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Preparation of activated carbon from date stones by microwave induced chemical activation: Application for methylene blue adsorption
Chemical Engineering Journal 170 (2011) 338–341
Contents lists available at ScienceDirect
Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej
Short communication
Preparation of activated carbon from date stones by microwave induced chemical activation: Application for methylene blue adsorption K.Y. Foo, B.H. Hameed ∗ School of Chemical Engineering, Engineering Campus, University of Science Malaysia, 14300 Nibong Tebal, Penang, Malaysia
a r t i c l e
i n f o
Article history: Received 10 November 2010 Received in revised form 21 February 2011 Accepted 24 February 2011 Keywords: Activated carbon Adsorption Date stone Methylene blue Microwave
a b s t r a c t In this work, a low cost activated carbon was prepared from date stones char (DSAC) under microwave induced KOH chemical activation. The activation step was performed at the microwave input power of 600 W and irradiation time of 8 min. Porous texture, surface and functional characteristics were analyzed by N2 adsorption, scanning electron microscopy, Fourier transform infrared spectroscopy, and equilibrium studies. Adsorption isotherm was fitted by Freundlich, Langmuir and Temkin isotherm models. Result showed that the monolayer adsorption capacity of the DSAC for methylene blue was 316.11 mg/g, while the BET surface area, Langmuir surface area and total pore volume of DSAC were 856 m2 /g, 1275 m2 /g and 0.4680 cm3 /g, respectively. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Materials and methods
In principle, the preparation of activated carbon involves of two stages, namely pyrolysis and activation [1]. In the first stage, suitable carbon precursors are pyrolysed under inert atmosphere at moderate temperature to release volatile matters and produce chars with rudimentary pore structures. Subsequently, the resulting chars are subjected to partial gasification at higher temperature (usually above 900 ◦ C) with oxidizing gases, to produce activated carbons with well-developed and accessible internal porosities [2]. Nevertheless, in some cases, the thermal process may take long processing time, involve high energy consumption, require larger equipment size and generate improper heating rate, thereby resulting in a detrimental effect on the quality of the prepared activated carbons [3]. Furthermore, there is a considerable risk of overheating or even thermal runaway of local sample, leading to the complete combustion of the carbon [4]. Therefore, it is necessary to find a rapid and easy route for the preparation of activated carbon. Although microwave heating is today a mature technique which finds wide applications in the area of material science, food processing and analytical chemistry [5], there are relatively few studies in this field. The aim of this work was to prepare date stones based activated carbon (DSAC) using KOH as activating agent and heating carrier by microwave heating.
2.1. Adsorbate
∗ Corresponding author. Tel.: +60 45996422; fax: +60 45941013. E-mail address: [email protected] (B.H. Hameed). 1385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2011.02.068
Methylene blue (MB), an analytical grade cationic dye supplied by Merck (M) Sdn. Bhd, Malaysia was chosen as the adsorbate in this study, and was not purified prior to use. Deionized water supplied by USF ELGA water treatment system was used to prepare all the reagents and solutions. 2.2. Preparation and characterization of activated carbon Date stone (DS) used in the present study was obtained locally. The precursor was firstly washed to remove dirt particles from its surface and dried in an oven at 70 ◦ C. The dried sample was then ground and sieved to discrete sizes (1–2 mm), and carbonized at 700 ◦ C under purified nitrogen (99.995%) flow in a tube furnace. The char produced was soaked in potassium hydroxide (KOH) solution with an impregnation (char:KOH) ratio of 1:1.75 (wt%). The activation step was conducted in a tubular glass reactor placed in a modified microwave oven with a nitrogen flow (300 cm3 /min). The microwave power was set at 600 W and 8 min of irradiation time was selected as the heating period based on preliminary runs. The activated product was then washed with deionized water and hydrochloric acid of 0.1 M until the pH of the washing solution reached 6–7. Scanning electron microscope (SEM) analysis was performed to study the textural structure of adsorbent before and after the activation process. Surface physical properties of char and DSAC were characterized with Micromeritics ASAP 2020, using N2 as the
K.Y. Foo, B.H. Hameed / Chemical Engineering Journal 170 (2011) 338–341
339
Table 1 Langmuir, Freundlich and Temkin isotherm constants and regression correlation coefficients for the adsorption of MB onto DSAC. Langmuir isotherm model Q0 (mg/g) 316.11
Freundlich isotherm model 2
b (L/mg)
R
0.901
0.999
1/n
n
R
A (L/g)
B
R2
2.46
0.923
0.956
140.14
0.982
KF (mg/g) (L/mg) 42.65
Temkin isotherm model 2
Table 2 Comparison of adsorption capacities of various adsorbents for MB. Precursor Date stone Bamboo Cotton stalk Pine wood powder Coffee grounds Spent catalysts of vinyl synthesis Hevea brasiliensis seed coat Oil palm fiber Durian shell Norit SA3 (Commercial grade powdered activated carbon) Nuchar WWH (Commercial grade granular activated carbon)
Activation method Microwave heating Microwave heating Microwave heating Microwave heating Microwave heating Microwave heating Conventional heating Conventional heating Conventional heating – –
adsorbate at 77 K, while surface functional groups of DSAC were detected by Fourier transform infrared (FTIR) spectroscope (FTIR2000, PerkinElmer) from the scanning range of 4000–400 cm−1 . 2.3. Adsorption equilibrium studies Equilibrium sorption studies were conducted in a set of 250 mL Erlenmeyer flasks containing 0.20 g adsorbent and 200 mL dye solutions with various initial concentrations (50, 100, 200, 300, 400, and 500 mg/L). The flasks were agitated in an isothermal water-bath shaker at 120 rpm and 30 ◦ C until the equilibrium was reached. MB uptake at equilibrium, qe (mg/g), was calculated by Eq. (1): qe =
(C0 − Ce )V W
Activation time (min)
Adsorption capacity (mg/g)
8 10 10 10 12 40 120 120 60 – –
316.11 286.10 294.12 200.00 99.43 285.00 227.27 277.78 289.26 91.00 21.50
Reference Present study [10] [11] [12] [13] [14] [15] [16] [17] [18] [18]
combination of microporous and mesoporous structures (with the ˚ Meanwhile, the isotherm shows an average pore size of 21.82 A). apparent hysteresis loop (H4 types) in the desorption branch at relative pressures above 0.9, indicating the presence of mesopores. The saturated adsorption amount of N2 increased after microwave modification, implying development of additional pores in the activated carbon, with the BET surface area, Lang-
(1)
where C0 and Ce (mg/L) are the liquid-phase concentrations of dye at initial and equilibrium, respectively. V (L) is the volume of the solution, and W (g) is the mass of adsorbent used. The effect of pH on MB removal was tested by varying the pH from 2 to 12, with initial MB concentration of 300 mg/L, DSAC dosage of 0.20 g/200 mL and adsorption temperature of 30 ◦ C. 3. Results and discussion 3.1. Characterization of activated carbon Fig. 1 shows SEM images of the DS derived char and activated carbon. It can be found that the surface of the char was dense, planar, constricted and blocked by deposited tarry substances. However, the microwave irradiated sample demonstrated a well developed and uniform surface, forming an orderly pore structure. The obtained FTIR spectrum of char (Fig. 2) revealed the peaks at 3233, 2361, 1992, 1424 and 1054 cm−1 , corresponds to the presence of –OH (hydroxyl), C C (alkynes), –COOH (carboxylic acids), in-plane –OH, and C–O–C (esters, ether or phenol) functional groups. Meanwhile, the surface chemistry of DSAC illustrated intensive peaks, at 3233, 1424 and 1054 cm−1 , corresponds to the presence of –OH (hydroxyl), in-plane –OH bending vibrations, and C–O–C (esters, ether or phenol) derivatives. Nitrogen adsorption isotherm is a standard procedure for determination of porosity of carbonaceous adsorbents. In the present study, it can found that the isotherm of DSAC presents I–II hybrid shape as defined by IUPAC classification (Fig. 3), associated with a
Fig. 1. SEM micrographs of (a) char (1000×) and (b) DSAC (1000×).
340
K.Y. Foo, B.H. Hameed / Chemical Engineering Journal 170 (2011) 338–341
20.0
Char 19.0 18.0
1992 17.0
2361
3233
1424
16.0
1054
15.0
%T 14.0 13.0 12.0
11.0
DSAC
10.0 9.0
1424
3233
1054 8.0 4000
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
400
Wave number cm -1 Fig. 2. FTIR of char and DSAC.
muir surface area and total pore volume of 856 m2 /g, 1276 m2 /g and 0.4680 cm3 /g, respectively (compared with 66 m2 /g, 99 m2 /g 0.0385 cm3 /g for char).
(a)
0
0
50
100
150
200
250
Ce (mg/L)
(b)
315
200
100
280 270
305
qe (mg/g)
Quantity Adsorbed (cm³/g STP)
MB removal efficiency increased with prolonging the contact time. Initially, the amount of dye adsorbed onto the carbon surface increased rapidly, and at some point of time, the process slowed down and reached a plateau. In the present study, adsorption equilibrium, qe increased from 50.62 to 296.55 mg/g with an increase in initial concentration from 50 to 500 mg/L (Fig. 4a). Solution pH affects adsorption by regulating the adsorbents surface charge as well as the degree of ionization of adsorbent present in the solu-
qe (mg/g)
3.2. Adsorption equilibrium and isotherm studies
300
295 285
260 250 240
275 265
230
0
0.2
0.4
0.6
Relative Pressure (P/Po) Fig. 3. Nitrogen isotherm of DSAC.
0.8
1
0
2
4
6
8
10
12
14
pH Fig. 4. Equilibrium study (a) and effect of pH on the adsorption of MB onto DSAC.
K.Y. Foo, B.H. Hameed / Chemical Engineering Journal 170 (2011) 338–341
tion. Increasing pH from 2 to 12 illustrates an enhancement of the adsorption capacity (increased from 237.79 to 275.89 mg/g), associated with protonation of MB in the acidic medium, and presence of excess H+ ions, competing with dye cations for the adsorption sites (Fig. 4b). The behavior clearly suggests that the adsorption was dominated by the interaction between MB dyes and adsorbent surface. Equilibrium data was then fitted to Langmuir [6], Freundlich [7] and Temkin [8] isotherm models (Table 1). Ce 1 1 = + Ce qe Q0 KL Q0 log qe = log KF + qe =
RT ln AT + bT
(2)
1 log Ce n
RT bT
ln Ce
(3) (4)
where Q0 (mg/g) and KL (dm3 /g) are Langmuir constants related to adsorption capacity and rate of adsorption, respectively, and KF (mg/g) (L/mg) and 1/n are the Freundlich adsorption constant, and a measure of the adsorption intensity. B = RT/b, where b, A, R and T are the Temkin constant related to heat of sorption (J/mol), equilibrium binding constant (L/g), gas constant (8.314 J/mol K) and absolute temperature (K). Langmuir isotherm model yielded the best fit with R2 values higher than 0.99, suggesting homogeneous nature, and monolayer coverage of dye molecules at the outer surface of DSAC. Table 2 exhibits a comparison of maximum monolayer adsorption capacity of various adsorbents for MB. The adsorbent prepared in this work showed relatively high adsorption capacity of 316.11 mg/g, as compared to some previous works reported in the literature. Thus, it is inferred that considerable changes in the surface properties were achieved under microwave radiation (internal and volumetric heating), which facilitates the modification process. The main advantage of using microwave heating is that the treatment time can be considerably reduced, which in many cases represents a reduction in the energy consumption and cost as well. Moreover, microwave heating has offered the additional advantages as 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 [9]. 4. Conclusion The results revealed the feasibility to prepare activated carbon from date stone char by microwave induced KOH activation. The activation process took 8 min at the operating power of 600 W. The monolayer adsorption capacity of DSAC for MB was 316.11 mg/g, while the BET surface area and total pore volume were 856.23 m2 /g and 0.4680 cm3 /g, respectively.
341
Acknowledgement The authors acknowledge the financial support provided by University of Science Malaysia under the Research University (RU) Scheme (Project No. 1001/PJKIMIA/814072) and RU-PRGS grant scheme (Project 465 No. 8043030). References [1] T.H. Liou, Development of mesoporous structure and high adsorption capacity of biomass based activated carbon by phosphoric acid and zinc chloride activation, Chem. Eng. J. 158 (2) (2010) 129–142. [2] J. Acharya, J.N. Sahu, C.R. Mohanty, B.C. Meikap, Removal of lead(II) from wastewater by activated carbon developed from Tamarind wood by zinc chloride activation, Chem. Eng. J. 149 (1–3) (2009) 249–262. [3] I. Polaert, L. Estel, R. Huyghe, M. Thomas, Adsorbents regeneration under microwave irradiation for dehydration and volatile organic compounds gas treatment, Chem. Eng. J. 162 (3) (2010) 941–948. [4] P. Nowicki, M. Skrzypczak, R. Pietrzak, Effect of activation method on the physicochemical properties and NO2 removal abilities of sorbents obtained from plum stones (Prunus domestica), Chem. Eng. J. 162 (2010) 723–729. [5] M. Komorowska, G.D. Stefanidis, T. Van Gerven, A.I. Stankiewicz, Influence of microwave irradiation on a polyesterification reaction, Chem. Eng. J. 155 (3) (2009) 859–866. [6] I. Langmuir, The adsorption of gases on plane surfaces of glass, mica and platinum, J. Am. Chem. 57 (1918) 1361–1403. [7] H. Freundlich, Über die adsorption in lösungen (adsorption in solution), Z. Phys. Chem. 57 (1906) 384–470. [8] M.I. Tempkin, V. Pyzhev, Kinetics of ammonia synthesis on promoted iron catalyst, Acta Phys. Chim. USSR 12 (1940) 327–356. [9] K.Y. Foo, B.H. Hameed, Recent developments in the preparation and regeneration of activated carbons by microwaves, Adv. Colloid Interface Sci. 149 (2009) 19–27. [10] Q.S. Liu, T. Zheng, N. Li, P. Wang, G. Abulikemu, Modification of bamboo-based activated carbon using microwave radiation and its effects on the adsorption of methylene blue, Appl. Surf. Sci. 256 (10) (2010) 3309–3315. [11] H. Deng, G.X. Li, H.B. Yang, J.P. Tang, J.Y. Tang, Preparation of activated carbons from cotton stalk by microwave assisted KOH and K2 CO3 activation, Chem. Eng. J. 163 (3) (2010) 373–381. [12] T.H. Wang, S.X. Tan, C.H. Liang, Preparation and characterization of activated carbon from wood via microwave-induced ZnCl2 activation, Carbon 47 (2009) 1867–1885. [13] M. Hirata, N. Kawasaki, T. Nakamura, K. Matsumoto, M. Kabayama, T. Tamura, S. Tanada, Adsorption of dyes onto carbonaceous materials produced from coffee grounds by microwave treatment, J. Colloid Interface Sci. 254 (2002) 17–22. [14] Z.Y. Zhang, W.W. Qu, J.H. Peng, L.B. Zhang, X.Y. Ma, Z.B. Zhang, W. Li, Comparison between microwave and conventional thermal reactivations of spent activated carbon generated from vinyl acetate synthesis, Desalination 249 (1) (2009) 247–252. [15] B.H. Hameed, F.B.M. Daud, Adsorption studies of basic dye on activated carbon derived from agricultural waste: Hevea brasiliensis seed coat, Chem. Eng. J. 139 (2008) 48–55. [16] I.A.W. Tan, B.H. Hameed, A.L. Ahmad, Equilibrium and kinetic studies on basic dye adsorption by oil palm fiber activated carbon, Chem. Eng. J. 127 (2007) 111–119. [17] T.C. Chandra, M.M. Mirna, Y. Sudaryanto, S. Ismadji, Adsorption of basic dye onto activated carbon prepared from durian shell: studies of adsorption equilibrium and kinetics, Chem. Eng. J. 127 (2007) 121–129. [18] J. Yener, T. Kopac, G. Dogu, T. Dogu, Dynamic analysis of sorption of methylene blue dye on granular and powdered activated carbon, Chem. Eng. J. 144 (2008) 400–406.
Contents lists available at ScienceDirect
Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej
Short communication
Preparation of activated carbon from date stones by microwave induced chemical activation: Application for methylene blue adsorption K.Y. Foo, B.H. Hameed ∗ School of Chemical Engineering, Engineering Campus, University of Science Malaysia, 14300 Nibong Tebal, Penang, Malaysia
a r t i c l e
i n f o
Article history: Received 10 November 2010 Received in revised form 21 February 2011 Accepted 24 February 2011 Keywords: Activated carbon Adsorption Date stone Methylene blue Microwave
a b s t r a c t In this work, a low cost activated carbon was prepared from date stones char (DSAC) under microwave induced KOH chemical activation. The activation step was performed at the microwave input power of 600 W and irradiation time of 8 min. Porous texture, surface and functional characteristics were analyzed by N2 adsorption, scanning electron microscopy, Fourier transform infrared spectroscopy, and equilibrium studies. Adsorption isotherm was fitted by Freundlich, Langmuir and Temkin isotherm models. Result showed that the monolayer adsorption capacity of the DSAC for methylene blue was 316.11 mg/g, while the BET surface area, Langmuir surface area and total pore volume of DSAC were 856 m2 /g, 1275 m2 /g and 0.4680 cm3 /g, respectively. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Materials and methods
In principle, the preparation of activated carbon involves of two stages, namely pyrolysis and activation [1]. In the first stage, suitable carbon precursors are pyrolysed under inert atmosphere at moderate temperature to release volatile matters and produce chars with rudimentary pore structures. Subsequently, the resulting chars are subjected to partial gasification at higher temperature (usually above 900 ◦ C) with oxidizing gases, to produce activated carbons with well-developed and accessible internal porosities [2]. Nevertheless, in some cases, the thermal process may take long processing time, involve high energy consumption, require larger equipment size and generate improper heating rate, thereby resulting in a detrimental effect on the quality of the prepared activated carbons [3]. Furthermore, there is a considerable risk of overheating or even thermal runaway of local sample, leading to the complete combustion of the carbon [4]. Therefore, it is necessary to find a rapid and easy route for the preparation of activated carbon. Although microwave heating is today a mature technique which finds wide applications in the area of material science, food processing and analytical chemistry [5], there are relatively few studies in this field. The aim of this work was to prepare date stones based activated carbon (DSAC) using KOH as activating agent and heating carrier by microwave heating.
2.1. Adsorbate
∗ Corresponding author. Tel.: +60 45996422; fax: +60 45941013. E-mail address: [email protected] (B.H. Hameed). 1385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2011.02.068
Methylene blue (MB), an analytical grade cationic dye supplied by Merck (M) Sdn. Bhd, Malaysia was chosen as the adsorbate in this study, and was not purified prior to use. Deionized water supplied by USF ELGA water treatment system was used to prepare all the reagents and solutions. 2.2. Preparation and characterization of activated carbon Date stone (DS) used in the present study was obtained locally. The precursor was firstly washed to remove dirt particles from its surface and dried in an oven at 70 ◦ C. The dried sample was then ground and sieved to discrete sizes (1–2 mm), and carbonized at 700 ◦ C under purified nitrogen (99.995%) flow in a tube furnace. The char produced was soaked in potassium hydroxide (KOH) solution with an impregnation (char:KOH) ratio of 1:1.75 (wt%). The activation step was conducted in a tubular glass reactor placed in a modified microwave oven with a nitrogen flow (300 cm3 /min). The microwave power was set at 600 W and 8 min of irradiation time was selected as the heating period based on preliminary runs. The activated product was then washed with deionized water and hydrochloric acid of 0.1 M until the pH of the washing solution reached 6–7. Scanning electron microscope (SEM) analysis was performed to study the textural structure of adsorbent before and after the activation process. Surface physical properties of char and DSAC were characterized with Micromeritics ASAP 2020, using N2 as the
K.Y. Foo, B.H. Hameed / Chemical Engineering Journal 170 (2011) 338–341
339
Table 1 Langmuir, Freundlich and Temkin isotherm constants and regression correlation coefficients for the adsorption of MB onto DSAC. Langmuir isotherm model Q0 (mg/g) 316.11
Freundlich isotherm model 2
b (L/mg)
R
0.901
0.999
1/n
n
R
A (L/g)
B
R2
2.46
0.923
0.956
140.14
0.982
KF (mg/g) (L/mg) 42.65
Temkin isotherm model 2
Table 2 Comparison of adsorption capacities of various adsorbents for MB. Precursor Date stone Bamboo Cotton stalk Pine wood powder Coffee grounds Spent catalysts of vinyl synthesis Hevea brasiliensis seed coat Oil palm fiber Durian shell Norit SA3 (Commercial grade powdered activated carbon) Nuchar WWH (Commercial grade granular activated carbon)
Activation method Microwave heating Microwave heating Microwave heating Microwave heating Microwave heating Microwave heating Conventional heating Conventional heating Conventional heating – –
adsorbate at 77 K, while surface functional groups of DSAC were detected by Fourier transform infrared (FTIR) spectroscope (FTIR2000, PerkinElmer) from the scanning range of 4000–400 cm−1 . 2.3. Adsorption equilibrium studies Equilibrium sorption studies were conducted in a set of 250 mL Erlenmeyer flasks containing 0.20 g adsorbent and 200 mL dye solutions with various initial concentrations (50, 100, 200, 300, 400, and 500 mg/L). The flasks were agitated in an isothermal water-bath shaker at 120 rpm and 30 ◦ C until the equilibrium was reached. MB uptake at equilibrium, qe (mg/g), was calculated by Eq. (1): qe =
(C0 − Ce )V W
Activation time (min)
Adsorption capacity (mg/g)
8 10 10 10 12 40 120 120 60 – –
316.11 286.10 294.12 200.00 99.43 285.00 227.27 277.78 289.26 91.00 21.50
Reference Present study [10] [11] [12] [13] [14] [15] [16] [17] [18] [18]
combination of microporous and mesoporous structures (with the ˚ Meanwhile, the isotherm shows an average pore size of 21.82 A). apparent hysteresis loop (H4 types) in the desorption branch at relative pressures above 0.9, indicating the presence of mesopores. The saturated adsorption amount of N2 increased after microwave modification, implying development of additional pores in the activated carbon, with the BET surface area, Lang-
(1)
where C0 and Ce (mg/L) are the liquid-phase concentrations of dye at initial and equilibrium, respectively. V (L) is the volume of the solution, and W (g) is the mass of adsorbent used. The effect of pH on MB removal was tested by varying the pH from 2 to 12, with initial MB concentration of 300 mg/L, DSAC dosage of 0.20 g/200 mL and adsorption temperature of 30 ◦ C. 3. Results and discussion 3.1. Characterization of activated carbon Fig. 1 shows SEM images of the DS derived char and activated carbon. It can be found that the surface of the char was dense, planar, constricted and blocked by deposited tarry substances. However, the microwave irradiated sample demonstrated a well developed and uniform surface, forming an orderly pore structure. The obtained FTIR spectrum of char (Fig. 2) revealed the peaks at 3233, 2361, 1992, 1424 and 1054 cm−1 , corresponds to the presence of –OH (hydroxyl), C C (alkynes), –COOH (carboxylic acids), in-plane –OH, and C–O–C (esters, ether or phenol) functional groups. Meanwhile, the surface chemistry of DSAC illustrated intensive peaks, at 3233, 1424 and 1054 cm−1 , corresponds to the presence of –OH (hydroxyl), in-plane –OH bending vibrations, and C–O–C (esters, ether or phenol) derivatives. Nitrogen adsorption isotherm is a standard procedure for determination of porosity of carbonaceous adsorbents. In the present study, it can found that the isotherm of DSAC presents I–II hybrid shape as defined by IUPAC classification (Fig. 3), associated with a
Fig. 1. SEM micrographs of (a) char (1000×) and (b) DSAC (1000×).
340
K.Y. Foo, B.H. Hameed / Chemical Engineering Journal 170 (2011) 338–341
20.0
Char 19.0 18.0
1992 17.0
2361
3233
1424
16.0
1054
15.0
%T 14.0 13.0 12.0
11.0
DSAC
10.0 9.0
1424
3233
1054 8.0 4000
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
400
Wave number cm -1 Fig. 2. FTIR of char and DSAC.
muir surface area and total pore volume of 856 m2 /g, 1276 m2 /g and 0.4680 cm3 /g, respectively (compared with 66 m2 /g, 99 m2 /g 0.0385 cm3 /g for char).
(a)
0
0
50
100
150
200
250
Ce (mg/L)
(b)
315
200
100
280 270
305
qe (mg/g)
Quantity Adsorbed (cm³/g STP)
MB removal efficiency increased with prolonging the contact time. Initially, the amount of dye adsorbed onto the carbon surface increased rapidly, and at some point of time, the process slowed down and reached a plateau. In the present study, adsorption equilibrium, qe increased from 50.62 to 296.55 mg/g with an increase in initial concentration from 50 to 500 mg/L (Fig. 4a). Solution pH affects adsorption by regulating the adsorbents surface charge as well as the degree of ionization of adsorbent present in the solu-
qe (mg/g)
3.2. Adsorption equilibrium and isotherm studies
300
295 285
260 250 240
275 265
230
0
0.2
0.4
0.6
Relative Pressure (P/Po) Fig. 3. Nitrogen isotherm of DSAC.
0.8
1
0
2
4
6
8
10
12
14
pH Fig. 4. Equilibrium study (a) and effect of pH on the adsorption of MB onto DSAC.
K.Y. Foo, B.H. Hameed / Chemical Engineering Journal 170 (2011) 338–341
tion. Increasing pH from 2 to 12 illustrates an enhancement of the adsorption capacity (increased from 237.79 to 275.89 mg/g), associated with protonation of MB in the acidic medium, and presence of excess H+ ions, competing with dye cations for the adsorption sites (Fig. 4b). The behavior clearly suggests that the adsorption was dominated by the interaction between MB dyes and adsorbent surface. Equilibrium data was then fitted to Langmuir [6], Freundlich [7] and Temkin [8] isotherm models (Table 1). Ce 1 1 = + Ce qe Q0 KL Q0 log qe = log KF + qe =
RT ln AT + bT
(2)
1 log Ce n
RT bT
ln Ce
(3) (4)
where Q0 (mg/g) and KL (dm3 /g) are Langmuir constants related to adsorption capacity and rate of adsorption, respectively, and KF (mg/g) (L/mg) and 1/n are the Freundlich adsorption constant, and a measure of the adsorption intensity. B = RT/b, where b, A, R and T are the Temkin constant related to heat of sorption (J/mol), equilibrium binding constant (L/g), gas constant (8.314 J/mol K) and absolute temperature (K). Langmuir isotherm model yielded the best fit with R2 values higher than 0.99, suggesting homogeneous nature, and monolayer coverage of dye molecules at the outer surface of DSAC. Table 2 exhibits a comparison of maximum monolayer adsorption capacity of various adsorbents for MB. The adsorbent prepared in this work showed relatively high adsorption capacity of 316.11 mg/g, as compared to some previous works reported in the literature. Thus, it is inferred that considerable changes in the surface properties were achieved under microwave radiation (internal and volumetric heating), which facilitates the modification process. The main advantage of using microwave heating is that the treatment time can be considerably reduced, which in many cases represents a reduction in the energy consumption and cost as well. Moreover, microwave heating has offered the additional advantages as 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 [9]. 4. Conclusion The results revealed the feasibility to prepare activated carbon from date stone char by microwave induced KOH activation. The activation process took 8 min at the operating power of 600 W. The monolayer adsorption capacity of DSAC for MB was 316.11 mg/g, while the BET surface area and total pore volume were 856.23 m2 /g and 0.4680 cm3 /g, respectively.
341
Acknowledgement The authors acknowledge the financial support provided by University of Science Malaysia under the Research University (RU) Scheme (Project No. 1001/PJKIMIA/814072) and RU-PRGS grant scheme (Project 465 No. 8043030). References [1] T.H. Liou, Development of mesoporous structure and high adsorption capacity of biomass based activated carbon by phosphoric acid and zinc chloride activation, Chem. Eng. J. 158 (2) (2010) 129–142. [2] J. Acharya, J.N. Sahu, C.R. Mohanty, B.C. Meikap, Removal of lead(II) from wastewater by activated carbon developed from Tamarind wood by zinc chloride activation, Chem. Eng. J. 149 (1–3) (2009) 249–262. [3] I. Polaert, L. Estel, R. Huyghe, M. Thomas, Adsorbents regeneration under microwave irradiation for dehydration and volatile organic compounds gas treatment, Chem. Eng. J. 162 (3) (2010) 941–948. [4] P. Nowicki, M. Skrzypczak, R. Pietrzak, Effect of activation method on the physicochemical properties and NO2 removal abilities of sorbents obtained from plum stones (Prunus domestica), Chem. Eng. J. 162 (2010) 723–729. [5] M. Komorowska, G.D. Stefanidis, T. Van Gerven, A.I. Stankiewicz, Influence of microwave irradiation on a polyesterification reaction, Chem. Eng. J. 155 (3) (2009) 859–866. [6] I. Langmuir, The adsorption of gases on plane surfaces of glass, mica and platinum, J. Am. Chem. 57 (1918) 1361–1403. [7] H. Freundlich, Über die adsorption in lösungen (adsorption in solution), Z. Phys. Chem. 57 (1906) 384–470. [8] M.I. Tempkin, V. Pyzhev, Kinetics of ammonia synthesis on promoted iron catalyst, Acta Phys. Chim. USSR 12 (1940) 327–356. [9] K.Y. Foo, B.H. Hameed, Recent developments in the preparation and regeneration of activated carbons by microwaves, Adv. Colloid Interface Sci. 149 (2009) 19–27. [10] Q.S. Liu, T. Zheng, N. Li, P. Wang, G. Abulikemu, Modification of bamboo-based activated carbon using microwave radiation and its effects on the adsorption of methylene blue, Appl. Surf. Sci. 256 (10) (2010) 3309–3315. [11] H. Deng, G.X. Li, H.B. Yang, J.P. Tang, J.Y. Tang, Preparation of activated carbons from cotton stalk by microwave assisted KOH and K2 CO3 activation, Chem. Eng. J. 163 (3) (2010) 373–381. [12] T.H. Wang, S.X. Tan, C.H. Liang, Preparation and characterization of activated carbon from wood via microwave-induced ZnCl2 activation, Carbon 47 (2009) 1867–1885. [13] M. Hirata, N. Kawasaki, T. Nakamura, K. Matsumoto, M. Kabayama, T. Tamura, S. Tanada, Adsorption of dyes onto carbonaceous materials produced from coffee grounds by microwave treatment, J. Colloid Interface Sci. 254 (2002) 17–22. [14] Z.Y. Zhang, W.W. Qu, J.H. Peng, L.B. Zhang, X.Y. Ma, Z.B. Zhang, W. Li, Comparison between microwave and conventional thermal reactivations of spent activated carbon generated from vinyl acetate synthesis, Desalination 249 (1) (2009) 247–252. [15] B.H. Hameed, F.B.M. Daud, Adsorption studies of basic dye on activated carbon derived from agricultural waste: Hevea brasiliensis seed coat, Chem. Eng. J. 139 (2008) 48–55. [16] I.A.W. Tan, B.H. Hameed, A.L. Ahmad, Equilibrium and kinetic studies on basic dye adsorption by oil palm fiber activated carbon, Chem. Eng. J. 127 (2007) 111–119. [17] T.C. Chandra, M.M. Mirna, Y. Sudaryanto, S. Ismadji, Adsorption of basic dye onto activated carbon prepared from durian shell: studies of adsorption equilibrium and kinetics, Chem. Eng. J. 127 (2007) 121–129. [18] J. Yener, T. Kopac, G. Dogu, T. Dogu, Dynamic analysis of sorption of methylene blue dye on granular and powdered activated carbon, Chem. Eng. J. 144 (2008) 400–406.