Adsorption of Alizarin Red S onto Biosorbent of Lantana camara ...

1 downloads 0 Views 958KB Size Report
Abstract Adsorption of an anthraquinone dye Alizarin. Red S onto biosorbent of Lantana camara has been studied on aqueous solutions. The batch adsorption ...
Adsorption of Alizarin Red S onto Biosorbent of Lantana camara: Kinetic, Equilibrium Modeling and Thermodynamic Studies Ravindra K. Gautam, Pavan K. Gautam, M. C. Chattopadhyaya & J. D. Pandey

Proceedings of the National Academy of Sciences, India Section A: Physical Sciences ISSN 0369-8203 Proc. Natl. Acad. Sci., India, Sect. A Phys. Sci. DOI 10.1007/s40010-014-0154-4

1 23

Your article is protected by copyright and all rights are held exclusively by The National Academy of Sciences, India. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”.

1 23

Author's personal copy Proc. Natl. Acad. Sci., India, Sect. A Phys. Sci. DOI 10.1007/s40010-014-0154-4

RESEARCH ARTICLE

Adsorption of Alizarin Red S onto Biosorbent of Lantana camara: Kinetic, Equilibrium Modeling and Thermodynamic Studies Ravindra K. Gautam • Pavan K. Gautam M. C. Chattopadhyaya • J. D. Pandey



Received: 24 October 2013 / Revised: 14 March 2014 / Accepted: 21 March 2014  The National Academy of Sciences, India 2014

Abstract Adsorption of an anthraquinone dye Alizarin Red S onto biosorbent of Lantana camara has been studied on aqueous solutions. The batch adsorption experiments were conducted using simulated aqueous solutions and the effects of initial dye concentration, pH of solution, contact time and temperature were investigated. The prepared biosorbent was characterized using FTIR, SEM, elemental analysis and through the determination of pHzpc. The equilibrium data were modeled with Langmuir and Freundlich isotherms. Freundlich model fitted very well with the equilibrium adsorption data and this provided evidence of multilayer adsorption of the dye molecules onto the active sites on the biosorbent. The kinetic studies revealed that the process was quite rapid and more than 90 % of equilibrium capacity was achieved within 80 min. The rates of adsorption were found to confirm to the pseudo-second-order kinetics with good correlations (R2 [ 0.99). The thermodynamic studies showed that the Alizarin Red S-biosorbent system is spontaneous, exothermic and favourable in nature. Keywords Adsorption  Alizarin Red S  Freundlich  Lantana camara  Kinetics

Introduction Due to rapid growth of industrialization and urbanization, large amounts of wastes containing dyes and pigments are discharged into the receiving aquatic environment. It is

R. K. Gautam  P. K. Gautam  M. C. Chattopadhyaya  J. D. Pandey (&) Department of Chemistry, University of Allahabad, Allahabad 211002, India e-mail: [email protected]

reported that approximately 10–15 % of the dye produced is lost during the textile dyeing processes and finishing operations each year [1]. The dye-bearing wastewater is not only aesthetically displeasing but also restrains sunlight from penetrating into the aquatic system. This results in the disruption and gradual destruction of the aquatic ecosystem [2]. Moreover, some dyes and their products are highly toxic and potentially carcinogenic, mutagenic or allergenic to aquatic life [3]. The traditional methods for color removal, including chemical precipitation, reverse osmosis, and solvent extractions are limited because of the excessive usage of chemicals, accumulation of secondary concentrated sludge, expensive plant requirements, and high operational costs [4]. Adsorption has been found to be superior to the other techniques for dye wastewater treatment in terms of the operational cost, relative simplicity of design, easier operation and insensitivity to toxic substances. Therefore, there has been a fast growing research and development interest in testing and using low-cost, easily available materials for the adsorption of dyes. The main attractions of biosorption (i.e. using adsorbents which are derived from biomass) are its high selectivity and efficiency, cost effectiveness and efficient removal of dyes from large volumes over a number of sorption/desorption cycles. Low-cost materials have also been extensively studied as alternative adsorbents for dyes, and recent studies have shown that waste biomass [2], bagasse pith [5], de-oiled soya [6–8], hen feathers [9] and clay [10] may be used effectively as adsorbents. Alizarin Red S, an anthraquinone dye, used in many fields belongs to the group of the most durable dyes. It cannot be completely degraded by general physicochemical and biological processes because of the complex structures of the aromatic rings that afford high physicochemical, thermal, and optical stability [10]. Therefore, most of the treatments for such dye-laden effluents are

123

Author's personal copy R. K. Gautam et al.

largely inadequate. Only a few studies were found to have dealt with the sequestration of Alizarin Red S using nonbiomass based adsorbents. Moriguchi et al. [11] elucidated adsorption mechanism of bone-staining agent Alizarin Red S on hydroxyapatite, Ghaedi et al. [12] used multi-walled carbon nanotubes as adsorbents for the removal of Alizarin Red S molecules. Lantana camara L., (hereafter Lantana), a native of tropical America, belongs to the family Verbenaceae, and has been described as one of the world’s ten worst invasive weeds [13]. The plants can grow individually in clumps or as dense thickets, crowding out more desirable species. In disturbed native forests, it can become the dominant understorey species, disrupting succession and decreasing biodiversity. Yet, this potential biomaterial has not been applied for remediation of dye-laden wastewaters. In view to fill in the paucity of published data on the use of biomass based adsorbents for removing Alizarin Red S, in the present study, the removal of chemical grade Alizarin Red S was studied by using Lantana biosorbent. Batch adsorption experiments were conducted using synthetic aqueous solutions of Alizarin Red S and the effects of initial dye concentration, initial pH of solution, and temperature were investigated. The kinetics of adsorption has been studied, and various kinetic models, such as pseudofirst-order and pseudo-second-order models were tested with experimental data for their validity. The equilibrium sorption behavior of the biosorbent has been studied using the adsorption isotherm techniques. Thermodynamics of the adsorption processes has also been studied.

Materials and Methods Lantana Biosorbent Lantana was collected by the roadsides of University campus, Faculty of Science, University of Allahabad, Allahabad, India. The biomass of Lantana was first washed with distilled water twice and dried in sunlight for 3–5 days. Then, the completely dried biomaterial was crushed down to powder and washed again 5 times with double distilled water, and dried in a hot air oven up to 120 C for 24 h. The oven dried powder was then sieved with 44 BSS mesh. The fine particles were selected for the adsorption experiments, placed in air-tight glass bottles and finally kept in a dessicator. Alizarin Red S Adsorbate Alizarin Red S (sodium alizarin sulphonate, CI 58005, Product No.-13005) was purchased from British Drug House, Poole, England. Figure 1 shows the chemical

123

O

SO3 Na

O O

O

Fig. 1 Chemical structure of Alizarin Red S molecule

structure of the Alizarin Red S molecule. Alizarin Red S stock solutions (1,000 mg l-1) were prepared by dissolving the required amount in double distilled water, and the working solution was prepared daily with the required dilution. The concentration of the dye was determined at 423 nm. Solution pH was measured using a pH/ion meter (pH meter 335, Systronics, Ahmedabad, India) and absorption studies were carried out using UV–Visible spectrophotometer (spectrophotometer 2203, Systronics, Ahmedabad, India). All chemicals with the highest purity analytical reagent grade available were purchased: NaOH, HCl and NaCl (E. Merck, Mumbai, India). Characterization of Lantana Adsorbent Infrared spectra of unloaded and dye-loaded adsorbents at the optimum pH for maximum dye removal were obtained by use of a Fourier transform infrared spectroscopy using a FTLA 2000, ABB, Canada to determine the surface functional groups. Scanning electron microscopy (SEM) was used to study the surface morphology of the adsorbent. SEM studies were carried out using a scanning electron microscope (Scanning Electron Microscope-Zeiss EVO40) at an electron acceleration voltage of 20 kV. Prior to scanning, the adsorbent was coated with a thin layer of gold using a sputter coater to make it conductive. The surface area and pore volume were also determined with a BET (Brunauer, Emmett and Teller) surface area analyzer (Micromeritics ASAP 2020, surface area analyzer), by means of adsorption of ultra pure nitrogen at 77 K. The elemental analysis was performed using elemental analyzer (CHN Autoanalyzer, Australia). pH at pHzpc of the biosorbent was determined by the solid addition method [14]. Initial pH of 0.1 N KNO3 solutions (pHi) was adjusted from 2 to 12 by adding either 0.1 N HCl or 0.1 N NaOH. Adsorbent dose (0.5 g l-1) was added to 50 ml of 0.1 N KNO3 solutions in 150 ml conical flasks and stirred for 30 min of contact time and final pH (pHf) of solution was measured. The difference between the initial and final pH (pHf - pHi) was plotted against the initial pH (pHi) and the point where pHf - pHi = 0 was taken as pHzpc.

Author's personal copy Adsorption of Alizarin Red S onto Biosorbent of Lantana camara

Adsorption Experiments The removal efficiency of Lantana based biosorbent for Alizarin Red S was investigated by usual batch adsorption experiments. Stock solutions of Alizarin Red S were prepared by dissolving the required amount of Alizarin Red S in deionized water. Standard solutions of required concentrations were prepared by diluting the the stock solution. Batch adsorption experiments were conducted by taking 50 ml Alizarin Red S solution in 250 ml of Erlenmeyer conical flasks at desired pH value, contact time, temperature, dose, and adsorbate concentration. Adsorption experiments were conducted at 30 C (±0.5) and an agitation rate of 120 rpm on a shaking thermostat water bath (Macro scientific works Pvt. Ltd., MSW 275, Delhi). After the equilibrium time, the adsorbent was separated from the aqueous solutions by centrifugation (REMI R-8C BC, New Delhi, India) at 10,000 rpm for 15 min. The residual concentration of Alizarin Red S in each aliquot was determined by using a double beam UV–Vis spectrophotometer. The Alizarin Red S removal and amount of Alizarin Red S adsorbed were determined as follows: Alizarin Red S removal ð%Þ ¼ ðC0  Ce Þ  ð1=C0 Þ  100 ð1Þ Amount Alizarin Red S adsorbed ðqe Þ ¼ ðC0  Ce Þ  ð1=M Þ  V

case of deviation larger than 5 %, more experiments were performed. The experimental data could be reproduced with accuracy greater than 95 %. All the data of batch adsorption experiments are the average values of two tests.

Results and Discussion Textural Properties and Elemental Composition The textural properties such as pore volume and surface area are presented in Table 1, which indicated that the adsorbent had a high specific surface and high pore volume [16]. The average pore diameter was found to be 0.562 nm showing that adsorbent had pores in the microporous region. The specific surface area of adsorbent, obtained by BET analysis, was 123 m2 g-1, and the mean pore diameter was, with a total pore volume of 0.037 cm3 g-1. Rebitanim et al. [17] have also reported a similar total pore volume of 0.035 cm3 g-1 for raw empty fruit bunch biomass when used as adsorbent for methylene blue dye. The elemental analysis demonstrated that carbon is the major constituent of Lantana adsorbent and was present to the extent of 51.3 % indicating the carbonaceous nature of the adsorbent. The heteroatoms present were derived from the starting material.

ð2Þ

where C0 and Ce are the initial and equilibrium concentrations of Alizarin Red S (mg l-1), respectively, M is the mass of adsorbent (g), V is the volume of solution (l), and qe is the amount adsorbed (mg g-1). Desorption and Regeneration Studies The desorption study is important since the regeneration of adsorbent decides the economic success of the adsorption process [15]. In the present study, several solvents were tried to regenerate the biosorbent. The 0.1 mol l-1 NaOH aqueous solutions were found to be effective in desorbing Alizarin Red S from the loaded biosorbents. The biosorbent was regenerated using 0.1 mol l-1 NaOH aqueous solution, the procedure was repeated for many times until the Alizarin Red S dye could not be detected in the filtrate. Then, biosorbent was washed thoroughly with distilled water to a neutral pH. The regenerated biosorbent was reused in the following adsorption experiments and the procedure was repeated 5 times by using the same adsorbent.

Fourier Transform Infrared Spectroscopy (FTIR) Spectra Fourier transform infrared spectroscopy spectra of Lantana adsorbent and dye loaded Lantana adsorbent are shown in Fig. 2. From these spectra, it was observed that Lantana adsorbent contained a large number of functional groups which constituted this biosorbent material. These functional groups were notably the –OH group (3,500–3,300 cm-1), –CH2 and –CH3 in the 2,700–2,900 cm-1 range, water at 1,640 cm-1 and C–O–C between 1,300 and 1,000 cm-1. Kadam et al. [18] have also recently reported similar C–H when testing sugarcane bagasse which is equally a ligninbased biomass for adsorbing textile dyes. The band around 1,661 cm-1 confirmed the N–H stretching from the primary amine [15, 19]. –OH and N–H stretching has equally been reported by Kumar et al. [20] in their work on cashew nut shell. All the more, the bands at 860 and 500–800 cm-1 could be assigned to ester vibrations and monosubstituted aromatic rings, due to the lignin fraction in Lantana biomass [21, 22].

Replication of Batch Experiment

SEM Micrographs

Each batch adsorption experiment above was conducted twice to obtain reproductive results with error\5 %. In the

Scanning electron microscopy has been a primary tool for characterizing the surface morphology and fundamental

123

Author's personal copy R. K. Gautam et al. Table 1 Physicochemical properties of the Lantana biosorbent Specific surface area-BET (m2 g-1)

123 ± 4

Average pore volume (cm3 g-1)

0.071 ± 0.010

Total pore volume (cm3 g-1)

0.0370

Elemental analysis (%) C

51.3

H

11.2

N

4.48

Fig. 3 SEM micrograph of Lantana adsorbent

Effect of pH and the Zero Point Charge (pHzpc)

Fig. 2 FTIR spectra of a Lantana adsorbent and b dye loaded adsorbent

physical properties of the adsorbent surfaces [23]. It is useful for determining the particle shape, porosity and appropriate size distribution of the adsorbent. The SEM micrographs for the unloaded adsorbent are shown in Fig. 3. It is evident from the SEM micrograph of Lantana biosorbent that the fresh adsorbent has an extensive, well pronounced and irregular distribution of pore sizes which matched a honeycomb structure of variable hole sizes, indicating good possibility for the dyes to be trapped and adsorbed. Wang et al. [24] also observed a similar structure when testing activated carbons for the adsorption of methylene blue from wastewater. This variability in pore size implied a wide surface area for active sites for sorption to take place. The native adsorbent surface was also characterized by grooves, irregular ridges and channels which appeared highly undulated due to the presence of intermittently spaced protrusions indicated by bright spots. Hameed and Ahmad [2] have observed similar fibrous and porous morphologies changes for adsorbents studied in their respective work.

123

pH of a solution is a key factor in the adsorption process because it influences functional groups on the adsorbent surface and also determines the solubility of dye in the aqueous solution. It was found that the adsorption capacity of Alizarin Red S decreased with increasing pH over the pH range 2–10 (Fig. 4). When the pH of the solution was *2, the adsorbent would have been more positively charged sites through increased functional groups protonation than at higher pH values. The mechanisms of the adsorption process of Alizarin Red S onto biosorbent were seemingly due to be the electrostatic attraction of the dye molecule with the amino groups of the biosorbent. In aqueous solution, the Alizarin Red S was first dissolved and the sulphonate groups of Alizarin Red S (D-SO3Na) dissociate and were converted to anionic dye ions (D-SO3Na $ D-SO3- ? Na?). The amino groups of biosorbents were then protonated under acidic conditions as follow: R-NH2 ? H? $ R-NH3?. In addition, under acidic conditions (pH B 2), the sulphonate groups (D-SO3-) combined with H?, which decreased the adsorption capacity of Alizarin Red S, according to the following reaction: D-SO3- ? H? $ D-SO3H. As a result, the sorption processed preceded through electrostatic interaction between the two counterions (R-NH3? and D-SO3-) as follows [15]: R-NH3? ? D-SO3- $ R-NH3?… SO3-D. At pH 2, most of the –NH2 groups were protonated, which were favorable for the adsorption of Alizarin Red S [12]. However, at high pH, the number of protonated –NH2 groups were decreased and more –OH were available to compete with the anionic sulphonic groups. As a result, the adsorption capacity for the Alizarin Red S molecules decreased at high pH. The effect of pH on adsorption can be further studied on the basis of zero point charge (pHzpc), which is the point at

Author's personal copy Adsorption of Alizarin Red S onto Biosorbent of Lantana camara 100 90

% Removal

80 70 60

25 mg/l

50

50 mg/l

40

100 mg/l

30 0

2

4

6

8

10

12

pH

Fig. 4 Effect of pH on Alizarin Red S dye removal (adsorbent dose = 0.5 g; temperature = 303 K)

due to electrostatic attraction. Limitation of the sorption capacity of Alizarin Red S dye molecules increased with increase in electrostatic repulsion at higher pHi. This observation agreed with previous studies [25, 27]. Consequently, positively charged functional groups could have conversely exerted strong electrostatic attractions with the anionic Alizarin Red S dye molecules. It was observed that the adsorbent had showed better adsorption capacity in the lower pH. It was observed from the experiment that the maximum uptake of Alizarin Red S dye took place for 25 mg l-1 at pH 2 with 99.2 % colour removal and 95.1, 89 and 88.4 % colour removals at pH 4, 6 and 7, respectively. It was least 42 % colour removal for 100 mg l-1 at pH 10. With increase in initial concentration of Alizarin Red S molecule the adsorption capacity of biosorbent decreased drastically. Therefore, pH 2 was used for subsequent runs of the adsorption experiments. Effect of Initial Alizarin Red S Concentration and Contact Time

Fig. 5 Plots of pHf - pHi versus pHi (adsorbent dose = 10 g l-1; temperature = 303 K)

which the net charge of the adsorbent is zero. pHzpc of biosorbent was found to be 6.2 (Fig. 5). In principle, at pH \ pHzpc, the surface becomes positively charged and favors the uptake of anionic dye to increased electrostatic force of attraction [25]. It was observed that adsorptive removal of Alizarin Red S had increased when pH decreased from 7 to 2. Thereafter, further decrease in pH below a pH of 2 did not cause significant changes in the adsorbed amount of the Alizarin Red S molecules. For solutions with pH [ pHzpc, the adsorbent surface might have become negatively charged and led to competition which turned to disfavor of the sorption of Alizarin Red S dye molecules for vacant adsorption sites. This, therefore, induced a decrease in the dye molecules uptake. However, at pH \ pHzpc, the adsorbent surface could most seemingly have become positively charged to its maximum extent [26] and thereafter favored the sorption of Alizarin Red S

The effects of initial dye concentration and contact time for the adsorptive removal of Alizarin Red S dye from aqueous solutions were studied and the results are given in Fig. 6. It is evident from Fig. 6 that the percentage Alizarin Red S removal decreased with the increase in initial concentration of Alizarin Red S. In principle, the initial dye concentration provided the necessary driving force to overcome the resistance to the mass transfer of Alizarin Red S between aqueous phase and the solid phase of the biosorbent. The increase in initial Alizarin Red S dye concentration also enhanced the interaction between Alizarin Red S dye molecules and biosorbent. Therefore, an increase in initial concentration of Alizarin Red S enhanced the adsorption uptake of Alizarin Red S. This could be explained due to an increase in the driving force of the concentration gradient, as an increase in the initial dye concentration. While the percentage Alizarin Red S removal was found to be 80.2 % for 25 mg l-1 of initial concentration, this value was 60.4 % for that of 100 mg l-1. Similar conclusions on the effect of adsorbate concentration on the removal behavior have been reached by Kumar et al. [20] for the adsorption of Congo red dye from aqueous solution by cashew nut shell. It was observed that the removal of Alizarin Red S was rapid in the initial stages and up to the first 90 min of contact at all initial dye concentrations studied (Fig. 6). After 90 min, the removal efficiency reached equilibrium and quasi stabilized at a maximum value. The adsorption would hence be in a state of dynamic equilibrium between Alizarin Red S desorption and adsorption after the first 90 min of contact time. The reason could be that during the adsorption of Alizarin Red S dye molecules, initially Alizarin Red S dye molecules rapidly reached the boundary

123

Author's personal copy R. K. Gautam et al.

(a)

0.4 0.2

log (qe-qt)

0

0

20

40

60

80

0.2 0.4 0.6

25 mg/l

0.8

50 mg/l 100 mg/l

1

Time (min)

(b)

t/qt

Fig. 6 Effect of initial Alizarin Red S concentration and contact time

layer by mass transfer, then they slowly diffused from boundary layer film onto the adsorbent surface because many of the available external sites had been occupied, and finally, they diffused into the porous structure of Lantana biosorbent. Similar conclusions on the effect of contact time have been proposed by Hameed and Ahmad [2] for the adsorptive removal of methylene blue from aqueous solution by garlic peel. Adsorption Kinetics The adsorption kinetics of Alizarin Red S onto biosorbent was investigated with two kinetic models, namely the Lagergren pseudo-first-order and pseudo-second-order model. The Lagergren rate equation is one of the most widely used adsorption rate equations for the adsorption of solute from a liquid solution. The pseudo-first-order kinetic model (Eq. 3) can be expressed by the following equation [15]: lnðqe  qt Þ ¼ ln qe  k1 t

ð3Þ

where qe and qt refer to the amount of Alizarin Red S adsorbed (mg g-1) at equilibrium and at any time, t (min), respectively, and k1 is the equilibrium rate constant of pseudo-first-order sorption (min-1). The slope and intercept of the plot of log (qe - qt) versus t are used to determine the first-order rate constant, k1 (Fig. 7a). It was found that the correlation coefficient (R2) had a low value (\0.98) and a very large difference existed between qe (experimental) and qe (calculated) for the pseudo-firstorder model. In addition, the theoretical and experimental equilibrium adsorption capacities, qe obtained from this kinetic model varied widely at all concentrations. The inapplicability of the pseudo-first-order model to describe

123

45 40

25 mg/l

35

50 mg/l

30

100 mg/l

25 20 15 10 5 0 0

20

40

60

80

Time (min)

Fig. 7 a Pseudo-first-order kinetics and b pseudo-second-order kinetics for the adsorption of Alizarin Red S onto Lantana biosorbent

the kinetics of adsorption using the adsorbents was also observed in some previous works [15, 28]. The pseudo-second-order model is expressed by [29]: dqt ¼ k2 ðqe  qt Þ2 dt

ð4Þ

Integrating this equation for the boundary conditions t = 0 to t = t and q = 0 to q = qt, gives: t 1 t þ ¼ 2 qt qe k 2 qe

ð5Þ

where k2 is the equilibrium rate constant of pseudo-secondorder adsorption (g mg-1 min-1). The slope and intercept of the plot of t/qt versus t were used to calculate the secondorder rate constant, k2 (Fig. 7b). The corresponding kinetic parameters from both models are listed in Table 2. The correlation coefficient (R2) for the pseudo-second-order adsorption model has high values ([0.99). The calculated equilibrium adsorption capacity of biosorbent was found to be consistent with experimental adsorption capacity for all concentrations. These statistical parameters and adsorption capacity results suggested that the pseudo-second-order adsorption model represents the adsorption kinetics of Alizarin Red S onto biosorbent, which suggested that the adsorption of Alizarin Red S onto biosorbent was a multi-

Author's personal copy Adsorption of Alizarin Red S onto Biosorbent of Lantana camara

Adsorption Isotherms The successful representation of the dynamic adsorptive separation of solute from solution onto an adsorbent depends upon a good description of the equilibrium separation between the two phases. To elucidate the adsorption capacity of biosorbent, the equilibrium experimental data were analyzed for their fit to Langmuir and Freundlich isotherm equations. Langmuir sorption isotherm is valid for the adsorption of a solute from solution as monolayer adsorption on a surface containing a finite number of identical sites. The model is based on several basic assumptions: (i) the sorption takes place at specific homogeneous sites within the adsorbent; (ii) once a dye molecule occupies a site; (iii) the adsorbent has a finite capacity for the adsorbate (at equilibrium); (iv) all sites are identical and energetically equivalent [12]. The nonlinear equation of Langmuir isotherm model (Eq. 6) can be expressed as [30]: Q0 KL Ce qe ¼ ð1 þ KL Ce Þ

where KF (mg g-1) and n are the Freundlich constants characteristics of the system, indicating the adsorption capacity and the adsorption intensity, respectively. The values of KF and correlation coefficient (R2) are obtained from Freundlich curves (Fig. 8b). The adsorption of Alizarin Red S fitted to Freundlich isotherm model with R2 [ 0.97 (Table 3). Based on the comparison of Langmuir and Freundlich models and the results obtained, Freundlich model exhibits a better fit to the adsorption data than Langmuir model. n is an empirical parameter that varies with the degree of heterogeneity and is related to the distribution of bonded ions on the sorbent surface. In general, n [ 1 illustrates that adsorbate is favourably adsorbed on an adsorbent, and the higher the n value the stronger the adsorption intensity [32]. In particular, the

(a)

6 5

ð6Þ

where Q0 is the maximum adsorption capacity reflected on a complete monolayer (mg g-1); KL is the adsorption equilibrium constant (l mg-1) that is related to the apparent energy of sorption. Langmuir isotherm parameters can be obtained from its linearized form as shown by Eq. 7 [19]: Ce 1 Ce þ ¼ qe ðKL Q0 Þ Q0

4

30 °C

3

40 °C

2

50 °C

1 0 0

10

20

30

40

50

Ce

(b)

ð7Þ

2.5 2 1.5

lnqe

A plot of Ce/qe versus Ce should indicate a straight line of slope 1/Q0 and an intercept of 1/(KLQ0) (Fig. 8a). Table 3 shows the isotherm constants for the adsorption of Alizarin Red S onto Lantana biosorbent at different temperatures. Freundlich isotherm is an empirical equation based on adsorption on a heterogeneous surface. The equation is commonly represented by Eq. 8 [31]:   1 ln qe ¼ ln KF þ ð8Þ ln Ce n

8 7

C e /qe

step process involving sorption on the external surface and diffusion into the interior of adsorbent.

1

30 °C 40 °C

0.5

50 °C

0 0

1

2

3

4

lnCe

Fig. 8 Equilibrium adsorption data fitted to the a Langmuir isotherm and b Freundlich isotherm

Table 2 Kinetic parameters for pseudo-first-order and pseudo-second-order kinetic rate models applied to the adsorption process of Alizarin Red S onto Lantana biosorbent qexp (mg g-1) e

Alizarin Red S concentration (mg l-1)

Pseudo-first-order

Pseudo-second-order

k1 (min-1)

-1 qcal e (mg g )

R2

k2 (g mg-1 min-1)

R2

-1 qcal e (mg g )

25

0.019

6.441

0.988

0.094

0.999

1.97

2.00

50

0.022

4.149

0.964

0.035

0.995

3.3

3.28

100

0.049

1.489

0.989

0.015

0.998

6.4

6.08

123

Author's personal copy R. K. Gautam et al. Table 3 Isotherm constants for the adsorption of Alizarin Red S onto Lantana biosorbent at different temperatures Temperature K

Langmuir isotherm -1

Q0 (mg g )

Freundlich isotherm -1

KL (l mg )

R

2

KF (l g-1)

R2

n

303

0.507

0.645

0.951

0.816

1.890

0.968

313

0.683

14.641

0.891

1.189

1.992

0.976

323

1.165

9.803

0.860

1.581

1.680

0.973

Table 4 Comparison of the maximum monolayer adsorption of Alizarin Red S onto adsorbents from various sources

Table 5 Values of different thermodynamic parameters of Alizarin Red S adsorption on Lantana biosorbent at various temperatures DG8 (kJ mol-1)

DH8 (kJ mol-1)

DS8 (kJ mol-1 K-1)

303

2.307

-106.278

-333.351

313

0.905

323

-0.679

References

Temperature (K)

Present study

16. 32

[33]

Magnetic chitosan

40.12

[15]

Multiwalled carbon nanotubes

161.290

[12]

Adsorbents

Maximum monolayer adsorption capacity (mg g-1)

Biosorbent of Lantana camara Biosorbent of Cynodon dactylon

1.165

value of n was significantly higher than unity at all the temperatures and concentrations studied. For example, at 303 K, Freundlich constant n was 1.890, indicating a favourable process. This better fit to Freundlich isotherm in this study indicated that the adsorption took place at heterogeneous sites within Lantana adsorbent forming multilayer coverage of Alizarin Red S at the surface of Lantana powder. Comparisons of the maximum monolayer adsorption of Alizarin Red S onto adsorbents from various sources have been given in Table 4. Thermodynamic Studies Thermodynamic studies of the present adsorption of Alizarin Red S onto biosorbent were undertaken to explicate the mechanism involved. Different thermodynamic parameters such as change in standard free energy (DG8), enthalpy (DH8) and entropy (DS8) were estimated by using the following equations [6, 7]: log Kc ¼

DS DH   2:303R 2:303RT

DG ¼ DH   TDS

ð9Þ ð10Þ

where R (8.314 J mol-1 K) is the gas constant, T (K) is the absolute temperature, and Kc (l g-1) is the standard thermodynamic equilibrium constant defined by qe/Ce. The values of DH8 and DS8 were calculated from the slopes and intercepts of the plot log Kc versus 1/T. The various thermodynamic parameters at the three temperatures studied are given in Table 5. The values of DG8 were found to be negative at higher temperature which indicated that the

123

adsorption process of Alizarin Red S onto the active adsorption sites offered by the biosorbent was spontaneous in nature [34]. The observed decrease in the value of DG with increase in temperature suggested that higher temperatures would make the adsorption of Alizarin Red S onto biosorbent powder easier. A similar observation had been made by Chakraborty et al. [32] on the study of adsorption of Crystal Violet from aqueous solution onto NaOH-modified rice husk. The negative value of DH confirmed the exothermic nature of adsorption of Alizarin Red S dye over biosorbent. The negative value of DS8 suggested that there was decrease in the degree of randomness at the solid/solution interface occurring in the internal structure during the adsorption of Alizarin Red S onto biosorbent. This also supported the affinity of Lantana biosorbent for Alizarin Red S molecules. Effect of Recycling Adsorbents on Alizarin Red S Adsorption From practical point of view, reuse is a crucial factor for the advanced adsorbent [15]. Such adsorbents have higher adsorption capability as well as better desorption property which will reduce the overall cost of the adsorbents. To evaluate the possibility of regeneration and reusability of activated carbon, desorption experiments were performed in batch mode. Desorption of Alizarin Red S from adsorbent was demonstrated using three different eluents, namely 0.01 mol l-1 NaOH, 0.1 mol l-1 NaOH, and 0.5 mol l-1 NaOH. It was found that the quantitative desorption efficiencies using them were 84.2, 93.7 and 87.3 %, respectively. The reusability was checked by following the adsorption–desorption process for three eluents, the 0.1 mol l-1 NaOH was the optimum eluent.

Author's personal copy Adsorption of Alizarin Red S onto Biosorbent of Lantana camara

6.

95 90

% Removal

85 80

7.

75 70

The thermodynamic studies showed that the adsorption process of Alizarin Red S was feasible, spontaneous and exothermic in nature. Thus higher removals could be obtained at higher temperature. The biosorbent can be recycled with 0.1 mol l-1 NaOH solution and the recycled adsorbent can be reused for fourth dye adsorption.

65 60 0

2

4

6

8

n/Time

Fig. 9 The effect of recycling adsorbents on Alizarin Red S adsorption (pH 2, contact time = 90 min)

The effect of recycling times on the adsorption process was repeated 6 times, and the results are shown in Fig. 9, the uptake capacity of Alizarin Red S on the adsorbent decreased slowly with increasing cycle numbers. The percentage adsorption remained steady at about 84 % in the first four cycles, and then the uptake capacity of Alizarin Red S decreased. At the sixth regeneration cycle, the adsorption remained at 70.2 %. These results show that the biosorbent can be recycled for Alizarin Red S molecules adsorption with 0.1 mol l-1 NaOH, and the biosorbent can be reused. This could be ascribed to the fact that, in the basic solution, the positively charged amino groups were deprotonated and the electrostatic interaction between adsorbent surface and Alizarin Red S dye molecules became much weaker [15]. Therefore, the adsorbent can be reused for fourth dye adsorption.

Conclusions In the present work, the results of the adsorption have shown that Lantana adsorbent can be effectively used for the adsorption of Alizarin Red S from aqueous solutions. The findings can be summarized in the following points: 1.

2. 3. 4.

5.

Lantana adsorbent showed significant removal of Alizarin Red S from aqueous solutions, and higher removal has been obtained at low concentration ranges. The adsorption was also found to be highly dependent on pH with higher removals observed at pH range 2–3. The adsorption process followed the pseudo-secondorder rate kinetics. Freundlich isotherm model fitted very well with the equilibrium adsorption data and thus, multilayer adsorption of Alizarin Red S dye molecules taken place over biosorbent. FTIR spectra and clear porosity in SEM micrograph confirmed the adsorption of Alizarin Red S onto Lantana biosorbent.

Acknowledgments RKG thanks the University Grants Commission (UGC), New Delhi for the award of Junior Research Fellowship (JRF) and PKG to the UGC for its RGNF program.

References 1. Dawood S, Sen TK (2012) Removal of anionic dye Congo red from aqueous solution by raw pine and acid—treated pine cone powder as adsorbent: equilibrium, thermodynamic, kinetics, mechanism and process design. Water Res 46:1933–1946 2. Hameed BH, Ahmad AA (2009) Batch adsorption of methylene blue from aqueous solution by garlic peel, an agricultural waste biomass. J Hazard Mater 164:870–875 3. Chung KT, Cerniglia CE (1992) Mutagenicity of azo dyes: structure—activity relationship. Mutat Res 77:201–220 4. Xiong X-J, Meng X-J, Zhen TL (2010) Biosorption of C.I. Direct Blue 199 from aqueous solution by nonviable Aspergillus niger. J Hazard Mater 175:241–246 5. Gad HMH, El–Sayed AA (2009) Activated carbon from agricultural by—products for the removal of Rhodamine–B from aqueous solution. J Hazard Mater 168:1070–1081 6. Gupta VK, Mittal A, Gajbe V, Mittal J (2006) Removal and recovery of the hazardous azo dye acid orange 7 through adsorption over waste materials: bottom ash and de-oiled soya. Ind Eng Chem Res 45:1446–1453 7. Gupta VK, Mittal A, Krishnan L, Mittal J (2006) Adsorption treatment and recovery of the hazardous dye, Brilliant Blue FCF, over bottom ash and de-oiled soya. J Colloid Interface Sci 293:16–26 8. Gupta VK, Mittal A, Gajbe V, Mittal J (2008) Adsorption of basic fuchsin using waste materials—bottom ash and deoiled soya—as adsorbents. J Colloid Interface Sci 319:30–39 9. Gupta VK, Mittal A, Kurup L, Mittal J (2006) Adsorption of a hazardous dye, erythrosine, over hen feathers. J Colloid Interface Sci 304:52–57 10. Fu F, Gao Z, Gao L, Li D (2011) Effective adsorption of anionic dye, Alizarin Red S, from aqueous solutions on activated clay modified by iron oxide. Ind Eng Chem Res 50:9712–9717 11. Moriguchi T, Yano K, Nakagawa S, Kaji F (2003) Elucidation of adsorption mechanism of bone–staining agent alizarin red S on hydroxyapatite by FT-IR microspectroscopy. J Colloid Interface Sci 260:19–25 12. Ghaedi M, Hassanzadeh A, Kokhdan SN (2011) Multiwalled carbon nanotubes as adsorbents for the kinetic and equilibrium study of the removal of alizarin red s and morin. J Chem Eng Data 56:2511–2520 13. Aravind NA, Rao D, Ganeshaiah KN, Shaanker RU, Poulsen JG (2010) Impact of the invasive plant, Lantana camara, on bird assemblages at Male´ Mahadeshwara Reserve Forest, South India. Trop Eco 51:325–338 14. de Oliveira Brito SM, Andrade HMC, Soares LF, de Azevedo RP (2010) Brazil nut shells as a new biosorbent to remove methylene blue and indigo carmine from aqueous solutions. J Hazard Mater 174:84–92

123

Author's personal copy R. K. Gautam et al. 15. Fan L, Zhang Y, Li X, Luo C, Lu F, Qiu H (2012) Removal of alizarin red from water environment using magnetic chitosan with Alizarin Red as imprinted molecules. Colloids Surf B 91:250–257 16. Gupta VK, 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. J Hazard Mater 186:891–901 17. Rebitanim NZ, Wawak Ghani, Mahmoud DK, Rebitanim NA, Salleh MAM (2012) Adsorption capacity of raw empty fruit bunch biomass onto methylene blue dye in aqueous solution. J Purity Utility React Environ 1:45–60 18. Kadam AA, Lade HS, Patil SM, Govindwar SP (2013) Low cost CaCl2 pretreatment of sugarcane bagasse for enhancement of textile dyes adsorption and subsequent biodegradation of adsorbed dyes under solid state fermentation. Bioresour Technol 132:276–284 19. Fan L, Luo C, Li X, Lu F, Qiu H, Sun M (2012) Fabrication of novel magnetic chitosan grafted with graphene oxide to enhance adsorption properties for methyl blue. J Hazard Mater 215–216:272–279 20. Kumar PS, Ramalingam S, Senthamarai C, Niranjanaa M, Vijayalakshmi P, Sivanesan S (2010) Adsorption of dye from aqueous solution by cashew nut shell: studies on equilibrium isotherm, kinetics and thermodynamics of interactions. Desalination 261:52–60 21. Tserki V, Matzinos P, Kokkou S, Panayiotou C (2005) Novel biodegradable composites based on treated lignocellulosic waste flour as filler. Part I Surface chemical modification and characterization of waste flour. Compos A 36:965–974 22. Vieira AP, Santana SAA, Bezerra CWB, Silva HAS, Chaves JAP, de Melo JCP, da Silva Filho EC, Airoldi C (2009) Kinetics and thermodynamics of textile dye adsorption from aqueous solutions using babassu coconut mesocarp. J Hazard Mater 166:1272–1278 23. Mahmoodi NM, Hayati B, Arami M, Lan C (2011) Adsorption of textile dyes on Pine Cone from colored wastewater: kinetic,

123

24.

25.

26.

27.

28.

29. 30.

31.

32.

33.

34.

equilibrium and thermodynamic studies. Desalination 268:117–125 Wang S, Zhu ZH, Coomes A, Haghseresht F, Lu GQ (2005) The physical and surface chemical characteristics of activated carbons and the adsorption of methylene blue from wastewater. J Colloid Interface Sci 284:440–446 C¸elekli A, Birecikligil SS, Geyik F, Bozkurt H (2012) Prediction of removal efficiency of Lanaset Red G on walnut husk using artificial neural network model. Bioresour Technol 103:64–70 Jain R, Gupta VK, Sikarwar S (2010) Adsorption and desorption studies on hazardous dye Naphthol Yellow S. J Hazard Mater 182:749–756 Gupta VK, Jain R, Shrivastava M (2010) Adsorptive removal of Cyanosine from waste water using coconut husks. J Colloid Interface Sci 347:309–314 Han X, Wang W, Ma X (2011) Adsorption characteristics of methylene blue onto low cost biomass material lotus leaf. Chem Eng J 171:1–8 Ho YS, McKay G (1999) Pseudo-second order model for sorption processes. Process Biochem 34:451–465 Gupta N, Kushwaha AK, Chattopadhyaya MC (2012) Adsorption studies of cationic dyes onto Ashoka (Saraca asoca) leal powder. J Taiwan Inst Chem Eng 43:604–613 Fan L, Luo C, Sun M, Li X, Lu F, Qiu H (2012) Preparation of novel magnetic chitosan/graphene oxide composite as effective adsorbents toward methylene blue. Bioresour Technol 114:703–706 Chakraborty S, Chowdhury S, Saha PD (2011) Adsorption of Crystal Violet from aqueous solution onto NaOH-modified rice husk. Carbohydr Polym 86:1533–1541 Samusolomon J, Devaprasath PM (2011) Removal of Alizarin Red S (Dye) from aqueous media by using Cynodon dactylon as an adsorbent. J Chem Pharm Res 3:478–490 Jain R, Gupta VK, Sikarwar S (2010) Adsorption and desorption studies on hazardous dye Naphthol Yellow S. J Hazard Mater 182:749–756