Adsorptive removal of an acid dye by lignocellulosic waste biomass activated carbon: Equilibrium and kinetic studies

Chemosphere 82 (2011) 1367–1372

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Adsorptive removal of an acid dye by lignocellulosic waste biomass activated carbon: Equilibrium and kinetic studies S. Nethaji, A. Sivasamy ⇑ Chemical Engineering Area, Central Leather Research Institute (Council of Scientific & Industrial Research), Adyar, Chennai 600 020, India

a r t i c l e

i n f o

Article history: Received 23 July 2010 Received in revised form 26 November 2010 Accepted 26 November 2010 Available online 21 December 2010 Keywords: Amido Black Adsorption isotherms Kinetics Thermodynamics Activated carbon

a b s t r a c t Chemically prepared activated carbon material derived from palm flower was used as adsorbent for removal of Amido Black dye in aqueous solution. Batch adsorption studies were performed for the removal of Amido Black 10B (AB10B), a di-azo acid dye from aqueous solutions by varying the parameters like initial solution pH, adsorbent dosage, initial dye concentration and temperature with three different particle sizes such as 100 lm, 600 lm and 1000 lm. The zero point charge was pH 2.5 and the maximum adsorption occurred at the pH 2.3. Experimental data were analyzed by model equations such as Langmuir, Freundlich and Temkin isotherms and it was found that the Freundlich isotherm model best fitted the adsorption data and the Freundlich constants varied from (KF) 1.214, 1.077 and 0.884 for the three mesh sizes. Thermodynamic parameters such as DG, DH and DS were also calculated for the adsorption processes and found that the adsorption process is feasible and it was the endothermic reaction. Adsorption kinetics was determined using pseudo first-order, pseudo second-order rate equations and also Elovich model and intraparticle diffusion models. The results clearly showed that the adsorption of AB10B onto lignocellulosic waste biomass from palm flower (LCBPF) followed pseudo second-order model, and the pseudo second-order rate constants varied from 0.059 to 0.006 (g mg1 min) by varying initial adsorbate concentration from 25 mg L1 to 100 mg L1. Analysis of the adsorption data confirmed that the adsorption process not only followed intraparticle diffusion but also by the film diffusion mechanism. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction Evaluation of lignocellulosic waste biomass is getting increased attention all over the world as it is renewable, widely available, cheap, and environmental friendly. One of the effective uses of lignocellulosic waste biomass is the production of activated carbon and their applications in environmental remedial purposes (Karagoz et al., 2008). They include rice straw (Gong et al., 2006), sunflower seed hull (Thinakaran et al., 2008), corn cobs (Abdel et al., 2001), neem leaf (Sharma and Krishna, 2004), rubber tree waste (Hameed and Daaud, 2008), waste apricot (Onal, 2006), hazelnut shell (Dogan et al., 2009) and coconut shell (Babel and Kurniawan, 2004). Though palm flower is available in abundance and of no economical value, very less research works had been carried out to prepare the activated carbon from palm flower. The method of activation directly varies the nature of the carbon, as it can alter the physical and functional properties of the carbon surfaces. There are two basic processes to activate carbon materials; physical and chemical. Chemical activation can be accomplished in a single step by carrying out thermal decomposition of

⇑ Corresponding author. Fax: +91 44 24911589, +91 44 24912150. E-mail address: [email protected] (A. Sivasamy). 0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2010.11.080

raw material with chemical reagents. Chemical activation processes have been carried out with chemical reagents, i.e.; ZnCl2 (Yalcin and Sevinc, 2000), H3PO4 (Nakagawa et al., 2007), HCl (Alvarez et al., 2007), H2SO4 (Gercel et al., 2007), KOH (Guo and Lua, 2000), K2CO3 (Carvalho et al., 2004), NaOH (Lillo-Ro´denas et al., 2007), and Na2CO3 (Hayashi et al., 2000). Worldwide production of dyes especially from textile industry has increased in terms of volume, types and complexity. A total of 30% of world production of dyes may be lost during dyeing process. Dyes in wastewater are normally the result of inefficient dyeing processes, which cause as much as 10–15% unused dyestuff entering the watercourse directly. Dye effluent normally contain about 10–50 mg L1, but even at 1 mg L1 dyes are easily noticeable and thus may be perceived as being contaminated and unacceptable (Cheng et al., 2009). Thus the treatment of dye effluent has become a great challenge in modern days. Adsorption is found to be the efficient process for the treatment of effluents because of its low initial cost, ease of operation and the flexibility and the simplicity of the design. Amido Black 10B (AB10B), a di-azo, an anionic dye is mostly used in leather and textile industries and its application also extends to criminology for tracing the fingerprints of the suspect. It causes irritation of skin and eyes and the continuous intake of this dye may even be carcinogenic. Thus it becomes necessary to remove such dye from our day to day life. This study

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deals with the adsorption of Amido Black 10B (AB10B) in aqueous solution onto waste biomass activated carbon derived from lignocellulosic waste biomass from palm flower (LCBPF). 2. Materials and methods 2.1. Preparation of LCBPF Lignocellulosic waste biomass (palm flower) collected from the local agricultural fields from Pondicherry, India was cut into small pieces and washed with distilled water to remove sand and dust. Then the material was dried in sunlight for 48 h to remove moisture. The dried biomass was treated with concentrated H2SO4 (1:1 ratio) for 48 h. The carbonized biosorbent was then washed with distilled water until it became neutralized. Then the neutralized activated carbon is dried in a hot air over at 140 °C for 48 h. The dried palm flower activated carbon (LCBPF) was then sieved to three mesh sizes 100 lm, 600 lm and 1000 lm. 2.2. Characterization of LCBPF The prepared activated carbon was characterized for its zero point charge by solid addition technique (Balistrieri and Murray, 1981). The surface functionality of LCBPF was determined by Boehm method (Boehm, 1966). Surface morphology and semi quantitative elemental analysis of the samples were done in scanning electron microscope (Hitachi make and model S-3400 N) with the energy dispersive X-ray analysis attachment (Thermo Super Dry II). The BET surface area was measured by N2 adsorption isotherm at 77 K using QUADRASORB SI automated surface area and pore size analyzer (Quantachrome Corporation, USA). Brunauer– Emmett–Teller (BET) and Horvath–Kawazoe (HK) methods were used to calculate the surface area and the pore size distribution of LCBPF, respectively. 2.3. Preparation of dye solution Amido Black 10B (C4OH28N7NaO13S4) was purchased from M/s. s.d. fine chemicals limited, India and used without further purification. The AB10B stock solution (1000 mg L1) was prepared by dissolving accurately weighed amount of the dye in distilled water. All working solutions of the desired concentrations were prepared by diluting the stock solution with distilled water. H2SO4 and HCl were purchased from Merck (Specialties) Pvt. Ltd., Mumbai, India and NaOH received from Sisco Research Laboratories, India. All the chemicals used in this study were of analytical grade.

experimental procedures were also repeated for the adsorption at 293 K and 313 K. The amount of adsorbed AB10B at equilibrium, qe (mg g1) was calculated by Ayranci and Hoda (2005):

qe ¼

ðC 0  C e ÞV W

ð1Þ

where C0 and Ce (mg L1) are the liquid phase initial and equilibrium concentrations of the dye respectively. V is the volume of the solution (L), and W is the mass of dry adsorbent used (g). 2.6. Kinetic experiments The kinetics of dye adsorption onto LCBPF were carried out by taking measured amount of carbon dosage and varying the initial dye concentrations from 25 mg L1, to 100 mg L1 for all the particle sizes at 300 K. The amount of adsorption of dye was calculated at various time intervals. The amount of adsorption at time t was calculated by (Karagoz et al., 2008)

qt ¼

ðC 0  C t ÞV W

ð2Þ

where C0 and Ct (mg L1) are the liquid-phase concentrations of AB10B at initial and time t, respectively. V is the volume of the solution (L), and W is the mass of dry adsorbent used (g). 3. Results and discussion 3.1. Characterization of the adsorbent The surface area of LCBPF was found to be 9.57 m2 g1. Total pore volume is 0.073 cm3 g1 and the pore width is 246.56 nm. The surface acidity of LCBPF was determined by Boehm titration method and the total surface acidity is calculated as 0.593 meq g1 with the maximum composition of phenolic group (0.487 meq g1) with traces of lactonic (0.041 meq g1) and carboxylic (0.064 meq g1) groups. The surface morphology of the LCBPF has been studied by scanning electron microscopic technique. The pores of LCBPF are clearly seen from the SEM micrograph in Fig. 1 and the EDS analysis clearly suggested the presence of oxygen, sulphur and calcium, in which the composition

2.4. Analytical measurements Unknown concentration of dye was determined by finding out the absorbance at the characteristic wavelength using a double beam UV/visible spectrophotometer (Shimadzu UV-2102 PC). Standard calibration chart was prepared by measuring the absorbance of different dye concentrations at (kmax) 619 nm and unknown concentrations of dye before and after adsorption were computed form the calibration chart. The aqueous solutions pHs were measured by Digisun Electronics System (Digital pH meter model 2001). 2.5. Equilibrium experiments Adsorption equilibrium experiments were carried out by taking the required carbon dosage of different particle sizes by varying the initial dye concentrations from 0.001 mg L1 to 1000 mg L1 and agitating the solutions for 24 h at 100 rpm at 300 K. The same

Fig. 1. SEM micrograph of LCBPF.

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of oxygen and sulphur are the highest on the surface which leads to high surface reactivity of the carbon since these are the hetero atoms. 3.2. Effect of initial pH Adsorption of AB10B onto LCBPF was studied at different pH varying from 2.3 to 10.5 for all three particle sizes (100 lm, 600 lm and 1000 lm). Generally pH of the adsorption depends on the zero point charge of the adsorbent (pHzpc). The zero point charge was found to occur at the pH 2.5. The surface of the adsorbent will be negatively charged above pHzpc and positively charged below pHzpc. Since AB10B is an acid dye, it ionizes to form negative ions which have affinity towards the positive charge of the adsorbent surface at pH 2.3. The percentage adsorption was found to be 80% for 100 lm, 60–70% for 600 lm and 1000 lm. The further experiments were carried out at pH 2.3.

all the three isotherms at 293 K, 300 K and 313 K for all the three particle sizes are summarized in Table 1. The Langmuir isotherm is basically assumes homogenous surface energy distribution (Langmuir, 1916). It assumes that the adsorption rate is proportional to the number of free sites on the adsorbent and fluid phase concentration. The linear form of the Langmuir model is given as:

1 1 1 ¼ þ qe qm K L C e qm

where qe is the equilibrium dye concentration in the solid phase (mg g1), qm is the maximum monolayer dye concentration in the solid phase (mg g1), Ce is the equilibrium dye concentration in the aqueous phase (mg L1) and KL is the Langmuir equilibrium constant (mg L1). The essential characteristics of the Langmuir isotherm can be expressed by a dimensionless separation parameter, which is defined as:

3.3. Influence of adsorbent dosage

RL ¼ Effect of variation of mass of carbon was studied by increasing the carbon dosage from 0.001 g/10 mL to 0.5 g/10 mL. It was observed that, for 100 lm, 600 lm and 1000 lm, the % adsorption varied from 70 to 95, 65 to 80 and 55 to 70 respectively. As can be seen, the % adsorption increased with the increase in adsorbent dosage. This can be attributed to the increased sorbent surface area and availability of more adsorption sites when the carbon dosage is increased. 3.4. Effect of initial dye concentration at different temperatures The effect of initial dye concentration was studied by varying the dye concentrations from 1 mg L1 to 1000 mg L1 at different temperatures 293 K, 300 K and 313 K and the result suggested that the % adsorption decreased with the increase in initial dye concentration. Furthermore, adsorption increased with an increase in temperature, indicating that the process is endothermic.

1 1 þ K LC0

ð4Þ

RL indicates the nature of adsorption. Adsorption is favorable when the value of RL is between 0 and 1. The graph of 1/qe versus 1/Ce was plotted to determine qm and KL. From Table 1 it is clear that the value of qm and KL increases with decrease in particle size and increase in temperature. The value of RL also lies between 0.634 and 0.0005 which shows that the adsorption is favorable. Another adsorption isotherm commonly used for liquid phase adsorption on a surface having heterogeneous energy distribution is the Freundlich isotherm (Freundlich, 1906). It is derived by assuming a heterogeneous surface with a non-uniform distribution of heat of adsorption over the surface. This isotherm is suitable for a highly heterogeneous surface. The application of the Freundlich equation suggests that sorption energy exponentially decreases on completion of the sorptional centers of an adsorbent. The linear form of the Freundlich isotherm is expressed by the following equation:

3.5. Adsorption equilibrium

log qe ¼ log K F þ To optimize the design of the adsorption of the adsorbates, it is important to establish the most appropriate correlation for the equilibrium curves. Various isotherms such as Langmuir, Freundlich and Temkin isotherms have been used to discuss the equilibrium characteristics of the adsorption process. The constant parameters of the isotherm equations for this adsorption process were calculated by linear regression analysis. The constants of the adsorption parameters and the correlation coefficient (r2) for

ð3Þ

1 log C e n

ð5Þ

where KF (L g1) is the Freundlich constant and n (g L1) is the Freundlich exponent. Therefore, a plot of log qe versus log Ce as shown in Fig. 2 enables the constant and exponent n to be determined. From Table 1 it is evident that the value of KF and n increases with the increase in temperature and decrease in particle size. The Temkin equation suggests a linear decrease of sorption energy as the degree of completion of the sorptional centers of

Table 1 Analysis of Langmuir, Freundlich and Temkin adsorption isotherm parameters for three different mesh sizes. ISOTHERMS

100 lm 293 K

600 lm

1000 lm

300 K

313 K

293 K

300 K

313 K

293 K

300 K

313 K

Langmuir qm (mg g1) KL RL r2

3.68 0.576 0.634–0.0017 0.94806

3.834 1.377 0.420–0.0007 0.90203

4.033 2.208 0.311–0.004 0.88581

2.731 0.432 0.353–0.0005 0.98835

3.099 1.248 0.444–0.0008 0.91564

3.415 1.578 0.387–0.0006 0.90465

2.423 0.316 0.496–0.0009 0.99431

2.639 1.213 0.344–0.0005 0.98652

2.861 1.446 0.364–0.0005 0.98944

Freundlich KF (L g1) N r2

0.949 1.725 0.99854

1.214 1.846 0.99506

1.386 1.905 0.99117

0.8966 1.733 0.99877

1.077 1.807 0.99623

1.211 1.879 0.99206

0.7736 1.6488 0.99904

0.884 1.718 0.9994

0.95 1.728 0.99926

10.381 0.755 0.89629

9.974 1.154 0.87615

9.929 1.488 0.86366

7.666 2.243 0.83909

9.903 0.947 0.87924

6.826 1.679 0.88306

8.053 1.626 0.85363

7.760 2.156 0.83561

7.940 2.359 0.83885

Temkin B1 KT (L mg1) r2

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relationship, from which qe and k2 can be determined from the slope and intercept of the plot, and there is no need to know any parameter beforehand. Although the Elovich equation was firstly used in the kinetics of adsorption of gases on solids, it has been successfully applied for the adsorption of solutes from a liquid solution. The linear form of the Elovich equation is given as follows (Bulut and Ozacar, 2008):

2.0

1.0 0.5

qt ¼

0.0

100 µm 600 µm 1000 µm

-0.5 -1.0 -2.0 -1.5 -1.0 -0.5 0.0

0.5

1.0

1.5

2.0

2.5

3.0

log ce (mg/L) Fig. 2. Freundlich isotherm (ads. dosage = 0.1 g/10 mL; pH 2.3; T = 300 K; t = 24 h; agitation = 100 rpm).

an adsorbent is increased. The heat of adsorption of all the dye molecules in the layer would decrease linearly with coverage due to adsorbent–adsorbate interactions. The adsorption is characterized by a uniform distribution of binding energies, up to some maximum binding energy. The linear form of the Temkin isotherm is as follows:

qe ¼ B1 ln K T þ B1 ln C e

ð6Þ

where B1 = RT/b. KT is the equilibrium binding constant (L mg1) corresponding to the maximum binding energy and constant B1 is related to the heat of adsorption. A plot of qe versus ln Ce enables the determination of the isotherm constant B1 and KT from the slope and the intercept, respectively. The constants B1 and KT are tabulated in Table 1. From Table 1, it can be seen that the r2 values for Freundlich isotherm (>0.99) lies closer to unity when compared with the r2 values of Langmuir and Temkin isotherm models. Thus the adsorption of AB10B onto LCBPF follows Freundlich isotherm and hence the surface of LCBPF is heterogeneous. 3.6. Kinetic studies Four kinetic models pseudo first-order, pseudo second-order, Elovich and intraparticle diffusion model were considered to investigate the adsorption processes of AB10B onto LCBPF. Lagergren proposed a method for adsorption analysis which is the pseudofirst-order kinetic equation. The linear form of this equation is (Santhy and Selvapathy, 2006):

lnðqe  qt Þ ¼ ln qe  k1 t

ð7Þ

where qe (mg g1) and qt (mg g1) are the amounts of adsorbed adsorbate at equilibrium and at time t, respectively, and k1 (min1) is the rate constant of pseudo first-order adsorption. The sorption kinetics may be described by a pseudo second-order model. The linear form of this equation is (Bulut and Ozacar, 2008):

1 1 1 ¼ þ t qt k2 q2e qe

ð8Þ

where k2 (g mg1 min) is the equilibrium rate constant of pseudo second-order adsorption. Eq. (8) does not have the problem of assigning an effective qe. If the pseudo second-order kinetic equation is applicable, the plot of t/qt against t should give a linear

1 1 lnðabÞ þ ln t b b

ð9Þ

where a (mg g1 min) is the initial sorption rate, and the parameter b (g mg1) is related to the extent of surface coverage and activation energy for chemisorptions. In general, the mechanism for dye removal by adsorption on a sorbent material may be assumed to involve the following four steps (Cheung et al., 2007): (i) migration of dye from bulk of the solution to the surface of the adsorbent (bulk diffusion); (ii) diffusion of dye through the boundary layer to the surface of the adsorbent (film diffusion); (iii) transport of the dye from the surface to the interior pores of the particle (intraparticle diffusion or pore diffusion); (iv) adsorption of dye at an active site on the surface of material (chemical reaction via ion-exchange, complexation and/ or chelation). The dye sorption is governed usually by either the liquid phase mass transport rate or the intraparticle mass transport rate. Hence diffusive mass transfer is incorporated into the adsorption process. In diffusion studies, the rate can be expressed in terms of the square root time. The mathematical dependence of qt versus t1/2 is obtained if the process is considered to be influenced by diffusion in the particles and convective diffusion in the solution. According to the intraparticle diffusion model proposed by Weber and Morris, the root time dependence may be expressed by the following equation: 1

qt ¼ ki t 2 þ C

ð10Þ

where qt is the amount of solute on the surface of the sorbent at time t (mg g1), ki is the intraparticle diffusion rate constant (mg g1 min1/2) and C is the intercept (mg g1) and it gives an idea of the thickness of the boundary layer. The ki values are found from the slopes of qt versus t1/2 plots. If the intraparticle diffusion is involved in the adsorption process, then the plot of the square root of time versus the uptake (qt) would result in a linear relationship, and the intraparticle diffusion would be the controlling step if this line passed through the origin. When the plots do not pass through

20 18 16

t/qt (min.mg/g)

log qe (mg/g)

1.5

14 12 10

25 mg/L 50 mg/L 75 mg/L 100 mg/L

8 6 4 2 0

20

40

60

80

100

120

140

160

Time (min) Fig. 3. Pseudo second-order model for 100 lm (ads. dosage = 1.5 g/150 mL; pH 2.3; T = 300 K; agitation = 150 rpm).

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100 lm

600 lm 1

Pseudo first-order k1 (1 min1) qe (mg g1) r2

1

1

25 mg L

50 mg L

0.287 10.129 0.9062

0.170 15.845 0.96629

0.109 15.091 0.95009

0.013 5.212 0.99209

Pseudo second-order k2 (g mg1 min) 0.059 qe (mg g1) 2.55 r2 0.99504

75 mg L

1

100 mg L

25 mg L

0.062 10.781 0.98273

0.009 6.923 0.99594

0.689 0.803 0.9792 0.524 0.481

1000 lm 1

1

1

100 mg L

1

25 mg L1 50 mg L1 75 mg L1 100 mg L1

50 mg L

75 mg L

0.064 1.885 0.99874

0.066 4.548 0.99291

0.035 4.675 0.96961

0.025 4.601 0.98514

0.058 1.724 0.99586

0.041 3.238 0.99875

0.027 6.089 0.95461

0.021 5.564 0.96773

0.006 8.642 0.9965

0.047 2.397 0.99922

0.016 4.484 0.99747

0.011 6.157 0.99943

0.008 7.821 0.99914

0.05 2.21 0.99906

0.018 4.163 0.99916

0.00634 6.054 0.99985

0.0063 7.593 0.99976

0.899 0.633 0.97685

1.008 0.521 0.9707

0.713 2.152 0.97601

0.713 1.033 0.96985

1.175 0.854 0.96357

1.238 0.668 0.95769

0.696 2.452 0.96136

0.807 1.258 0.96151

0.557 0.824 0.99416

0.931 0.693 0.97792

0.557 1.153

0.587 1.713

0.163 0.805

0.315 1.092

0.306 2.115

0.363 2.609

0.123 0.855

0.208 1.446

0.310 1.263

0.336 2.282

Elovich equation

a

0.752 1.718 0.96574

b r2

Intraparticle diffusion Ki (mg g1 min1/2) 0.279 C 0.584

Table 3 Thermodynamic properties of adsorption. T (K)

100 lm

DG (kJ mol1) 293 300 313

1.342 0.795 2.061

600 lm

DH (kJ mol1) 48.194

DS (J mol1 K)

DG (kJ mol1)

161.04

2.043 0.551 1.186

the origin, this is indicative of some degree of boundary layer control and these further shows that the intraparticle diffusion is not the only rate controlling step, but also other processes may control the rate of adsorption. The plot for pseudo second-order model was shown in Fig. 3. The rate constants and the correlation coefficients for all the four models for the three particle sizes are tabulated in Table 2. The experimental data deviated slightly more from the linearity for the pseudo first-order model when compared to the pseudo second-order model. Also when the calculated qe value is compared to that of the experimental qe value, for pseudo first-order model it varied a lot. But in case of pseudo second-order model both those values almost coincided. Thus the observed adsorption process follows the pseudo second-order model. While we consider the Elovich equation, the correlation coefficient is comparatively low when compared to the first two discussed models and hence the observed adsorption process does not follow the Elovich equation. A plot of qt versus t1/2 should be a straight line if intraparticle diffusion is involved in the adsorption process and if this line passes through the origin the intraparticle diffusion is the rate controlling step. But the plot was identified as an initial curve portion followed by a flat portion. During the initial curve portion, the adsorption process followed boundary layer diffusion and the later flat portion is the indication of the intraparticle diffusion. This indicates that there was also a presence of some boundary layer diffusion and thus intraparticle diffusion was not the sole process that controlled the studied adsorption process (Batzias and Sidiras, 2007). From Table 2, it can be understood that the thickness of the boundary layer increased with increase in concentration and with the increase in particle size. 3.7. Thermodynamics of adsorption Adsorption of thermodynamic parameters includes Gibbs free energy change (DG), enthalpy change (DH) and entropy change

1000 lm

DH (kJ mol1) 44.989

DS (J mol1 K)

DG (kJ mol1)

DH (kJ mol1)

DS (J mol1 K)

148.46

2.806 0.481 0.957

52.129

120.91

(DS) were calculated from the following equations (Tahir and Rauf, 2006):

DG ¼ RT ln K L ln K L ¼

DS DH  R RT

ð11Þ ð12Þ

where R is the gas constant, T is temperature in K and KL is the Langmuir constant. The values of DH and DS were determined from the slope and intercept of the plot of ln KL versus 1/T. Thermodynamic parameters obtained are shown in Table 3. From Table 3, the values of DG were found to be negative at 303 K and 313 K indicating that the adsorption is spontaneous process. The positive values of DH indicate the endothermic nature of the process. The values of DS are positive, reflecting the affinity of the adsorbent material towards AB10B. 4. Conclusion The adsorption of AB10B onto LCBPF was proved to be an efficient process. The adsorption of AB10B was best below the zero point charge and the % adsorption increased with the increase in the carbon dosage. When the initial concentration was increased, the % adsorption gradually decreased and the equilibrium data were tested with Langmuir, Freundlich and Temkin isotherm models and found that the Freundlich isotherm fitted the data well. The kinetic study was made for all the three particle sizes with different initial dye concentrations and the data were interpreted with pseudo first-order, pseudo second-order, Elovich and intraparticle diffusion models and found that the adsorption process followed the pseudo second-order model. Thermodynamic study revealed that the process is spontaneous and endothermic. When the particle size of the adsorbents increased, the surface area available for the adsorbate decreased and since the % adsorption is directly proportional to the surface area of the adsorbent, it was observed that

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there was a decrease in % adsorption with increasing particle size of the adsorbents. Overall, it is concluded that the adsorption process is better with smaller adsorbent particle size and higher temperature.

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