Research Journal of Chemical Vol. 4(7), 36-42, July (2014) International Science Congress Association Adsorption o f Methylene Blue Activated Carbon Prepared from Thermodynamic Studies K. Ramesh 1 Department of Chemistry, Arasu Engineering College, Kumbakonam, Tamilnadu, INDIA 2 Department of Chemistry, Sri Manakula Vinayagar Engineering College, Pondicherry, INDIA 3 Department of Chemistry, A.V.V.M Sri Pushpam College, Poondi, Available online at: Received 18 th Abstract Delonix regia (Flame tree) pods were utilized to prepare activated carbon by using orthogonal array experimental design method with the parameters such as microwave radiation power, radiation time, concentration of ZnCl impregnation time. Optimized conditions were found to be ra impregnation time 24 hours. Carbon prepared was designated as MWZAC (Microwave assisted Zinc chloride Activated Carbon). The characteristics of the MWZAC were determined by BET analysis and pH Methylene blue dye from aqueous solution by batch mode adsorption technique. dye concentration and temperature on adsorption was studied Tempkin, Dubinin-Raduskevich, Harkins - on R value. Various thermodynamic parameters such as Analysis o f these values inferred that this adsorption was endothermic, spontaneous and proceeded with increased randomness. Keywords: Adsorption, ZnCl activated microwave carbon Introduction Discharged wastewater by some industries under and unsuitable conditions is causing significant environmental problems. Natural water bodies such as ponds, lakes, rivers and their watershed will be subjected to serious environmental issue, if untreated effluent is discharged into them as s Researchers have investigated the removal of dyes from the effluent water which was released by large tiny printing and dyeing units, using activated charcoal as adsorbent process is the most powerful technique and used for separating or ganic and inorganic pollutants from water and waste water and it is embodied in carbon adsorption systems and ion exchangers. Activated carbon is the most common adsorbent for the removal of many organic contaminants. The adsorption process of activated carbon, however, is prohibitively expensive, which limits its application. Therefore, there is a need to produce activated carbon from cheaper and readily available materials. In the past years, several investigations have been reported the removal of dye s using activated carbons developed from industrial or agricultural wastes . Also several studies of dye removal were carried out using adsorbents developed from natural materials4,5. Chemical Sciences _________________________________ ______ International Science Congress Association f Methylene Blue o nto Microwave Assisted Zinc Chloride Activated Carbon Prepared from Delonix Regia Pods - Isotherm and Thermodynamic Studies K. Ramesh , A. Rajappa2 and V. Nandhakumar3* Department of Chemistry, Arasu Engineering College, Kumbakonam, Tamilnadu, INDIA Department of Chemistry, Sri Manakula Vinayagar Engineering College, Pondicherry, INDIA Department of Chemistry, A.V.V.M Sri Pushpam College, Poondi, Tamilnadu, INDIA Available online at: www.isca.in, www.isca.me th May 2014, revised 9th June 2014, accepted 7th July 2014 utilized to prepare activated carbon by using orthogonal array experimental design method with the parameters such as microwave radiation power, radiation time, concentration of ZnCl impregnation time. Optimized conditions were found to be ra diation power 850 W, radiation time 12 min, 60 % of ZnCl impregnation time 24 hours. Carbon prepared was designated as MWZAC (Microwave assisted Zinc chloride Activated Carbon). The characteristics of the MWZAC were determined by BET analysis and pH ZPC. MWZAC blue dye from aqueous solution by batch mode adsorption technique. Influence of the parameters such as initial dye concentration and temperature on adsorption was studied . Equilibrium data were fitted with Langmuir, Fr - Jura and Sips isotherms. The order of best describing isotherms was given based Various thermodynamic parameters such as H°, S°, an d G° have been evaluated using Vant Hoff plots. f these values inferred that this adsorption was endothermic, spontaneous and proceeded with increased activated microwave carbon , isotherms, Methylene blue dye. Discharged wastewater by some industries under uncontrolled and unsuitable conditions is causing significant environmental problems. Natural water bodies such as ponds, lakes, rivers and their watershed will be subjected to serious environmental issue, if untreated effluent is discharged into them as s uch. Researchers have investigated the removal of dyes from the effluent water which was released by large tiny printing and dyeing units, using activated charcoal as adsorbent . Adsorption process is the most powerful technique and used for separating ganic and inorganic pollutants from water and waste water and it is embodied in carbon adsorption systems and ion Activated carbon is the most common adsorbent for the removal of many organic contaminants. The adsorption process of carbon, however, is prohibitively expensive, which limits its application. Therefore, there is a need to produce activated carbon from cheaper and readily available materials. In the past years, several investigations have been reported the s using activated carbons developed from . Also several studies of dye removal were carried out using adsorbents developed from Figure - Structure of MB In the present study, an attempt has been made to prepare carbon from Delonix regia (flame tree) pods by microwave irradiation technique. The above mentioned plant belongs royal Poinciana or flamboyant which is a member of bean family and produces brown woody seed pods purely a waste material. Recently, microwave energy has been widely used in research and industrial processes . The microwave irradiation technique has the following advantages rather than conventional heating techniques8,. i. Interior heating, ii. selection of heating, iii. Extensive heating rates, iv. Good control of heating process, v. Small equipment size, vi. Reduced wastage production, vii. No direct contact between heating source and heating materials. ______ _______ ISSN 2231-606X Res. J. Chem. Sci. 36 nto Microwave Assisted Zinc Chloride Isotherm and Department of Chemistry, Arasu Engineering College, Kumbakonam, Tamilnadu, INDIA Department of Chemistry, Sri Manakula Vinayagar Engineering College, Pondicherry, INDIA Tamilnadu, INDIA utilized to prepare activated carbon by using orthogonal array experimental design method with the parameters such as microwave radiation power, radiation time, concentration of ZnCl solution and diation power 850 W, radiation time 12 min, 60 % of ZnCl 2 and impregnation time 24 hours. Carbon prepared was designated as MWZAC (Microwave assisted Zinc chloride Activated MWZAC was used to remove Influence of the parameters such as initial Equilibrium data were fitted with Langmuir, Fr eundlich, Jura and Sips isotherms. The order of best describing isotherms was given based G° have been evaluated using Vant Hoff plots. . f these values inferred that this adsorption was endothermic, spontaneous and proceeded with increased - 1 Structure of MB In the present study, an attempt has been made to prepare (flame tree) pods by microwave The above mentioned plant belongs to royal Poinciana or flamboyant which is a member of bean woody seed pods purely a waste Recently, microwave energy has been widely used in research . The microwave irradiation technique has the following advantages rather than conventional heating heating, ii. selection of heating, iii. Extensive heating rates, iv. Good control of heating process, v. Small equipment size, vi. Reduced wastage production, vii. No direct contact between heating source and heating materials. Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(7), 36-42, July (2014) Res. J. Chem. Sci. International Science Congress Association 37 Table-1 Nomenclature Nomenclature i t and Initial Concentration, at the time ‘t’ and at equilibrium respectively Polanyi potential e and qQuantity adsorbed at the time ‘t’ and at equilibrium respectively E Mean free energy of adsorption V Volume of the dye solution in liter (L) R Gas Constant W Mass of the adsorbent in gram (g) T Temperature (K) Q Amount of solute adsorbed per unit weight of adsorbent (mg/g) h Initial adsorption rate (mg/g min) Adsorption efficiency aEquilibrium binding constant Adsorption energy qConstant related to adsorption capacity (mg/g) Separation factor B and A Isotherm constants and n The constants incorporating all factors affecting the adsorption capacity and intensity of adsorption respectively Theoretical saturation capacity (mg/g) Tempkin constant related to heat of sorption (J/mg) B Constant related to the mean free energy Equilibrium constant S° Entropy of adsorption G° Standard free energy H° Enthalpy of adsorption Methodology Preparation of Adsorbents: The air dried pods were cut into small pieces and powdered in a pulveriser. Taguchi experimental design method was used to prepare and to determine optimal parameters to prepare efficient carbon6,10. 20 g of the crushed and ground pods was admixed with 75 mL ZnCl solution of desired strength (20, 40 and 60 %). The slurry was then allowed to stand as such at ordinary conditions of temperature and pressure for a day (24 hours) to ensure the access of the ZnCl2 to the Delonix Regia pods. Then the slurry was subjected to microwave heating of pre- determined power (450,600, 850 watts) for pre- determined duration (8, 10, 12 minutes). Thus the carbonized samples were washed with 0.5 M HCl followed with hot distilled water and cold distilled water until the pH of the washings reach 7. Then the carbon was filtered and dried at 423 K. Totally 27 number of carbons were prepared by varying parameters such as concentration of ZnClsolution, Microwave heating watts power and radiation times11. Preparation of stock Solution: The stock solution of dye was prepared by dissolving appropriate amount of exactly weighed dye in double distilled water to a concentration of 1000 mg/L. The experimental solutions were prepared from the stock solution by proper dilutions. Characterization of MWZAC: Particle size (µm), Surface area (m/g), Pore volume (cm/g), Pore size or Pore width (nm), Bulk density (g/mL), Fixed Carbon (%), Moisture content (%) and pHzpc were determined. Adsorption experiments: The effect of parameters such as initial concentration of dye solution, adsorbent dose, pH of the solution and contact time was studied by batch mode technique because of its simplicity. Pre-determined dose of the adsorbent was taken in 250 mL iodine flask and 50 mL and pre - determined concentration of the dye solution was poured into the flask. Then the content flask was agitated using rotary shaker with 180 rpm for pre- determined duration. Then the aliquot was centrifuged. Concentration of the centrifugate was measured after proper dilution using Systronics Double Beam UV-visible Spectrophotometer: 2202 at the wave length of 680 nm. Effect of pH was studied by bringing the desired pH of the solutions by adding concentrated HCl acid / 1N NaOH solution. The kinetics experiments were performed with the working pH 7 and for contact times 5, 10, 20, 40, 60, 80, 100, 120, 140 and 160 minutes12. Results and DiscussionOptimization of adsorbent preparation parameters: Efficiency of the prepared samples to remove MB dye from the aqueous solution were accessed with 20 mg of the adsorbent , 50 mL of MB dye solution of concentrations of 100, 150 and 200 mgL-1 and 1 hour agitation time. The results inferred that percentage of removal of MB dye increased with the increase of radiation time, radiation power and concentration of ZnCl solution. Hence carbon prepared using 60 % ZnCl2 solutions,radiation power 850 watts, radiation time 12 minutes and impregnation time 24 hours was chosen with the dosage of 20 mg/50 mL for further studies.Physico-chemical characteristics of MWZAC: Physico-chemical characteristics of MWZAC were collected in the table 3. Percentage of fixed carbon, surface area, pHzpc and other values are reasonable to function as a good adsorbent. Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(7), 36-42, July (2014) Res. J. Chem. Sci. International Science Congress Association 38 Table-2 Data Processing Tools S. No. Parameters Formulae 1. Mass balance relationships % of Removal (C i - C t )×V/C i Quantity adsorbed at equilibrium, e (Ci - C) ×V/W Quantity adsorbed at the time t, q t (C i - C t ) × V/ W 2. Isotherms Langmuir Separation factor C /Q = 1/Qb + Ce /Q0 L = 1 / (1+ bC 0 ) Freundlich log Q e = log K f + 1/n log C e Tempkin q e = RT/b T ln a T + RT/b T ln C e Sips C e 1/n /q e = 1/q m .b + 1/q m C e 1/n Harkins – Jura 1/q e ² = [B/A]-[1/A] log C e Dubinin – Raduskevich, Polanyi potential Mean free energy of adsorption ln q = ln q - B 2 = RT ln (1+1/C) E = 1/ (2B) ½ 3. Thermodynamic Parameters Standard Free energy Change G° =-RT ln K c Van’t Hoff equation ln K c =S°/R - H°/RT Table-3 Physico-chemical characteristics of MWZAC Properties Values Properties Values pHzpc 7.01 Pore size (Pore width), nm 2.7174 Particle size, µm 53 - 90 Bulk density, g/mL 0.52 Surface area (BET), m/g 586 Fixed Carbon, % 71.11 Pore volume, cm/g 0.3986 Moisture content, % 4.36 Effect of temperature on adsorption: Percentage of removal increased with the increase of temperature of the solution for all studied initial concentrations of the dye. It is further noticed that percentage of removal was found to be high when the initial concentration of the dye solution was high. Isotherm studies: The presence of equilibrium between two phases (liquid and solid phase) is rationalized by adsorption isotherm. The data pertaining to equilibrium have been obtained at different temperatures then made such as Langmuir, Freundlich, Tempkin, sips, Harkins - jura, and Dubinin-Raduskevich adsorption isotherm models13. These isotherms are depicted in figure 2. Results of various isotherms are collected in table 4. Langmuir isotherm: The Langmuir adsorption isotherm was developed to explain the adsorption of gas on to solid surface. It evidences the existence of monolayer and also the surface is energetically homogeneous14, where, Q is a constant related to adsorption capacity (mg/g) and b is Langmuir constant related to energy of adsorption. The essential characteristics of Langmuir isotherm can be expressed by dimensionless separation factor, R15. The R values of this adsorption process were in between 0 and 1 indicates favourable adsorption. Freundlich isotherm: It is a most popular model for a single solute system, based on the distribution of solute between the solid phase and aqueous phase at equilibrium. The Freundlich model describes the adsorption within a restricted range only16. The ‘n’ values are in between 1 and 10 which represent favourable adsorption15. Tempkin isotherm: The Tempkin isotherm assumes that the heat of sorption in the layer would decrease linearly with coverage due to sorbate/sorbent interactions. Further the fall in the heat of adsorption is not logarithmic as stated in Freundlich expression. ‘b’ is the Tempkin constant related to heat of sorption (J/mg) and ‘a’ is the equilibrium binding constant corresponding to the maximum binding energy (L/g) 17. Sips isotherm: Sips isotherm describes the characteristics of Freundlich and Langmuir isotherm with respect to concentration of adsorbate. At low concentration of the adsorbate, it turns into Freundlich isotherm and at high concentration of adsorbate; it predicts a monolayer adsorption capacity characteristic of Langmuir isotherm 18. ‘q’ is a constant related to adsorption capacity (mg/g) and ‘b’ is Langmuir constant related to energy of adsorption (L/mg). Harkins – Jura isotherm: The Harkins-Jura adsorption isotherm explains multilayer adsorption and can be accounted with the existence of heterogeneous pore distribution19. Dubinin – Raduskevich isotherm: In Dubinin-Radushkevich isotherm, ‘q’ is the theoretical saturation capacity (mg/g) B is a constant related to the mean free energy of adsorption per mole of the adsorbate (mol/J) and is Polanyi potential. The energy of activation from this reaction accounts for the adsorption. The adsorption will be physisorption if energy of activation is less than 8 kJ/mol and will be chemisorption and if it is lie between 8–16 kJ/mol20. Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(7), 36-42, July (2014) Res. J. Chem. Sci. International Science Congress Association 39 Analysis of isotherm results: In this present study Q0 value ranged from 364.61 to 370.37, hence it indicates that the surface area of the adsorbent is carried by the monolayer of the adsorbate. The R value was ranged from 0.07 to 0.17, hence is indicate favourable adsorption.A value of 1/n below one is indicates a normal Langmuir isotherm, while n value from 2.98 to 3.64 hence is indicative of cooperative adsorption. values of these isotherm plots reveal that Harkins – Jura isotherm well describes the present system that is the existence of heterogeneous pore distribution. The B value of Dubinin-Raduskevich isotherm was ranged from 0.028 to 0.016 hence is indicating the adsorption physisorption in nature. The adsorption capacities (mg/g) obtained from these isotherms indicate that MWZAC is a potential adsorbent when compared to the adsorption capacities of adsorbents prepared from plant bio masses which are given in the table 5. Figure-2Adsorption Isotherm 10.0020.0030.0040.0050.0060.0070.0080.00/qCeLangmuir Isotherm 305 K 315K 325 K 335 K 2.272.322.372.422.472.521.151.351.551.751.95log qlog CeFreundlich Isotherm 305 K 315 K 1501701902102302502702903103302.73.23.74.24.7ln CeTempkin Isotherm 305 K 315 K 5.25.35.45.55.65.75.80100200300ln qD-R Isotherm 305 K 315 K 325 K 0.050.10.150.20.250.30.350501001/n/qCe1/nSips Isotherm 305 K 315 K 0.0030.00350.0040.00450.0050.00551.20001.40001.60001.80002.00001/ qlog CeH-J Isotherm 100 ppm 150 ppm 200 ppm Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(7), 36-42, July (2014) Res. J. Chem. Sci. International Science Congress Association 40 Table-4 Isotherm parameters for removal of Methylene blue by MWZAC Temperature (K) Langmuir Isotherm Dubinin Raduskevich (mg/g) (L/mg) L (mg/g) B×10-4 (mol/J) (kJ/mol) 100 ppm 150 ppm 200 ppm 305 364.61 0.05 0.17 0.12 0.09 0.999 303.65 0.028 0.01337 0.961 315 370.37 0.062 0.12 0.09 0.14 0.999 303.53 0.021 0.01543 0.948 325 370.37 0.071 0.09 0.14 0.10 0.999 304.29 0.017 0.01715 0.947 335 370.37 0.075 0.14 0.10 0.07 0.998 306.45 0.016 0.01768 0.939 Temperature (K) Freundlich Isotherm Sips Isotherm n f (mg1-1/n.L1/n.g-1 n (L/mg) (mg/g) 305 2.98 71.95 0.993 2.98 0.044 384.61 0.999 315 3.32 84.72 0.997 3.32 0.054 370.37 0.998 325 3.59 94.41 0.996 3.59 0.063 370.37 0.999 335 3.64 97.05 0.998 3.64 0.065 370.37 0.998 Temperature (K) Tempkin Isotherm Harkins – Jura Isotherm (J/mg) T (L/g) Concentration (ppm) A B R 305 3.22 0.53 0.999 315 4.62 0.79 1.000 100 384.61 - 0.061 0.997 325 6.12 1.09 1.000 150 294.12 0.558 0.999 335 7.31 1.17 0.999 200 222.22 1.177 0.999 Table-5 Adsorption capacities of few adsorbents prepared from plant bio masses Adsorbent Adsorption capacity(mg/g) Reference Bamboo-based activated carbon Q=454.2 B.H. Hameed, et al, 2006 Bark Q0 = 914.59 McKay et al, 1999 Rice husk – H3PO4 impregnated Q=333.33 Singh and Srivastava, 2001 Coal Q=323.68 McKay et al, 1999 Rice husk Q=312.26 McKay et al, 1999 Cotton Waste Q=277.78 McKay et al, 1999 NaOH treated Raw Clay Q=204.0 Ghosh and Bhattacharyya, 2001 Tree Leaves Q=133.33 Singh and Srivastava, 1999 Saw dust Q=32.26 De and Basu, 1998 Raw Clay Q=27.49 Ghosh and Bhattacharyya, 2001 MWZAC Q=370.37 Present Study Thermodynamics studies: Various Thermodynamic parameters such as H°, S° and G° have been determined using Van’t Hoff’s plot. The thermo dynamical parameters calculated are presented in table 6. Negative standard free energy of adsorption indicates that the adsorption process is spontaneous in nature. The positive H° values infer that the adsorption is endothermic nature, which was supported by the experimental data i.e., adsorption capacity increased with the increase of temperature, as shown in the table. 6. Since H° values are small the bonding between MB and MWZAC surface should be very weak. Positive value of S°suggests that the adsorption proceeds with increased randomness 21. Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(7), 36-42, July (2014) Res. J. Chem. Sci. International Science Congress Association 41 Table-6 Thermodynamic Parameters and their resultsThermodynamic Parameters and their results Concentration (ppm) Temperature (K) G° kJ/mol H° kJ/mol S° kJ/mol 100 305 9.4617 -5.6995 8.4553 46.5750 315 10.8976 -6.2565 325 12.0688 -6.7310 335 12.7253 -7.0857 150 305 5.8761 -4.4914 3.5218 26.2971 315 6.1645 -4.7642 325 6.4734 -5.0475 335 6.6352 -5.2716 200 305 2.3319 -2.1473 2.7045 15.913 315 2.4264 -2.3219 325 2.4755 -2.4496 335 2.5758 -2.6357 Figure-3 Thermodynamics Studies ConclusionMicrowave assisted zinc chloride activated carbon (MWZAC) was prepared from Delonix regia (Flame tree)pods found to have good capacity of adsorption. Experimental data indicated that MWZAC was effective in removing MB dye from aqueous solution. Equilibrium adsorption was achieved in about 60 minutes for the dosage of 20 mg/50 mL of solution at room temperature of 305 K for the initial concentration of dye solutions ranging from 100 to 200 mg/L. Tempkin isotherm represents the equilibrium adsorption data well when compared to other isotherms studied. The adsorption data was also fitted with Langmuir adsorption model. The fitness of Langmuir’s model indicated the formation of monolayer coverage of the sorbate on the surface of the adsorbent. The R values of Langmuir isotherms were in between 0 to 1 indicating the favourable adsorption. The B value was ranged from 0.028 to 0.016 hence is indicate the adsorption physisorption in nature. Extensive study on thermodynamics with the help of thermodynamic parameters reveals that the adsorption system 0.50001.00001.50002.00002.50000.00300.00300.00310.00310.00320.00320.00330.0033ln kd1/TThermodynamics Studies 100 ppm 150 ppm 200 ppm Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(7), 36-42, July (2014) Res. J. Chem. Sci. International Science Congress Association 42 was spontaneous, endothermic with increased randomness. References 1.Moreno-Castilla C., Adsorption of organic molecules from aqueous solutions on carbon materials, Carbon,42, 83-94, 2004). 2.Abechi E.S., Gimba C.E., Uzairu A. and Kagbu J.A., Kinetics of adsorption of Methylene blue onto activated carbon prepared from palm kernel shell, Arch. Appl. Sci. Res.3 (1), 154-164 (2011)3.Salleh M.A.M., Mahmoud D.K., Karim W.A. and Idris A., Cationic and Anionic Dye Adsorption by Agricul- tural Solid Wastes: A Comprehensive Review, Desalination,280(1-3), 1-13 (2011)4.Wang J., C. Chen., Biosorption of heavy metals by Saccharomyces cerevisiae: A review, Biotechnol. Adv. 24: 427-451 (2006). 5.Mahvi A.H., D. Naghipour, F. Vaezi and S. Nazmara., Tea waste as an adsorbent for heavy metal removal from industrial wastewaters, Am. J. Appl. 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