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Adsorption of Congo Red Dye from Aqueous Solutions using leaves of Syzgium Cumini as a Bioadsorbent: Adsorption. Kinetics and Thermodynamics Studies.

Adsorption of Congo Red Dye from Aqueous Solutions using leaves of Syzgium Cumini as a Bioadsorbent: Adsorption Kinetics and Thermodynamics Studies Type: Original research Abstract: In this study, adsorption of Congo Red (CR) dye from aqueous solution using leaves powder of sygium cumini (SC) was investigated. Batch experiments were carried out for further sorption kinetics and isotherms studies.The effect of several operating endowmentess on adsorption namely contact time, adsorbent dose, temperature and ionic strength on the removel of dye from aqueous solution have been also investigated. The adsorption kinetics were described by using different Kinetic models such as pseudo-first-order, pseudo-second, Elovich models, liquid film diffusion model, the modified Freundlich equation and the Bangham equation. The experimental data fitted very well to the pseudo-second-order kinetic model. Thermodynamic endowments namely change in Gibbs free energy (∆G°), Change in enthalpy (∆H°) and Change in entropy (∆S°) were calculated for adsorption of CR on the leaves powder of SC. It showed that adsorption of CR on the leaves powder of SC was exothermic process. These studies demonstrate that leaves powder of sygium cumini (SC) are effective, environmentally friendly and low-cost biomaterial for dye removal from aqueous dye solutions and industrial effluents. Authors: Dr Muhammad Imran Khan

School of Chemistry and Material Science, University of Science and Technology, Hefei 230026, Anhui, China.

Dr Muhammad Ali Khan

Fujian Institute of Research on Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002,China;

Master Shagufta Zafar

Department of Chemistry, the Islamia University of Bahawalpur, Bahawalpur 63000, Pakistan;

Master Samina Ahmad Hussain

Department of Chemistry, Bahauddin Zakariya University (BZU), Multan, Pakistan (60800).

Master Akbar Ali

National Center for Nanoscience and Technology, Chinese academy of science, Beijing, China

Dr ShahNawaz Phulpoto

College of Material Science & Engineering, Beijing University of Chemical Technology, Beijing China

Dr Khalid Hussain Thebo

Institute of Metal Research

Keywords: adsorption, Congo red, exothermic

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Adsorption of Congo Red Dye from Aqueous Solutions using leaves

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of Syzgium Cumini as a Bioadsorbent: Adsorption Kinetics and

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Thermodynamics Studies

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Muhammad Imran Khan,1 Muhammad Ali Khan,2 Shagufta Zafar 3 Samina Ahmad

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Hussain,4 Akbar Ali,5 ShahNawaz Phulpoto,6 Khalid H.Thebo 7* 1

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School of Chemistry and Material Science, University of Science and Technology, Hefei 230026, Anhui, China. 2 Fujian Institute of Research on Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002,China; 3 Department of Chemistry, the Islamia University of Bahawalpur, Bahawalpur 63000, Pakistan; 4 Department of Chemistry, Bahauddin Zakariya University (BZU), Multan, Pakistan (60800). 5 National Center for Nanoscience and Technology, Chinese academy of science, Beijing, China 6 College of Material Science & Engineering, Beijing University of Chemical Technology, Beijing China 7 Institutes of Metal Research, Chinese Academy of Science (CAS), Shenyang, China E-Mail: [email protected] * ,

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Abstract

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In this study, adsorption of Congo Red (CR) dye from aqueous solution using

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leaves powder of sygium cumini (SC) was investigated. Batch experiments were carried

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out for further sorption kinetics and isotherms studies.The effect of several operating

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endowmentess on adsorption namely contact time, adsorbent dose, temperature and

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ionic strength on the removel of dye from aqueous solution have been also

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investigated. The adsorption kinetics were described by using different Kinetic models

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such as pseudo-first-order, pseudo-second, Elovich models, liquid film diffusion model,

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the modified Freundlich equation and the Bangham equation. The experimental data

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fitted very well to the pseudo-second-order kinetic model. Thermodynamic endowments

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namely change in Gibbs free energy (∆G°), Change in enthalpy (∆H°) and Change in

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entropy (∆S°) were calculated for adsorption of CR on the leaves powder of SC. It

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showed that adsorption of CR on the leaves powder of SC was exothermic process.

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These studies demonstrate that leaves powder of sygium cumini (SC) are effective,

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environmentally friendly and low-cost biomaterial for dye removal from aqueous dye

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solutions and industrial effluents.

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Keywords: Adsorption, Congo Red, Syzgium cumini, Pseudo-first-order model,

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Exothermic Process .

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1. Introduction

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Nowadays, environmental problems have becoming major focus of scientific

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attention because of their impact on public health. Among these issues, study on the

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separation of dyes from aqueous solutions is important not only from the point of

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selective separation for industrial uses but also from the environmental aspects. Dyes

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are commonly used in textile, rubber, paper and leather industries. Moreover, effluents

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containing dyes pose serious health threats to human due to their carcinogenicity and

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lead to mutagenic and toxic effects on organisms. Among numerous separation

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techniques attempted for dye removal, the adsorption process is commonly favored

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owing to its simplicity and effectiveness. The applied adsorbents include natural and

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synthetic materials with adsorption efficiencies varying from one to another. Synthetic

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dyes are mostly employed for textile dyeing, leather dyeing, color photography, paper

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printing and as additives in petroleum product [1]. Reactive dyes are the most common

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dyes used because of their importance, such as bright colors, excellent color fastness

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and ease of application [2, 3]. These dyes have different chemical structures

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majority oof reactive dyes are azo compounds that are linked by an azo groups [4].

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Many reactive dyes are toxic to some organisms and they are very harmful for living

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creature in water [5]. In addition, since reactive dyes are highly soluble in water and

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their removal from effluent is difficult by conventional physicochemical and biological

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treatment methods [6, 7] such as adsorption [8], coagulation [9], oxidation [10],

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reduction [11], filteration [12], and biological treatment [13]. Among them, adsorption

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and biological treatment are two important methods available for wastewater treatment.

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The biological treatment is difficult to start up and control [14] and intermediate product

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(aromatic amines) formed during anaerobic reduction of azo dyes are known to be

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potential carcinogens [15].

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procedure due to their advantages of low cost (or even free of expense), accessibility,

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and eco-friendliness. The adsorption capacity depends on several factors such as

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nature of adsorbent, the nature of adsorbate and the solution condition [16]. Generally,

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the commercial activated carbon is indeed effective for color removal but the high cost

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of activated carbon has restricted its widespread use. Therefore, searching a low-cost

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and effective adsorbents should be of considerable significance for practical application

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but

Adsorption on the other hand, should be a favourable

Manuscript body Download source file (473.36 kB) 69

of adsorption [17]. In recent years, research studies have particularly focused on the

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adsorbents made from plant wastes materials like walnut husk [18], composites [19],

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biochars from crop residues [20], natural clinoptilolite [21], sesame hull [22], biomass of

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penicillium YWO1 [23], natural zealite [24], cross-linked succinyl chitosan [25], modified

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bentonite [26], modified attapulgite [27], clay material [28-30], activated carbon [31],

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dehydrated beet pulp carbon [32], polyurethane foam [33], etc as adsorbent for removal

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of dyes from wastewater. In this contex, agriculture by-products have shown its potential

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as a low-cost adsorbent and they are usually being modified chemically in order to

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enhance their adsorption capacty toward dye [34]. However, there are some adsorbents

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which do not have good adsorption capacities for anionic dyes because most have

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anionic or hydrophobic surfaces. Hence, there is a need to search for more effective

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adsorbents [35].

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In this study, the leaves powder of SC was used as adsorbent for removal of Congo

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Red (CR) anionic dye from aqueous solution. The effect of various parameters such as

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contact time, amount of adsorbent, temperature and ionic strength on removal of CR

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dye from aqueous solution was also investigated. The adsorption kinetics and

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thermodynamics for adsorption of CR on the leaves powder of SC was also part of

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study.

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Fig. 1 Chemical structure of Congo Red dye (C32H22N6Na2O6S2)

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2. Experimentals

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2.1. Materials and Methods

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2.1.1. Adsorbent

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The syzgium cumini (jamun) is an evergreen tropical tree found in south asia i.e.

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India, Burma, Ceylon and the Andaman Islands etc. Analyses of the leaves show: crude

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protein, 9.1%; fat, 4.3%; crude fiber, 17.0%; ash, 6.0%; calcium, 1.3%; phosphorus,

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0.19%. They are rich in tannin and contain the enzymes esterase and galloyl

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carboxylase which are presumed to be active in the biosynthesis of the tannins. The

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essential oil distilled from the leaves is used to scent soap and is blended with other

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materials in making inexpensive perfume. The leaves, steeped in alcohol, are

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prescribed in diabetes. The leaf juice is effective in the treatment of dysentery, either

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alone or in combination with the juice of mango leaves. Jambolan leaves may be helpful

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as poultices on skin diseases.

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2.1.2. Adsorbate

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Congo Red (Sodium salt of benzdinediazobis-1-nephthylamine-4-sulphonic acid) is a

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benzidine-based azo dye as a adsorbate in this study. The molecular formula of CR is

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C32H22N6Na2O6S2 and its molecular stucture (Fig. 1). Congo Red (CR) mainly occurs in

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the effluents discharged from textile, paper, printing, leather industries etc. [36-37] All of

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the reagents were of analytical grade and deionized water was used throughout the

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experiments.

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2.13. Adsorption

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Batch adsorption of Congo Red (CR) dye was carried out by immersing leaves

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powder of SC into measured volume of dye aqueous solution at room temperature. The

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bottles were shaked at constant speed of 120 rpm. The concentration of CR was

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determined by UV/VIS spectrophotometer (UV-2550, SHIMADZU) at 490 nm. The CR

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adsorption on the leaves powder of SC at time t, was calculated by equation 1.

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qt 

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C o  Ct V W

(1)

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Where C o and C t are the concentration of CR at initial state and at time t respectively.

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Similarly V and W are volume of CR aqueous solution and weight of adsorbent

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respectively.

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3.0. Results and Discussion

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3.1. Effect of operational parameters

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Herein, the effect of operational parameters namely contacts time, dosage,

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temperature and ionic strength on the removal of CR dye from aqueous solution has

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been investigated. Their details are given below.

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3.1.1. Effect of contact time

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The influence of contact time on the removal of CR from aqueous solution by leaves

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powder of SC was investigated keeping SC dosage (0.1 g), concentration of dye 25

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mg/L, volume of solution (40 ml) and stirring speed (120 rmp) at room temperature (Fig.

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2a). It is clear that the uptake of CR dye is very fast in the start and then it continue to

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increase slowly with contact time until it got a state of equilibrium after 130 minutes. It is

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due to the fact that that several vacant sites are present for adsorption of dye on the

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leaves power of SC in the initial stage of reaction. But with the passage of time the

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available active sites are hard to be occupied due to repulsive forces between solute

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molecules on the solid and bulk phase.

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3.1.2. Effect of dosage

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The adsorbent dose is a crucial parameter. It has significant influence on the

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adsorption of dyes. The effect of dosage on the removal of CR from aqueous solution

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was studies keeping the other conditions constant (Fig. 2b). The percentage removal of

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CR increases with the adsorbent dosage. The percentage removal of CR is found to be

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increased from 90.20% 96.60 % with increase in the amount of leaves powder from

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0.02 g to 0.1 g. This enhanced removal of CR dye is attributed to the increase in the

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number of available sorption sites on the surface of the SC leaves powder. As shown in

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Fig. 2b, that the removal of CR was rapid in the initial stage and then it becomes almost

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unchange with further increasing the amount of SC leaves powder. It can be seen that

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the removal of CR was maximum at SC dosage of 0.1 g. Therefore, 0.1 g was selected

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as optimum amount and used in further experiments to get excellent results. The

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observed two stage-dependent adsorption behaviour have also been reported in the

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literature [38].

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3.1.3. Effect of temperature

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The percentage removal of CR from aqueous solution with temperature was

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studied keeping the contact time, dosage of SC, stirring speed, volume of solution and

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concentration constant (Fig.2c). It has been observed that the removal of CR decreases

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with increasing temperature. The removal of CR decreases from 90.20 % to 56.05 %

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with increasing the temperature from 273 K to 333 K. These results show that

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adsorption of CR on leaves poder of SC was exothermic process.

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3.1.4. Effect of ionic strength

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The ionic strength of the solution is a crucial parameter that control both electrostatic

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and nonelectrostatic intractions between the dye and the adsorbent surface. The effect

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of ionic strengh on the removal of CR from solution was investigated by addition of

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different quantity of sodium chloride to the dye solution (Fig. 2d). Moreover, the Fig.

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2d, showed that the romoval of CR dye decreases with increasing the concentration of

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salt. The removel of dye is found to be decreased from 90.20 % to 56.87 % with

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increasing the concentration of salt from 0 M to 0.5M . This could be due to the

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competition between the CR anions and Cl- for the active sorption sites [39].

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Fig. 2. (a) Effect of time on the removal of CR from aqueous solution by leaves powder of SC. (b)Effect of dosage on the removal of CR from aqueous solution by leaves powder of SC. (c) Effect of temperature on the removal of CR from aqueous solution by leaves powder of SC. (d) Effect of ionic strength on the removal of CR from aqueous solution by leaves powder of SC

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Manuscript body Download source file (473.36 kB) 173

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2.2.

Adsorption Kinetics studies

Several adsorption models are used to study the controlling mechanism of adsorption

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process such as chemical reaction and diffusion control

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3.2.1. Pseudo-first-order model The linearized form of the Lagergren Pseudo-first-order rate equation is given by

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[40]

loq(qe  qt )  log qe 

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K1t 2.303

(2)

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Where qe and qt is the amount of adsorbate adsorbed at equilibrium and time t

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repectively and k1 (min-1) is the rate constant of pseudo-first-order adsorption model.

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The plots of log(qe-qt) vs time for pseudo-first-order model is shown in Fig. 3a. The

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value K1 is calculated from slope of eq. 2 (Table 1). These plots are linear, however the

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linearity of these curves does not necessarily assure the mechanism due to the inherent

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disadvantage of correctly estimating equilibrium adsorption capacity [41]. Further, there

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is a large difference between experimental adsorption capacity value (q e,

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calculated adsorption capacity value (q e,

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not explain the rate process.

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Table 1: Pseudo-first-order, pseudo-second-order and Elovich model rate constants

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Pseudo-first-order

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qe (exp) qe (cal) k1 10-2

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R2

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5.63

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0.922

5.98

1.80

Pseudo-second-order qe

6.39

k2 10-3

9.38

0.996

R2

Elovich model α

β

2.94

0.29

0.971

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and

therefore pseudo-first-order model does

(qe : mg/g; k1: (/min); k2: g/mg.min; α: mg/g.min; β: g/mg)

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cal),

exp)

R2

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3.2.2. Pseudo-second-order model The linearized form of pseudo-second kinetic model is expressed as [42]

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t 1 t   qt k 2 qe2 qe

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(3)

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where k2 (g/mg.min) is the rate constant of pseudo-second-order model. The graphical

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representation of pseudo-second-order model (Fig. 3b). The value of adsorption

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capacity (qe) can be calculated from slope (Fig. 3b) and (Table 1). This value of

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adsorption capacity is in good agreement with the experimental value (5.63 mg/g). The

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value of correlation cofficient is (R2>0.99) which shows that experimental data fitted

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well to the pseudo-second-order model.

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3.2.3. Elovich model The most interesting model to describe the activated chemisorption is the Elovich

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equation [43]

qt 

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1



ln( ) 

1



ln t

(5)

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Where

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(mg/g.min) and β is related to the extent of surface coverage and activation energy for

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the chemisorption. The plot of q t vs lnt for Elovich model (Fig. 3c). The values of α and β

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are determined from intercept and slope (Fig. 3c) and

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correlation cofficient (R2) was 0.971 lower than that of pseudo-second-order model.

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3.2.4. Liquid film diffusion model

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The liquid film model is expressed as [44]

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α and β are constant. The parameter α is considered as initial sorption rate

Ln (1  F )   K fd t 10

(Table 1). The values of

(4)

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Where Kfd is liquid film diffusion rate constant, and F=q t/q. The plot of ln(1-F) vs time for

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liquid film model (Fig.3d) . The value of K fd is calculated from slope (Fig. 3d) and are

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shown in (Table 2). The value of correlation coefficient (R2) is 0.922 which is lower than

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pseudo-second-order model. It indicates that liquid film diffusion model is not suitable to

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explain the experimental data.

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Table 2. Liquid film diffusion model, modified Freunlich equation and Bangham equation

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rate constant (kfd: (/min); k : L/g.min; ko: mL/g/L)

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Liquid film diffusion

Modified Freunlich

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model

equation

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kfd10-2

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4.3

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0.922

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Cfd 0.058

R2

m 2.78

k 0.042

0.965

Bangham equation

R2

ko 102 α10-3 5.8 0.984

11

5.13

R2

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235

Fig.3 (a) Pseudo-first-order kinetics for adsorption of CR on the leaves powder of SC. (b) Pseudo-second-order kinetics for adsorption of CR on the leaves powder of SC. (c) Elovich model for adsorption of MO on the leaves powder of SC. (d) Liquid film diffusion model for adsorption of CR on the leaves powder of SC.

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3.2.5. The modified Freunlich model

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The modified Freundlich eaquation was orignally developed by Kuo and Lotse

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[45]

qt  kCo t 1/ m

(7)

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where qt amount of adsorbed dye (mg/g) at time t, k apparent adsorption rate constant

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(L/g.min), C o the initial dye concentration (mg/L), t the contact time (min) and m is the

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Kuo-Lotse constant. The values of k and m were used to eualuate the effect of dye

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surface loading and ionic strength on the adsorption process.

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Linear form of modified Freundlich equation is given as

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ln qt  ln kCo  

1 ln t m

(8)

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The graphical representation modified Freundlich model (Fig. 4a). The values of m and

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k were determined from slope and intercept (Fig. 4a) and are given in (Table 2). The

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correlation coefficient value was 0.965 for CR adsorption onto leaves powder of SC.

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Table 3. Thermodynamic parameters for adsorption of CR on the leaves powder of SC. G (KJ/mol)

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H (KJ/mol)

S (J/mol)

273K

278K

288K

298K

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-6.31

-17.18

4.76

4.94

5.11

5.71

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3.2.6. The Bangham Equation Bangham equation [46] is given as  Co   km    log  o log log     log t  2.303V   Co  qt m 

(9)

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Where C o is the initial concentration of dye solution (mg/L), V is volume of solution

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(mL), qt is amount of dye adsorbed (mg/g) at time t, m is weight of adsorbent used (g/L).

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α (

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