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Removal of a Cationic Dye from Wastewaters by Adsorption on Activated Carbon Developed from Coconut Coir Yogesh C. Sharma,*,† Uma,† and Siddh N. Upadhyay‡ Institute of Technology, Banaras Hindu UniVersity, Varanasi 221 005, India ReceiVed February 6, 2009. ReVised Manuscript ReceiVed April 5, 2009
Biosorption of a cationic dye, methylene blue (MB) onto coconut coir activated carbon (CCAC) developed by thermal activation has been investigated. Coconut coir is a byproduct of Coconut based industries. The unusable part of the coconut coir was used to develop activated carbon. The effect of contact time and temperature on the removal of dye was studied. The process of dye removal followed a first-order kinetics, and the value of the rate constant of adsorption was found to be 1.15 × 10-2 min-1 under optimum conditions. Adsorption data was fitted to Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherm equations. The thermodynamic studies for the process of removal of dye were carried out, and the parameters, namely, free energy (∆Go), enthalpy (∆Ho), and entropy (∆So) changes, were determined. The removal increased from 74.20 to 93.58% with decrease in concentration of dye from 100 to 60 mg/L at 30 °C, 150 rpm, and pH 5.3. The removal exhibited an increasing trend with increasing temperature, exhibiting the endothermic nature of the removal process.
Introduction Wastewaters from industries like textile, dying, printing, cosmetics, food coloring, papermaking, etc. are the major contributors of colored effluents.1 However, textile industries consume large amount of water and different type of dyes imparting color to effluents. The dyes and colors are toxic, and their adverse effects on fauna, flora, and human beings are well documented.2 Color is probably the only contaminant that could be recognized in water even at minute levels. Color has to be removed from wastewater before discharging it into water bodies as it impedes light penetration and retards photosynthesis. Color increases COD and BOD levels of aquatic sources. It has a tendency to chelate metal ions, which results in microtoxicity to aquatic lives. Most of the dyes are stable to photodegradation and biodegradation.1-5 Several physical and chemical methods used to treat colored effluents are precipitation, coagulation, flocculation, membrane filtration, etc. However, these processes are costly and cannot effectively be used to treat the wide range of colored wastewaters. The adsorption process is well-known for its simple design and easy operation. It is inexpensive as compared with other physical and chemical processes. The adsorption technique has * To whom correspondence should be addressed. E-mail: ysharma.apc@ itbhu.ac.in; phone: +91 542 6702865. † Department of Applied Chemistry. ‡ Department of Chemical Engineering and Technology. (1) Yener, J.; Kopac, T.; Dogu, G.; Dogu, T. J. Colloid Interface Sci. 2006, 294, 255–264. (2) Wang, S.; Boyjoo, Y.; Choueib, A. Chemosphere. 2005, 60, 1401– 1408. (3) Tsai, W. T.; Chang, C. Y.; Lin, M. C.; Chien, S. F.; Sun, H. F.; Hsieh, M. F. Chemosphere. 2001, 45, 51–58. (4) Liu, M.-H.; Huang, J.-H. J. Appl. Polym. Sci. 2006, 101, 2284– 2291. (5) Strickland, A. F.; Perkins, W. S. Chemist Colorist. 1995, 27, 11– 16.
been used effectively for the removal of metallic pollutants6-8 and dyes from wastewater.9-12 Activated carbon is a widely used adsorbent for the treatment of industrial wastewater containing color, heavy metals, and other inorganic and organic pollutants. Due to high cost of activated carbon, its use is limited, especially in developing countries such as India. Researchers have tried to search for inexpensive materials that can be waste or a biowaste such as rice husk,13coconut coir,14 banana pith,15 baggase,16 olive stone,17 sawdust,18 orange peel,19 and corncob20 for removal of dyes. Methylene blue (MB) is an organic dye and has wider applications including paper and hair colorant, dyeing textile and wools, etc. MB is a toxic dye, and acute exposure to this (6) Sharma, Y.C; Uma; Srivastava, V.; Srivastava, J.; Mahato, M. Chem. Eng. J. 2007, 127, 151–156. (7) Sharma, Y. C.; Weng, C. H. J. Hazard. Mat. 2007, 142, 449–454. (8) Sharma, Y.C.; Uma; Singh, S.N.; Paras; Gode, F. Chem. Eng. J. 2007, 132, 319–323. (9) Ho, Y. S.; McKay, G. Process Biochem. 2003, 38, 1047–1061. (10) Derbyshire, F.; Jagtoyen, M.; Andrews, R.; Rao, A.; Martin-Gullon., G. E.; Carbon materials in environmental applications. In: Chemistry and Physics of Carbon; Marcel Dekker: New York, Radovic, L. R. Ed.; 2001; Vol. 27, pp 1-66. (11) Jain, A. K.; Gupta, V. K.; Bhatnagar, A.; Suhas., J. Hazard. Mater. B 2003, 101, 31–42. (12) Singh, K. P.; Mohan, D.; Sinha, S.; Tondon, G. S.; Gosh, D. Ind. Eng. Chem. Res. 2003, 42, 1965–76. (13) Kalderis, D.; Bethanis, S.; Paraskeva, P.; Diamadopoulos, E. Bioresour. Technol. 2008, 99, 6809–6816. (14) Kavitha, D.; Navasivayam, C. Bioresour. Technol. 2007, 97, 14– 21. (15) Kanchana, N. Uptake of dyes from solution using banana pith., Bharathiar University, Coimbatore. Masters Dissertation. 1991. (16) Mohan, D.; Singh, K. P. Water Res. 2002, 36, 2304–2318. (17) El-Sheikh, A. H.; Newman, A. P. J. Anal. Appl. Pyrolysis 2004, 71, 151–164. (18) Jadhav, D. N.; Vanjara, A. K. Ind. J. Chem. Technol. 2004, 11, 35–41. (19) Namasivayam, C.; Muniaswamy, N.; Gayathri, K.; Rani, M.; Ranganathan, K. Biores. Technol. 1996, 57, 37–43. (20) Amphol, A.; Thiravetyanb, P.; Nakbanpotec, W. Colloids Surf., A 2009, 333, 19–25.
10.1021/ef9001132 CCC: $40.75 2009 American Chemical Society Published on Web 05/05/2009
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Percentage dye removal ) 100(Co-Ce)/Co
(1)
The amount of adsorbed dye molecules per gram of solid, Figure 1. Structure of methylene blue.
dye has been reported to cause vomiting, dizziness, cyanosis, increased blood pressure, and jaundice in humans.21 The present study focuses on development of activated carbon from coconut coir and then investigating its feasibility for the removal of MB from wastewaters. Effect of various parameters, namely, contact time and initial concentration, temperature, and pH on removal of MB has been studied. Kinetic, equilibrium, and thermodynamic studies have also been conducted. Materials and Methods Preparation of Carbon and Activated Carbon. Coconut coir was collected from the nearby Durga temple, Varanasi, U.P., India and was dried in sunlight. At the temple, coconuts are offered to the deity, wherefrom the coir was collected. The dried coir pith was chopped into small pieces. It was then subjected to carbonization at 700 °C for 1 h using a tubular muffle furnace in indigenous experimental set up. A constant flow of 150 mL/min high purity (99.99%) nitrogen was maintained throughout the process of carbonization. The carbon so formed was then cooled to room temperature and washed with hot deionized water and 0.5 N hydrochloric acid until the pH of sample reached 7.0. The product was then dried in a hot air oven at 110 °C overnight. The primary carbon was impregnated with 20% zinc chloride (ZnCl2) solution for 24 h. ZnCl2 is a catalyst in the reaction. The ratio of primary carbon and zinc chloride solution was 1:1 (w/w).The mixture was then dehydrated in an oven at 110 °C 12 h to remove moisture and activated under the same condition as carbonization but to a final temperature of 700 °C for 2 h. The activated product was cooled under nitrogen gas flow to room temperature and then was washed with hot deionized water and 0.1 M hydrochloric acid until the pH of washing solution reached 7.0. The activated carbon was then dried in a hot air oven at 110 °C, ground, sieved to obtain desired particle size (150 µm), and stored in desiccators for use in adsorption studies. Adsorbate. All the reagents used were of analytical reagent grade chemicals and were obtained from Merck, Mumbai, India. Stock solutions of the reagents were made by dissolving them in deionized water. The chemical formula of MB: C16H18CN3S · 3H2O, molecular weight: 373.91, λmax ) 663 nm. The structure of the dye (MB), C.I. No. 52015, is shown in Figure 1. Adsorption Studies. Adsorption experiments were carried out by agitating 0.25 g of coconut coir activated carbon (CCAC) with 50 mL of dye solution of the desired concentration (60-100 mgl-1) in 250 mL stoppard conical flasks, at 150 rpm, 30 °C in a thermo stated water bath shaker. The pH of solution was measured using a pH meter. The samples were withdrawn from the shaker at predetermined time intervals (viz., equilibrium time) and the dye solution was separated from the adsorbent by centrifugation at 10 000 rpm for 10 min using a centrifuge (Remi 21, India). The effect of pH was studied by adjusting the pH of dye solutions using dilute HCl and NaOH solutions and 50 mL of 60, 80, and 100 mg/L dye solutions at equilibrium time. Concentration of the dye was estimated spectrophotometrically by monitoring the absorbance at λmax 663 nm using a UV-visible spectrophotometer (Spectronic 20, Bausch & Lomb, USA). For the study of isotherms, the adsorption experiments were carried out by agitating solutions of different concentrations at different temperatures. The percentage removal of MB and uptake at equilibrium adsorption on solid phase, qe (mg/g), was calculated using the following relationships: (21) Porter, J. F.; McKay, G.; Choy, K. H. Chem. Eng. Sci. 1999, 54 (24), 5863–5885.
qe ) (Co - Ce)V/w
(2)
where, Co (mg/L) is the initial concentration of MB, Ce(mg/L) is the equilibrium concentration of dye, V is the volume of the solution (L), and w (g) is the mass of the coconut coir activated carbon.
Results and Discussion Physical Characteristics of CCAC. The specific surface area and the pore diameter of activated carbon prepared were measured by nitrogen adsorption isotherm obtained with the help of an ASAP 2020 Micromeritics instrument and by the Brunaer-Emmett-Teller (BET) method at 77 K. Pore size distribution was calculated by Barrett-Joyner-Halenda (BJH) method. The data are given in Table 1. This table shows that BET surface area of CCAC activated carbon is 205.27 m2/g, whereas micropore and mesopore surface area were 181 and 24 m2/g, respectively. Effect of Contact Time and Initial Concentration. Contact time and initial concentration of adsorbate species have significant effect on removal, and the same has been depicted in Figure 2. This figure shows that the removal increases from 74.2 to 93.58% by decreasing the initial concentration of MB from 100 to 60 mg/L. The reaction attained equilibrium in 100 min. It is also clear from Figure 2 that the graphs are single and smooth, indicating monolayer coverage of the adsorbent surface by MB. Further, the removal is rapid in the initial stages, decreases slowly, and acquires a maximum at the time of equilibrium. Removal was found to be dependent on the initial concentration of MB, and maximum removal was found to be 93.58% at 60 mg/L MB. Kinetic Studies. Kinetic study for the removal of MB was taken up by using different rate equations. The kinetic data were found to be fitting in first-order rate equation. Lagergren’s model22,23 was used to determine the value of rate constant: log (qe - q) ) log qe - (Kad/2.303)t
(3)
where qe and q (both in mg/g) are amounts of MB adsorbed at any time and at equilibrium, respectively; and Kad (min-1) is the rate constant of adsorption. The straight line plots of “log (qe - q) vs t” (Figure 3) confirm that the process of removal is governed by first-order kinetics. The Kad value was calculated from the slope of the plot and was found to be 1.15 × 10-2 min-1 at 60 mg/L concentration and 30 °C. The values of Kad show that CCAC is a good adsorbent for removal of MB from aqueous solutions. Effect of Temperature. Temperature is one of the important parameters affecting adsorption. It has a pronounced influence on the percent removal of MB by adsorption on CCAC. The removal of MB increased from 93.58 to 97.66% by increasing the temperature from 30 to 50 °C (Figure 4). The experimental results show that in present investigations, adsorption of MB on CCAC was an endothermic adsorption. Activation energy, Ea, for the removal of MB by CCAC was calculated by using Arrhenius eqation: ln k1 ) ln A - Ea/RT
(4)
where A is the frequency factor (min-1), k1 is the rate constant value for the metal adsorption, Ea is the activation energy in kJ (22) Tabak, A.; Eren, E.; Afsin, B.; Caglar, B. J. Hazard. Mater. 2009, 161, 1087–1094. (23) Hameed, B. H. J. Hazard Mater. 2009, 161, 753–759.
Biosorption of a Cationic Dye by ActiVated Carbon
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Table 1. Physical Characteristics of Activated Carbon BET surface area (m2/g)
total pore volume, Vp (cm3/g)
micropore surface area, smic (m2/g)
mesopore sueface area, smes (m2/g)
mean pore diameter, D (Å)
205.27
0.0246
181.37
23.90
41.24
mol-1, T is the temperature (K), and R ) 8.314 kJ mol-1 k-1. The value of Ea can be calculated by the slope of graph “ln k vs 1000/T” (Figure 5). The activation energy was found to be
5.18 kJ/mol. Low activation energy indicates that physical adsorption controls the removal.16 Effect of pH. Determination of pHzpc was done to investigate the surface charge of activated carbon prepared. For the determination of pHZPC, 0.01 M NaCl was prepared, and its initial pH was adjusted between 2.0 to 12.0 by using NaOH/ HCl in each batch. Then, 50 mL of 0.01 M NaCl was taken in the 250 mL Erylenmeyer flasks and 0.20 g of activated carbon was added to each solution. These flasks were kept for 48 h and the final pH of the solutions was measured by using a pH meter. Graphs were plotted between “pHfinal vs pHinitial” (Figure 6). The point of intersection of the curves of pHfinal vs pHinitial, which lies at 5.1 in the present case has been recorded as pHZPC of the surface of activated carbon.24,25 Thus, pHZPC of activated carbon sample prepared is 5.1. Therefore, at pH values greater than pHZPC, the removal must be higher. Adsorption of MB increases with negative charge surface of adsorbent. Generally, the net positive charge of adsorbate decreases with increasing pH value, leading to decrease in the repulsion between the adsorbent surface and dye,
Figure 2. Effect of initial concentration on removal of MB on CCAC.
Figure 3. Lagergren’s plot for kinetic modeling of the adsorption process of MB on CCAC.
Figure 5. Plot for determination of activation energy for the removal of MB on CCAC.
Figure 4. Effect of temperature on removal of MB on CCAC.
Figure 6. Initial vs final pH plot for determination of pHZPC of CCAC.
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Figure 8. Langmuir’s isotherm plot for the adsorption of MB on CCAC. Figure 7. Effect of pH on percent removal of MB on CCAC.
thus improving the adsorption capacity. Activated carbon of coconut coir carried negative charged surface in solution, which has a significant role in adsorption processes in which cationic dye is involved.26-28 As reported,29 acidity and basicity of adsorbent can be understood by following two expressions:
Table 2. Values of Constants of Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich Isotherms for Adsorption of MB on CCAC parameters isotherms Langmuir
CCAC-OH + H+ f CCAC-OH2+
(5)
temperature (K)
-
+
(6) CCAC-OH f CCAC-O + H where the equations 5 and 6 show the nature of surface of CCAC to be basic and acidic, respectively. The effect of pH was investigated by conducting experiments at pH 4.0, 6.0, 8.0, and 10.0, and maximum removal (96.08%) of MB was found to be at pH 8.0. Otherwise, at all other values of pH selected for the present studies, also removal was significant (Figure 7). Equilibrium Modeling. Equilibrium modeling of adsorption processes provides significant information about suitability of the adsorbent for the system. Selection of an isotherm equation depends on the nature and type of the system. In the present investigation, rather extensive studies have been carried out by using a number of available isotherm equations. The data obtained was analyzed by using Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherm equations. Langmuir Isotherm. The Langmuir model assumes that uptake of adsorbate ions occurs on a homogeneous surface by monolayer adsorption. The Langmuir equation is expressed by the following expression.30 Ce/qe ) (1/Q )b + Ce/Q o
o
(7)
(24) Namdeo, M.; Bajpai, S. K. EJEAFChe. 2008, 7 (7), 3082–3094. (25) Tombacz, E.; Majzik, A.; Horvat, Z. S.; Illes, E. Rom. Rep. Phys. 2006, 58, 281–286. (26) Emad, N. El.; Stephen, J. A.; Gavin, M. W. Chem. Eng. J. 2008, 135, 174–184. (27) Al-Degs, Y. S. Adsorption of anionic reactive dyes on activated carbon from aqueous solution; PhD Thesis, Queen’s University Belfast: Belfast, UK, 2000. (28) Sastri, M. V. C. Studies on ActiVe Carbon. Part IV. Adsorption of MB by ActiVated Charcoal: Effect of Anions and Cations; General Chemistry Section, India Institute of Science, Bangalore, India, 1942, 145-161. (29) Mall, I. D.; Srivastva, V. C.; Agarwal, N. K.; Mishra, I. M. Chemosphere 2005, 61 (4), 492–501. (30) Ko, D. C. K.; Tsang, D. H. K.; Porter, F. J.; McKay, G. Langmuir 2003, 19, 722–730.
b (L/mg)
R2
303 313 323
15.59 17.62 20.62
0.81 0.90 0.75
0.8982 0.9985 0.9761
303 313 323
Kf (L/g) 0.98 1.03 1.04
1/n 0.14 0.15 0.24
0.8655 0.9879 0.9964
303 313 323
B1 (mg/g) 740.90 691.03 849.72
A (L/mg) 1.83 2.07 3.48
0.8781 0.9963 1.0
Qm (mg/g)
E (kJ mol-1)
2.40
10.04 × 10-4
Freundlich
and
Qo (mg/g)
Temkin
DubininRadushkevich 303
0.8929
where Ce (mg/L) is the equilibrium concentration of the solute, qe (mg/g) is the amount adsorbed at equilibrium, and Qo (mg/ g) and b (L/mg) are constants related to the adsorption capacity and energy of adsorption, respectively. A plot of “Ce/qe vs Ce” (Figure 8) gives a straight line. Further, the Langmuir constants were used for “favorable” or “unfavorable” adsorption by a dimensionless parameter, RL:31,32 RL ) 1/(1 + KC0)
(8)
where K is the Langmuir constant (L/g), and C0 (mg/L) is the highest initial dye concentration. The value of RL indicates the isotherm to be unfavorable, linear, or favorable. RL > 1 indicates an unfavorable; RL ) 1, a linear; RL < 1, favorable; and RL ) 0 indicates the adsorption process to be irreversible in nature. The value of RL at different temperatures 30, 40, and 50 °C were found to be 0.020, 0.018, and 0.021, respectively. Values of RL are greater than zero and less than unity, and it shows that Langmuir isotherm is favorable for adsorption of MB on CCAC. The values of Qo and b were determined by the slopes and intercepts of Figure 8 and are given in Table 2. (31) McKay, G.; El Guendi, M.; Nassar, M. Water Res. 1987, 21 (12), 1513–1520. (32) Weber, T. W.; Chakkravorti, R. K. AIChE J. 1974, 20, 228.
Biosorption of a Cationic Dye by ActiVated Carbon
Energy & Fuels, Vol. 23, 2009 2987 Table 3. Thermodynamic Parameters for Removal of MB temperature (K) ∆Go (kcal mol-1) ∆Ho (kcal mol-1) ∆So (kcal mol-1K1) 303 313 323
Figure 9. Plot of Freundlich adsorption isotherms of MB on CCAC.
-0.64 -1.25 -1.36
17.91 2.09
0.056
of the constants, Kf and n, were calculated from the slopes and intercepts of the straight line plots and are given in Table 2. It may be noted that the values of Kf and n increase with an increase in temperature for all the adsorbates on activated carbon, indicating that adsorption is favorable at higher temperature. The dye having the greater value of Kf has high affinity toward the adsorbent as compared to another having low Kf value.33,34 Temkin Isotherm. Temkin isotherm exhibits the effect of indirect interaction between adsorbate by adsorption isotherm. It can be characterized by uniform distribution of binding energy. According to Temkin isotherm the adsorption in the layer decreases with the coverage due to interaction between adsorbate and adsorbent:35 qe ) (RT/b)ln ACe qe ) B1 ln A + B1 ln Ce
Figure 10. Temkin plots for adsorption of MB at different temperatures.
(10)
where B1 ) RT/b; T is the absolute temperature (K); R is the gas constant (8.314J/mol K); A is equilibrium binding; qe is the amount of adsorbed dye on per unit weight of solid surface (mg/g); and Ce is the concentration of dye in aqueous solution at equilibrium. The value of B1 and A have been calculated by slopes and intercepts of the plots, respectively, from a graph “qe vs ln Ce” (Figure 10). b is related with the heat of adsorption. Increasing trend of value of B1 indicates the endothermic nature of adsorption reaction. The Temkin isotherm constants are given in Table 2. Dubinin-Radushkevich Isotherm. For the analysis of high degree of rectangularity another well-known equation was used that Dubinin- Radushkevich isotherm to investigate the nature of adsorption. D-R isotherm does not assume a homogeneous surface or constant sorption potential.36 The D-R equation can be expressed as follows: qe ) qm exp(-KE 2)
(11)
The linear form of above equation can be expressed as:
Figure 11. D-R plots for adsorption of MB on CCAC.
Freundlich Isotherm. Adsorption data for the dyes on activated carbon of coconut coir was fitted to the linear form of Freundlich isotherm:
ln qe ) ln qm(-KE 2)
(12)
E 2 ) RT ln(1+1/Ce)
(13)
The value of qm and K can be obtained by the intercept and slope of the graph of “ln qe vs E2” (Figure 11). E, the mean free energy of sorption per molecule of the sorbate (kJ/mol) involved in the processs can be calculated by D-R isotherm equation as follows: E ) 1/(2K)-1/2
(14)
(9)
The plots of Figure 11 are straight lines, and this indicates that adsorption follows D-R equation in this study. The value
where x/m is the amount adsorbed per unit mass of the adsorbate, Cs is the equilibrium concentration, and 1/n and Kf are constants. The constant Kf is related to the degree of adsorption, and n provides the tentative estimation of the intensity of the adsorption. The straight line plots of Figure 9 show fitness of the experimental data in Freundlich isotherm equation. The values
(33) Walker, G.; Weatherley, L. Chem. Eng. J. 2001, 83, 201–206. (34) Freundlich, H.; Uberdie J. Phys. Chem. 1985, 57, 387–470. (35) Temkin, M. J.; Pyzhev, V. Acta Physiochim. 1940, URSS 12, 217– 222. (36) Dubinin, M. M.; Radushkevich, L. V. Equation of the characteristic curve of activated charcoal, Proc. Acad. Sci., Phys. Chem. Sec., USSR 1947, 55, 331-333.
log x/m ) log Kf + (1/n) log Cs
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Table 4. Comparison of Adsorption Capacities of Different Adsorbents for Removal of MB raw materials apricot shell hazelnut shell walnut shell raw date pith neem sawdust sugar cane dust hazelnut shell saw dust-walnut saw dust-pitch pine coconut coir
concentration range
contact time
adsorption capacities (mg/g)
refs
20-400 mg L-1 12 mg L-1 12.0 mg L-1 50-1000, 50-500 mg L-1 50-1000, 50-500 mg L-1 50-1000, 50-500 mg L-1 60-100 mg L-1
24 h 24 h 24 h 24 h 30 min 30 min 60-180 min 60- 180 min 60-180 min 100 min
4.11 8.82 3.53 80.30 3.62 3.74 76.90 59.17 27.78 15.59
34 34 34 35 36 36 37 37 37 this work
of different parameters of D-R isotherm are given in Table 2. The magnitude of “E” determines the type of adsorption process.37 All the selected isotherm models are suitable for the equilibrium data in the concentration range studied, and the same is clear from the values of correlation coefficient (Table 2) determined for data at each temperature. Thermodynamic Studies. Thermodynamic studies help to understand the adsorption process in a better way. In the present studies also, thermodynamic studies were performed and the parameters, namely, ∆Go, ∆Ho, and ∆So, were determined at the temperatures 30, 40, and 50 °C, respectively. The negative value of Gibbs free energy changes indicate feasibility and spontaneous nature of adsorption process. Values of the thermodynamic parameters and the equilibrium constant “Kc” were calculated by using following equations: Kc ) Cae/Ce
(15)
∆G ) -RT ln Kc
(16)
∆Ho ) R(T2T1/T2 - T1) ln(K2/K1)
(17)
∆So ) (∆Ho-∆Go)/T
(18)
o
where R (1.987 kcal/mol) is the universal gas constant, and T (K) is the absolute temperature. Ce is the equilibrium concentration of MB in the solution (mg/L), and Cae(mg/L) is the amount adsorbed on adsorbent at equilibrium. The values of Kc increased by increasing the temperature, which indicates the endothermic nature of the process of removal. The values of these parameters have been given in Table 3. (37) Aygun, A.; Yenisoy-Karakas, S.; Duman, I. Microporous Mesoporous Mater. 2003, 66, 189–195. (38) Banat, F.; Al-Asheh, S.; Al-Makhadmeh, L. Process Biochem. 2003, 39, 193–202. (39) Khattri, S. D.; Singh, M. K. Adsorpt. Sci. Technol. 1999, 17, 269– 282. (40) Ferrero, F. J. Hazard. Mater. 2007, 142, 144–152.
Comparison of the Adsorption Capacities of Activated Carbons with CCAC. A number of agricultural materials are used to derive activated carbons for variety of applications. Activated carbons are prepared under different experimental conditions and they display varied adsorption capacities. Table 4 presents adsorption capacities of activated carbons prepared from apricot shell, raw date pith, hazel nut shell, etc. for the removal of MB. Adsorption capacities displayed by all the activated carbons are significant. However, maximum adsorption capacity (80.30 mg/g) was observed in case of activated carbon prepared from raw date shell, and the minimum (3.62 mg/g) was reported for activated carbon prepared from walnut shell. The adsorption capacity for the activated carbon prepared in the present studies was found to be 15.59 mg/g. Activated carbon of coir was efficiently utilized as an adsorbent for the removal of MB from the aqueous solutions. The adsorption capacity (mg/g) of the CCAC shows its suitability for dsorption of MB from aqueous solutions. Up to 74.20 and 93.58% color removal could be achieved in 100 min contact time from aqueous solutions with initial concentrations 60 and 100 mg/L. The amount of dye uptake (mg/g) was found to increase with decrease in solution concentration. A kinetic study of the process of removal shows that the process of removal of MB from wastewater is rapid enough. Removal (%) was found to be higher in low concentration ranges, and this finding has industrial applications. The data of equilibrium modeling is significant and recommends application of CCAC for the removal of MB in particular and other dyes from aqueous solutions in general. Acknowledgment. The authors are thankful to AICTE, Government of India, for providing financial assistance to Uma.
EF9001132
