International Journal of Chemistry and Pharmaceutical Sciences

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1 V. Nandhakumar et al IJCPS, 2014, Vol.2(8): Research Article ISSN: International Journal of Chemistry and Pharmaceutical Sciences Kinetics of Adsorption of Methylene Blue onto Microwave Assisted Zinc Chloride Activated Carbon Prepared from Delonix regia pods K. Ramesh 1, A. Rajappa 2 and V. Nandhakumar 3* 1 Department of Chemistry, Arasu Engineering College, Kumbakonam , India. 2 Department of Chemistry, Sri Manakula Vinayagar Engineering College, Pondicherry , India. 3 Department of Chemistry, A.V.V.M Sri Pushpam College, Poondi , India. Received: 13 May 2014, Accepted: 21 July 2014, Published Online: 27 August 2014 Abstract The activated carbon from Delonix regia (Flame tree) pods was prepared using orthogonal array experimental design method with the parameters such as microwave radiation power, radiation time, concentration of ZnCl 2 solution and impregnation time. Optimized conditions were found to be radiation power 850 W, radiation time 12 min, 60 % of ZnCl 2 and impregnation n 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, SEM and ph ZPC. Batch mode adsorption experiments were carried out for the removal of Methylene Blue dye (MB dye) from aqueous solution using MWZAC. Influence of the parameters such as dose of the adsorbent, agitation time, initial dye concentration, ph of the solution on adsorption were studied. Kinetics of the system was studied with linearised forms of Legergren, Ho and Webber Morris models. The SSE % result revealed that present system followed pseudo second order kinetics equation with the intra particle diffusion as the rate determining step. The exhausted MWZAC was regenerated by desorption processes using 1 M NaOH and microwave irradiation processes. Comparison of readsorption results showed that microwave irradiation method was more effective regeneration method. Keywords: Adsorption, ZnCl 2 activated ted microwave carbon, ph effect, methylene blue dye, Desorption, Kinetics, Readsorption Contents 1. Introduction Experimental Data Processing Tools Results and discussion Conclusion References *Corresponding author V. Nandhakumar Department of Chemistry, A.V.V.M Sri Pushpam College, Poondi , India. Manuscript ID: IJCPS2121 Copyright 2014, IJCPS All Rights Reserved 1. Introduction Dyes are widely used in textile industries. Coloured effluents pose major problems to the living organism. Many treatment methods have been used to remove the dyes from wastewater. Among the various methods, adsorption is an effective separation process which is now recognized as an effective and economical method for the removal of International Journal of Chemistry and Pharmaceutical Sciences PAPER-QR CODE 1032

2 V. Nandhakumar et al IJCPS, 2014, Vol.2(8): both organic and inorganic pollutants from wastewater. The most widely used adsorbents are activated carbon because of their high surface area due to the presence of micro and meso pores. A number of studies have also been performed using activated carbon prepared from agricultural wastes for the removal of dyes from aqueous solution. Methylene blue dye is used as model adsorbate for adsorption of organic substance because of its known strong adsorption to activated carbon [1, 2]. Structure of MB In this present study, pods of Delonix regia (flame tree) have been used to prepare activated carbon. Delonix regia belongs to royal Poinciana or flamboyant, a member of the bean family which produces brown woody seed pods merely a waste material [3]. Recently, microwave energy has been widely used in research and industrial processes 3. Compared with conventional heating techniques, microwave heating has the following additional advantages as follows: interior heating, higher heating rates, selective heating, greater control of the heating process, no direct contact between the heating source and heated materials, and reduced equipment size and waste [4,5]. Hence microwave radiation is used to prepare carbon from the plant material instead of conventional heating methods. 2. Materials and Methods 2.1 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 carbon [3, 7]. 20 g of the powdered pods was mixed with 75 ml of ZnCl 2 solution of desired concentration (20, 40 and 60 %). The slurry was kept at room temperature for 24 hours, to ensure the access of the ZnCl 2 to the Delonix Regia pods. Then the slurry was subjected to microwave heating of pre- determined power (450, 600, 850 watts) for pre- samples were washed with 0.05 M HCl followed with hot distilled water determined duration (8, 10, 12 minutes).thus the carbonized and cold distilled water until the ph of the washings reach 7. Then the carbon was filtered and dried at 378 K. Totally 27 number of carbons were prepared by varying preparation parameters such as concentration of ZnCl 2 solution, Microwave heating watts power and radiation times which are given in the Table Preparation of stock Solution Analar grade Methylene blue dye of Merck Company was used without further purification. The dye stock solution was prepared by dissolving appropriate amount of accurately weighed dye in double distilled water to a concentration of 0 mg/l. The experimental solutions were prepared from the stock solution by proper dilution. 2.3 Characterization of MWZAC Particle size (µm), Surface area (m 2 /g), Pore volume (cm 3 /g), Pore size or Pore width (nm), Bulk density (g/ml), Fixed Carbon (%), Moisture conte nt (%) and ph zpc were determined. 2.4 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,, 120 and 140 minutes Desorption and readsorption process Regeneration of spent carbon for the reuse was studied with two techniques. In one method aqueous 1 M NaOH solution was used as desorbing agent in and another method microwave irradiation was adoptedd using 450, 600 and 850 watts for 10 minutes. Re-adsorption experiments were performed following the procedure described above [9, 10]. International Journal of Chemistry and Pharmaceutical Sciences 1033

3 3. Data Processing Tools 3.1 Kinetics Studies Pseudo First order kinetics Legergren equation is [11] log (q e -q t )=log q e - k 1 /2.303 t Where qe and qt are the amounts of dye adsorbed (mg/g) at equilibrium and at time t (min), respectively and k 1 is the rate constant of adsorption (l/min) [12] Pseudo Second order kinetics Ho equation is [13] t/q t = 1/ k 2.q 2 e +1/q e t The initial adsorption rate, h (mg/(g min)), as t 0 can be defined as 2 h = k 2 q e The initial adsorption rate (h), the equilibrium adsorption capacity (q e ), and the second-order constants k 2 (g/ (mg min)) can be determined experimentally from the slope and intercept of plot of t/q t versus t Intra particle diffusion Weber Morris equation is [14] q t = k p t 1/2 + C Where k p is the intra-particle diffusion rate constant, a plot of q t versus t 1/2 should be a straight line with a slope k p which is the rate constant for intra particle diffusion and intercept C is the thickness of the boundary film [12] Test for kinetics models The sum of error squares is given as follows; SSE (%) = [(q e ) exp -(q e ) cal ] 2 / N Where N is the number of data points, (q e ) exp is the experimental q e, (q e ) cal is the calculated q e [12]. 4. Result and Discussion 4.1 Optimization 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, 150 and 200 mgl -1 and 1 hour agitation time. Samples and their percentage removal of MB dye were shown in Table 1. The results inferred that percentage of removal of MB dye increased with the increase of radiation time, radiation power and concentration of ZnCl 2 solution. Hence carbon prepared using 60 % ZnCl 2 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. 4.2 Physico-chemical characteristics of MWZAC Physico-chemical characteristics of MWZAC were collected in the Table 2. Percentage of fixed carbon, surface area, ph zpc and other values are reasonable to function as a good adsorbent. 4.3 SEM studies SEM is widely used to study the morphological features and surface characteristics of the adsorbent materials. The morphology of prepared MWZAC was examined before adsorption is shown in the Fig. 3 SEM micrograph ( using Fe - SEM technique, Model: JEOL JSN 6701F, Japan) of MWZAC particles showed cavities, pores and more rough surfaces on the carbon samples. This shows that ZnCl 2 was effective to create well developed pores with uniform distribution leading to large surface area and porous structure Effect of contact time for different initial concentrations The percentage of removal of MB from aqueous solution with respect to different contact times and with different initial concentrations at different temperatures was shown in Fig.1.The adsorption process is characterized by a rapid uptake of the adsorbate in the initial stages as shown by the curves. The percentage of removal increased with the increase in contact time and decreased with the increase of initial concentration of the dye. However the amount of dye adsorbed on the adsorbent increased with the increase of initial concentration of the dye solution as depicted in the Fig. 1. The time to attain equilibrium was found to increase when the initial concentration of the dye was increased. At the same time, time to attain equilibrium decreased with the increase of temperature [8]. 4.5 Effect of ph Fig. 1 shows the effect of initial ph of the dye solution on the removal of MB dye. The percent removal increased as the ph of the solution increased. At lower ph, positively charged surface of the adsorbent render electrostatic repulsion towards dye cations. Basically, Methylene blue and other cationic dyes produce an intense molecular cation (C + ) and reduced ions (CH + ). Hence dye removal was low at lower ph. At higher ph, OH - on the surface of adsorbent favored the adsorption of cationic dye molecules Kinetic models The adsorption kinetics shows the evolution of the adsorption capacity through time and it is necessary to International Journal of Chemistry and Pharmaceutical Sciences 1034

4 identify the types of adsorption mechanism in a given system. Plots of different kinetic models applied were given in the Fig. 2 and the kinetic parameters calculated were given in the Table 3. Between the first order and second order, second order kinetic model seems to best describe the above adsorption system as it has R 2 value which were very close to unity. Moreover, difference between q e (cal) and q e (exp) values of second order is small when compared to first order kinetic model. Statistically it is tested with the tool sum of error squares (SSE %) [1 7 ]. The SSE % values were given in the Table 3, from which it was concluded that second order kinetic model was more appropriate rather than first order kinetic model. In Fig. 2, plot of mass of dye adsorbed per unit mass of adsorbent (q t ) versus t 1/2 is presented for MB dye. The linear plots are attributed to the macro pore diffusion which is the accessible sites of adsorption. This is attributed to the instantaneous utilization of the most readily available adsorbing sites on the adsorbent surface. The values of k p obtained from the slopes of straight lines are listed in Table 3 [18]. Table 1: Preparation parameters Sample number C RP RT Sample name % of Removal MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC MWZAC RP= Radiation power in watts; RT = Radiation time in minutes; C = Concentration of ZnCl 2. International Journal of Chemistry and Pharmaceutical Sciences 1035

5 Table 2: Physico-chemical characteristics of MWZAC Properties Values phzpc 7.01 Particle size, µm Surface area (BET), m 2 /g 586 Pore volume, cm 3 /g Pore size (Pore width), nm Bulk density, g/ml 0.52 Fixed Carbon, % Moisture content, % 4.36 Table 3A: Kinetic parameters for the removal of Methylene Blue dye or MB dye by MWZAC Concentration (ppm) First Order Kinetics Temperature (K) k 1 q e(cal) q e(exp) (min -1 R 2 SSE ) (mg/g) (mg/g) % Concentration (ppm) Table 3B: Kinetic parameters for the removal of Methylene Blue dye or MB dye by MWZAC Temperature (K) k (g/mg.min) Second Order Kinetics q e(cal) (mg/g) h R 2 SSE % Intra Particle Diffusion k p (mg/g.min) R 2 International Journal of Chemistry and Pharmaceutical Sciences 1036

6 V. Nandhakumar et al IJCPS, 2014, Vol.2(8): Effect of initial concentration 305 K Effect of initial concentration 315 K % Removal Time in min ppm 150 ppm 200 ppm % Removal Time in min ppm 150 ppm 200 ppm Figure1: Effect of initial concentration and ph First order kinetics 305 K Second order kinetics 305 K Log(qe-qt) Time in min ppm 150 ppm 200 ppm t/q t Time in min ppm 150 ppm 200 ppm Figure 2: Kinetic models International Journal of Chemistry and Pharmaceutical Sciences 1037

7 Figure 2: Kinetic models Figure 3: Scanning electron micrograph of MWZAC 5. Conclusion Microwave 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 to 200 mg/l. Kinetic studies revealed that the process of adsorption follows pseudo second order kinetics. Re-adsorption studies inferred that microwave irradiation was more effective than NaOH treatment to regenerate the adsorbent. 6. References 1. C Moreno-Castilla. Carbon, 2004, 42, E.S Abechi; C.E Gimba; A Uzairu; J.A Kagbu. Arch. Appl. Sci. Res, 2011, 3 (1), Yuh-Shan Ho, R Malarvizhi, N Sulochana. Journal of Environmental Protection Science, 2009, Vol. 3, pp E Yagmur; M Ozmak; Z Aktas. Fuel, 2008, 87: Y.V Bykov; K.I Rybakov; V.E Semenov. J Phys, 2001, 34:55 6. Foo Keng Yuen; B.H Hameed. Advances in Colloid and Interface Science, 2009, 149, M Makeswari; T V Santhi. Journal of chemistry, 2013, Volume B.R Venkatraman; K Hema; V Nandhakumar; S Arivoli, J. Chem. Pharm. Res, 2011, 3(2), Chao-Yin Kuo. J. Hazard. Mater, 2008, P.C Chiang ; E.E Chang; J.S Wu. Water Sci. Tech, 1997, 35, S Lagergren; B.K Svenska; Vetenskapsakad. Handl, 1898, K Ramesh; A Rajappa; V Roopa; V Nandhakumar. Int.J.Curr.Res.Chem.Pharma.Sci, 2014, 1(1), International Journal of Chemistry and Pharmaceutical Sciences 1038

8 13. G McKay; Y.S Ho. Processe Biochem, 1999, 34, W.J Weber Jr; J.C Morris. J. Sanit. Eng. Div, 1963, ASCE. 89 (SA2), C Namasivayam; D Kavitha. Microchemical Journal, 2006, 82, V.K Gupta; A.I Suhas; V.K Saini. Ind. Eng. Chem. Res. 43, 2004, B.H Hameed; A.T.M Din; A.L Ahmad. J. Hazard Mater, 2006, July 28, S Arivoli; V Nandhakumar; S Saravanan; Sulochana Nadarajan. The Arabian Journal for Science and Engineering, 2009, Volume 34, Number 1A, January. International Journal of Chemistry and Pharmaceutical Sciences 1039