The Use of Activated Carbon Prepared from Jackfruit (Artocarpus heterophyllus) Peel Waste for Methylene Blue Removal

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1 JOURNAL OF ENVIRONMENTAL PROTECTION SCIENCE (28), Vol. 2, pp The Use of Activated Carbon Prepared from Jackfruit (Artocarpus heterophyllus) Peel Waste for Methylene Blue Removal Devarly PRAHAS, Yoga KARTIKA, Nani INDRASWATI, and Suryadi ISMADJI* Department of Chemical Engineering, Widya Mandala Surabaya Catholic University Kalijudan 37, Surabaya 6114, Indonesia Abstract Jackfruit peel waste which has no economic value has been utilized for activated carbon preparation. The preparation of the activated carbon was carried out using chemical activation with phosphoric acid as activating agent. The impregnation ratio was 4:1 (g H 3 PO 4 /g raw material) and semi carbonization process was conducted at 2oC and followed with carbonization at 55 o C. The applicability of this adsorbent for organic pollutant removal purpose was then evaluated using Methylene Blue adsorption in aqueous solution. Langmuir and Freundlich equations were used to model the adsorption equilibria data, and pseudo-first order and pseudosecond order models were used to correlate the kinetic data. The Langmuir equation gave better correlation for methylene blue adsorption onto activated carbon produced from jackfruit peel. The kinetic adsorption data follows pseudo-second order model. Keywords: Activated carbon; Adsorption; Jackfruit peel; Phosphoric acid; Surface Chemistry; Methylene Blue. JEPS (28), Vol. 2, pp Introduction Colored wastewater could be generated from several industries such as textile, ceramic, rubber, paper, leather, printing, plastic, cosmetics, etc. These industries commonly use synthetic dyestuff as their colorant [1-3]. Discharge of this dye-containing-wastewater into environment can contaminate surface water and ground water system [4]. The presence of dyes even in very small amounts in water system is undesirable since dyes are highly visible and can result in a hazard to the aquatic life [5]. Furthermore, some of dyes have been reported to be mutagenic and carcinogenic especially for human [1, 6]. Several methods are available to remove dyes from wastewater before it safely discharged into environment, and the most widely used technique is adsorption using activated carbons since it can remove dyes even in trace amount [1, 2, 4]. However, commercially available activated carbons are expensive so they may not be economical for wastewater treatment purpose. If an activated carbon for a specific purpose such as for wastewater treatment can be produced from low-cost or waste materials, than its use as an adsorbent should be economical. The use of activated carbon prepared from jackfruit peel using sulphuric acid as activated agent for heavy metal removal has been reported by Inbaraj and Sulochana [8]. In the present study we used phosphoric acid as activating agent for activated carbon preparation using jackfruit (Artocarpus heterophyllus) peel waste as the precursor [7]. Here we used the activated carbon from jackfruit peel to remove methylene blue from aqueous solution. The adsorption equilibria and kinetic of methylene blue onto activated carbon prepared from jackfruit peel waste were also studied. Methylene Blue (MB) is one of frequently used dyes. MB is a dark green powder or crystalline solid which can dissociates in aqueous solution like electrolytes into Methylene Blue cation and the chloride ion [5]. This cationic dye is usually selected as a model compound to evaluate the capacity of activated carbon due to its vast field of application, i.e. for coloring paper, temporary hair colorant, dyeing cottons and wools, and coating for paper stock, etc [3]. Furthermore, as an indicator for evaluation for activated carbon in liquid phase adsorption, MB has xxx * To whom all correspondence should be addressed. Dr. Suryadi ISMADJI; suryadiismadji@yahoo.com, Tel: , Fax:

2 stable color toward a ph change in the solution compared with other dyes, for example Congo Red, which is affected by the ph of solution [1]. Experimental Technique Activated carbon preparation In this section we just give a brief description about the activated carbon preparation and characterization, detail about the preparation and characterization can be found elsewhere [7]. Chemical activation method using phosphoric acid was used to prepare the activated carbon. 2 grams of jackfruit peel was impregnated by weighing and mixing certain amount of 85 wt % phosphoric acid with occasional stirring. The amount of phosphoric acid solution used was adjusted to give a certain impregnation ratio (weight of activating agent/weight of raw material) of 4:1. The resulting slurry was then kept in a desiccator for 24 hours. After 24 hours, the slurry was then ready to have two-stage activation process with semicarbonisation as first stage [9]. In the first stage, the slurry was put in a horizontal tubular reactor and kept in a muffle furnace to experience semicarbonisation at a temperature 2 o C for 3 minutes. After semi-carbonisation, the black and sticky dry powder was heated until certain heat treatment temperature (HTT) was reached. The carbonisation was performed under a nitrogen flow of cm 3 min-1 STP for 45 minutes. After activation, the activated carbon product was cooled in a desiccator. The activated carbon product was then repeatedly washed with warm distilled water (7 o C) until the ph of the solution close to the initial ph of rinsing water. Finally, the activated carbon was dried in a vacuum oven at 11 o C for 24 hours. The resulting carbon was then characterized its pore structure and surface morphology using nitrogen adsorption, SEM, XRD, Boehm titration, ph Drift and FTIR. Adsorption procedure Adsorption experiments were conducted using basic dye, i.e. Methylene Blue as an adsorbate and jackfruit peel activated carbon as an adsorbent. Methylene Blue used on this experiment was purchased from Sigma-Aldrich and was used as it is without any further purification. Methylene Blue stock solutions were prepared by dissolving analytically 5 mg of Methylene Blue into ml of distilled water. Experimental solutions of the desired concentration (5,, 15, and 2 mg/l) were obtained by dilutions from stock solutions. Adsorption experiments were conducted by adding gram of activated carbons into a series of 25 ml Erlenmeyer each filled with ml of Methylene Blue experimental solution with each initial concentration. All of the erlenmeyers then covered with aluminium foil and were placed to a thermostatic shaker bath (Memmert Type W- 35) and shaken for 72 hours. After equilibrium time had been reached, activated carbon was separated from the solution by centrifugation at 3 rpm for 5 min. The absorbance of clarified supernatant solution was analyzed using spectrophotometer (Shimadzu 84S) at the maximum wavelength of the Methylene Blue observed, which was 664 nm. Results and Discussions Physical characteristic of jackfruit peel activated carbon Yield of jackfruit peel activated carbon (JPAC) used in this study was found to be %. The yield here was calculated as final weight of activated carbon produced after activation, washing, and drying, divided by initial weight of raw material; both on a dry basis [1]. Pore characteristic of the activated carbon was determined by N2 adsorption. The nitrogen adsorption/desorption isotherms of the jackfruit peel activated carbon is illustrated in Figure 1. Volume Adsorbed (cc/g) P/P JPAC Adsorption JPAC Desorption Figure 1. Nitrogen adsorption/desorption isotherm of jackfruit peel activated carbon. The activated carbon possessed combination of type I and type II of IUPAC isotherm, indicating simultaneous presence of micropores and mesopores. This isotherm also exhibited a type H4 hysteresis loop, characteristic of slitshaped pores. The pore characteristics of jackfruit peel activated carbon are given in Table 1. The present of micropores and mesopores in the activated carbon prepared from jackfruit peel waste also indicated by the pore size distribution as depicted in Figure 2. Table 1. Pore characteristic of jackfruit peel activated carbon. Sample S BET, m 2 /g V micro, cm 3 /g V meso, cm 3 /g JPAC

3 Scanning electron micrograph of the surface morphology of jackfruit peel activated carbon is given in Figure 3. It is obvious that the activated carbon produced have already had cavities on their external surface. It seems that the cavities on the surfaces of carbons resulted from the evaporation of the activating agent in this case is phosphoric acid during carbonization, leaving the space previously occupied by the activating agent Activated carbon can be crystallographically characterized by means of X-Ray Diffraction (XRD). XRD spectrum for jackfruit peel activated carbon is given in Figure 4. Here, the XRD analysis was measured by CuKα with wavelength of.154 nm. From the XRD spectrum, the interlayer spacing d 2 can be determined using the Bragg equation: d = λ 2sinθ where λ is the X-ray wavelength and θ is the scattering angle for the peak position. The crystallite size along c- axis, Lc, and the size of the layer planes, La, are determined from the half-width of the diffraction peak using the Scherrer equation: (1).1.8 L = Kλ B cosθ (2) Pore Width (A) Figure 2. Pore size distribution of jackfruit peel activated carbon. where L is L c or L a, B is the half-width of the peak in radians, and K is the shape factor. The quantities L c and L a are named stack height and stack width, respectively. The (2) and (1) peaks are used to calculate L c and L a, respectively. The shape factor K =.9 and K = 1.84 are used for calculation of L c and L a, respectively [11]. The values of d 2, L c, and L a of activated carbon prepared from jackfruit peel are given in Table 2. Table 2. Nanographitic structures of jackfruit peel activated carbon. Sample d 2 (nm) L c (nm) L a (nm) JPAC As shown in Table 2, it can be seen that the value of d 2 was close to that of graphite (.335 nm) and still in the range for activated carbon of L c and L a values were also of the order 1-3 nm, typical of activated carbon. For this activated carbon, the diffraction profiles exhibited broad peaks at around 24 and 42 o which are assigned to the reflection from (2) and (1) planes, respectively. The occurrence of broad peaks at these 2θ indicated a regularity of crystal structure and resulting in better layer alignment [12]. Figure 3. SEM image of jackfruit peel activated carbon. Surface chemistry characteristic of jackfruit peel activated carbon The carbon matrix does not consist of carbon atoms alone, but is also formed by other heteroatom like hydrogen, oxygen, nitrogen, halogen, sulfur, phosphorus, etc. These heteroatoms bonded to the edges of the carbon layers, which govern the surface chemistry of activated carbon. The surface chemistry of carbon materials is 3

4 (2) (1) (11) CuKα 2 Θ (degree) Figure 4. XRD spectrum of jackfruit peel activated carbon. basically determined by the acidity and basicity of their surface. The existence of surface functional groups such as carboxyl, lactone, phenol, carboxylic anhydride, etc., has been postulated as constituting the source of surface acidity. Whereas the basic properties of activated carbon is associated with two types of structures: (i) the presence of oxygen containing groups, i.e. pyrone, chromene and carbonyl structures, at the edge of carbon crystallite; and (ii) oxygen free Lewis basic site on the graphene layers. The Lewis basicity of delocalized π electrons is influenced by the aromatic system on the carbon surface [13]. Table 3 shows quantitative surface chemistry analyses, which consist of the amount of acidic and basic functional groups of jackfruit peel activated carbons. Low ph PZC value was consistent with Boehm titration result, which indicated a dominance of acidic group at the surface of the activated carbons. While quantitative analysis of the surface chemistry was given by Boehm titration and ph drift method, a qualitative analysis of activated carbon can be carried out by FTIR spectrum. The spectrum of jackfruit peel activated carbon is illustrated in Figure 5. As shown in Figure 5, it can be interpreted that there is broad absorption band around cm -1. A peak around 171 cm -1 shows the presence of stretching vibration of C=O in ketones, aldehyde, lactone, and carboxyl. The presence of broad band around cm -1 and peak around 171 cm -1 indicates the presence of carboxylic acid [14,15]. Very weak peak around 29 cm -1 is C-H xxxxxxx stretching vibration in methyl group [15]. A strong band at 159 cm -1 can be ascribed to C=C aromatic ring stretching vibration enhanced by polar functional groups [16,17]. There is also a presence of broadband between 13- cm -1 with the strong band around 12 cm -1 and a shoulder around 18 cm -1. According to Puziy et al [16,17], the peak at cm -1 may be ascribed to the stretching mode of hydrogen bonded P=O, O-C stretching vibrations in P-O-C linkage, and P=OOH; and the shoulder at cm -1 can be ascribed to ionized linkage P + - O - in acid phosphate esters and to symmetrical vibration in a chain of P-O-P. Surface chemistry characterization by Boehm titration, ph drift, and FTIR spectrum has shown that activated carbons from jackfruit peel waste activated with phosphoric acid are rich in acidic surface functional groups. Therefore, ph PZC value of the jackfruit peel activated carbon was low, i.e Methylene blue adsorption Figure 6a shows the amount of Methylene Blue (expressed as qt, mg/g) adsorbed with time (min). The effect of contact time was observed by having adsorbent dose fixed to.3 g/l and initial Methylene Blue concentration of 5 mg/l. The amount of Methylene Blue adsorbed steeply increased at initial progress of adsorption and then reached relatively constant value at later time. Very rapid adsorption was found during the adsorption time of 4 minutes. Table 3. Quantitative surface chemistry of jackfruit peel activated carbon. Sample ph PZC Carboxylic (meq/g) Lactonic (meq/g) Phenolic (meq/g) Acidic (meq/g) Basic (meq/g) JPAC

5 However, the amount of Methylene Blue adsorbed increases with time and reaches a constant value after 3 minutes. After the equilibrium time, the amount of Methylene Blue adsorbed did not alter with time. Thus, referred to this experiment, the mixing time for the rest of adsorption studies was set to be 72 hours (432 minutes) to ensure the equilibrium in adsorption and kinetic studies. For higher initial concentration studied, i.e.,15, and 2 mg/l, it was found that there was no significant change on the equilibrium time at the observed initial MB concentration range. As shown in Figure 6b, the removal efficiency of Methylene Blue decreased from 95 to 41 % by the increase of initial Methylene Blue concentration from 5 to 2 mg/l. Smooth and continuous curves indicates a formation of monolayer coverage on the surface of jackfruit peel activated carbon [1]. Effect of ph on methylene blue adsorption Figure 7 shows effect of initial ph of solution on the removal efficiency and amount adsorbed (q e ). The removal efficiency increased from 78 to 98 % and qe from 232 to 294 mg/g when initial ph range was raised from 1.5 to 1.. At ph 1.5, which is lower than ph PZC of the JPAC adsorbent, the removal efficiency slightly decrease because of electrostatic repulsion. The repulsion occurred since Methylene Blue is one of cationic dyes so when the ph solution lower than ph PZC the activated carbon surface is positively charged. On the contrary, as the initial ph became higher, ionic interaction between Methylene Blue cation and negatively charged surface of activated carbon enhanced the adsorption. Adsorption of the cationic dye was found to be more favorable at higher ph q t 15 5 C 2mg/L C 15 mg/l C mg/l C 5 mg/l Wavenumbers (cm -1 ) 15 5 time (minutes) Figure 5. FTIR spectrum of jackfruit peel activated carbon. Figure 6a. The effect of contact time on Methylene Blue adsorption at different initial concentration (adsorbent dose =.3 g/l) % Removal (%) 6 4 % Removal (%) 9 85 q e C 5 mg/l C mg/l C 15 mg/l C 2 mg/l time (minutes) Figure 6b. The effect of contact time on removal Figure 7. The effect of initial ph solution on Methylene efficiency of Methylene Blue at different initial Blue adsorption. concentration. 5 initial ph

6 Methylene blue adsorption isotherm studies Adsorption equilibria are the most important information in understanding adsorption for analysis and design of the adsorption separation process [18]. Interpretation of adsorption isotherms data obtained in this study were carried out by two well-known isotherm models, Langmuir and Freundlich models. The Langmuir isotherm has the following form: b. Ce q e = q. 1+ b. C where C e is the equilibrium concentration (mg/l), q e is the amount adsorbed at equilibrium, and q o and b are Langmuir constants related to the adsorption capacity and energy of adsorption, respectively. The parameter q o and b are obtained from optimization of the equilibrium concentration data, C e, versus amount adsorbed data, q e, by nonlinear regression method. The regression curves as optimization result are illustrated in Figure 8a. Figure 8a shows adsorption data analyzed by Langmuir model at different temperatures of adsorption, i.e. 3, 4, and 5 o C; while Figure 8b shows the adsorption at different initial solution ph, i.e. 1.5, 6., and 1.. The Langmuir fitted parameter q o and b, as well as favourable or unfavourable constant RL which is defined as: RL = 1/(1+bC ) is presented in Table 4. The RL value indicates the type of isotherm is given as follows [19]: R L value R L >1 R L =1 <R L <1 R L = e (3) Type of isotherm Unfavorable Linear Favorable Irreversible Temperature has also played an important role in adsorption and generally has reducing influence on adsorbed amount of adsorbate since the adsorption of organic compounds is an exothermic process and physical bond between Methylene Blue and active sites of adsorbent weaken as temperature increases. In addition, increased temperature results in stronger interaction forces between Methylene Blue and its solvent due to solubility rising. This evidence explains that Langmuir adsorption capacity q o decreases as temperature increases as shown in Table 4. Table 4. Parameters of Langmuir equation. T (ºC) q b (L/mg) R L R q e q e Table 4. Parameters of Langmuir equation (continued). ph initial q b (L/mg) R L R (a) (b) Ce (mg/l) Ce (mg/l) 3 ºC 4 ºC 5 ºC Langmuir Model ph 1.5 ph 6. ph 1. Langmuir Figure 8. Adsorption isotherms of Methylene Blue on activated carbon produced from jackfruit peel waste and Langmuir model at (a) 3, 4, and 5 o C, and (b) ph 1.5, 6., and 1.. 6

7 Moreover, the heat of adsorption can be estimated by integrated van t Hoff equation as follow: 35 3 (a) Ea b = b.exp (4) R. T where E a is the adsorption activation energy and b o is the adsorption equilibrium coefficient. R is the gas constant and equals to J/mole.K and T is the temperature of Metylene Blue solution. The values of b o and E a obtained by linear regression of equation (4) were.7621 L/gram and kj/mole, respectively; low E a value indicates that the adsorption of methylene blue over activated carbon prepared from jackfruit peel waste is physical adsorption. The correlation between ln(b) and 1/T is illustrated in Figure q e (b) Ce (mg/l) 3 ºC 4 ºC 5 ºC Freundlich Model ln (b) q e /T vs ln (b) van't Hoff equation ph 1.5 ph 6. ph 1. Freundlich Figure 9. Linear regression of van t Hoff equation. Freundlich equation can be written in the form as follow: q e = K f.c e 1/n where q e is the mass of adsorbate adsorbed per unit mass of adsorbent, C e is the equilibrium concentration of the solute being adsorbed, and both K f and n are empirical constants. While K f is related to adsorption capacity, n represents heterogeneity of the system. The parameter K f and n are obtained from optimization of the equilibrium concentration data, C e, versus amount adsorbed data, q e, by nonlinear regression method. The regression curves as optimization result on different solution temperatures 3, 4, and 5 o C are illustrated in Figure 1a. Figure 1b shows the adsorption isotherms at different initial solution ph, i.e. 1.5, 6., and 1.. The resulting fitted parameters of Freundlich equation are presented in Table 5. n values between 1 and 1 represent favorable adsorption [19]. 1/T (5) Ce (mg/l) Figure 1. Adsorption isotherms of Methylene Blue on activated carbon produced from jackfruit peel waste and Freundlich model at (a) 3, 4, and 5 o C, and (b) ph 1.5, 6., and 1.. Table 5. Parameters of Freundlich Equation. K f (L/g) n R T (ºC) ph initial Both Langmuir and Freundlich equations show good calculated correlations on Methylene Blue adsorption isotherm since the values of R 2 are more than.95. However, as depicted on Figure 9 and 11, Langmuir provides better relationship of the data for the adsorption isotherm of Methylene Blue on jackfruit peel activated carbon. 7

8 q t (a) time (minutes) C 2mg/L C 15 mg/l C mg/l C 5 mg/l Pseudo-First-Order Pseudo-Second-Order Methylene blue adsorption kinetics studies Several models can be used to analyze the adsorption kinetics. One of them that is widely used to describe adsorption kinetics is pseudo-first-order model which also known as Lagergren equation. The equation is as follow: dqt dt = k ( q q ) (6) 1 e t where k 1 is the rate constant for the first order (min -1 ), q e is equilibrium adsorption capacity, and q t is measured adsorption capacity at any time. Integrating equation (6) with initial conditions t = to t = t and q t = to q t = q t gives [2]: q t, mg/g (b) t, minutes ph 1.5 ph 6. ph 1. Pseudo-First-Order Pseudo-Second-Order Figure 11. (a) Comparison of Pseudo-First-Order and Second-Order Models on Methylene Blue Adsorption with different initial MB concentration of 5,, 15, and 2 mg/l (adsorbent dose.3 g/l), and (b) Comparison of Pseudo-First-Order and Second-Order Models on Methylene Blue Adsorption at ph 1.5, 6., and 1. (adsorbent dose.5 g/l). Significant influence of ph on the adsorption of Methylene Blue on jackfruit peel activated carbon is also obviously described on those figures and parameters shown in tables 4 and 5. It can be found that at basic condition the adsorption is more favorable. Both of adsorption capacity (K L in Langmuir and K f in Freundlich) and adsorption intensity (b in Langmuir and n in Freundlich) show increasing tendency as the ph of solution had more basic condition. The effect of ph on the adsorption behavior is due to the ph PZC of the jackfruit peel activated carbon. ph PZC of the activated carbon used has acidic value of 1.9, which is favorable for cation adsorption. Ionic interaction between Methylene Blue cation and negatively charge surface of activated carbon will enhance the adsorption [2]. q t = q e (1 exp(-k 1 t)) (7) where q t is the amount of compound adsorbed in mg/g at time t, q e is the amount of compound adsorbed in mg/g at equilibrium time and k 1 is the rate constant of adsorption in min -1 [19]. Kinetic data also treated with the Ho and McKay s pseudo second order kinetic model. The differential equation of this model can be written as follows: dq t dt = k (8) 2 2 ( qe qt ) Integrating equation (8) for boundary conditions t = to t = t and q t = to q t = q t gives following equation [2]: q t q ek2t = q e 1+ qek2t Both of pseudo-first-order and pseudo-second-order models are used to predict the kinetic data of Methylene Blue adsorption on jackfruit peel activated carbon. The kinetic experimental data and the models fit of Methylene Blue adsorption on the jackfruit peel activated carbon at different initial concentrations 5,, 15, and 2 mg/l are showed in Figure 11a, and Figure 11b for the kinetic adsorption data at different initial ph, i.e. 1.5, 6., and 1.. The pseudo-first order and pseudo-second order parameters are summarized in Table 6. From the values of R 2 for both models, it can be seen that pseudo second order model gives better correlation than the pseudo first order. In addition, with variation in initial concentration of Methylene Blue, pseudo-second order gives more reasonable parameter since the value of k 2 decreases when initial concentration increases. The rate of adsorption should decreases with increasing initial concentration due to higher driving force needed for (9) 8

9 adsorption. Therefore, the adsorption kinetics of Methylene Blue adsorption on jackfruit peel activated carbon could be approximated more favorably by second order kinetic model. The better applicability of pseudosecond order model rather than pseudo first order model on the adsorption of Methylene Blue was also reported by other authors [21,22]. Activated carbons are material which has amphoteric characteristic, so the ph on its surface always changes depends on initial ph of the solution. Generally, the adsorption capacity and rate constant have increasing tendency as initial ph of the solution increases. This is due to the ph PZC of jackfruit peel activated carbon has acidic value of 1.9, which is favorable for cation adsorption. Methylene Blue is one of cationic dyes so that at ph solution higher than ph PZC, the carboxyl groups would deprotonize so that the activated carbon will be negatively charged [2]. Ionic interaction between Methylene Blue cation and negatively charged surface of activated carbon would enhance the adsorption [2]. According to Ofomaja [21], this enhancement of adsorption may follow the mechanism of reaction between monomeric and dimeric micelles of Methylene Blue {MB + or (MB) 2 2+ } and the polar sites on the activated carbon surface {JPAC and JPAC-H} as follows: MB + + JPAC (MB)JPAC (MB) JPAC-H (MB) 2 JPAC 2 + 2H + Table 6. Pseudo order 1 and 2 fitted parameters of the adsorption of Methylene Blue at different initial concentration (adsorbent dose =.3 g/l) and ph condition (adsorbent dose =.5 g/l); T=3 o C. Pseudo First Order Pseudo Second Order C (mg/l) q e k 1 (1/min) R 2 q e exp E (%) q e k 2 (g/mg.min) R 2 q e exp E (%) Pseudo First Order Pseudo Second Order ph q e k 1 (1/min) R 2 q e exp E (%) q e k 2 (g/mg.min) R 2 q e exp E (%)

10 Conclusion This study shows the application of activated carbon prepared from jackfruit for removal of methylene blue from aqueous solution. From the experimental results it was found that ph of the solution played a significant role in adsorption process. The removal efficiency increased with increased ph. Widely used isotherm equations, Langmuir and Freundlich, were used to correlate the adsorption equilibria data, while the kinetic data were correlated using pseudo first and second order models. References 1. Tor A, Cengeloglu Y, (26) Removal of congo red from aqueous solution by adsorption onto acid activated red mud; J Hazard Mater 138: Chandra TC, Mirna MM, Sudaryanto Y, Ismadji S, (26) Adsorption of basic dye onto activated carbon prepared from durian shell: Studies of adsorption equilibrium and kinetics; Chem Eng J 127: Han R, Zou W, Yu W, Cheng S, Wang Y, Shi J, (26) Biosorption of methylene blue from aqueous solution by fallen phoenix tree s leaves; J Hazard Mater 141: Acemioğlu B, (24) Adsorption of congo red from aqueous solution onto calcium-rich fly ash; J Colloid Interface Sci 274: El Qada EN, Allen SJ, Walker GM (26) Adsorption of Methylene Blue onto activated carbon produced from activated bituminous coal: A study of equilibrium adsorption isotherm; Chem Eng J 124: Lorenc-Grabowska E, Gryglewicz G, (27) Adsorption characteristics of Congo Red on coal based mesoporous activated carbon; Dyes Pigments 74: Prahas D, Kartika Y, Indraswati N, Ismadji S, (27) Activated carbon from jackfruit peel waste by H3PO4 chemical activation: pore structure and surface chemistry characterization; Chem Eng J, in press. 8. Inbaraj BS, Sulochana N, (23) Carbonised jackfruit peel as an adsorbent for the removal of Cd(II) from aqueous solution; Biores Technol 94: Hu Z, Srinivasan MP, (1999) Preparation of highsurface-area activated carbons from coconut shell; Microporous Mesoporous Mater 27: Diao Y, Walawender WP, Fan LT, (22) Activated carbons prepared from phosphoric acid activation of grain sorghum; Biores. Technol 81: Bandosz TJ, Briggs M, Gubbins KE, Kaneko K, Thomson K, (23) Molecular models of porous carbons,, In Chemistry and Physics of Carbon, Radovic L, ed. Marcel Dekker, New York, Yang T, Lua AC, (26) Textural and chemical properties of zinc chloride activated carbons prepared from pistachio-nut shells; Mater Chem Physics: Wibowo N, Setiyadhi L, Wibowo D, Setiawan J, Ismadji S, (27) Adsorption of benzene and toluene from aqueous solutions onto activated carbon and its acid and heat treated forms: Influence of surface chemistry on adsorption; J Hazard Mater 146: Guo Y, Rockstraw DA, (26) Physical and chemical properties of carbons synthesized from xylan, cellulose, and Kraft lignin by H3PO4 activation; Carbon 44: Boonamnuavitaya V, Sae-ung S, Tanthapanichakoon W, (23) Preparation of activated carbons from coffee residue for the adsorption of formaldehyde; Separ Purif Technol 42: Puziy AM, Poddubnaya OI, Martinez-Alonso A, Suarez-Garcia F, Tascon JMD, (25) Surface chemistry of phosphorus-containing carbons of lignocellulosic origin; Carbon 43: Puziy AM, Poddubnaya OI, Martinez-Alonso A, Suarez-Garcia F, Tascon JMD, (22) Synthetic carbons activated with phosphoric acid I. Surface chemistry and ion binding properties; Carbon 4: Ismadji S, Bhatia SK, (2) Adsorption of flavour esters on granular activated carbon; Can J Chem Eng 78: Kadirvelu K, Namasivayam C, (22) Activated carbon from coconut coirpith as metal adsorbent: adsorption of Cd (II) from aqueous solution; Adv Environ Res 7: Rodriguez-Reinoso F, (1998) The role of carbon materials in heterogeneous catalysts; Carbon 36: Ofomaja AE, (27) Kinetic and mechanism of methylene blue sorption onto palm kernel fibre; Process Biochem 42: Kavitha D, Namasivayam C (27) Experimental and kinetic studies on methylene blue adsorption by coir pith carbon; Biores Technol 98: