initial Hg2+ concentration (10 - 40 mg/L) and stirring speed (50 150 rpm). The initial mercury concentrations were selected to simulate real industrial wastewaters. The best experimental adsorption conditions were: a contact time of 35 min, adsorbent mass of 60 mg, pH of 5, initial mercury concentration of 25 mg/L and a stirring speed of 100 rpm. A statistical analysis showed that the most significant factors affecting the mercury adsorption were the initial concentration followed by contact time and adsorbent mass. Mercury adsorption isotherm was obtained at the optimum conditions and was fitted to Langmuir, Freundlich and DubininRadushkevich models. Langmuir isotherm model provided the best fit where a monolayer adsorption capacity of 16.39 mg/g was estimated. Equilibrium


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data were also satisfactorily fitted with Dubinin-Radushkevich isotherm model. In particular, the Dubinin-Radushkevich adsorption E parameter was found to be 19.84 kJ/mol. Authors concluded that adsorption processes of Hg2+ using this adsorbent could be carried out via complex formation between Hg2+ ions and the amide groups of the adsorbent. Adsorption kinetics were performed at 25 - 70°C for 5 - 60 min. Kinetics results were modeled using the pseudo-first and pseudo-second order equations where the last model was the best. Note that this model is more robust to estimate the kinetics when the chemical adsorption mechanism is the rate-controlling step (Ho et al., 1999). Thermodynamic analysis suggested that the feasibility and spontaneity of Hg2+ adsorption diminished with increments of the temperature. However, the low negative ΔG° (2.9x10-6 kJ/mol) confirmed the viability of the adsorption process. ΔH° (-24.65 kJ/mol) indicated that Hg2+ adsorption was exothermic. FTIR results were used to establish the bonding interactions of C=O and NH2 groups with the metal ions. Finally, Saleh et al., (2017) investigated the regeneration performance of this adsorbent. Mercury desorption was conducted using different concentrations of HNO3. The recovery ranged from 50 to 95% where three adsorption/desorption cycles were performed. The results showed that regeneration efficiency of the adsorbent was stable after these cycles where the Hg2+ removal efficiency still remained around 90%. In summary, these studies provide an overview of mercury adsorption on activated carbons. Overall, several key aspects can be highlighted. First, the surface chemistry of activated carbons is fundamental for mercury adsorption. According to the literature, the adsorption of an adsorbate by activated carbon can be categorized into chemical and physical adsorption where physical adsorption is governed by the weak Van der Waals interaction between the adsorbate and adsorbent; while the chemical adsorption is determined by the bonding between the functional groups on the adsorbent surface and adsorbate (Tchobanoglous et al., 1991). Surface functional groups play a key role on the adsorption of mercury (Sun et al., 2011). In particular, the enhanced mercury adsorption related to oxygen-containing functional groups has been explained by the Lewis characteristic of Hg2+



99

(Nabais et al., 2006). In the aqueous medium, this type of functional groups tends to lose its protons and become ionized, thus leading to unbalanced charge on the adsorbent surface where ion exchange with the Hg2+ can occur (Sun et al., 2011). As these functional groups largely determine the surface properties and the intensity of ion exchange, the manipulation of the adsorbent surface chemistry has been of great interest in mercury adsorption. With respect to parameters of adsorption processes, it should be noted that the particle size plays an important role in determining the rate and adsorption capacity for Hg2+ removal. It has been demonstrated that the Hg2+ adsorption capacity showed an increment when the size of the adsorbent particles decreased (Mckay et al., 1989; Peniche-Covas et al., 1992). This improvement is due to the fact that reducing the adsorbent particle size increases the effective surface area and enhances the availability of adsorption sites (Kara et al., 2007). Also, the diffusion path becomes shorter and the adsorbate molecules can more easily penetrate into the internal pores of the adsorbent (Gupta et al., 2011). On the other hand, different studies have shown that temperature plays a significant role in the uptake of Hg2+. Depending upon the adsorption mechanism, the thermodynamic behavior of mercury adsorption with activated carbons can be endothermic or exothermic (Inbaraj et al., 2006).

CONCLUSION Mercury adsorption from water using activated carbons has been shown a promising and effective treatment technology if proper adsorbent and operating conditions are used. It is clear that the effects of textural properties and functional groups of the activated carbons on mercury uptake have been examined in several studies. Results showed that a tradeoff between these adsorbent properties is fundamental for mercury removal. It appears that a combination of medium-to-high surface area with well-functionalized surface properties of the activated carbon may enhance the mercury adsorption. Despite these findings, the simultaneous optimization of surface chemistry and textural characteristics of activated carbons has not been


100


performed. Furthermore, a number of studies has focused on the sulfurization of activated carbons with the aim of improving the mercury uptake. However, the mechanism of sulfurization process, including the type and quantity of sulfur-containing moieties loaded onto the activated carbon surfaces, and their role in the mercury adsorption mechanism have not been analyzed in detail. In addition, there are not enough studies about the recyclability of the adsorbents used in Hg2+ removal. Therefore, the study and analysis of adsorbent activation strategies and the mercury adsorptiondesorption mechanisms will assist in the design of proper adsorption systems for optimal mercury abatement in drinking water, groundwater and industrial effluents. In summary, it is clear that the adsorption process offers a variety of options to develop low cost and effective treatment methods for Hg2+ removal from aqueous solution and further studies should be focused on solving its potential disadvantages.

REFERENCES Agarwal, H., Sharma, D., Sindhu, S. K., Tyagi, S., Ikram, S. (2010). Removal of mercury from wastewater use of green adsorbents -a review, Electronic Journal of Environmental, Agricultural and Food Chemistry, 9, 1551-1558. AlOmar, M. K., Alsaadi, M. A., Hayyan, M., Akib, S., Ibrahim M., Hashim, M. A. (2017). Allyl triphenyl phosphonium bromide based DESfunctionalized carbon nanotubes for the removal of mercury from water, Chemosphere, 167, 44-52. Anirudhan, T., Sreekumari, S. (2011). Adsorptive removal of heavy metal ions from industrial effluents using activated carbon derived from waste coconut buttons, Journal of Environmental Science, 23, 1989-1998. Anitha, D., Sridevi, O. A., Subha, R. (2015). Removal of mercury from aqueous solution- review on current status and development, International Conference on Systems, Science, Control, Communication, Engineering and Technology, 195-198.



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Asasian, N., Kaghazchi, T. (2013). Optimization of activated carbon sulfurization to reach adsorbent with the highest capacity for mercury adsorption, Separation Science and Technology, 48, 1-14. Asasian, N., Kaghazchi, T., Faramarzi, A., Hakimi-Siboni, A., AsadiKesheh, R., Kavand, M., Mohtashami, S. A. (2014). Enhanced mercury adsorption capacity by sulfurization of activated carbon with SO2 in a bubbling fluidized bed reactor, Journal of the Taiwan Institute of Chemical Engineers, 45, 1588-1596. Asasian, N., Kaghazchi, T. (2015). Sulfurized activated carbons and their mercury adsorption/desorption behavior in aqueous phase, International Journal of Environmental Science and Technology, 12, 2511-2522. Azargohar, M. R., Dalai, A. K., Shewchuk, S. R. (2013). Mercury removal by bio-char based modified activated carbons, Fuel, 103, 570-578. Babic, B. M., Milonjic, S. K., Polovina, M. J., Kaludierovic, B. V. (1999). Point of zero charge and intrinsic equilibrium constants of activated carbon cloth, Carbon, 37, 477-481. Babic, B. M., Milonjic, S. K., Polovina, M. J., Cupic, S., Kaludjerovic, B.V. (2002). Adsorption of zinc, cadmium and mercury ions from aqueous solutions on an activated carbon cloth, Carbon, 40, 1109-1115. Baeyens, R., Ebinghous, R., Vasilev, O. (1996). Global and Regional Mercury Cycles: Sources, Fluxes and Mass Balances, Kluwer Academic Publishers, 21. Basha, S., Murthy, S. V. P., Jha, B. (2009). Sorption of Hg(II) onto Carica papaya: Experimental studies and design of batch sorber, Chemical Engineering Journal, 147, 226-234. Boening, D.W. (2000). Ecological effects, transport, and fate of mercury: a general review, Chemosphere, 40, 1335-1351. Cheung, C. W., Chan, C. K., Porter, J. F., Mckay G. (2001). Combined diffusion model for the sorption of cadmium, copper, and zinc ions onto bone char, Environmental Science and Technology, 35, 1511-1522. Cai, J. H., Jia, C. Q. (2010). Mercury removal from aqueous solution using coke-derived sulfur-impregnated activated carbons, Industrial and Engineering Chemical Research, 49, 2716-2721.


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Clarkson, T. W. (1992). Mercury: major issues in environmental health, Environmental Health Perspectives, 100, 31-38. Dawlet, A., Talip, D., Mi, H. Y., MaLiKeZhaTi. (2013). Removal of mercury from aqueous solution using sheep bone charcoal, Procedia Environmental Sciences, 18, 800-808. Di Natale, F., Lancia, A., Molino, A., Di Natale, M., Karatza, D., Musmarra, D. (2006). Capture of mercury ions by natural and industrial materials, Journal of Hazardous Materials, 132, 220-225. Fitzgerald, W. F., Clarkson, T. W. (1991). Mercury and mono methyl mercury: present and future concerns, Environmental Health Perspectives, 19, 159-166. Fu, F. L., Wang, Q. (2011). Removal of heavy metal ions from wastewaters: a review, Journal of Environmental Management, 92, 407-418. Gautam, R. K., Sharma, S. K., Mahiya, S., Chattopadhyaya, M. C. (2014). Contamination of heavy metals in aquatic media: transport, toxicity and technologies for remediation, Heavy Metals in Water: Presence, Removal and Safety, 1-24. Gupta, V., Ali, I., Mohan, D. (2003). Equilibrium uptake and sorption dynamics for the removal of a basic dye (basic red) using low-cost adsorbents, Journal of Colloid and Interface Science, 265, 257-264. Gupta, V. K., Gupta, B., Rastogi, A., Agarwal, S., Nayak, A. (2011). A comparative investigation on adsorption performances of mesoporous activated carbon prepared from waste rubber tire and activated carbon for a hazardous azo dye-Acid Blue 113, Journal of Hazardous Materials, 186, 891-901. Hadi, P., To, M. H., Hui, C. W., Lin, C. S., McKay, G. (2015a). Aqueous mercury adsorption by activated carbons, Water Research, 73, 37-55. Hadi, P., Xu, M., Ning, C., Lin, C., McKay, G. (2015b). A critical review on preparation, characterization and utilization of sludge-derived activated carbons for wastewater treatment, Chemical Engineering Journal, 260, 895-906. Hashim, M., Mukhopadhyay, S., Sahu, J. N., Sengupta, B. (2011). Remediation technologies for heavy metal contaminated groundwater, Journal of Environmental Management, 92, 2355-2388.



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Hassan, S. S. M., Awwad, N. S., Aboterika, A. H. A. (2008). Removal of mercury(II) from wastewater using camel bone charcoal, Journal of Hazardous Materials, 154, 992-997. Ho, Y. S., McKay, G. (1999). Comparative sorption kinetics studies of dyes and aromatic compounds onto fly ash, Journal of Environmental Science and Health, A34, 1179-1204. Ho, Y. S. (2006). Review of second-order models for adsorption systems. Journal of Hazardous Materials, 136, 681-689. Huang, Y., Du, J. R., Zhang, Y., Lawless, D., Feng, X. (2015). Removal of mercury (II) from wastewater by polyvinylamine-enhanced ultrafiltration, Separation and Purification Technology, 154, 1-10. Inbaraj, B. S., Sulochana, N. (2006). Mercury adsorption on a carbon sorbent derived from fruit shell of Terminalia catappa, Journal of Hazardous Materials, 133, 283-90. Kadirvelu, K., Kavipriya, M., Karthika, C., Vennilamani, N., Pattabhi, S. (2004). Mercury (II) adsorption by activated carbon made from sago waste, Carbon, 42, 745-752. Kara, S., Aydiner, C., Demirbas, E., Kobya, M., Dizge, N. (2007). Modeling the effects of adsorbent dose and particle size on the adsorption of reactive textile dyes by fly ash, Desalination, 212, 282-293. Kazemi, F., Younesi, H., Ghoreyshi, A. A., Bahramifar, N., Heidari, A. (2016). Thiol-incorporated activated carbon derived from fir wood sawdust as an efficient adsorbent for the removal of mercury ion: batch and fixed-bedcolumn studies, Process Safety and Environmental Protection, 100, 22-35. Kokkinos E., Simeonidis K., Pinakidou F., Katsikini M., Mitrakas M. (2017). Optimization of tetravalent manganese feroxyhyte's negative charge density: A high-performing mercury adsorbent from drinking water, Science of the Total Environment, 574, 482-489. Kumar, U. (2006). Agricultural products and by-products as a low cost adsorbent for heavy metal removal from water and wastewater: a review, Scientific Research and Essays, 1, 33-37.


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Kyzas, G. Z., Kostoglou, M. (2015). Swelling-adsorption interactions during mercury and nickel ions removal by chitosan derivatives, Separation and Purification Technology, 149, 92-102. Li, P., Feng, X. B., Qiu, G. L., Shang, L. H., Li, Z. G. (2009). Mercury pollution in Asia: a review of the contaminated sites, Journal of Hazardous Materials, 168, 591-601. Li, Y., Li, W., Liu, Q., Meng, H., Lu, Y., Li, C. (2017). Alkynyl carbon materials as novel and efficient sorbents for the adsorption of mercury(II) from wastewater, Journal of Environmental Science, http://dx.doi.org/10.1016/j.jes.2016.12.016. Lloyd-Jones, P. J., Rangel-Mendez, J. R., Streat, M. (2004). Mercury sorption from aqueous solution by chelating ion exchange resins, activated carbon and a biosorbent, Trans IChemE, Part B, Process Safety and Environmental Protection, 82, 301-311. Lopez-Gonzales, J. D., Moreno-Castilla, C., Guerrero-Ruiz, A., RodriguezReinoso, F. (1982). Effect of carbon–oxygen and carbon sulphur surface complexes on the adsorption of mercury chloride in aqueous solutions by activated carbon, Journal of Chemical Technology and Biotechnology, 32, 575-579. Macia-Agullo, J. A., Moore, B. C., Cazorla-Amoros, D., Linares-Solano, A. (2004). Activation of coal tar pitch carbon fibres: physical activation vs. chemical activation, Carbon, 42, 1367-1370. Manohar, D., Krishnan, K. A., Anirudhan, T. (2002). Removal of mercury (II) from aqueous solutions and chlor-alkali industry wastewater using 2-mercaptobenzimidazole-clay, Water Research, 36, 1609-1619. Mckay, G., Blair, H. S., Findon, A. (1989). Equilibrium studies for the sorption of metal-ions onto chitosan, Indian Journal of Chemistry Section a-Inorganic, Bio-Inorganic Physical, Theorical and Analytical Chemistry, 28, 356-360. Miretzkya, P., Cirelli, A. F. (2009). Hg(II) removal from water by chitosan and chitosan derivatives: a review, Journal of Hazardous Materials, 167, 10-23. Mohan, D., Gupta, V. K., Srivastava, S. K., Chander, S. (2001). Kinetics of mercury adsorption from wastewater using activated carbon from



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fertilizer waste, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 177, 169-181. Mohmood, I., Lopes, C. B., Lopes, I., Ahmad, I., Duarte, A. C., Pereira, E. (2013). Nanoscale materials and their use in water contaminants removal-a review, Environmental Science and Pollution Research, 20, 1239-1260. Morel, F. M. M., Kraepiel, A. M. L., Amyot, M. (1998). The chemical cycle and bioaccumulation of mercury, Annual Review of Ecology and Systematics, 29, 543-566. Nabais, J. V., Carrott, P. J. M., Carrott, M. M. L. R., Belchior, M., Boavida, D., Diall, T., Gulyurtlu, I. (2006). Mercury removal from aqueous solution and flue gas by adsorption on activated carbon fibers, Applied Surface Science, 252, 6046-6052. Nasser, M. S., Khraisheh, M., Atieh, M. A. (2016). Heavy metal removal from aqueous solution by advanced carbon nanotubes: critical review of adsorption applications, Separation and Purification Technology, 157, 141-161. Namasivayam, C., Radhika, R., Suba, S. (2001). Uptake of dyes by a promising locally available agricultural solid waste: coir pith, Waste Management, 21, 381-387. Pearson, R. G. (1963). Hard and soft acids and bases, Journal of American Chemistry Society, 85, 3533-3539. Peniche-Covas, C., Alvarez, L. W., Argüelles-Monal, W. (1992). The adsorption of mercuric ions by chitosan, Journal of Applied Polymer Science, 46, 1147-1150. Pérez-Quintanilla, D., Sánchez, A., Sierra, I. (2016). Preparation of hybrid organic-inorganic mesoporous silicas applied to mercury removal from aqueous media: Influence of the synthesis route on adsorption capacity and efficiency, Journal of Colloid and Interface Science, 472, 126-134. Pillay, K., Cukrowska, E. M., Coville, N. J. (2013). Improved uptake of mercury by sulphur-containing carbon nanotubes, Microchemical Journal, 108, 124-130. Rao, M. M., Reddy, D. H. K. K., Venkateswarlu, P., Seshaiah, K. (2009). Removal of mercury from aqueous solutions using activated carbon


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prepared from agricultural by-product/waste, Journal of Environmental Management, 90, 634-643. Saleh, T. A., Sari, A., Tuzen, M. (2017). Optimization of parameters with experimental design for the adsorption of mercury using polyethylenimine modified-activated carbon, Journal of Environmental Chemical Engineering, 5, 1079-1088. Sharma, A., Sharma, A., Arya, R. K. (2014). Removal of mercury (II) from aqueous solution: a review of recent work, Separation Science and Technology, doi: 10.1080/01496395.2014.968261 Silva, H. S., Ruiz, S. V., Granados, D. L., Santángelo, J. M. (2010). Adsorption of mercury (II) from liquid solutions using modified activated carbons, Materials Research, 13, 129-134. Sun, X., Hwang, J. Y., Xie, S. (2011). Density functional study of elemental mercury adsorption on surfactants, Fuel, 90, 1061-1068. Tchobanoglous, G., Burton, F. L., Stensel, H. D. (1991). Wastewater Engineering Treatment and Reuse, Fourth edition, 317. Wahby, A., Abdelouahab-Reddam, Z., El Mail, R., Stitou, M., SilvestreAlbero, J., Sepúlveda-Escribano, A., Rodríguez-Reinoso, F. (2011). Mercury removal from aqueous solution by adsorption on activated carbons prepared from olive stones, Adsorption, 17, 603-609. Wahi, R., Ngaini, Z., Jok, V. U. (2009). Removal of mercury, lead and copper from aqueous solution by activated carbon of palm oil empty fruit bunch, World Applied Sciences Journal, 5, 84-91. WHO. (2011). Guidelines for drinking-water quality, Geneva, World Health Organization. Zhang, F. S., Nriagu, J. O., Hideaki, I. (2005). Mercury removal from water using activated carbons derived from organic sewage sludge, Water Research, 39, 389-395. Zhang, L., Wong, M. H. (2007). Environmental mercury contamination in China: sources and impacts, Environment International, 33, 108-121.




Chapter 4

SURFACE PROPERTIES AND PREPARATION CONDITION OPTIMIZATION OF AMINATION BAMBOO/LIGNITE AC Guojie Zhang*, Yongfa Zhang, Fuai Tian, Guoqiang Li and Ying Xu Key Laboratory of Coal Science and Technology, Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan, China

ABSTRACT This chapter used bamboo char and lignite as raw materials to prepare the new material of amination bamboo/lignite activated carbon through carbonization and activation. It also investigated the influences of the preparation conditions on the desulfurization performance of the new carbon material. BET and XPS were adopted to carry out the physical and

*

Corresponding author: Guojie Zhang. Key Laboratory of Coal Science and Technology, Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan 030024, PR China. Email: [email protected]; [email protected].


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Guojie Zhang, Yongfa Zhang, Fuai Tian et al. chemical structural characterization of the newly prepared carbon material. BET and XPS indicated that the pore structure of bamboo/lignite activated carbon through ammonia activation was similar to that through steam activation and the activated carbons after both activations contained carbon groups of the same variety. The difference between ammonia activation and steam activation lies in the two new nitrogen-containing groups in the carbon material after the ammonia activation: para-pyridine or para-nitrile group and amine, amine, amide, imide and para-pyrrole. After the desulfuration through simulation flue gas, protonation para-pyridine nitrogen or amine salt occurred on the bamboo/lignite activated carbon and the content of the introduced nitrogen groups decreased. After the regeneration of desorption SO2 activated carbon, the content of parapyridine increased and the contents of protonation para-pyridine and amine salt decreased. These results indicated that the activity of bamboo/lignite activated carbon was related to the para-pyridine group introduced by ammonia activation. Studies on the preparation of activation conditions showed that the sulfur capacity of bamboo/lignite activated carbon increased along with the increasing activator concentration. The sulfur capacity increased first and decreased later along with the increasing activation temperature; and it increased along with the extension of activation time. The optimal activation condition is 8.5-14.5% ammonia concentration, 850C-950C activation temperature and 120 min-150 min activation time.

Keywords: bamboo desulfurization

char,

lignite,

activated

carbon,

ammonia,

1. INTRODUCTION China is a country with rich coal resources while deficient oil and gas resources [1]. The coal consumption accounts for about 75% of the primary energy resources and the major utilization way of coal is combustion. However, in the combustion process, there are a large number of SO2-rich flue gases. According to statistics, 80%-90% of SO2 in the atmosphere in China is from the flue gases of coal combustion [2-4]. In the atmosphere, the water spray containing H2SO4 or sulfates is generated through the complicated atmospheric physical and chemical reactions of SO2, which further created the acid rain. Acid rain can cause serious harm to the tissues


Surface Properties and Preparation Condition Optimization …

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and organs and genetic materials of animals and plants. Statistics demonstrated that polluted land area of SO2-type acid rain accounted for nearly 40% of the total territory in China and leaded to over RMB 110 billion yuan losses to China, occupying 2%-3% of annual GDP [5]. Along with the increasingly prominent environmental problems of SO2 pollution and the improving China’s environmental protection requirements, SO2 pollution control in the flue gas has been paid more and more attention. Thus, the research and development of new flue gas desulfurization technology has been one of the key and urgent problems of the environmental protection in China. In recent years, the catalytic performance of carbon adsorbent has been widely studied [6-15], for example, halogenation and dehydrohalogenation reactions of catalytic hydrocarbon, oxalic acid oxidation reaction, and oxidation desorption reaction of H2S and SO2 over activated carbon. In the studies of the catalytic oxidation reaction of carbon on oxalic acid solution, Brigitte found that the nitrogen-containing activated carbon owned extremely high catalytic performance [16]. When Boehm utilized the oxidation reaction of sulfurous acid solution to test the catalytic activity of carbon adsorbent, it was found that the charcoal and carbon black after ammonia high-temperature treatment had relatively high catalytic activity [6]. Studies found that carbon catalytic activity not only was related to the changes of the surface physical form of activated carbon, but also concerned with the some nitrogen-containing species in the amination process [6, 17]. Under the condition of relative high energy, nitrogen-containing groups can provide extra electrons to transfer to the conduction band, whose electrons again continues transferring to the adsorbed species, which is activated due to accepting electrons [17]. With further and profound studies, the excellent performances of nitrogen-rich activated carbon become increasingly prominent and studies on the utilization of nitrogen-rich activated carbon to remove SO2 in the flue gas also have aroused extensive attention at home and abroad [18]. Compared with the traditional desulfurization technology, the carbonbased flue gas desulphurization technology owns various advantages [1823]: (1) few desulfurizer consumptions, regeneration and low cost; (2) its


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Guojie Zhang, Yongfa Zhang, Fuai Tian et al.

desulfurization products can be recycled in form of sulfuric acid and sulphur; (3) it needs few facilities and the technology is simple and easy to operate; (4) and this is no problem of secondary pollution. The major material of carbon-based desulphurization is activated carbon. The loose grain of plant raw materials, representative of timber, saw dust and pit, is beneficial to the entrance of activator, so the reactivity property is sound. The prepared activated carbon has developed micropore volume, large specific surface area and good adsorption performance. However, this kind of raw materials costs a lot and its resource is very limited. For these reasons, researchers have turned to the coal with abundant reserves and at low cost. Most studies mainly focused on the investigations of the adsorption performance of single activated carbon while few of them reported the plant-coal activated carbon catalyst and catalytic performance. Studies have showed that the desulphurization capacity of activated carbon not only lies in its specific surface area and pore structure [24, 25], but also is influenced by the variety of surface functional groups and delocalized π electron on graphite crystalline carbon plane layer [24, 26]. This paper took bamboo and lignite as raw materials and adopted the ammonia high temperature activation to prepare amination bamboo/lignite activated carbon with nitrogen-rich groups. This paper also studied the surface physical and chemical properties of bamboo/lignite activated carbon and investigated the influences of different activation conditions on the catalytic desulphurization performance of bamboo/lignite activated carbon.

2. ABOUT OUR RESEARCH 2.1. Influences of Activation Conditions on Activated Carbon Yield Table 1 shows the influences of different activation conditions on activated carbon yield. It can be seen from Table 1 that under the conditions of the same activation temperature (850C) and activation time (120 min),



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the activated carbon yield after the ammonia activation of different concentrations increased along with the increasing ammonia concentration. It indicated that the ammonia activation rate was slower than that of steam activation rate. Though the molecular diameter of water is close to that of ammonia (H2O = 2.65Å, NH3 = 2.60Å), the ablation rate of activated carbon after ammonia activation significantly decreased. The reason may be related to that NH3 ablated the peripheral carbon on the graphite-like structure carbon layer and generated stable nitrogen-containing groups, which passivated the active site of the activation reaction and further resulted in the slow activation rate and high yield. When adopting steam and ammonia to activate the artificial carbon fiber, Tomlinson also reported the same conclusions [7]. It also can be seen from Table 1 that under the condition of the same ammonia concentration (8.48%), the yield of activated carbon (BLAC2, BLAC5-12) increased along with the increasing activation temperature while decreased with the extension of activation time. This mainly lies in the local aggravating gasification rate of carbon accompanying with the increase of activation temperature and the extension of activation time, which will further cause the increase of the sample ablation and the decrease of the yield.

2.2. Influences of Activation Conditions on Pore Structure Table 2 shows the data about specific surface area and pore structure of bamboo/lignite activated carbon prepared under different activation conditions. From Table 2, it can be known that under the conditions of the same activation temperature (850C) and activation time (120 min), the specific surface area of activated carbon samples (BLAC1-4) decreased firstly and increased later along with the increasing ammonia concentration. When the ammonia concentration was more than 8.48%, the increasing range of specific surface area tended to slow down, the pore volume started to decrease.


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Guojie Zhang, Yongfa Zhang, Fuai Tian et al. Table 1. Activated carbon yield under the different activation conditions

No.

Samples

1 2 3 4 5 6 7 8 9 10 11 12 13 14

BLC BLAC BLAC1 BLAC2 BLAC3 BLAC4 BLAC5 BLAC6 BLAC7 BLAC8 BLAC9 BLAC10 BLAC11 BLAC12

Carbonization Conditions (C, min) 500,30 500,30 500,30 500,30 500,30 500,30 500,30 500,30 500,30 500,30 500,60 500,30 500,30 500,30

Activation Conditions (C, min) 850,120 850,120 850,120 850,120 850,120 850,120 750,120 800,120 900,120 950,120 850,30 850,60 850,90 850,150

Ammonia Concentration (wt. %)

Flow (ml/min)

Yield (%)

0.00 2.42 8.48 14.53 21.91 8.48 8.48 8.48 8.48 8.48 8.48 8.48 8.48

0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

24.09 10.80 11.55 12.53 14.21 15.14 19.44 15.42 10.00 8.35 21.75 18.16 15.68 12.02

Table 2. Specific surface areas, pore volume and pore size Sample name BLC BLAC

Specific surface area (m2/g) 31.72 586.58

pore volume (cm3/g) 0.0081 0.4439

pore size (nm) 1.021 3.027

BLAC1 BLAC2 BLAC3 BLAC4 BLAC5 BLAC6 BLAC7 BLAC8 BLAC9 BLAC10 BLAC11 BLAC12

496.44 571.24 551.01 589.49 279.10 479.48 560.84 545.35 195.72 323.87 410.01 597.96

0.3954 0.4531 0.4183 0.4158 0.3563 0.3596 0.4014 0.4091 0.2400 0.3657 0.3879 0.5029

3.186 3.173 3.037 2.821 5.106 3.000 2.863 3.001 4.905 4.517 3.784 3.364



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Figure 1. Pore distribution of BLAC and BLAC1-4 samples.

Figure 2. The effect of activation temperature on specific surface area.

Figure 1 is the pore size distribution diagram of activated carbon samples (BLAC, BLAC1-4). It can be seen that the pore after the ammonia activation was similar to that after the steam activation, mainly distributed between 10Å-25Å. The increase of the ammonia concentration had no significant influence on the pore size distribution. Figure 2 shows the


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influences of activation temperature on the specific surface area of the activated carbon samples (BLAC2, BLAC5-8). From Figure 2 and Table 2, it can be seen that under the conditions of the same activation time and ammonia concentration, the specific surface area of activated carbon sample increased firstly and decreased later along with the increasing activation temperature; while the pore volume gradually increased. The reason can be that the increasing temperature aggravates the local gasification reaction rate. When the activation temperature is over 850C, the most closed micropores are opened. The activation reaction gradually consumes the pore wall carbon and causes the collapse of micro-pores. In this way, meso-pores and macro-pores are generated. The over activation leads to the collapse of newly-generated macro-pores, which results in the decrease of the specific surface area [21].

2.3. Surface Characteristic Analysis of Activated Carbon The results of XPS and elemental analysis on the four samples (BLAC, BLAC1, BLAC4, BLAC4a and BLAC4b) are shown as Table 3 and Figure 3. It can be seen that the carbon contents of BLAC, BLAC1 and BLAC4 has no significant changes while the oxygen content decreased with the increase of the ammonia concentration. The major reason for the decreasing oxygen content lies in that-NH- (decomposed by NH3) replaces para-ether oxygen in xanthenes in the high-temperature ammonia modification process. Furthermore, it can be found that the nitrogen content in BLAC4a sample increased compared with that in BLAC4. This may be due to the nitrogen adsorption of activated carbon in the process of catalytic flue gas desulphurization. The nitrogen content in BLAC4b sample after desorption SO2 regeneration obviously decreased compared with that in BLAC4. This is likely to be related to the ammonium salt formed in the acidization process of amine, amide, imide nitrogen-containing group introduced in the ammonia activation process, which came about the thermal decomposition in the thermal regeneration process [26, 27].



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Figure 3. N1s XPS spectrum of the sample.

Table 3. Elemental analysis of activated carbon samples by XPS Sample name BLAC4 BLAC4a BLAC4b BLAC1 BLAC

C 91.56 79.50 89.92 91.59 91.44

Element, Content/% O N 7.30 1.14 16.04 1.50 8.86 0.88 7.52 0.89 8.56 -

S 2.96 0.36 -

N1s spectrogram of BLAC, BLAC1 and BLAC4 activated carbon samples is shown in Figure 3. It can be seen that there is no N1s peak in BLAC sample prepared by steam activation, while there are obvious N1s peaks in BLAC1 and BLAC4 samples prepared by ammonia activation. This indicated that, nitrogen in the ammonia was introduced into activated carbon in the ammonia activation process.


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Guojie Zhang, Yongfa Zhang, Fuai Tian et al. Table 4. Relative content of C and N functional group

Functional groups C C-C C-O C=O COOH π-π* N N-6 N-5 N-Q

Electron binding energy (eV) 284.0-285.1 285.3-286.3 286.8-288.1 288.5-290.0 290.2-291.1 398.3-398.9 400.2-400.8 401.0-401.6

BLAC4 71.50 20.41 4.12 0.69 3.28 29.55 70.45 -

Relative intensity (%) BLAC4a BLAC4b BLAC1 70.80 20.13 5.17 0.81 3.08 8.39 38.47 21.17 16.36 46.93 78.83 75.25 14.60 -

BLAC 58.25 24.92 9.42 2.21 5.20 -

Table 5. Relative content of S functional group Functional groups S Adsorbed SO3 SO42Chemisorption SO2 SO32S-x

Electron binding energy (eV) 171.0 169.2 168.3 167.0 163.4~163.9

BLACa 11.69 53.59 34.72 -

Relative intensity (%) BLACb BLAC4a BLAC4b 3.62 7.91 2.07 65.42 70.93 36.90 18.36 21.16 33.74 3.08 15.60 9.52 11.69

XPS is used to analyze the surface states of BLAC, BLAC1 and BLAC4 before and after sulphur adsorption and desorption, respectively. The analysis results are shown as Table 4, Table 5 and Figure 4-6. C1s XPS spectrogram of BLAC, BLAC1 and BLAC4 activated carbon samples is shown in Figure 4. It can be seen that there are several complicated carbon species on the surfaces of BLAC, BLAC1 and BLAC4 samples. They are graphitic carbon (peak1, 284.0-285.1eV), carbon bonded with phenols group (peak2, 285.3~286.3eV), alcohol group and ether group (peak3, 286.8~288.1eV), carbonyl compound, carboxyl group or esters group (peak4, 288.5~290.0eV), and vibration half peak caused by aromatic nucleus π-π* transition (peak5, 290.2~291.1eV) [9, 11, 28-31]. Combined with the elemental analysis results in Table 3, it can be seen that carbon contents in these three samples are of no great difference, but the carbon content of C



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after steam activation is a little higher than that of BLAC1 and BLAC4 after ammonia activation. However, it can be seen from the relative content of C group in Table 4 that the relative content of C-C group in samples (BLAC1 and BLAC4) after ammonia activation obviously increased (12.55%13.25%), while C-O, C = O and COOH groups obviously decreased (respectively decreased by 4.5%-4.8%, 4.3%-5.3% and 1.4%-1.5%) compared with those in samples (BLAC) after steam activation. This result may be caused by the following reasons. –COOH on the surface of bamboo/lignite activated carbon bonded with NH3 to form ammonium salt, which would generate carboxyl amide and nitriles group under the heating condition [28].  H 2O  H 2O COOH  NH 4  CO  NH 2  C  N

a

b

Figure 4. (Continued)


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c 1: graphitic carbon; 2: carbon bonded with phenols group; 3: alcohol group and ether group; 4: carbonyl compound, carboxyl group or esters group; 5: vibration half peak caused by aromatic nucleus π-π* transition. Figure 4. C1s XPS spectrum of the samples.

a

b

Figure 5. (Continued)



c

119

d

A: para-pyridine or para-nitrile group (N-6); B: para-pyrrole, amine, amide and imide group (N-5); C: protonation pyridine nitrogen and amine salt (N-Q). Figure 5. N1s XPS spectrum of the samples.

Among them, -OH bonded with NH3 to generate amine group [28].

OH  NH3   NH 2  H 2O In the reaction of high-temperature ammonia activation process, NH3 was decomposed into H·, NH· and other radicals. Among them, it is easy for -NH- in radical NH2·to replace para-ether oxygen in xanthenes and after dehydration formed para-pyridine or acridine group at the edge of carbon layer [32], shown as the figure below.

N1s XPS spectrogram of BLAC1, BLAC4, BLAC4a and BLAC4b activated carbon samples is shown as Figure 5. It can be seen that there are


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several complicated nitrogen-containing groups on the surfaces of these four samples. They are para-pyridine or para-nitrile group (called N-6) (peak A, 398.3-398.9eV), para-pyrrole, amine, amide and imide group (called N-5) (peak B, 400.2-400.8eV). Through comparison, it was found that in BLAC4a sample after SO2 adsorption and BLAC4b sample after desorption SO2 regeneration, there was a new nitrogen-containing group, protonation pyridine nitrogen and amine salt (called N-Q) (peak C, 401~401.6eV) [17, 31-34]. Besides, it can be seen from XPS elemental analysis in Table 3 that the nitrogen content of BLAC1 prepared by 2.4% ammonia activation was higher than BLAC4 prepared by 21.9% ammonia activation. From the relative contends of various nitrogen-containing groups in Table 4, it can be seen that the relative content of N-5 in BLAC1 was higher than that in BLAC4. It indicated that under the condition of low-concentration ammonia activation (2.4%), ammonia firstly reacted with –COOH, –OH and other oxygen-containing groups on the bamboo/lignite activated carbon surface and generated N-5 group. While under the condition of high-concentration ammonia activation (21.9%), NH3 reacted with oxygen-containing groups, at the same time, some of NH3 decomposed into H·, NH2· and NH· and other radicals under the high temperature. Radicals (NH2· and NH·) had substitution reactions with xanthenes and formed para-pyridine at the edge of carbon layer after dehydration. Besides, radical NH· combined with the active site produced by evaporation (shown as the figure below) or directly ablated the edge of carbon layer to generate N-6 nitrogen species [35].

Therefore, N-6 content in BLAC4 was higher than that in BLAC1. Though contents of N-5 and N-6 in BLAC1 and BLAC4 have differences, the contents of these two kinds of nitrogen species were at the same quantity level. The relative contents of N-5 and N-6 in C4a were obviously lower



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than those in BLAC4 and the content of N-Q in BLAC4a is high. This may be related to the ammonium salt of N-Q generated from the acid in the flue gas desulphurization process and amine in N-5 or protonation pyridine nitrogen of N-Q generated from the proton in H2O and pyridine nitrogen in N-6 [27, 29]. Compared with BLAC4a, the relative contents of N-5 and N6 in BLAC4b relatively increased and the relative content of N-Q dramatically decreased. The reason for this may be attributed to the pyrolysis of the amine salt in the activated carbon regeneration process. However, there is still 14.6% N-Q. This part may be protonation pyridine nitrogen, its property is relatively stable. Compared with BLAC4b and BLAC4, it can be found that N-5 tended to transform into N-6 after the activated carbon regeneration. The desulphurization performance of samples after ammonia activation has great improvements compared with original sample BLC and BLAC after steam activation. This mainly lies in the introduced nitrogen-containing species with catalytic oxidation activity after ammonia activation. The nitrogen atoms in these nitrogen-containing species contain arc electrons, so they manifest strong alkalinity and have strong affinity to acid SO2 gas, which thus improve the desulphurization performance. Besides, nitrogen group with arc electron pairs can provide free electrons eˉ, which can be transferred to the conduction band under the condition of high energy, further promoting the transfer to the absorption species. For example, the absorption species is O2 [6, 37], then,

O2ads  e  O2 Superoxide species O2ˉ generated from the arc electron transfer has strong catalytic oxidation activity. The catalytic oxidation performance of nitrogen-containing bamboo/lignite activated carbon mainly depends on the electric conduction performance of nitrogen heterocyclic atom. In the electron transfer reaction, carbon catalytic activity increases along with the decrease of band-gap energy △E of condensation nitrogen-containing system. Quantum chemistry calculation results showed that pyrrole nitrogen and pyridine nitrogen group had extremely high electric charge mobility and


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electron donor-acceptor performance [28]. The comprehensive studies demonstrated that N-6 group introduced by ammonia activation had significant influence on the desulphurization performance of activated carbon [36, 37].

a

b

c

d

A: physical adsorbed state SO3; B: SO42-; C: chemical adsorbed state SO2; D: SO32-; E: S-X. Figure 6. S2p XPS spectrum of the samples.



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S2p spectrogram of samples after SO2 adsorption and desorption of steam and ammonia activation is shown as Figure 6. Compared with Figure 5, the activated carbon sample after adsorption and desorption contained the following sulphur-containing groups: SO3 of physical adsorbed state (peak A, 171.0eV), SO42- (peak B, 169.2eV), SO2 of chemical adsorbed state (peak C, 168.3eV), SO32- (peak D, 167.0eV) and S-X (peak E, 167.0eV). From the relative contents of each S2p functional group in samples shown in Table 5, it can be seen that S2p functional groups on BLACa surface existed in forms of SO2 of chemical adsorbed state, SO42- and SO3 of physical adsorbed state, respectively accounting for 34.72%, 53.59% and 11.69%. S2p functional groups on BLAC4a surface also existed in these three forms, but its content of SO42- shall reach up to 70.93%, with only 21.16% SO2 of chemical adsorbed state and 7.91% SO3 of physical adsorbed state. This indicated that nitrogen-containing group in activated carbon introduced by ammonia activation promoted the generation of H2SO4 from SO2 in form of catalytic oxidation, instead of existing in activated carbon in form of SO2 of physical or chemical adsorbed state. Furthermore, from the relative contents of S2p functional groups in activated carbon samples (BLACb and BLAC4b) after desorption SO2 regeneration, it can be seen that after the thermal regeneration of BLACa and BLAC4a, some of SO2 didn’t go through complete desorption. SO42content in BLACb shall reach 65.42%, while SO42- content in BLAC4b only was 36.90%. It indicated that the desorption performance of activated carbon after ammonia activation was superior to the activated carbon after steam activation, under the same thermal regeneration conditions. What’s more, SO2 of chemical adsorbed state in BLACb accounted for 18.36%, while that in BLAC4b was only 33.74%. At the same time, a new S-x species (163.4eV-163.9eV) occurred. This indicated that the chemical adsorption capacity of BLAC4b to SO2 to was higher than that of BLACb. This also was a reason for the higher desulphurization capacity of BLAC4b.


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a

b Figure 7. Effect of ammonia concentration on desulphurization performance and sulfur capacity.



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2.4. Influences of Preparation Conditions on the Desulphurization Performance 2.4.1. I Influences of Ammonia Concentration Figure 7 shows the influences of ammonia concentration on the desulphurization performance of samples. It can be seen from Figure 7 that the desulphurization performance of BLC sample without activation could be penetrated in 20 min and its sulfur capacity was 3.4 mg/g. For C prepared by steam activation, its desulphurization performance was further improved and its sulfur capacity reached 69.8 mg/g. Unfortunately, its desulphurization performance was still not significant. For BLAC1 prepared by low-concentration ammonia activation (2.42%), its desulphurization performance dramatically improved and its sulfur capacity was 1.52 times of that of BLAC. Under the same activation temperature (850C) and activation time (120 min), the desulphurization performance of activated carbon samples (BLAC1-4) gradually increased along with the increasing activator ammonia concentration. However, when the ammonia concentration was above 8.48%, the increasing trend of desulphurization performance of samples became slow down. When the ammonia concentration was 8.48%, the sulfur capacity of BLAC2 increased to 132.2 mg/g. When the ammonia concentration was 21.9%, the sulfur capacity of BLAC4 was only 155.90 mg/g. Thus, the optimal ammonia concentration is 8.48%-14.53%. Generally, the larger the specific surface area of the material is, the better the adsorption performance of the material is and the larger the sulfur capacity is. However, the data comparison in Table 3 presented that the specific surface area of BLAC1 after ammonia activation was obviously less than that of activated carbon BLAC after steam activation, while its sulfur capacity and desulphurization performance increased dramatically. This result may be attributed to the introduction of some N-6 nitrogen-containing group with catalytic oxidation performance into bamboo/lignite activated carbon in the preparation process of bamboo/lignite activated carbon by ammonia activation. Also, the relative content of N-6 increased with the increase of ammonia concentration, the sulfur capacity of BLAC4 with


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higher N-6 elative content (29.55%) was higher than that of BLAC1 with lower N-6 elative content (21.17%). This demonstrated that the amino-group introduced by ammonia activation had an important influence on the desulphurization performance.

2.4.2. Influences of Activation Temperature Figure 8 shows the influences of different activation temperatures on the desulphurization performance of samples. It can be seen that under the same activation time (120 min) and ammonia concentration (8.48%), the desulphurization performance of activated carbon samples increased firstly and decreased later along with the increasing activation temperature. This is probably a consequence of the speeding-up local gasification reaction rate and the development of specific surface area and pore structure along with the rising activation temperature. At the same time, the quantity of active sites in favor of the reaction with ammonia, which were left by the reaction of steam and carbon, increased correspondingly. Along with the increase of activation temperature, the ablation rate of edge carbon at the carbon layer of radicals H·, NH2· and NH· decomposed from ammonia at high temperature also speeded up and N-6 nitrogen-containing groups with catalytic activity in bamboo/lignite activated carbon increased also. In this way, its desulphurization performance increased. However, when the temperature was above 900C, the desulphurization performance of nitrogen-containing bamboo/lignite activated carbon decreased, because of the excessive collapse of micropore structure for overactivation, leading to the substantially decrease of specific surface area. Furthermore, the excessive ly high temperature may transform N-6 nitrogen-containing groups introduced by ammonia activation into other nitrogen-containing groups [26]. Seen from above, the optimal activation temperature is 850C900C.



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a

b Figure 8. Effect of activation temperature on desulphurization performance and sulfur capacity.

2.4.3. Influences of Activation Time Figure 9 shows the influences of activation time on the desulphurization performance of samples. It can be seen from Figure 9 and Table 3 that under the same activation time and ammonia concentration, the specific surface


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area of BLC sample without activation was only 31.72 m2/g, its pore structure was not developed and the sulfur capacity was only 3.43 mg/g.

A

b Figure 9. Effect of activation time on desulphurization performance and sulfur capacity.



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Thus it was penetrated within 20 min of desulphurization. After activation, the specific surface area, sulfur capacity and desulphurization performances of activated carbon substantially improved. At the same time, along with the extension of activation time, the aggravating local gasification reaction rate of steam, ammonia and carbon, the blocked meso-pore and micro-pore were opened. The specific surface area and pore structure were developed. At the same time, nitrogen-containing groups introduced by ammonia activation were beneficial to desulphurization. When the activation time was 150 min, the specific surface area of BLAC12 reached 597.96 m2/g and its sulfur capacity was 152.41 mg/g. It also can be seen from Figure 9 and Table 3 that under the same activation time (850C) and ammonia concentration (8.48), the desulphurization performance of sample improved along with the extension of activation time. However, along with the extension of activation time, the yield of activated carbon decreased. When the activation time was 150 min, the yield was only 12.0%. Comprehensive consideration, the optimal activation time is 120 min-150 min.

CONCLUSION The pore structure of bamboo/lignite activated carbon after ammonia activation was similar to that after steam activation. The pore size distribution mainly fell between 10Å~25Å. Along with the increase of ammonia concentration, the yield of activated carbon gradually increased; the specific surface area decreased firstly and increased later; and the pore volume gradually decreased. The specific surface area increased firstly and decreased later, the pore volume gradually increased, along with the increase of activation temperature. Compared with steam activation, there were N1s peaks of two new materials on the surface of the bamboo/lignite activated carbon of ammonia activation: N-6 (para-pyridine) and N-5 (para-pyrrole and amine). The studies confirmed that N-6 group introduced by ammonia activation owned extremely high electric charge mobility and electron donor-acceptor


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performance, which increased the electric conduction performance of activated carbon after activation and further dramatically improved the catalytic oxidation desorption performance of flue gas SO2. In the flue gas desulphurization process, some para-pyridine nitrogen-containing groups with nitrogen at different positions generated protonation para-pyridine nitrogen N-Q in the acidization process. At the same time, the introduced amine activity group (N-5) generated into ammonium salt in the acidization process. It resulted in the inactivation of activated carbon. Studies on the preparation of activation conditions were found that along with the increases of ammonia activation concentration and activation time, the sulfur capacity and desulphurization performances of the activated carbon improved. However, the excessively long activation time could decrease the yield coefficient of activated carbon. Along with the increase of activation temperature, the desulphurization performance and specific surface area presented the trend of increasing firstly and decreasing later and excessively high temperature was not good to the formation of active material N-6 group. In conclusion, the optimal activation conditions are 8.48%-14.53% ammonia concentration, 850C-900C activation temperature and 120 min-150 min activation time.

ACKNOWLEDGMENTS Project supported by the Natural Science Foundation of China (Grant Nos. 21376003, 21676174 and U1610115), National Basic Research Program of China (Grant No. 2005CB221202), National Science and Technology Pillar Program (Grant No. 2012BAA04B03) and the Joint Fund of Shanxi Provincial Coal Seam Gas (2015012019).



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REFERENCES [1]

Li, Y., (2001). Property conversion of activated coke from lignite and research on its performance of desulfurization. Coal Process. Compr. Util. 4, 30-32. [2] Chen, P, (1998). Basic research concerning high efficiency and clean utilization of coal. Clean Coal Technol. 4, 5-7. [3] Zhang, G., Hao, L., Tian, F., Zhang, Y., (2016). Synthesis of amination bamboo-lignite activated carbon and their properties. Mater. Res. Innov. 20(3), 170-176. [4] Li, G.Q., Tian F.H., Zhang Y.F., Ding, J.L., Fu Y.L., Wang, Y., Zhang G.J,(2014) Bamboo/lignite-based activated carbons produced by steam activation with and without ammonia for SO2 adsorption. New Carbon Mater. 29(6): 486-492). [5] Guo, R., (2009). Study on Removal of Sulfur Dioxide and Nitric oxides by Activated Semi-Coke (Doctoral dissertation, Masters thesis, Ocean University of China, Qingdao). [6] Boehm, H.P., Mair, G., Stoehr T., (1984). Carbon as a catalyst in oxidation reactions and hydrogen halide elimination reactions. Fuel 63, 1061-1063. [7] Cariaso, O.C., Walker Jr, P.L., (1975). Oxidation of hydrogen sulfide over microporous carbons. Carbon 13, 233-239. [8] Sreeramamurthy, R., Menon, P.G., (1975). Oxidation of H2S on active carbon catalyst. J. Catal. 37, 287-296. [9] Shang Guan, J., Li, C., Miao, M., Yang, Z., (2008). Surface characterization and SO2 removal activity of activated semi-coke with heat treatment. New Carbon Mater. 23, 37-43. [10] Rubio, B., Lzquierdo, M.T., (1997). Influence of low-rank coal char properties on their SO2 removal capacity from flue gases: I. Nonactivated chars. Carbon 35, 1005-1011. [11] Shalaby, C., Ma, X., Song, C., (2013). Preparation of HighPerformance Adsorbent from Coal for Adsorptive Denitrogenation of Liquid Hydrocarbon Streams. Energy Fuels 27, 1337-1346.


132


[12] Shalaby, C., Ma, X., Zhou, A., Song, C., (2009). Preparation of Organic Sulfur Adsorbent from Coal for Adsorption of Dibenzothiophene-type Compounds in Diesel Fuel. Energy Fuels 23, 2620-2627. [13] Guo, Y., Li, Y., Zhu, T., Ye, M., (2013). Effects of Concentration and Adsorption Product on the Adsorption of SO2 and NO on Activated Carbon. Energy Fuels 27, 360-366. [14] Tang, L., Huang, H., (2005). Plasma Pyrolysis of Biomass for Production of Syngas and Carbon Adsorbent. Energy Fuels 19, 11741178. [15] Bain, E.J., Calo, J. M., Steinberg, R., Kirchner, J., Axén, J., (2010). Electrosorption/Electrodesorption of Arsenic on a Granular Activated Carbon in the Presence of Other Heavy Metals. Energy Fuels 24, 34153421. [16] Stöhr, B., Boehm, H.P., (1991). Enhancement of the catalytic activity of activated carbons in oxidation reactions by thermal treatment with ammonia or hydrogen cyanide and observation of a superoxide species as a possible intermediate. Carbon 29, 707-720. [17] Tomlinson, J.B., Freeman, J.J., Theocharis, C.R., (1993). The preparation and adsorptive properties of ammonia-activated viscose rayon chars. Carbon 31, 13-20. [18] Piñero, E.R., Amorós, D.C, Solano, A.L., (2003). The role of different nitrogen functional groups on the removal of SO2 from flue gases by N-doped activated carbon powders and fibres. Carbon 41, 1925-1932. [19] Liu, Q., Li, C., Li, Y., (2003). SO2 removal from flue gas by activated semi-cokes: 1. The preparation of catalysts and determination of operating conditions. Carbon, 41(12), 2217-2223. [20] Liu, Q., Shang-Guan, J., Li, J., (2003). SO2 removal from flue gas by activated semi-cokes: 2. Effects of physical structures and chemical properties on SO2 removal activity. Carbon 41, 2225-2230. [21] Tan, Z., Qiu, J., Zeng, H., Liu, H., Xiang, J., (2011). Removal of elemental mercury by bamboo charcoal impregnated with H2O2. Fuel 90, 1471-1475.



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[22] Li, S., Shi, Y., Yang, Y., Zheng, Y., Cai, N., (2013). HighPerformance CO2 Adsorbent from Interlayer Potassium-Promoted Stearate-Pillared Hydrotalcite Precursors. Energy Fuels 27, 53525358. [23] Ochiai, R., Uddin, M. A., Sasaoka E., Wu, S., (2009). Effects of HCl and SO2 Concentration on Mercury Removal by Activated Carbon Sorbents in Coal-Derived Flue Gas. Energy Fuels 23, 4734-4739. [24] Rubio, B., Teresa, M., (1998). Low cost adsorbents for low temperature cleaning of flue gases. Fuel 77, 631-637. [25] Molina-Sabio, M., Muñecas, A. M. A., Rodriguez-Reinoso, F., McEnaney, B., (1995). Adsorption of CO2 and SO2 on activated carbons with a wide range of micropore size distribution. Carbon 33(12), 1777-1782. [26] Davini, P., (1989). Adsorption of Sulphur dioxide on thermally treated active carbon. Fuel 68(2), 145-148. [27] Cheng, H., Endo, H., Okabe, T., Saito, K., Zheng, G., (1999). Graphitization behavior of wood ceramics and bamboo ceramics as determined by X-ray diffraction. J. Porous Mater 6, 233-237. [28] Henriette, E.S., (2004). XPS photoemission in carbonaceous materials: a ‘defect’ peak beside the graphitic asymmetric peak. Carbon 42, 1713-1721. [29] László, K., Tombácz, E., Josepovits, K., (2001) Effect of activation on the surface chemistry of carbons from polymer precursors. Carbon 39, 1217-1228. [30] Desimoni, E., Casella, G.I., Salvi, A.M., (1992). XPS/XAES study of carbon fibres during thermal annealing under UHV conditions. Carbon 30, 521-526. [31] Biniak, S., Szymański, G., Siedlewski, J., Swiatkowski, A., (1997). The Characterization of activated carbons with oxygen and nitrogen surface groups. Carbon 35, 1799-1810. [32] Stöhr, B., Boehm, H. P., and Schlögl, R., (1991). Enhancement of the catalytic activity of activated carbons in oxidation reactions by thermal treatment with ammonia or hydrogen cyanide and observation of a superoxide species as a possible intermediate. Carbon 29(6), 707-720.


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[33] Pels, J.R., Kapteijn, F., Moulijn, J.A., Zhu, Q., Thomas, K.M., (1995). Evolution of nitrogen functionality in carbonaceous materials during pyrolysis. Carbon 33, 1641-1653. [34] Jansen, R.J.J., Bekkum, H.V., (1995). XPS of nitrogen-containing functional groups on activated carbon. Carbon 33, 1021-1027. [35] Strelko, V.V., Kuts, V.S., Thrower, P.A., (2000). On the mechanism of possible influence of heteroatoms of nitrogen, boron and phosphorus in carbons in electron transfer reactions. Carbon 38, 14991503. [36] Li, K., Ling, L., Liu, L., Zhang, B., Liu, Z., (2000). Desulfurization of active carbon f ibers activated with ammonia water. Acta Sci. Circumstantiae 21, 74-78. [37] Zawadzki, J., (1987). Infrared studies of SO2 on Carbon-II. The SO2 species adsorbed on carbon films. Carbon 25, 495-502.

BIOGRAPHICAL SKETCHES Yongfa Zhang, Eng.D. Dr. Zhang is Professor and Vice Director of Key Laboratory of Coal Science and Technology of Ministry of Education, Taiyuan University of Technology. He received his BS in Engineering from the East China University of Science and Technology and Doctor of Engineering from Taiyuan University of Technology. He is the Secretary General of the Shanxi Energy and Conservation Association, and is an associate editor of Journal of the China Coal Society, The coal process and application and The China Journal of Energy and Conservation. Dr. Yongfa Zhang has published over 120 refereed papers in academic and professional journals, mainly related to coal, energy, various issues in clean coal technology, and coal education. His papers have appeared in Fuel, Carbon, Fuel Science and Technology Int’l, Catalysis Today, Chemical Engineering Journal, Journal of the China Coal Society, Chemical Engineering (China), Modern Chemical Industry, Chemical Reaction Engineering and Technology, The



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Chinese Journal of Process Engineering and Frontiers of Chemical Engineering in China. Prof. Zhang is a world-famous scholar who has published the most research works internationally among clean coal technology. His major teaching and research areas are clean coal and coal gasification. He is a consultant expert of the Organization Department of the CPC Central Committee.

Guoqiang Li, Eng.D. Dr. Li is teacher of Key Laboratory of Coal Science and Technology of Ministry of Education. Dr. Li received both his PhD in Engineering from the Taiyuan University of Technology. He is a Fellow of the Shanxi Energy and Conservation Association. He teaches Process analysis and optimization, Coal Chemistry and Coking technology. Dr. Li has numerous publications in academic and professional journals, mainly related to issues in energy and environment. Current research interests include clean coal technology, wastewater treatment.

Ying Xu, Eng.D. Dr. Xu is teacher of Key Laboratory of Coal Science and Technology of Ministry of Education. Dr. Xu received both her PhD in Engineering from the Taiyuan University of Technology. She is a Fellow of the Shanxi Energy and Conservation Association. She teaches Process analysis and optimization, Coal Chemistry and Coking technology. Dr. Xu has numerous publications in academic and professional journals, mainly related to issues in Coal and environment. Current research interests include clean coal technology.


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Guojie Zhang Affiliation: Associate Professor, Key Laboratory of Coal Science and Technology of Ministry of Education, Taiyuan University of Technology, Taiyuan China, Email: [email protected]; [email protected] Homepage: http://cst.tyut.edu.cn/list.asp?id=338 Education  PhD in Chemical Engineering Taiyuan University of Technology, Taiyuan, Shanxi, China, 2012  Master of Science in Energy and Chemical Engineering Taiyuan University of Technology, Taiyuan, Shanxi, China, 2006  Bachelor of Energy and Chemical Engineering Anhui University of Technology, Maanshan, Anhui, China, 2001 Work Experience Taishan Steel Group Co., Ltd 09/2001-09/2003 The University of Western Australia (Visitor) 11/2014-11/2015 Taiyuan University of Technology 09/2006Research Interests  Energy  Coal, CH4 reforming, Biomass  Chemical Engineering  Environment  Water and Wastewater Treatment  Gas treatment Professional Experience  Editorial Member  Chemical and Biomolecular Engineering(CBE)


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Peer Reviewer  International Journal of Hydrogen Energy  Fuel  Energy and Fuels  Fuel Processing Technology  Journal of Colloid and Interface Science  Journal of Industrial and Engineering Chemistry  Journal of CO2 Utilization  Applied Catalysis B: Environmental  Journal of Natural Gas Chemistry  Journal of the Taiwan Institute of Chemical Engineers  Applied Bioenergy  Applied Energy  Asia-Pacific Journal of Chemical Engineering  Energy  Energy Conversion and Management  Environmental Engineering Science  Environmental Progress and Sustainable Energy  International Journal of Petroleum Engineering  Journal of Cleaner Production  Journal of Energy Engineering  Journal of Environmental Management  Journal of Petroleum and Environmental Biotechnology

Professional Society  Member, Chinese Chemical Society, 2016–Present  Member, The Chemical Industry and Engineer Society of China, 2016–Present  Deputy secretary general, Shanxi Energy Research Association, 2015–Present


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Journal Articles  Characterization of Ca-promoted Co/AC catalyst for CO2-CH4 reforming to syngas production. Journal of CO2 Utilization, 2017, 18: 326-334.  Characteristic and kinetics of corn stalk pyrolysis in a high pressure reactor and steam gasification of its char. Journal of Analytical and Applied Pyrolysis, 2016, 122: 249-257.  Synthesis of ZrO2-based catalyst for coke oven gas CO shift via an orthogonal experiment design. Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 2016, 46(1): 91-94.  Optimization of process conditions for raw materials production of fertilizer by non-catalytic partial oxidation of COG. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2016, 38(21): 3229-3235.  Synthesis of amination bamboo-lignite activated carbon and their properties. Materials Research Innovations, 2016, 20(3): 170-176.  CO2 reforming of CH4 over Efficient bimetallic Co-Zr/AC catalyst for H2 production. International Journal of Hydrogen Energy. 2015, 40(37):12868-12879.  Towards understanding the carbon catalyzed CO2 reforming of methane to syngas. Journal of Industrial and Engineering Chemistry. 2015, 21(1): 311-317.  Effects of preparation conditions on performance of discarded biological oil as coal flotation collectors. International Journal of Oil, Gas and Coal Technology. 2015, 10(2):94-99.  Shrinkage character in the process of semi-coke formation. Chiang Mai Journal of Science, 2015, 42(2): 401-406.  Effects of preparation methods on the properties of cobalt/carbon catalyst for methane reforming with carbon dioxide to syngas. Journal of Industrial and Engineering Chemistry. 2014, 20(4):16771683.


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Desulfurization reaction model and experimental analysis of high sulfur coal under hydrogen atmosphere. Journal of Industrial and Engineering Chemistry. 2014, 20(2):487-493. Thermogravimetric study of the kinetics and characteristics of the pyrolysis of lignite. Reaction Kinetics Mechanisms and Catalysis, 2013, 110(1): 225-235. Selective methanation of carbon monoxide over Ru-based catalysts in H2-rich gases. Journal of Industrial and Engineering Chemistry. 2012, 18(5): 1590-1597. Syngas production by carbon dioxide reforming of methane over different semi-cokes. Journal of Power Sources, 2013, 231:82-90.

Proceedings  Taotal China Scientific Forum, Beijing, China, 2016  Coal Ash Asia, Shuozhou, China, 2016  The International Conference on Energy Equipment Science and Engineering, Guangzhou, China, 2015 Honors, Awards, and Fellowships  2000 Outstanding Intellectuals of the 21st Century - 2016 (10th EditionInternational Biographical Centre, Cambridge, England);  The Cambridge Certificate for Outstanding Scientific Achievement (International Biographical Centre, Cambridge, England);  Marquis Who’s Who in the World 2015 (32nd Edition), US  2000 Outstanding Scientists 2016, International Biographical Centre, Cambridge, UK





Chapter 5

POLYMER-WASTE-DERIVED NANOPOROUS CARBON FOR REMOVAL OF METHYL ORANGE AND BROMOPHENOL BLUE FROM AQUEOUS SOLUTIONS B. Tsyntsarski1,*, I. Stoycheva1, B. Petrova1, T. Budinova1, N. Petrov1, A. Sarbu2 and A. Radu2 1

Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Sofia, Bulgaria 2 National Research- Development Institute for Chemistry and Petrochemistry, INCDCP-ICECHIM, Bucharest, Romania

ABSTRACT Polyolefin wax, an industrial by-product from polyethylene processing at low pressure, is used to obtain activated carbon by thermochemical treatment and subsequent hydro-pyrolysis. The structure and surface properties of the activated carbon obtained are characterized by

*

Corresponding Author Email: [email protected].


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B. Tsyntsarski, I. Stoycheva, B. Petrova et al. different methods - N2 adsorption, IR spectrometry, and surface oxygen groups content. The adsorption of methyl orange and bromophenol blue from aqueous solutions by thus synthesized activated carbon was studied in a batch adsorption system. Langmuir model is applied to investigate the adsorption process. The activated carbon obtained from polyolefin wax demonstrates high adsorption capacity towards dyes - 106 mg/g for bromоphenol blue and 269 mg/g for methyl orange, respectively. The effect of pH on the adsorption was investigated. The obtained results show that the synthetic activated carbon produced from polyolefin wax can be successfully used for the removal of dyes from water solutions.

Keywords: activated carbon, adsorption, dyes, hydro-pyrolysis, pyrolysis

1. INTRODUCTION The low quality of the surface and underground waters is important environmental challenge worlwide nowadays. The contamination as a result of insufficient control of municipal, industrial and agricultural wastes represents significant risk for ecosystems and humans. Water quality is not only a basic element of the application of integrated water resources management in the water basins, it is also an issue that may generate social conflicts at national and international level. For this reason it requires more attention of the society in general, and subsequent preventive measures to preserve the quality of the available water resources and their treatment, by applying methods and facilities that are environmentally friendly and close to the nature. Based on its origin, wastewater can be classified as sanitary, commercial, industrial, agricultural or surface wastewater. The sources of industrial wastewater are cement, pharmaceutical, food, textile, pulp paper, rubber, leather, cosmetics, plastic industries, color photography, organic compost, etc. 17-20% of industrial water pollution is result of textile dyeing and treatment. 300,000 tons of dyes used during the manufacturing of textile products is released into the environment worldwide annually [1-4]. The textile sector alone consumes about 60% of total dye production for coloration of various fabrics. 10-15% of dyes are dumped in waters after


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dyeing, which generates a strongly colored wastewater, typically with dye concentration 10-200 mg/l. Synthetic dyes are one of the most dangerous water pollutants. They have toxic, carcinogenic, mutagenic and teratogenic effects on humans, microorganisms, fish, etc. [1, 5]. There are many removal techniques such as chemical oxidation, precipitation, filtration, aerobic and anaerobic microbial degradation, coagulation, membrane electrochemical treatment, flotation, hydrogen peroxide catalysis and reverse osmosis, ozonation and biological techniques, which can be employed to remove various pollutant from textile industry wastewater [4]. Methyl orange and bromophenol blue can be removed by adsorption on carbon materials [6-19], oxides [20-23], phosphates [24], or zeolites [25-30], by photodegradation [31-38], electrochemical oxidation [39, 40], biodegradation [41], etc. The adsorption process provides an attractive alternative to other above mentioned processes, because it is inexpensive and ensures easy control of various pollutants in wastewaters. Due to their highly porous structure and large adsorption capacity, activated carbons are widely used as adsorbents in technologies connected to pollution abatement, pharmaceutical and food industries. In the last years appeared many reports, dedicated to the preparation of activated carbons from various cheap and alternative precursors - coal, agricultural by-products and other biomass materials, polymer materials, etc. [42-64]. Various polymer production technologies emit a large amount of byproducts, however most of these polymer wastes have not found appropriate utilization till now. Polymers and polymer wastes are suitable precursors for production of activated carbons, due to their availability and low price. Thermo-chemical conversion of polymer wastes is a promising way to produce energy as well as activated carbons with good adsorption properties and insignificant content of mineral matter. In this paper we will focus on the investigation of adsorption properties towards methyl orange and bromophenol blue of novel low-cost activated carbon, synthesized by hydropyrolysis of polymer waste - polyolefin wax, a by-product from production of polyethylene - which have not find suitable application till now. This work is intended to bring environmental contribution, connected not only with dye removal from water, but also with


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B. Tsyntsarski, I. Stoycheva, B. Petrova et al.

valorization of polymer wastes by converting them to valuable materials like efficient nanoporous adsorbents.

2. EXPERIMENTAL 2.1. Adsorbent Preparation The polyolefin wax sample is a waste product of polyethylene production at low pressure (Burgas petroleum plant, Bulgaria), and has melting point around 115oC, with average molecular mass of 1100 g/mol. When heating in air at 360oC it decomposes to low-molecular products. A mixture of 120 g polyolefin wax (POW) and 80 g furfural was heated up to 115oC until melting. Conc. sulfuric acid was added by drops during continuous stirring, and the temperature was increased up to 160oC. The obtained solid product was washed with water, and then dried at 150oC and carbonized at 600oC. The carbonizate was subjected to steam pyrolysis at 800 C for 1 h. The obtained solid product is denoted as FPOW-AC.

2.2. Surface Measurements Textural characterization was carried out by measuring the N2 adsorption isotherms at -196oC using Quantachrome NOVA 1200 apparatus. Prior to the adsorption measurements the samples were outgassed under vacuum at 300oC overnight, to remove any adsorbed moisture and gases. The isotherms were used to calculate specific surface area SBET and total pore volume Vt. Micropore and mesopore volumes were obtained by applying the DFT model to the N2 adsorption data, assuming a slit-shaped pore geometry [43].



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2.3. Determination of Oxygen Groups The content of oxygen-containing functional groups with acidic character on the carbon surface was determined applying the Boehm method by neutralization with bases of increasing strength: NaHCO3, Na2CO3, NaOH and sodium ethoxide. Four portions of the sample with mass 0.5 g were introduced to four 0.05 N 100 cm3 base solutions in sealed flasks. The suspensions were shaken at least 16 h (960 min), and then filtered. The excess of bases remaining in the solutions was determined from backtitration after adding an excess of standard HCl water solution. It was assumed that NaHCO3 was capable of neutralizing all carboxylic groups, Na2CO3 - carboxylic and lactonic groups, NaOH - carboxylic, lactonic and phenolic groups, and sodium ethoxide - all acidic groups [65]. The basic sites were determined by titration with 0.05 N HCl [66]. The procedure is the same as above mentioned, as back-titration of the excess of HCl was performed with 0.05 N NaOH water solution.

2.4. pH Determination The following procedure was carried out: 4.0 g of carbon was put into a 250 cm3 beaker and 100 cm3 of distilled water was added. The beaker was covered with a watch glass and heated to a boiling temperature for 5 min. The mixture was then set aside and the supernatant liquid was poured off at 60oC. The decanted portion was cooled down to room temperature. The initial pH was adjusted with NaOH or HCl solutions. All of the reagents were analytical grade.

2.5. Adsorption Studies Methyl orange (MO) and bromophenol blue (BPhB) from Merck company were used in our investgations. The chemical structures of MO and BPhB are shown in Scheme 1:


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Bromophenol blue Stock solutions of 1000 mg/l were prepared by dissolving accurately weighted amounts of MO (solubility in water 0.5 g/100 ml) and BPhB in separated volumes of 1000 ml distilled water. The desirable concentrations of experimental solutions were adjusted by diluting the stock solution with additional amounts of distilled water. To study the effect of different parameters - contact time, initial concentration, pH of the solution - on the removal of adsorbate on activated carbons, batch experiments were performed in 250 ml stoppered flasks, containing definite volumes (100 ml in each flask) of dye solutions with fixed initial concentrations. The sample suspensions were filtered equilibrium using filter paper in order to determine the residual concentrations. The amount of dye adsorbed at equilibrium conditions, qe (mg/g) was calculated by the following equation: qe = (Co - Ce)V/M where qe is the amount of dye adsorbed (mg/g), Co and Ce are the initial and equilibrium dye concentration (mg/l), V is the solution volume (l) and M is the amount of adsorbent (g) used.



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3. RESULTS AND DISCUSSION 3.1. Synthesis and Characterization of Activated Carbon The chemical characteristics (chemical composition, water and ash content) of the synthesized activated carbon is presented in Table 1. Elemental analysis show that activated sample has high carbon content, and low ash and sulfur content. The N2 adsorption isotherms show that FPOW-AC is characterized with an opening of the knee at low relative pressures. This indicates the development of mesoporosity (also confirmed by the presence of hysteresis loop) and a widening of the microporosity for this activated carbon. The surface characteristics are presented in Table 2. The results show that FPOW-AC is characterized by very high surface area and micropore volume. The oxygen-containing functional groups on the surface of carbon are a very important specific characteristic. The experimental data show that various oxygen-containing groups (carboxyl groups, carboxyl groups in lactone-like binding, phenolic hydroxyl and carbonyl groups) of acidic and basic character, and with different chemical properties, are present on the surface of the sample. These results are confirmed by the high oxygen content (10%) from the elemental analysis. Stretch vibrations of associated -OH groups (3400-3230 cm-1). The band at 3100 cm-1 is due to normal vibration modes of C-H at positions -3 and -4 of an aromatic ring as well as CH vibration corresponding to sp2 carbon atoms. Stretch vibrations of C = O (in -CHO, C = O, -COOH) around 1700 cm-1. The band at 1704 cm-1 could be related to the stretching of C = O in linear aliphatic aldehydes, ketones and carboxyles. The band at 1600 cm-1 cannot be interpreted unequivocally. It could be due to: 1) aromatic ring stretching coupled to highly conjugated carbonyl groups (C = O); 2) stretch vibrations of C = C bonds in aromatic structures; 3) OH groups. Stretching vibrations in the region of 3000-2800 cm-1 and deformation vibrations in the region 1470-1350 cm-1 are related to aliphatic structures in the investigated products. The bands in the region of 1360-1150 cm-1 are due to C-O in


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complex ethers and ring structures, and the bands around 600 cm-1 - to C-H deformation modes.

Figure 1. N2 adsorption isotherm (a) and pore size distribution (b) of the carbon sample.


Polymer-Waste-Derived Nanoporous Carbon … 2916 (CH2)as (CH2)s

x8

2847

C=O 1475 1709

2865

2902

x20

(CH3)s (C-C-H)

C=C

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1089

1660

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1122

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absorbance, a.u.

149

C-O 3100

3000

2900

2800

2700

2600

2000

1800

1600

1400

568

598

1000

900

1200

-1 wavenumber, cm

-1 wavenumber, cm

562

3200

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600

-1 wavenumber, cm

500

Figure 2. IR spectra of the investigated sample FPOW-AC.


1000

150

B. Tsyntsarski, I. Stoycheva, B. Petrova et al. Table 1. Chemical composition of the activated carbon

Sample Wa, wt. % Ad, wt. % C, wt. % H, wt.% FPOW-AC 2.02 2.78 84.54 2.18 a d W - water content, ash free basis; A - ash content, dry basis.

S, wt.% 1.65

O, wt.% 0.02

Table 2. BET surface area and pore volume of the sample determined by N2 adsorption Sample FPOW-AC

SBET m2/g 1015

Vtot cm3/g 0.886

Vmicro cm3/g 0.338

Vmeso cm3/g 0.033

Average pore diameter Dav, nm 2.7

3.2. Adsorption of MO and BPHB from Water Solution 3.2.1. Effect of Solution Initial pH on Dye Uptake MO chemical structures contain chromophores such as anthraquinone or azo bond, depending on the pH of the solution. The effect of pH on the removal of MO is illustrated in Figure 3. Our investigation demonstrated that under alkaline and neutral conditions, the change of initial pH has no significant effect on the adsorption for MO onto activated carbon. Therefore, the effect of the initial pH of the solution on MO removal was studied under acidic condition and the results are shown in Figure 3. It was clearly shown that the removal decreases with pH increase: the removal is around 99% when the value of pH is 2.5; when the value of pH is 5, the removal decreases down to 95%; at pH close to neutral the removal is 94%. The data obtained reveal that the alkaline medium decreases adsorption of MO. The results show that pH of the solution significantly influences the amount of MO dye adsorbed on the surface of the carbon.



Figure 3. Influence of pH on the removal of MO.

Figure 4. pH effect on BPhB removal.


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B. Tsyntsarski, I. Stoycheva, B. Petrova et al. Table 3. Nature and amount (mmol/g) of the oxygen groups on carbon surface

Sample FPOW-AC *

Carboxyl groups BDL*

Lactonic groups 0.135

Phenolic groups 0.280

Carbonyl groups 2.334

Basic groups 0.552

pH 8.0

BDL - below detection limits.

Such phenomenon may be due to the abundance of H+ ions on the surface of activated carbon, attracted to the anions in MO molecules, which enhanced the ability of adsorption of MO onto activated carbon. In contrast OH- ions cause repulsion between the negatively charged surface and the dye molecule. As shown in Figure 4, pH value influences significantly the adsorption of BPhB on activated carbon. It was found that the removal of BPhB was 92% at pH 3, and it decreases with pH increase. When the value of pH is 4 the removal is 57%, and then continues to decrease simultaneously with pH increase to 8. There is a difference between the adsorption of MO and BPhB in basic medium - for BPhB, the removal increases at pH > 7, which is due to the chemical nature of the dye molecule, while pH had no significant effect on the adsorption for MO onto activated carbon.

3.2.2. Effect of Contact Time and Initial Concentration Equilibrium time is one of the most important parameters in the design of economical wastewater treatment system. The adsorption of dyes on the activated carbon at various concentrations was studies as function of contact time in order to determine the necessary adsorption equilibrium time. Rapid uptake and quick establishment of equilibrium implies high efficiency of particular adsorbent for wastewater treatment. Figure 5 and Figure 6 show the effect of contact time and initial concentrations on adsorption of both dyes on the activated carbon surface. Data show that the adsorption at different dye concentrations is rapid at the initial stages and then gradually decreases with the progress of adsorption until the equilibrium is reached. The rapid adsorption at the initial contact with the carbon surface can be attributed to the availability of the positively



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charged activated carbon surface. The slow rate of dye adsorption is probably due to the slow pore diffusion of the solute ion into the bulk of the adsorbent. As shown in Figure 5 and Figure 6, the contact time required for MO and BPhB solutions to reach equilibrium is 5 min to 10 min, respectively. However, when using higher initial concentrations of MO and BPhB, longer equilibrium times was established. For the sake of combined study, an equilibrium time of 60 min was considered to be optimal for further experiments. It was also seen that an increase in initial dye concentrations resulted in increased dye uptake. The amounts of adsorbed MO and BPhB are 25 and 75 mg/l, respectively. In addition the curves are smooth and continuous towards saturation, indicating the formation of monolayer coverage of dye molecules on activated carbon surface.

Figure 5. Contact time (min) for MO adsorption on AC.


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Figure 6. Contact time (min) for BPhB adsorption on AC.

3.2.3. Adsorption Isotherms Equilibrium data, commonly known as adsorption isotherms, describe how the adsorbate interacts with adsorbents, and give a comprehensive understanding of the nature of interaction. It is essentially important to optimize the nature of assumption system. The parameters obtained from the different models provide important information about the surface properties of the adsorbent and its affinity towards definite adsorbate. Several isotherm equations have been developed for such analysis, however in this study the most important Lagmuir isotherm is applied. The Langmuir isotherm is based on the assumptions that: 1) the adsorption process takes place at specific homogenous sited within the adsorption surface; 2) once a dye molecule occupied a site, no further adsoption can take place at that site - therefore the adsorption process, according to Langmuir is monolayer in nature [43]. The equation of Langmuir isotherm is represented as follows: Ce/qe = Ce/qm + 1/(bqm)



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where Ce is the equilibrium concentration (mg/l), qe is the amount of adsorbent adsorbed per unit mass of adsorbent at equilibrium (mg/g), qm is the theoretical maximum adsorption capacity (mg/g), b is the Langmuir isotherm constant related to the energy of adsorption (l/mg). It is estimated that adsorption capacity of obtained activated carbon is 106 mg/g towards BPhB, and 269 mg/g MO, respectively. The comparison with literature data [6-30] demonstates that these values are among the highest values of adsorption capacity towards MO and BPhB. The obtained data indicate that high adsorption ability of activated carbon toward dyes depends on the surface area, and it increases with increasing the content of mesopores. The molecule size of MO and BPhB 26.1 Å [65] and 27 Å [66], respectively - determines the affinity of these molecules to be adsorbed dominantly on activated carbons with higher amount of mesopores and wide micropores.

Figure 7. Langmuir isotherm of MO adsorption on AC.


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Figure 8. Langmuir isotherm of BPhB adsorption on AC.

CONCLUSION The activated carbon prepared from polymer waste is established to be an effective adsorbent for the removal of MO and BPhB from aqueous solutions. The adsorbent is distinguished by a relatively high surface area (1015 m2/g), with a well-developed microporous texture. Both dyes were found to be adsorbed strongly on the surface of the activated carbon, with high adsorption capacity - 106 mg/g for bromоphenol blue and 269 mg/g for methyl orange, respectively. Adsorption parameters for Langmuir isotherm were determined and the equilibrium data were best described by Langmuir model. The activated carbon demonstrates very high wastewater treatment potential, which suggests that it could be employed as a promising low-cost adsorbent for removal of MO and BhB from aqueous solutions.



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ACKNOWLEDGMENT This work was supported the Project DFNI E 02-2 (12.12.2014) with the Bulgarian Ministry of Education and Science, and also by WAPUMECA project in the frame of collaboration between Bulgarian Academy of Sciences and Romanian Academy of Sciences.

REFERENCES [1]

[2] [3]

[4]

[5]

[6]

[7]

Zahrim, A. Y., Hilal, N. Treatment of highly concentrated dye solution by coagulation/flocculation-sand filtration and nanofiltration. Water. Res. Ind. 2013, 3, 23-34. Metcalf, E. Wastewater engineering-treatment and reuse (4th ed.); Tata McGraw-Hill: New Delhi, 2003. Hariani, P. L., Faizal, M., Marsi, R., Setiabudidaya, D. Synthesis and Properties of Fe3O4 Nanoparticles by co-precipitation Method to Removal Procion Dye. Int. J. Environ. Sci. Dev. 2013, 4 (3), 336-340. Gonawala, K. H., Mehta, M. J. Removal of Color from Different Dye Wastewater by Using Ferric Oxide as an Adsorbent. Int. J. Eng. Res. Appl. 2014, 4 (5), 102-109. Badruddoza, A. Z. M., Hazel, G. S. S., Hidajat, K., Uddin, M. S. Synthesis of carboxymethyl-beta-cyclodextrin conjugated magnetic nano-adsorbent for removal of methylene blue. Colloids Surf. 2010, А367, 85-95. Li, H., Sun, Z., Zhang, L., Tian, Y., Cui, G., Yan, Sh. A cost-effective porous carbon derived from pomelo peel for the removal of methyl orange from aqueous solution. Colloids Surf. 2016, A489, 191-199. Li, H., An, N., Liu, G., Li, J., Liu, N., Jia, M., Zhang, W., Yuan, X., Adsorption behaviors of methyl orange dye on nitrogen-doped mesoporous carbon materials. J. Colloid Interface Sci. 2016, 466, 343351.


158 [8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

[16]

B. Tsyntsarski, I. Stoycheva, B. Petrova et al. Veksha, A., Pandya, P., Hill, J. M. The removal of methyl orange from aqueous solution by biochar and activated carbon under microwave irradiation and in the presence of hydrogen peroxide. J. Environ. Chem. Eng. 2015, 3, 1452-1458. Robati, D., Mirza, B., Rajabi, M., Moradi, O., Tyagi, I., Agarwal, S., Guptam, V. K. Removal of hazardous dyes-BR 12 and methyl orange using graphene oxide as an adsorbent from aqueous phase. Chem. Eng. J. 2016, 284, 687-697. Chen, S., Zhang, J., Zhang, Ch., Yue, Q., Li, Ya., Li, Ch. Equilibrium and kinetic studies of methyl orange and methyl violet adsorption on activated carbon derived from Phragmites australis. Desalin. 2010, 252, 149-156. Mohammad, Н., Khani, H., Kumar Gupta, V., Amereh, E., Agarwal, Sh. Adsorption process of methyl orange dye onto mesoporous carbon material-kinetic and thermodynamic studies. J. Collоid Interface. Sci. 2011, 362, 457-462. Wu, F.-Ch., Tseng, R.-L. High adsorption capacity NaOH-activated carbon for dye removal from aqueous solution. J. Haz. Mat. 2008, 152, 1256-1267. Ghaedi, М., Hajati, S., Zaree, M., Shajaripour, Y., Asfaram, A., Purkait, M. K. Removal of methyl orange by multiwall carbon nanotube accelerated by ultrasound devise: Optimized experimental design. Adv. Powder Technol. 2015, 26, 1087-1093. Yao, Yu., He, B., Xu, F., Chen, X. Equilibrium and kinetic studies of methyl orange adsorption on multiwalled carbon nanotubes. Chem. Eng. J. 2011, 170, 82-89. Zhao D., Zhang W., Chen Ch., Wang X. Adsorption of methyl orange dye onto multiwalled carbon nanotubes. J. Colloid. Interface. Sci. 2012, 386, 277-284. Ghaedi, M., Ghaedi, A. M., Negintaji, E., Ansari, A., Vafaei, A., Rajabi, M. Random forest model for removal of bromophenol blue using activated carbon obtained from Astragalus bisulcatus tree. J. Ind. Eng. Chem. 2014, 20, 1793-1803.



159

[17] Ghaedi, М., Ghayedi, М., Nasiri Kokhdan, S., Sahraei, R., Daneshfar, A. Palladium, silver, and zinc oxide nanoparticles loaded on activated carbon as adsorbent for removal of bromophenol red from aqueous solution. J. Ind. Eng. Chem. 2013, 19, 1209-1217. [18] Haider, S., Bukhari, N., Park, S. Y., Iqbal, Y., Al-Masry, W. A. Adsorption of bromo-phenol blue from an aqueous solution onto thermally modified granular charcoal. Chem. Eng. Res. Design 2011, 89, 23-28. [19] Bhatnagar, A. Removal of bromophenols from water using industrial wastes as low cost adsorbents. J. Haz. Mat. 2007, B139, 93-102. [20] Jia, Zh., Liu, J., Wang, Q., Ye, M., Zhu, R. Facile preparation of mesoporous nickel oxide microspheres and their adsorption property for methyl orange from aqueous solution. Mat. Sci. Semicond. Proc. 2014, 26, 716-725. [21] Iida, Y., Kozuka, T., Tuziuti, T., Yasui, K. Sonochemically enhanced adsorption and degradation of methyl orange with activated aluminas. Ultrasonics 2004, 42, 635-639. [22] Zhao, H., Zhang, G., Zhang, Q. MnO2/CeO2 for catalytic ultrasonic degradation of methyl orange. Ultrasonics Sonochemistry 2014, 21, 991-996. [23] El-Gamal, S. M. A., Amin, M. S., Ahmed, M. A. Removal of methyl orange and bromophenol blue dyes from aqueous solution using Sorel’s cement nanoparticles. J. Environ. Chem. Eng. 2015, 3, 17021712. [24] Zhang, F., Zhao, Z., Tan, R., Guo, Ya., Cao, L., Chen, L., Li, J., Xu, W., Yang Y., Song W. Selective and effective adsorption of methyl blue by barium phosphate nano-flake. J. Colloid Interface Sci. 2012, 386, 277-284. [25] Arshadi, M., Faraji, A. R., Amiri, M. J., Mehravar M., Gil A. Removal of methyl orange on modified ostrich bone waste - A novel organicinorganic bio composite. J Colloid Interface Sci 2015, 446, 11-23. [26] Xing, X., Chang, P.-H., Lv, G., Jiang, W.-T., Jean, J.-Sh., Liao, L., Li, Zh. Ionic-liquid-crafted zeolite for the removal of anionic dye methyl orange, J. Taiwan Inst. Chem. Eng. 2016, 59, 237-243.


160


[27] Das, Sh., Barman, S. Studies on removal of safranine-T and methyl orange dyes from aqueous solutions using NaX zeolite synthesized from fly ash. Int. J. Sci. Environ. Technol. 2013, 2, 735-747. [28] Kan, T., Jiang, X., Zhou, L., Yang, M., Duan, M., Liu, P., Jiang, X. Removal of methyl orange from aqueous solutions using a bentonite modified with a new gemini surfactant. Appl. Clay Sci. 2011, 54, 184187. [29] Nezamzadeh-Ejhieh, A., Zabihi-Mobarakeh, H. Heterogeneous photodecolorization of mixture of methylene blue and bromophenol blue using CuO-nano-clinoptilolite. J. Ind. Eng. Chem. 2014, 20, 1421-1431. [30] You, L., Wu, Zh., Kim, T., Lee, K. Kinetics and thermodynamics of bromophenol blue adsorption by a mesoporous hybrid gel derived from tetraethoxysilane and bis(trimethoxysilyl) hexane. J. Colloid Interface Sci. 2006, 300, 526-535. [31] Ge, M. Photodegradation of rhodamine B and methyl orange by Ag3PO4 catalyst under visible light irradiation. Chinese J. Catal. 2014, 35, 1410-1417. [32] Lee, H. J., Kim, J. H., Park, S. S., Hong, S. S., Lee, G. D. Degradation kinetics for photocatalytic reaction of methyl orange over Al-doped ZnO nanoparticles. J Ind. Eng. Chem. 2015, 25, 199-206. [33] Wakimotoa, R., Kitamura, T., Ito, F., Usami, H., Moriwaki, H. Decomposition of methyl orangeusing C60 fullerene adsorbed on silica gel as a photocatalyst via visible-light induced electrontransfer. Appl. Catal. 2015, B166-167, 544-550. [34] Tripathy, N., Ahmad, R., Song, J. E., Ko, H. A., Hahn, Yo.-B., Khang, G. Photocatalytic degradation of methyl orange dye by ZnO nanoneedle under UV irradiation. Mat. Lett. 2014, 136, 171-174. [35] Jiang, T., Zhang, L., Ji, M., Wang, Q., Zhao, Q., Fu, X., Yin, H. Carbon nanotubes/TiO2 nanotubes composite photocatalysts for efficient degradation of methyl orange dye. Particuology 2013, 11, 737-742.



161

[36] Lai, Ch. W., Sreekantan, S. Fabrication of WO3 nanostructures by anodization method for visible light driven water splitting and photodegradation of methyl orange. Mat. Sci. Semicond Proc 2013, 16, 303-310. [37] Bouanimba, N., Zouaghi, R., Laid, N., Sehili, T. Factors influencing the photocatalytic decolorization of bromophenol blue in aqueous solution with different types of TiO2 as photocatalysts. Desalin. 2011, 275, 224-330. [38] Yang, J., Cui, Sh., Qiao, J.-Q., Lian, H.-Zh. The photocatalytic dehalogenation of chlorophenols and bromophenols by cobalt doped nano TiO2. J. Mol. Catal. 2014, A395, 42-51. [39] Kong, Yo., Wang, Zh.-L., Wang, Yu., Yuan, J., Chen, Zh.-D. Degradation of methyl orange in artificial wastewater through electrochemical oxidation using exfoliated graphite electrode. New Carbon Materials 2011, 26, 459-464. [40] Li, W., Li, B., Ding W., Wu, J., Zhang, Ch., Fu, D. Response surface methodology as a tool to optimize the electrochemical incineration of bromophenol blue on boron-doped diamond anode. Diamond Relat. Mat. 2014, 50, 1-8. [41] Murali, V., Ong, S.-A., Ho, L.-N., Wong, Y.-Sh. Evaluation of integrated anaerobic-aerobic biofilm reactor for degradation of azo dye methyl orange. Biores. Technol. 2013, 143, 104-111. [42] Bandosz, T. Activated carbon surfaces in environmental remediation (Interface Science and Technology), Elsevier: New York, 2006. [43] Bansal, R. C., Goyal, M. Activated Carbon Adsorption, Taylor & Francis: Boca Raton, USA, 2005. [44] Gergova, K., Petrov, N., Eser, S. Adsorption properties and microstructure of activated carbons produced from agricultural byproducts by steam pyrolysis. Carbon 1994, 32, 693-702. [45] Laszlo, K., Bota, A., Nagy, V., Cabasso, I. Porous carbon from polymer waste materials. Colloids Surf. 1999, A151, 311-320.


162


[46] Savova, D., Apak, E., Ekinci, E., Ferhat Yardim, M., Petrov N., Budinova, T., Razvigorova, M., Minkova, V., Biomass conversion to carbon adsorbents and gas. Biomass Bioen. 2001, 21, 133-142. [47] Minkova, V., Razvigorova, M., Bjornbom, E., Zanzi, R., Budinova, T., Petrov, N. Effect of water vapour and biomass nature on the yield and quality of the pyrolysis products from biomass. Fuel. Proc. Technol. 2001, 70, 53-61. [48] Bacaoui, A., Yaacoubi, A., Dahbi, A., Bennouna, C., Phan Tan Luu, R., Maldonado-Hodar, F. J., Rivera-Utrilla, J., Moreno-Castilla, C., Optimization of conditions for the preparation of activate carbon from olive waste cakes. Carbon 2001, 39, 425-432. [49] Ekinci, E., Ferhat Yardim, M., Razvigorova, M., Minkova, V., Goranova, M., Petov, N., Budinova T. Characterization of liquid products from pyrolysis of sub bituminous coals. Fuel. Proc. Technol. 2002, 77-78, 309-315. [50] Ryu, Z., Rong, H., Zheng, J., Wang, M., Zhang, B. Microstructure and chemical analysis of PAN-based activated carbon fibers prepared by different activation methods. Carbon 2002, 40, 1144-1147. [51] Park, S.-J., Jung, W.-Y. Preparation and structural characterization of activated carbons based on polymer resin. J. Colloid Interface Sci. 2002, 250, 196-200. [52] San Miguel, G., Fowler, G. D., Sollars, C. J. A study of the characteristics of activated carbons produced by stream and carbon dioxide activation of waste tyre rubber. Carbon 2003, 41, 1009-1016. [53] Tamai, H., Kouzu, M., Yasuda, H. Preparation of highly mesoporous and high surface area activated carbons from vinylidene chloride copolymer containing yttrium acetylacetonate. Carbon 2003, 41, 1678-1681. [54] Khezami, L., Chetouani, A., Taouk, B., Capart, B. Production and characterization of activated carbon from wood components in powdered: cellulose, lignin, xylan. Powder Technol. 2005, 157, 48-56. [55] Shalaby, C. S., Ucak-Astarliog, Iu. M. G., Artok. L., Sarici C. Preparation and characterization of activated carbons by one-step



[56]

[57]

[58]

[59]

[60]

[61]

[62]

[63]

[64]

163

pyrolysis/activation from apricot stones. Micropor. Mesopor. Mater. 2006, 88, 126-134. Ania, C. O., Parra, J.-B., Arenillas, A., Rubiera, F., Bandosz, T. J., Pis, J. J. On the mechanism of reactive adsorption of dibenzothiophene on organic waste derived carbons. Appl. Surf. Sci. 2007, 253, 5899-5903. Petrov, N., Budinova, T., Razvigorova, M., Parra, J.-B., Galiatsatou, P. Conversion of olive wastes to volatiles. Biomass Bioen. 2008, 32, 1303-1310. Budinova, T., Krzesinska, M., Tsyntsarski, B., Zachariasz, J., Petrova, B. Activated carbon produced from bamboo pellets for removal of arsenic (III) ions from water. Bul. Chem. Comm. 2008, 40, 166-172. Budinova, T., Savova, D., Tsyntsarski, B., Ania, C. O., Cabal, B., Parra, J.-B., Petrov, N. Biomass waste-derived activated carbon for the removal of arsenic and manganese ions from aqueous solution. Appl. Surf. Sci. 2009, 255, 4650-4657. Petrov, N., Budinova, T., Tsyntsarski, B., Petrova, B., Teodosiev, D., Boncheva, N. Synthesis of nanoporous carbon from plant wastes and coal treatment pyrolysis. Bul. Chem. Commun. 2010, 42, 16-19. Petrova, B., Budinova, T., Tsyntsarski, B., Petrov, N, Ania, C. O., Parra, J.-B. Phenol adsorption on activated carbons with different structure and properties. Bul. Chem. Commun. 2010, 42, 141-146. Petrova, B., Tsyntsarski, B., Budinova, T, Petrov, N, Ania, C. O., Parra, J.-B., Mladenov, M., Tzvetkov, P. Synthesis of nanoporous carbons from mixtures of coal tar pitch and furfural and their application as electrode materials. Fuel. Proc. Technol. 2011, 91, 1710-1716. Asasian, N., Kaghazchi, T., Soleimani, M. Elimination of mercury by adsorption onto activated carbon prepared from the biomass material. J. Ind. Eng. Chem. 2012, 18, 283-89. Tsyntsarski, B., Petrova, B., Budinova, T., Petrov, N., Teodosiev, D., Sarbu, A., Sandu T., Ferhat Yardim M., Sirkecioglu, A. Removal of detergents from water by adsorption on activated carbons obtained from various precursors. Desalin. Water. Treat. 2014, 52, 3445-3452.


164


[65] Danish, M, Hashim, R, Mohammad Ibrahim, M. N., Sulaiman, O. Characterization of physically activated Acacia Mangium wood-based carbon for the removal of methyl orange dye. Bio Resources 2013, 8, 4323-4339. [66] Iqbal, M. J., Ashiq, M. N. Thermodynamics and kinetics of adsorption of dyes from aqueous media onto alumina. J. Chem. Soc. Pak. 2010, 32, 419-428.




Chapter 6

THE PREPARATION AND APPLICATION OF ACTIVATED CARBON FOR GAS ADSORPTION A. R. Hidayu* Faculty of Chemical Engineering, Universiti Teknologi MARA Johor, Masai, Johor, Malaysıa

ABSTRACT Activated carbon (AC) is a carbonaceous matter originated from wood, coal, peat and biomass sources. AC is a predominantly amorphous solid that has an extraordinary large internal surface area, pore volume and pore diameter. AC is also known as the most effective adsorbent and has been extensively used. Most of its chemical and physical properties (i.e., surface area, fast adsorption kinetics, adsorption capacities) can be designed and adjusted according to the required applications, either for gas adsorption or liquid adsorption. Besides, the adsorption on activated carbon appears to be the most common technique because of the simplicity of operation since the sorbent materials can be highly efficient, easy to handle and in some cases can be regenerated. Basically, the structure of AC containing pores that is classified according to IUPAC and divided into

*

Corresponding Author address. Email: [email protected].


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A. R. Hidayu three groups; micropores (pore size < 2mm), mesopores (pore size 2nm50nm) and macropores (pore size > 50 nm). Usually for gas-adsorbing carbons, we used the most pore volume in the micropore and macropore ranges, whereas liquid-phase adsorbing carbons have significant pore volume in the mesopore range. The most common precursor used to produce AC is organic materials that are rich in carbon. These precursors will be converted into ACs because of their hardness and high strength in which are due to its high lignin, high carbon content and low ash content of the materials. The most frequently used methods for the preparation of activated carbon is carbonization of the precursors at high temperature in an inert atmosphere followed by the activation process. The activation process is subdivided into physical and chemical activation. Physical activation process comprises treatment of char obtained from carbonization with oxidizing gases, generally steam or carbon dioxide at high temperature (400-1000oC). The porous structure is created due to the elimination of volatile matter during pyrolysis while the carbon on char is removed during activation. As for chemical activation, a chemical agent typically an acid, strong base or a salt that is impregnated to the precursors prior to heat treatment in an inert atmosphere. The pores are developed by dehydration and oxidation reactions of chemicals. Activated carbons are commonly used in gas purification, decaffeination, gold purification, metal extraction, water purification, medicine, sewage treatment, air filters in gas masks and respirators, filters in compressed air and many other applications. In this chapter, the application of activated carbon will be focusing more on gas adsorption.

1. INTRODUCTION Activated carbon (AC) is a carbonaceous matter originated from wood, coal, peat and biomass sources. AC is an amorphous solid that composed mainly of carbon, which have an extraordinary large internal surface area, pore volume and pore diameter. AC is also known as the most effective adsorbents and has been widely used since most of its chemical and physical properties (i.e., surface area, fast adsorption kinetics, adsorption capacities) could be designed and adjusted according to the required application, either for gas adsorption or liquid adsorption. Furthermore, the adsorption on activated carbon appears to be favorable technique because of the simplicity of operation since various sorbent materials can be highly efficient, easy to handle and in some cases they can be regenerated [1].


The Preparation and Application of Activated Carbon …

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AC is prepared from organic materials that is rich in carbon. These precursors will be converted into AC because of their hardness and high strength. These desired properties are due to the high lignin, high carbon content and low ash content of the materials [2, 3]. The method most frequently used for preparation of activated carbon is carbonization of the precursors at high temperature in an inert atmosphere followed by the activation process (heat treatment with an oxidizing agent) or by simultaneous carbonization and activation with a dehydrating compound [4]. The activation process, is subdivided into physical and chemical activation. Physical activation process comprises treatment of char obtained from carbonization with oxidizing gases, generally steam or carbon dioxide at high temperature (400-1000oC) [5]. The porous structure is created from the elimination of volatile matter during pyrolysis, then the carbon on char is removed during activation. As for chemical activation, a chemical agent, typically an acid, strong base or a salt is impregnated to the precursor prior to heat treatment in an inert atmosphere [6]. The pores are developed by dehydration and oxidation reaction of chemicals. The choice of the adequate preparation variables is the license to tailor the pore size distribution of the AC and its surface chemistry, so that it meets the requirements of a given application, both in the liquid and in the gas phase. Basically, the structure of AC is classified according to the International Union of Pure and Applied Chemistry (IUPAC, 1972) and divided into three groups, micropores (pore size < 2mm), mesopores (pore size 2nm-50nm) and macropores (pore size > 50 nm). Usually for gas-adsorbing carbons, pore volumes in the micropore and macropore ranges are used, whereas liquid-phase adsorbing carbons have significant pore volume in the mesopore range [7]. AC is commonly used in gas purification, decaffeination, gold purification, metal extraction, water purification, medicine, sewage treatment, air filters in gas masks and respirators, filters in compressed air system and many other applications. The impurities from these processes is adsorbed on the surface of AC mainly by Van der Waals force (dispersion force). The ability of AC to play its role depends on the internal surface area which ranges 500-1500 m2/g, of which higher internal surface area enables more molecules penetration into the pores [9]. However, the formation of


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chemical bonds between the adsorbing molecules and active sites on the carbon surface is also possible, and thus the number of active sites that are able to chemisorb the desired type of molecules and promote the adsorption process are increased [10].

Figure 1. Schematic representation of porous structure on activated carbon [8].

2. SYNTHESIS Activated carbon can be produced from nearly organic materials that are rich in carbon. For example, nut shells, fruit stones, charcoal, wood, types of coal, etc. Actually, the properties of AC strongly depend on the raw material used and the preparation procedure. Raw materials (fruit stones, coconut shells, etc.) with high bulk density will produce hard AC in granular form with large pore volume which can be used in many applications. For example, removing a variety of contaminants from water. Meanwhile, materials with high content of volatile constituents and low density (e.g., wood) will produce an AC with a large pore volume but low bulk density [4]. Indeed, one way to establish a good activated carbon is by having no bubbles released when placed in water [11]. Generally, two main steps are involved in the preparation of activated carbon. Firstly, it starts with the



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carbonization of raw material (lignocellulosic biomass) at temperature lower than 800oC in an inert atmosphere followed by an activation process to facilitate amorphous material with high surface area area (300-2000 m2/g) [12]. The activation process is divided into two different methods which are physical activation and chemical activation. Carbonization process is a phase to enrich the carbon content in the carbonaceous material by removing non-carbon species using thermal decomposition in order to create initial porosity in char [13, 14]. In this process, the carbonization temperature has the most significant effect, followed by heating rate, nitrogen flow rate, and residence time [15]. The common carbonization temperature is from 500oC to 700oC. After carbonization, the char will be activated into an activated carbon, either utilizing the physical or chemical activation procedure.

2.1. Physical Activation The objective of physical activation is to increase the pore volume, widen the diameter of pores and enhance the porosity of AC. Physical activation process comprises treatment of char obtained from carbonization with oxidizing gases, generally steam or carbon dioxide at high temperature (800oC-1000oC) [4, 16]. The preparation of AC is schematized in Figure 2. Firstly, the raw material is pyrolyzed in an inert atmosphere (carbonization process) to create an initial pore. This process eliminates volatile matters such as hydrogen and oxygen, and forms a carbon skeleton (char) with a rudimentary pore structure. Then, the char has to be activated to widen the pores, thereby creating large mesoporosity which was initially blocked by tar [17]. This is due to the penetration of oxidizing agent into the internal surface of char. The possible reaction for activation is as shown in Equations 1,2,3 and 4 [18]:


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Raw Material

Screening/ Grinding

Carbonization (Nitrogen)

Activation (H2O, CO2)

Activated Carbon

Figure 2. Basic flow sheet of physical activation.

Steam (water vapor) C + H2O → CO + H2 C + 2H2O → CO2 + 2H CO + H2O → CO2 + H2

(Equation 1) (Equation 2) (Equation 3)

Carbon dioxide C + CO2 → 2CO

(Equation 4)

In steam activation, the blocked pores will be opened and micropores are developed. At a long of period time, the developed micropores become wider and form mesopores and macropores. Meanwhile, CO2 activation will only developed micropores [8, 19]. A review study by Gottipati [20] showed various physical activating agents and precursors used for AC production (Table 1). However, taken together, many literature studies done by various researchers agreed that physical activation is the most preferred method as it produces activated carbons with high surface area, high porosity, with a relatively clean and simpler process.



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Table 1. Various physical activating agents and precursors used for AC production [20] Activating agent Steam

Material

Sources

Rice rusk, corn cob, olive residues, sunflower shells, pinecone, rapeseed, cotton residues, olivewaste cakes, coal, rubberwood sawdust, fly ash, coffee endocarp.

CO2

Oak, corn hulls, coconut shells, corn stover, rice straw, rice hulls, pecan shells, pistachio nutshells, coffee endocarp, sugarcane bagasse, corn cob, waste tyres, textile fibers, anthracite

Air

Peanut hulls, almond shells, olivetree wood, almond tree pruning, coal

Bacaoui (2001); El-Hendawy et al., (2001); Haykiri-Acma et al., (2006); Lazaro et al., (2007); Lu et al., (2010); Malik (2003); Nabais et al., (2008); Prakash Kumar et al., (2006); Zhang et al., (2011). Ahmedna et al., (2000); Aworn et al., (2009); Lua et al., (2004); Betancur et al., (2009); Guo et al., (2009); Nabais et al., (2008); Salvador et al., (2009); Yang & Lua, (2003); Zhang et al., (2004); Zhu et al., (2011). Ganan et al., (2006); Girgis et al., (2002), Marcilla at al., (2000); Ould-Idriss et al., (2011).

2.2. Chemical Activation Chemical activation process involves loading a chemical agent (i.e., ZnCl2, KOH, H3PO4, NaOH, K2CO3, etc.) is loaded to the precursor, prior to heat treatment in an inert atmosphere. These chemical agents will develop the pores and surface area by dehydration and oxidation reactions [13]. Firstly, the raw material is crushed and sieved at a desired particle size, and then mixed with a chemical agent solution and kept for about 24h at room temperature. The mixture is then dried and transferred into a stainless steel reactor or furnace under inert atmosphere at temperatures between 400700oC [13, 21]. After the activation process has been completed, the samples are taken out and washed using distilled water in order to remove the activating agent. The basic procedure of the process is as shown in Figure 3.


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Figure 3. Basic flow sheet of chemical activation.

Generally, chemical activation (300-500oC) takes place at a lower temperature than physical activation [22]. Chemical activation is more preferable over physical activation due to the lower treatment temperature and shorter activation time, and is capable of producing higher surface area and better porosity. Furthermore, the yield of AC from chemical activation is greater than physical activation [23]. Although, the surface area, pore size distribution, functional group presence and other attributes of the AC are dependent upon the type of chemical agents used and different impregnation ratio (i.e., the ratio of raw material and the ratio of chemical agent) [24]. Table 2 shows the review of previous researches with different type of chemical agents. AC can be characterized from its physical properties and chemical properties. These properties are the important factors that influence the adsorption process. Physical properties describe the particle size, pore structure and surface area. According to a study by Skodas et al. 25, with increasing particle size of activated carbon from 75-106 µm to 150-250 µm, mercury absorptive capacity is decreased from 707 ng/mg to 505 ng/mg. It seems that finer particle produces a delay of the breakthrough and the reduction in gas adsorption capacity. Table 3 shows the factors affecting adsorbent selections. From the table, AC gives the highest adsorption



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capacity because it has a higher BET surface area and larger pore volume. According to the theory of pure physisorption process, the higher specific surface area of the activated carbons results in greater adsorptive capacity [26]. Table 2. Various chemical activating agents and precursors used in AC production [20] Chemical agent ZnCl2

KOH

H3PO4

K2CO3

Material

Source

Corn cob, coconut shells, macadamia nutshells, peanut hulls, almond shells, hazelnut shells, apricot stones, rice husk, tamarind wood, cattle-manure, pistachio-nut shells, bagasse, sunflower seed hulls. Rice straw, corn cob, macadamia nutshells, peanut hulls, olive seed, rice straw, casava peel, petroleum coke, coal, cotton stalk, pineapple peel.

Acharya et al., (2009); Ahmadpour & Do, (1997); Aygun et al., (2003); Azevedo et al., (2007); Cronje et al., (2011); Girgis et al., (2002); Liou, (2010); Lua & Yang (2005); Qian et al., (2007); Sahu et al., (2010); Tsai et al., (1997); Yalcin & Sevinc, (2000).

Hemp, peanut hulls, almond shells, pecan shells, corn cob, bagasse, sunflower seed hulls, lignin, grain sorghum, rice straw, oak, birch, sewage sludge, chesnut wood, rice hull, cotton stalk, jackfruit peel. Pineapple peel, corn corb, cotton stalk, almond shell, coconut shell, oil palm shell, pistachio shell, walnut shell, bamboo.

Basta et al., (2009); Deng et al., (2010); Foo et al., (2011); Girgis et al., (2002); Oh & Park (2002); Kawano et al., (2008); Stavropoulos & Zabaniotou (2005); Sudaryanto et al., (2006); Tsai et al., (2001); Tseng et al., (2008); Wu et al., (2011). Ahmedna et al., (2004); Deng et al., (2010); Diao et al., (2002); Fierro et al., (2010); Girgis et al., (2002); Liou, 2010; Montane et al., (2004); Prahas et al., (2008); Rosas et al., (2009); Wang et al., (2011); Zuo et al., (2009); Gomez-Serrano et al., (2005). Adinata et al., (2007); Deng et al., (2010); Foo et al., (2011); Hayashi et al., (2002); Horikawa et al., (2010); Tsai et al., (2001).


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A. R. Hidayu Table 3. Factors affecting adsorbent selections

Adsorbent

Surface Area (m2/g) 500-1500

Pore Volume (cm3/g) 0.6-0.8

Sorptive Capacity (kg/kg) 0.3-0.7

Activated Carbon

Activated Alumina

100-300

0.4-0.5

0.1-0.33

Zeolite

500-1000

0.5-0.8

0.12-0.42

Silica Gel

200-600

0.4

0.35-0.5

Description

Large adsorption capacity, high surface area, well develop porosity, reasonable cost Limited moderate porous structure, low surface area, low adsorption capacity High capacity via adsorption and cation exchange. High adsorption capacity of CO2 at mild operating condition Excellent capacity for adsorption of water but low adsorption capacity for gases

Meanwhile, the chemical property is characterized as the functional groups that are present in the surface of the activated carbon, i.e., oxygen which relates to the acidic properties of the surface. Virgin AC with large oxygen surface functional groups such as carbonyl and lactone has a higher possibility to improve the performance of mercury adsorption because both of them generates higher active site on an activated carbon surface [26, 27]. In this process, stronger bonds are formed during the adsorption process between functional groups on the surface of the AC with gas molecules.



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3. APPLICATIONS Commonly, AC is utilized in water pollution control and air pollution control. Activated carbon with pore volume in the mesopore range (2nm50nm) is usually used for aqueous solution, whereas for gas adsorption, pore size in the micropore region, i.e., RPAC > SAC > RPAC. This can be explained from the viewpoint of specific surface area. Adsorbent with a higher surface area will promote better interaction probabilities between adsorbate molecules and active sites. The maximum values were recorded as 42.6 mg/g, 29.5 mg/g, 36.7 mg/g and 29.0 mg/g for PAC, RPAC, SAC and RPAC, respectively.

Isotherm Models Interpretation Interactive behaviour between adsorbate and adsorbent, and the design of adsorption system can be interpreted from isotherm models. The commonly used empirical equations to describe the adsorption behaviour are the Langmuir and Freundlich models. The Langmuir isotherm is based on the assumptions of constant heat of adsorption for finite number of active sites, and monolayer adsorption on homogeneous adsorbent surface. The Langmuir equation is expressed as, qe = qmbCe/(1 + bCe), where qm (mg/g) is the Langmuir maximum capacity and b (L/g) is the adsorption affinity. The linear plot of Ce/qe against Ce gives a straight line with slope of 1/qm and y-intercept of 1/qmb. A dimensionless factor of Langmuir equation, RL can be used to describe the favourability of adsorption. It is given as RL = 1/(1 + bCo). The RL value indicates whether the adsorption is unfavourable (RL > 1), linear (RL = 1), favourable (0 < RL < 1) or irreversible (RL = 0). On the other hand, the Freundlich equation is based on the assumptions of exponentially decrease adsorption energy, heterogeneous adsorbent surface and interaction between the adsorbed molecules with molecules in the bulk solution, which allows the formation of multilayer. The Freundlich model is given as, qe = KFCe1/n, where KF and n are the Freundlich constants related to maximum capacity and adsorption intensity, respectively. The Freundlich constants can be determined from a linear plot of log qe against log Ce.


Adsorbents from the Residue of Waste Tyre Pyrolysis …

211

50

qe ( mg/g )

40

30

20 PAC SAC

10

RPAC RSAC

0 0

20

40 Ce ( mg/L )

60

80

Figure 2. Equilibrium removal of Rhodamine B by adsorbents. Lines were predicted using Langmuir (solid) and Freundlich (dashed) models.

Table 2. Isotherm constants Adsorbent PAC SAC RPAC RSAC

Langmuir model qm (mg/g) b (L/mg) 45.65 0.221 33.67 0.0954 40.98 0.143 30.77 0.0872

R2 0.985 0.998 0.989 0.996

Freundlich model KF (mg/g(L/mg)1/n) n 12.26 3.10 4.19 1.99 6.56 2.15 3.52 1.89

R2 0.980 0.965 0.973 0.978

Figures 3 and 4 represent the linear plots of Langmuir and Freundlich isotherm models, respectively. The isotherm constants are summarized in Table 2. Judging from the R2 values, the Langmuir model is more fitted to linear proximity compared to the Freundlich model. From Figure 2, it is obvious that the Freundlich model began to deviate from the experimental data at higher concentration. In addition, the Langmuir model shows small deviation for the predicted maximum capacity in comparison with the experimental ones. Hence, the removal of


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Constance Joe Ondi and Muhammad Abbas Ahmad Zaini

Rhodamine B dye by pyrolysis residue-based adsorbents can be described by Langmuir model whereby the adsorption renders monolayer dye molecules onto homogeneous surface sites. It was also found that the affinity for Rhodamine B adsorption increased with increasing surface area, and this is in agreement with the pattern of maximum removal capacity. Rhodamine B exhibits single layer coverage of one molecule thickness with qm values of 45.65 mg/g, 40.98 mg/g, 33.67 mg/g and 30.769 mg/g for PAC, RPAC, SAC and RPAC, respectively. The values correspond to saturated monolayer of dye molecules on adsorbent surface with constant energy, no lateral interaction and steric hindrance between the adsorbed molecules, and no transmission and interaction between the readily adsorbed molecules and the molecules in the bulk solution. In a related work on Rhodamine B adsorption, Vijayakumar et al. (2012) reported a 67.9 mg/g removal capacity using natural perlite. The performance of PAC is comparable with that of natural perlite. However, the waste tyre-based activated carbon by steam activation showed a tremendous removal of 307 mg/g Rhodamine B due to its superior surface area of 720 m2/g (Li et al., 2010). From Table 2, the Langmuir constant, b for PAC, RPAC, SAC, and RPAC are 0.221 L/mg, 0.1426 L/mg, 0.0954 L/mg and 0.0872 L/mg, respectively. The constant also denotes the adsorption energy as a result of monolayer surface formation to hold the adsorbate molecules. PAC exhibits a greater affinity of Rhodamine B, which indicates the ability of adsorbent to adsorb dye molecules at low concentration. The comparatively high b values shown by RPAC and RSAC, denotes the feasibility of adsorbents prepared using the recovered reagents to capture dye molecules. The constant, b were utilized to determine the favourability of adsorbents for Rhodamine B adsorption using a dimensionless separation factor, RL. The RL profiles are shown in Figure 5, with values ranging between 0.043 and 0.695, indicating the suitability of these adsorbents for dye adsorption.



213

3

Ce/ (qe (g/L)

2.5 2 1.5 PAC 1

SAC RPAC

0.5

RSAC 0

20 Ce ( mg/L ) 40

0

60

80

Figure 3. Langmuir isotherm plot.

1.8 1.6 1.4 1.2 log qe

1 0.8 PAC SAC RPAC RSAC

0.6 0.4 0.2 0 -2

-1

0

log Ce

1

2

Figure 4. Freundlich isotherm plot.


3

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Constance Joe Ondi and Muhammad Abbas Ahmad Zaini 0.8 PAC

0.7

SAC

0.6

RPAC RSAC

RL

0.5 0.4 0.3 0.2 0.1 0.0 0

20

40

60 Co ( mg/L)

80

100

120

Figure 5. RL profiles of Rhodamine B removal by adsorbents.

CONCLUSION Adsorbents were prepared using the residue of waste tyre pyrolysis via metal hydroxide activation. Activation using fresh potassium hydroxide yielded a 65% adsorbent (PAC) with a surface area of 71.2 m2/g, and Rhodamine B removal capacity of 42.6 mg/g. The removal of Rhodamine B is directly related to the development of the surface area of adsorbents. The adsorption data can be well described by the Langmuir isotherm; monolayer adsorption on the adsorbents with homogenous surface. All adsorbents portrayed a greater removal efficiency of more than 70% at an initial concentration of 5 mg/L. PAC exhibited a greater adsorption affinity for Rhodamine B at low concentrations. The pyrolysis residue is a promising candidate of adsorbent for wastewater treatment, although the surface area developed is not as high as that of commercial activated carbon. The present findings opened-up for further investigations to boost the surface area of the pyrolysis residue-based adsorbents.



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ACKNOWLEDGMENT This work was funded by Universiti Teknologi Malaysia through Research University Grant #14H19.

REFERENCES Li, L., Liu, S. and Zhu, T. 2010. Application of activated carbon derived from scrap tires for adsorption of Rhodamine B. Journal of Environmental Sciences, 22(8): 1273-1280. Ming-Twang, S., Zhi-Yong, Q., Lin-Zhi, L., Pei-Yee, A.Y. and Zaini, M.A.A. 2015. In: J.C. Taylor, Advances in Chemistry Research, Vol. 23, Nova Science Publishers Inc., New York, pp. 143-156. Teng, H.S., Lin, Y.C. and Hsu, L.Y. 2000. Production of activated carbons from pyrolysis of waste tires impregnated with potassium hydroxide. Journal of the Air & Waste Management Association, 50(11): 19401946. Vijayakumar, G., Tamilarasan, R. and Dharmendirakumar, M. 2012. Adsorption, kinetic, equilibrium and thermodynamic studies on the removal of basic dye Rhodamine B from aqueous solution by the use of natural adsorbent perlite. Journal Materials & Environmental Science, 3(1): 157-170. Zaini, M.A.A., Ngiiik, T.C., Kamaruddin, M.J., Setapar, S.H.M. and Yunus, M.A.C. 2014. Zinc chloride-activated waste carbon powder for decolourization of methylene blue. Jurnal Teknologi, 67(2): 37-44. Zaini, M.A.A, Zakaria, M., Mohd-Setapar, S.H. and Che-Yunus, M.A. 2013. Sludge-adsorbents from palm oil mill effluent for methylene blue removal. Journal of Environmental Chemical Engineering, 1: 10911098.





Chapter 9

ACTIVATED CARBON: A POTENTIAL APPLICANT FOR SOLID-STATE HYDROGEN STORAGE Amandeep S. Oberoi1,, Baljit Singh2, Muhammad Fairuz Remeli3 and Navdeep Singh4 1

Department of Mechanical Engineering, Chitkara University Institute of Engineering and Technology, Chitkara University, Punjab, India 2, 3 Faculty of Mechanical Engineering, Universiti Teknologi MARA (UiTM), Selanor, Malaysia 4 Concordia University, Montreal, Quebec, Canada

ABSTRACT Beside commonly known applications of activated carbon in numerous fields, it has attracted considerable amount of research attention as a medium for solid-state hydrogen storage (also known as 

Corresponding author e-mail: [email protected].


218 Amandeep S. Oberoi, Baljit Singh, Muhammad Fairuz Remeli et al. electrochemical hydrogen storage). Hydrogen in solid-state could be stored either by physical adsorption (or physisorption) or by forming chemical bonds (or chemisorption). Activated carbon offers large internal pore surface area and high porosity that favors both physisorption and chemisorption. Other advantages of using activated carbon for electrochemical hydrogen storage are different pore sizes - macropores, mesopores, micropores and ultramicropores, low atomic weight and easy availability. The present chapter reports on experimental investigation on different grades of activated carbons, made from coal, for their electrochemical hydrogen storage capacity. The fabrication process of activated carbon-based solid electrodes is explained. The steps involved in testing of the fabricated electrodes for their electrochemical hydrogen storage capacity are given. The obtained hydrogen storage capacity of certain activated carbon electrodes is found to be above 1 wt% which is comparable with commercially available metal hydride-based hydrogen storage canisters, lithium-ion and lithium polymer batteries. The results pave a way forward towards commercializing activated carbon-based hydrogen storage electrodes for polymer electrolyte membrane fuel cell or PEMFC, and battery applications.

Keywords: activated carbon, electrochemical hydrogen storage, fuel cell, battery applications

INTRODUCTION Our planet earth is experiencing a slow and gradual but continuous change in climatic conditions owing to global warming resulting from greenhouse effect caused by increased concentration of Green House Gases (known as GHGs). As per a published report, one of the major contributors of GHGs is burning of fossil fuels [1]. Therefore, human activities involving burning of fossil fuels are responsible for increased concentration of GHGs in the atmosphere. On the other hand, increased population, continuous development and increased dependency on fossil fuels to meet the world’s energy needs have pushed all the oil reserves across the world to near extinction [2]. To mitigate the effect of increasing concentration of GHGs and to meet the challenge of depleting fossil fuels, what is required is to find


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219

an alternative fuel that could not only replace fossil fuels but could also be stored on-board vehicles running on petrol, diesel, etc and give zeroemission when burnt. John O’Bockris, a renowned scientist, proposed in 1975 the production of hydrogen from renewable sources and its storage for reuse in fuel cells [3]. This noble idea offered a solution to the problem of storing intermittent renewable energy by storing it on-board vehicles as a ‘zero-emission’ transport fuel. Also, hydrogen obtained from renewable sources can be utilized in electricity supply systems as a long-term energy source capable of meeting continuous energy supply demand. Due to these reasons, major economies of the world have formulated their goals to adopt ‘Hydrogen as a Future Fuel’ which is considered to be an alternative to the depleting reserves of fossil fuels [4-5]. Hydrogen is available in abundance in nature in the form of a chemical compound e.g., in water and other organic matter. Besides, it is light in weight and has got immense energy content (Gross Calorific value is around 143 MJ/kg) that offers zero-emission solution to the automobile industry. However, finding safe and efficient hydrogen storage medium still remains a challenge that needs to be addressed [6]. Hydrogen could be stored as a compressed gas, as a liquid or in solidstate as a chemical compound. But, in gaseous form, hydrogen needs to be stored at a high pressure of 70-80 bars and liquid hydrogen storage needs cryogenic temperatures that involve energy expenditure [7]. Solid-state hydrogen storage, also known as electrochemical hydrogen storage, requires a porous storage medium. The process of hydrogen adsorption as a chemical compound is known as chemisorptions and if hydrogen ions are held physically in minute pores of a porous material with Van der Waals forces, the process is called physisorption [8]. Researchers are exploring various materials with acceptable electrochemical hydrogen storage capacity in terms of gravimetric energy density (mass of hydrogen stored per mass of the storage material) and volumetric energy density (volume of hydrogen stored per volume of the storage material). A conventional solar-hydrogen/fuel cell hybrid systemfor power generation includes a photovoltaic cell to produce electricity required to run


220 Amandeep S. Oberoi, Baljit Singh, Muhammad Fairuz Remeli et al. an electrolyser (to split water into hydrogen and oxygen); a compressor to reduce the volume of the produced hydrogen gas, a storage cylinder and a fuel cell to generate electricity [9]. Due to high number of components, the round-trip efficiency or the system efficiency i.e., ratio of energy output to energy input from fuel cell is considerably low. In 2013, a modified Unitized Regenerative Fuel Cell (URFC) was proposed with an integrated solid hydrogen storage electrode and termed as ‘proton flow battery’ that could run both as an electrolyser and as a fuel cell [10]. This novel device offers high round-trip efficiency as compared to the conventional hydrogen production and storage system because of comparatively lesser number of components [11].

Carbon as a Medium for Electrochemical Hydrogen Storage The newly proposed device – ‘proton flow battery’ has reportedly been tested with an integrated metal-hydride electrode for electrochemical hydrogen storage. Other materials tested for hydrogen storage include Carbon Nano Tubes (CNTs) [12]. Out of many available materials, carbon has emerged as a promising candidate for the goal. The inherent properties of carbon make it suitable for the purpose of hydrogen adsorption. Some of these properties are porous nature, lighter weight as compared to other materials, high internal pore surface area, and diverse pore size distribution ranging from macro to ultra-micro level [13-14].The atomic structure of carbon is shown in Figure 1. However, raw carbon material needs to be activated before using it for electrochemical hydrogen storage to offer increased internal pore surface area. The present chapter gives the process of electrochemical hydrogen storage in a porous activated carbon electrode for fuel cell and battery applications.


Activated Carbon

221

Figure 1. Atomic structure of activated carbon [15].

Experimental Set-Up and Experiment It is clear from the literature review that there is an opportunity to explore the potential of activated carbon as a medium for electrochemical or solid-state hydrogen storage. The concept behind the project is that a solid electrode made from activated carbon could absorb hydrogen protons generated from splitting of water and form weak chemical bonds on internal surfaces of carbon pores. The project has been a step forward towards development of a novel carbon-based energy storage device (in the form of hydrogen energy) with potential applications in automobile industry and remote area power supply. The experimentation comprises activation of coal powder or carbon powder, fabrication of solid electrodes from activated carbon powder and their testing in a 3-electrode electrolytic cell to determine the hydrogen storage capacity using dilute sulphuric acid as electrolyte. The carbon samples activated by adding potassium hydroxide (chemical symbol – KOH) with different ratios by weight are incorporated as working electrodes in a 3-electrode electrolytic cell of 300 ml capacity as shown in Figure-2. Platinum and Hg/HgO electrodes are employed respectively as counter and reference electrodes (refer Figure 3 and 4). Dilute sulphuric acid (chemically known as H2SO4) of 1 mol concentration is used as electrolyte in the electrolytic cell. The cell comprises two number of gas outlets, each made of glass for working and counter electrodes. The gas outlets are the hollow glass tubes that cover the working and counter electrodes completely


222 Amandeep S. Oberoi, Baljit Singh, Muhammad Fairuz Remeli et al. in order to transfer any gas generated to the gas-collection cylinders shown in Figure 5. The gas-collection cylinders are filled with water and graduated to note the amount of gas generated over working and counter electrodes separately. The electrolytic cell and its top-cover are made from glass and polytetrafluoroethylene (PTFE) respectively to avoid reaction with sulphuric acid used as electrolyte.

Figure 2. Three-electrode electrolytic cell of 300 ml capacity [13].


Activated Carbon

Figure 3. Counter Electrode made of platinum [13].

Figure 4. Reference electrode – Hg/HgO [13].


223

224 Amandeep S. Oberoi, Baljit Singh, Muhammad Fairuz Remeli et al.

Figure 5. Graduated cylinder for gas collection [13].

The fabricated carbon electrodes are employed as working electrodes in the electrolytic cell and tested for hydrogen storage capacity using galvanostatic charging and discharging. Before starting experimentation, the cell is filled with dilute sulphuric acid with 1 mol concentration and it is ensured that the cell is properly sealed to avoid any leakage. The electric potential is applied across the cell using DC supply. The process of applying the voltage is known as ‘charging’ of cell. A constant current of 150 mA is maintained until a rapid increase in gas production rate is observed. Equation 1 shows thereaction that takes place while water contained in the electrolyte is disassociated.

H2O → 2H+ + 0.5O2

(Eq. 1)

Oxygen gas is liberated at the counter electrode as a result of the chemical reaction and is collected in a graduated cylinder as shown in Figure 5. On the other hand, the disassociated hydrogen ions from electrolyte move towards working electrode and get stored over there. Hydrogen ions that are unable to get adsorbed in working electrode, form hydrogen gas over


Activated Carbon

225

electrode which is collected separately in a graduated cylinder. After certain period of time, a rapid increase in hydrogen gas production rate is observed indicating that the storage is now full and all the produced hydrogen ions from the electrolyte are liberated as hydrogen gas. The operation is stopped and the process is termed as ‘charging’. The apparatus is allowed to rest for 1 hour before starting to draw current from the stored hydrogen energy. The process of drawing out current from the stored hydrogen energy is termed as ‘discharging’. While discharging, the cell is isolated from the working-electrode side gas collecting cylinder carrying previously produced hydrogen gas to ensure that the hydrogen stored in carbon electrode is the only source of power generation. The cell was allowed to discharge at constant discharge pressure until the operation ceased automatically when the cell was not able to maintain the set discharging current indicating that almost all the stored hydrogen has been used from the storage. The total amount of hydrogen produced in charging is partly stored electrochemically in carbon electrodes and the remaining is liberated as gas which is collected. It is ensured that there is no leakage or any other escape path for gases other than the graduated collection cylinders.

RESULTS AND DISCUSSIONS The process of charging and discharging is shown in form of the obtained graph in Figure 6. While discharging the total charge flow ‘Q’ due to the stored hydrogen is calculated from equation 2.

Q = ix t

(Eq. 2)

where, i → discharge current in amperes. t → time of discharging in seconds until the operation is automatically ceased.


226 Amandeep S. Oberoi, Baljit Singh, Muhammad Fairuz Remeli et al. Mass of hydrogen released from the storage while discharging is calculated using equation 3. M = (I x t) / 1000 F

(Eq. 3)

where, M → mass of hydrogen in grams I → discharging current in mA t → total time of discharging in seconds. F → Faraday’s constant = 96485 C mol-1 The weight percent of hydrogen stored in storage is calculate, using equation 4. Mass% = M / M+Mc

(Eq. 4)

where, M → mass of hydrogen in grams. Mc → mass of carbon powder in the electrode in grams. It can be seen from Figure 6 that the cut-in voltage recorded is 1.4 V. It is the voltage at which actual water disassociation started and some gas bubbles in gas collection cylinders were observed. After a significant amount of time a rapid increase in gas bubble generation is observed and the operation is stopped. Then discharging operation is started and current is drawn at a constant value. The time of discharging cycle is noted and used in Eq.3 to determine the amount of hydrogen in grams that is stored in carbon electrode. The plateau in the graph shown in Figure 6 on the discharging cycle represents the hydrogen storage in carbon electrode.


Activated Carbon

227

Figure 6. Graph showing galvanostatic charging and discharging cycle at a constant current.

CONCLUSION The project was successful in demonstrating the generation of hydrogen from water disassociation and its storage and release from the fabricated carbon electrode immersed in a liquid electrolyte i.e., sulphuric acid of 1 mol. concentration. Carbon based electrode was successful in adsorbing hydrogen electrochemically (as a chemical compound) and the highest achieved mass% of hydrogen was above 1wt%. The achieved hydrogen storage capacity is comparable with the commercially available metalhydride based hydrogen storage canisters and best performing lithium-ion and lithium-polymer batteries. So far, porous carbon-based materials have proven to be ideal for electrochemical hydrogen storage. Unlike other commercially available batteries, electrochemically stored hydrogen in carbon does not come out on its own i.e., the energy stored in form of


228 Amandeep S. Oberoi, Baljit Singh, Muhammad Fairuz Remeli et al. hydrogen in carbon is not self-discharging. This project has proved to be a step forward towards commercializing activated carbon-based hydrogen storage electrodes with potential applications in the field of fuel cells.

ACKNOWLEDGMENTS The author would like to acknowledge the support of Commonwealth Government of Australia for funding higher degree research study (PhD)at RMIT University, Australia.

REFERENCES [1]

[2] [3] [4] [5]

[6]

Pachauri, R.K. and Reisinger, A. (eds) (2007), ‘IPCC, 2007: Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change’, pp 104. R. W. Bentley (2002), ‘Global oil and gas depletion: an overview’, Energy Policy, vol. 30 (3), pp. 189-205. John O’M.Bockris (1999), ‘Hydrogen economy in the future’, International Journal of Hydrogen Energy, vol. 24 (1), pp 1-15. Amandeep Singh Oberoi (2016), ‘Hydrogen as future fuel’, Resnovae, bi-annual research magazine, Chitkara University, issue 5, pp. 1-2. Amandeep Singh Oberoi, Baljit Singh and Muhammad Fairuz Remeli (2016), ‘A commercial activated carbon as a medium for electrochemical hydrogen storage: an experimental investigation on electrochemical hydrogen storage capacity with potential application in automobiles’, Proceedings of 41st IASTEM International Conference, Melbourne, Australia 06-07 December, pp. 19-24. D. Mori and K. Hirose (2009), ‘Recent challenges of hydrogen storage technologies for fuel cell vehicles’, International Journal of Hydrogen Energy, vol. 34 (10), pp. 4569-4574.


Activated Carbon [7] [8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

229

Lennie Klebanoff (2016), ‘Hydrogen storage technology: materials and applications’, A Taylor and Francis book, CRC press, pp. 65-85. SeyedHamedBarghi, Theodore T. Tsotsis, and Muhammad Sahimi (2014), ‘Chemisorption, physisorption and hysteresis during hydrogen storage in carbon nanotubes’, vol. 39 (3), pp. 1390-1397. Yilanci, I. Dincer, and H.K. Ozturk (2009), ‘A review on solarhydrogen/fuel cell hybrid energy systems for stationary applications’, Progress in Energy and Combustion Science, vol. 35 (3), pp. 231-244. Arun Kumar Doddathimmaiah (2008), ‘Unitised regenerative fuel cells in solar-hydrogen systems for remote area power supply’, PhD thesis, RMIT University. Doddathimmaiah A.K. and Andrews J. (2009), ‘Theory, modeling and performance measurement of unitised regenerative fuel cells’, International Journal of Hydrogen Energy, Vol. 34, pp. 8157-8170. John Andrews and Saeed SeifMohammadi (2014), ‘Towards a proton flow battery: investigation of a reversible PEM fuel cell with integrated metal-hydride hydrogen storage’, International Journal of Hydrogen Energy, vol. 39, pp. 1740-1751. Amandeep Singh Oberoi (2015), ‘Reversible electrochemical storage of hydrogen in activated carbons from Victorian brown coal and other precursors’, PhD thesis, RMIT University. Amandeep Singh Oberoi (2016), ‘Hydrogen storage capacity of selected activated carbon electrodes made from brown coal’, International Journal of Hydrogen Energy, vol. 41, pp. 23099-23108. Peter J. F. Harris, Zheng Liu, and KazuSuenaga (2008), ‘Imaging the atomic structure of activated carbon’, Journal of Physics: condensed matter, vol. 20, p. 5.



INDEX # 2,4-dinitrochloro-benzene, 3 500-1500 m2/g, 167

A activated carbon, ix, xiii, xv, 1, 4, 7, 33, 37, 38, 42, 51, 88, 112, 161, 163, 165, 166, 168, 175, 204, 218 activation parameters, 96 active compound, 13 active site, 63, 93, 96, 111, 120, 126, 168, 174, 209, 210 adsorbing, xiii, 32, 166, 167, 168, 227 adsorption, v, vi, ix, x, xi, xiii, xiv, xv, 2, 4, 7, 13, 16, 18, 19, 27, 28, 31, 32, 33, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 47, 49, 50, 51, 53, 54, 55, 56, 58, 59, 60, 61, 62, 63, 64, 65, 67, 69, 71, 72, 73, 74, 75, 77, 78, 79, 80, 81, 83, 84, 86, 87, 88, 89, 90, 91, 92, 94, 96, 97, 98, 99, 101, 102, 103, 104, 105, 106, 110, 114, 116, 120, 123, 125, 131, 132, 133, 142, 143, 144, 145, 147, 148, 150, 152, 153, 154, 155, 156,

157, 158, 159, 160, 161, 163, 164, 165, 166, 168, 172, 174, 175, 176, 177, 180, 181, 182,183, 201, 204, 206, 207, 208, 209, 210, 212, 214, 215, 218, 219, 220 adsorption isotherms, 59, 64, 71, 73, 144, 147, 154 ammonia, xii, 108, 109, 110, 111, 113, 114, 115, 117, 119, 120, 121, 122, 123, 124, 125, 126, 127, 129, 130, 131, 132, 133, 134, 176 ammonium, 114, 117, 121, 130 aqueous solutions, xiii, 34, 38, 41, 42, 43, 44, 45, 71, 73, 75, 79, 81, 82, 85, 86, 93, 100, 101, 102, 104, 105, 106, 142, 156, 157, 158, 159, 160, 161, 163, 175, 215 aromatic compounds, 22, 103 aromatic hydrocarbons, 14 aromatic rings, 22 atmosphere, xiii, 4, 7, 81, 87, 108, 139, 166, 167, 169, 171, 195, 218 automobile, 219, 221, 228

B bamboo char, xii, 107, 108, 132 battery(ies), xv, 47, 204, 218, 220


232

Index

benzene, 3, 21, 22, 23, 208 binding energy, 116 bioaccumulation, 74, 105 biodegradation, 9, 143 biodiesel, 7, 200 biodiversity, 9 biogas, 175 biomass, x, xiii, 2, 7, 8, 25, 26, 29, 31, 34, 37, 40, 43, 46, 48, 51, 74, 143, 162, 163, 165, 166, 169, 181, 200, 201 biomass materials, 51, 143 biomaterials, 8 biotechnology, 41 bonds, 21, 22, 23, 58, 71, 96, 147, 168, 174 by-products, 46, 103, 143, 161

C cadmium, 101 carbamazepine, 52 carbon atoms, 6, 147, 197 carbon dioxide (CO2), xiv, 3, 6, 14, 16, 34, 35, 55, 81, 86, 133, 137, 138, 139, 162, 166, 167, 169, 170, 171, 174, 175, 176, 182, 183 carbon film, 134 carbon materials, x, 36, 37, 49, 53, 54, 104, 143, 157, 200 carbon monoxide, 5, 6, 17, 139 carbon nanotubes, 100, 105, 220, 229 carbon powder, 132, 204, 205, 207, 215, 221, 226 carbonaceous matter, xiii, 165, 166 carbonization, xii, xiii, 5, 6, 17, 19, 20, 21, 24, 38, 107, 166, 167, 169 carbonyl groups, 147 carboxyl, 116, 118, 147 carboxylic acid, 23, 86, 88 carboxylic acids, 23 carboxylic groups, 145, 208 castor residue, xiv, 185, 186, 198

catalysis, ix, 2, 3, 4, 33, 143, 201 catalyst, x, 2, 3, 18, 28, 31, 32, 33, 35, 46, 110, 131, 138, 160, 175 catalytic activity, 109, 121, 126, 132, 133 catalytic properties, 3, 37 cellulose, xi, 26, 39, 50, 51, 162 challenges, 228 charge density, 103 charging, 224, 225, 227 chemical activation, xi, xiii, 3, 4, 5, 6, 38, 50, 51, 54, 72, 74, 75, 80, 81, 88, 89, 91, 104, 166, 167, 169, 171, 172, 182, 183 chemical agent, xiv, 166, 167, 171, 172, 175, 205 chemical bonds, xv, 168, 208, 218, 221 chemical characteristics, 8, 72, 147 chemical compound, 219, 227 chemical interaction, 65, 95 chemical properties, x, 3, 16, 49, 51, 54, 55, 89, 110, 132, 147, 172, 204 chemical reactions, 96, 108 chemical stability, 16 chemical structures, 145, 150 chemical vapor deposition, 35 chemicals, xiv, 74, 166, 167 chemisorption, x, xv, 2, 33, 95, 116, 218, 229 chromatography, ix, 1, 42 CNTs, 220 coagulation process, 46 coal, xiii, xv, 36, 78, 94, 104, 108, 110, 131, 134, 135, 138, 139, 143, 163, 165, 166, 168, 171, 173, 178, 183, 218, 221, 229 coal tar, 104, 163 cobalt, 138, 161 coke, 101, 131, 138, 173 coke formation, 138 combustion, 55, 108, 175, 183 composites, 39, 43, 188 contact time, 79, 89, 91, 93, 94, 97, 146, 152 contaminant, xi, 44, 50


Index contaminated sites, 104 contaminated soils, 45 contamination, 8, 106, 142 conventional, 9, 51, 52, 53, 186, 199, 219 copolymer, 16, 17, 19, 20, 24, 33, 37, 162 copper, 38, 101, 106 corn stover, 171 counter electrodes, 221 cut-in voltage, 226 cylinders, 222, 225, 226

233 discharging, 224, 225, 226, 227 drawing, 225 drinking water, 52, 53, 73, 75, 78, 100, 103 dyeing, 41, 43, 142, 143 dyes, x, xi, xiii, 2, 3, 4, 9, 10, 11, 12, 13, 14, 16, 31, 33, 36, 41, 42, 43, 50, 51, 52, 53, 62, 63, 72, 73, 74, 75, 103, 105, 142, 152, 155, 156, 158, 159, 160, 164, 182, 200, 208

E D DC, 224 decomposition, ix, 3, 5, 15, 16, 24, 36, 46, 86 deformation, 21, 22, 23, 147, 198 degradation, 6, 9, 13, 31, 35, 42, 44, 45, 46, 143, 159, 160, 161, 204 degradation process, 13 dehydration, xiv, 5, 6, 119, 120, 166, 167, 171, 197 density functional theory, 55 desorption, xi, xii, 27, 28, 41, 50, 54, 55, 56, 69, 70, 71, 85, 91, 96, 98, 100, 101, 108, 109, 114, 116, 120, 123, 130 desulfurization, xii, 107, 108, 109, 131 detection, 55, 152 detergents, 163 deviation, 211 DFT, 55, 144 dielectric constant, 187, 188, 190, 191, 192, 193, 194 dielectric loss, 188 dielectric material, 186 dielectric properties, xiv, 185, 186, 187, 188, 189, 190, 193, 194, 195, 197, 199, 201 diesel, 219 dipole polarization, 187 disassociation, 226, 227

earth, 218 electric charge, 121, 129 electric field, 187, 190, 193 electrical conductivity, 7 electricity, 219 electrochemical, xv, 14, 41, 45, 143, 161, 218, 219, 220, 221, 227, 228, 229 electrochemical hydrogen storage, xv, 218, 219, 220, 227, 228 electrode, 44, 132, 161, 163, 220, 221, 222, 223, 224, 225, 226, 227 electrodeposition, 78 electrolyser, 220 electrolyte, xiv, xv, 185, 189, 190, 191, 192, 193, 194, 197, 199, 218, 221, 224, 227 electrolytic cell, 221, 222, 224 electromagnetic, xiv, 185, 186, 188, 190, 193, 195, 197 electron, 18, 24, 25, 64, 71, 90, 110, 121, 129, 134, 193, 195 electron pairs, 121 electrons, 109, 121, 195 energy, xiv, 8, 13, 41, 44, 56, 108, 109, 116, 121, 134, 135, 143, 155, 185, 186, 187, 188, 193, 195, 197, 199, 200, 205, 210, 212, 218, 219, 220, 221, 225, 227, 229 energy density, 219 energy expenditure, 219 energy input, 220


234

Index

energy supply, 219 environmental impact, 41 environmental management, 180 environmental protection, ix, 1, 3, 78, 109 experimental condition, 14, 30, 63 experimental design, 97, 106, 158 extinction, 218 extraction, 34, 79, 188

F fabricated, xv, 218, 224, 227 Fenton reagent, 14 fertilizers, 78 fixed bed reactors, 8 flue gas, xii, 105, 108, 109, 114, 121, 130, 131, 132, 133, 175, 177, 182, 183 fluidized bed, 48 fossil fuels, 218, 219 FTIR, 18, 55, 57, 88, 95, 98, 189, 197, 207, 209 fuel cell, xv, 218, 219, 220, 228, 229 future fuel, 219

hazardous materials, 43, 44, 46, 182 high temperature (800oC-1000oC, 169 human health, 9, 53, 74, 78, 208 hybrid, 9, 13, 15, 18, 39, 44, 105, 160, 219, 229 hybrid systems, 13 hydrocarbons, ix, 3 hydrogen, xv, 3, 6, 14, 15, 16, 17, 18, 19, 35, 36, 55, 86, 88, 94, 131, 132, 133, 139, 143, 158, 169, 188, 217, 218, 219, 220, 221, 224, 225, 226, 227, 228, 229 hydrogen cyanide, 132, 133 hydrogen gas, 220, 224, 225 hydrogen peroxide, 6, 14, 15, 16, 18, 19, 88, 143, 158 hydrogen sulfide, 131 hydrogenation, ix, 3, 36 hydrophilicity, 3, 6 hydro-pyrolysis, xii, 141, 142 hydroxide, xiv, 6, 90, 203, 204, 205, 208, 214, 215, 221 hydroxyapatite, 87 hydroxyl, 15, 16, 147, 208 hydroxyl groups, 208 hysteresis loop, 27, 147

G gas adsorption, xiii, 165, 166, 172, 175 gas bubble, 226 gasification, 5, 6, 48, 111, 114, 126, 129, 135, 138, 183, 197 generation, 15, 123, 187, 219, 225, 226, 227 glass, 18, 145, 221 global warming, 218 graduated cylinder, 224 gravimetric, 219 green house gases (GHGs), 218

H

I industries, industry(ies), x, 2, 3, 8, 9, 13, 52, 71, 74, 78, 104, 142, 143, 208, 219, 221 internal pore surface area, xv, 218, 220 ions, 35, 78, 79, 94, 96, 98, 101, 102, 104, 105, 152, 163, 190, 219, 224 IR spectra, 57, 149 iron, x, 2, 6, 14, 15, 17, 21, 28, 29, 30, 31, 33, 35, 36, 37, 41, 44, 45 irradiation, 158, 160 isotherms, 27, 28, 54, 55, 56, 60, 65, 74, 90, 91, 144

halogenation, ix, 3, 109


Index K K+, 96 KBr, 96, 177, 189 ketones, 147 kinetic curves, 59 kinetic model, 63 kinetic studies, 74, 83, 158 kinetics, xiii, 38, 41, 43, 46, 73, 74, 75, 91, 94, 98, 138, 139, 160, 164, 165, 166 KOH, 171, 173, 176, 205, 207, 221

L Langmuir isotherm, 97, 154, 155, 156, 210, 213, 214 layered double hydroxides, 41 lignin, xi, xiii, 3, 26, 47, 50, 51, 53, 74, 162, 166, 167, 173 lignite, xii, 107, 108, 110, 111, 117, 120, 121, 125, 126, 129, 131, 138, 139 lignocellulosic wastes, x, 34, 49, 50 liquid, ix, xiii, 3, 106, 145, 159, 162, 165, 166, 167, 189, 190, 196, 197, 206, 219, 227 liquid electrolyte, 227 lithium polymer, xv, 218 lithium-ion, xv, 47, 218, 227 loss tangent, xiv, 185, 187, 190, 191, 192, 193, 194, 195

M macropores, x, xiii, xv, 2, 4, 33, 56, 166, 167, 170, 218 mercury, vi, xi, 36, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 132, 133, 163, 172, 174, 177, 181, 182, 183

235 mesopore range, xiii, 166, 167, 175 mesopores, xiii, xv, 4, 26, 27, 28, 29, 33, 56, 64, 155, 166, 167, 170, 218 metal extraction, xiv, 166, 167 metal hydride, xv, 218, 220, 227, 229 metal hydroxides, 205 metal ion, 94, 95, 98, 100, 102, 201 metals hydroxide activation, xiv, 203, 204 methylene blue, x, 2, 16, 18, 19, 31, 32, 33, 42, 43, 53, 62, 63, 64, 65, 71, 72, 73, 157, 160, 181, 215 micropores, x, xiii, xv, 2, 4, 5, 28, 29, 33, 56, 64, 155, 166, 167, 170, 218 microporous materials, 27, 86 microwave heating, xiv, 186, 187, 188, 195, 197, 198, 199, 200, 201 microwave radiation, 186, 200 microwaves, 186, 187, 188, 195 molecules, 4, 62, 71, 99, 152, 153, 155, 167, 174, 175, 187, 190, 195, 197, 208, 209, 210, 212 monolayer, 61, 62, 90, 97, 153, 154, 210, 212, 214 multiwalled carbon nanotubes, 158

N nature, 14, 51, 64, 65, 72, 80, 142, 152, 154, 162, 189, 204, 219, 220 nitrogen, xii, 3, 17, 18, 27, 28, 55, 86, 88, 108, 109, 110, 111, 114, 115, 119, 120, 121, 123, 125, 126, 129, 130, 132, 133, 134, 157, 169, 188 novel, 34, 104, 143, 159, 183, 220, 221

O organic compounds, x, 3, 5, 15, 16, 26, 46, 47, 49, 50, 52, 53, 62, 175, 208 organic matter, 14, 219


236

Index

oxidation, ix, x, xiv, 2, 3, 9, 13, 14, 15, 18, 19, 31, 32, 33, 35, 36, 44, 45, 46, 53, 73, 86, 88, 92, 109, 121, 123, 125, 130, 131, 132, 133, 138, 143, 161, 166, 167, 171, 183 oxygen, xiii, 3, 9, 15, 36, 46, 86, 88, 90, 93, 97, 98, 104, 114, 119, 120, 133, 142, 145, 147, 152, 169, 174, 188, 220 ozonation, 143

P PEMFC, xv, 218 penetration depth, 196 petroleum, 14, 137, 144, 173 pH, xiii, xiv, 3, 9, 36, 52, 54, 55, 63, 64, 79, 86, 89, 90, 91, 92, 94, 97, 142, 145, 146, 150, 151, 152, 189, 203, 206, 207, 208 pharmaceutical compounds, 51, 52 pharmaceuticals, 14, 45, 52, 71, 75 phenol, 3, 36, 44, 46, 64, 72, 86, 159 phenolic compounds, 14, 45 phosphates, 143, 159 phosphorus, 134 phosphorylation, 47 photocatalysis, 14 photodegradation, 143, 161 photovoltaic cell, 219 physical activation, 5, 6, 7, 37, 81, 104, 166, 167, 169, 170, 172 physicochemical properties, 79 physisorption, xv, 54, 90, 92, 94, 173, 218, 219, 229 platinum, 36, 221, 223 polymer, xv, 8, 19, 29, 39, 48, 133, 143, 156, 161, 162, 201, 218, 227 polymer chains, 29 polymer composites, 8, 39 polymer electrolyte membrane fuel cell, xv, 218 polytetrafluoroethylene, 222

porosity, ix, x, xv, 2, 4, 5, 6, 7, 16, 18, 24, 50, 51, 73, 93, 169, 170, 172, 174, 218 porous, xiv, 8, 24, 25, 26, 34, 36, 38, 62, 93, 143, 157, 166, 167, 168, 174, 175, 204, 219, 220, 227 porous carbon, 34, 36, 157, 227 potassium, xiv, 6, 18, 19, 96, 204, 205, 214, 215, 221 preparation of activated carbon, 4, 37 priority water pollutants, 78 proton flow battery, 220, 229 purification, xiv, 53, 166, 167, 204 pyrolysis, x, xii, xiv, 2, 5, 6, 7, 17, 19, 20, 26, 37, 48, 72, 86, 87, 88, 93, 121, 134, 138, 139, 141, 142, 144, 161, 162, 163, 166, 167, 200, 203, 204, 205, 207, 209, 212, 214, 215 pyrolysis residue, xiv, 203, 204, 205, 207, 209, 212, 214

Q quartz, 54 quinone, 22, 23, 58, 86

R raw materials, xii, 7, 80, 107, 110, 138, 204 reaction rate, 114, 126, 129 reactions, ix, xiv, 3, 5, 6, 15, 36, 88, 109, 131, 132, 133, 134, 166, 171, 208 reagents, 91, 145, 205, 206, 207, 209, 212 reference, 80, 221 regeneration, xi, xii, 50, 69, 71, 78, 80, 96, 98, 108, 109, 114, 120, 121, 123 relaxation time, 195, 196 renewable energy, 219 reverse osmosis, 79, 143 rhodamine B, xiv, 204, 205, 206, 208, 209, 211, 212, 214, 215 rice husk, xi, 50, 53, 54, 56, 57, 65, 70, 173


Index rich in carbon, xiii, 166, 167, 168, 204 rights, iv round-trip efficiency, 220

S self-discharging, 228 sludge, 43, 53, 81, 91, 102, 106, 173 SO42, 116, 122, 123 sodium hydroxide, xiv, 6, 69, 204, 205 solid waste, x, 2, 16, 105 solid-state, xv, 217, 219, 221 solubility, 9, 146, 208 sorption kinetics, 103 specific surface, ix, xiv, 2, 3, 4, 5, 7, 16, 18, 29, 31, 33, 55, 56, 73, 86, 94, 110, 111, 113, 114, 125, 126, 127, 129, 130, 144, 173, 203, 204, 206, 207, 210 spectroscopy, 58, 88 splitting, 161, 221 steam activation, xii, 37, 108, 111, 113, 115, 117, 121, 123, 125, 129, 131, 170, 212 styrene, 7, 16, 17, 19, 20, 24, 33, 37 sulfur, xii, 3, 42, 86, 87, 94, 96, 100, 101, 108, 124, 125, 127, 128, 130, 139, 147 sulfur dioxide, 87 sulfuric acid, 6, 86, 110, 144 sulphur, 55, 86, 104, 105, 110, 116, 123, 188 sulphuric acid, 221, 224, 227 surface chemistry, 47, 62, 88, 93, 98, 99, 133, 167, 181, 200 surface properties, xii, 99, 141, 154, 208 surfactants, 52, 106, 160

T temperatures between 400-700oC, 171 textural properties, 31, 57, 71, 80 thermal decomposition, 114, 169 thermal stability, 8

237 thermal treatment, 24, 87, 88, 132, 133 thermodynamics, 41, 96, 160 toxicity, 9, 41, 45, 46, 52, 78, 102, 208 transesterification, 47 transformation, x, 2, 16, 73 treatment, xi, xii, xiv, 13, 14, 16, 34, 37, 38, 43, 44, 45, 46, 50, 51, 52, 74, 75, 78, 86, 88, 89, 92, 99, 102, 109, 131, 135, 136, 141, 142, 143, 152, 156, 157, 163, 166, 167, 169, 171, 172, 182, 183, 204, 206, 214 treatment methods, 78, 100

U ultramicropores, xv, 218 URFC, 220 UV irradiation, 160 UVA irradiation, 46

V Van der Waals, 98, 167, 219 volatile organic compounds, 26, 46, 175 volumetric, 66, 69, 187, 219

W wastewater, x, xi, 2, 3, 7, 9, 13, 14, 15, 18, 34, 36, 43, 44, 45, 50, 51, 52, 53, 74, 78, 100, 102, 103, 104, 135, 142, 143, 152, 156, 161, 204, 214 water, xi, xiii, xiv, 5, 8, 9, 14, 15, 17, 18, 34, 37, 38, 39, 40, 41, 43, 44, 45, 46, 50, 51, 52, 53, 54, 69, 70, 71, 73, 74, 75, 78, 79, 86, 89, 92, 94, 96, 99, 100, 102, 103, 104, 105, 106, 108, 111, 134, 136, 142, 143, 144, 145, 146, 147, 150, 157, 159, 161, 162, 163, 166, 167, 168, 170, 171, 174, 175, 180, 182, 186, 189, 190, 197,


238

Index

198, 199, 204, 206, 207, 208, 219, 220, 221, 222, 224, 226, 227 water pollution, 78, 142, 175 water purification, xiv, 166, 167 water treatment, 37, 78, 89

X XPS, xii, 47, 96, 107, 114, 115, 116, 118, 119, 120, 122, 133, 134 X-ray diffraction (XRD), x, 2, 18, 20, 133

Z zeolites, 16, 143 zero-emission, 219 zinc, xiv, 6, 35, 101, 159, 180, 183, 185, 186, 189, 190, 197, 198, 199, 201, 207 zinc chloride, xiv, 6, 183, 185, 186, 189, 190, 197, 198, 199, 201, 207 zinc oxide (ZnO), 35, 159, 160
