Preparation of activated carbon from agricultural wastes (almond shell and orange peel) for adsorption of 2-pic from aqueous solution

Journal of Industrial and Engineering Chemistry 20 (2014) 1892–1900

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Preparation of activated carbon from agricultural wastes (almond shell and orange peel) for adsorption of 2-pic from aqueous solution Saeedeh Hashemian *, Khatereh Salari, Zahra Atashi Yazdi Islamic Azad University, Yazd Brunch, Chemistry Department, Yazd, Iran

A R T I C L E I N F O

A B S T R A C T

Article history: Received 4 April 2013 Accepted 9 September 2013 Available online 16 September 2013

Activated carbon from agricultural waste almond shells (CAS) and orange peels (COP) was prepared. CAS and COP were characterized by FTIR, XRD and SEM. Adsorption of 2-pic by CAS and COP has been investigated. The kinetic of 2-pic was fitted well the pseudo-second-order kinetic model and rate constants of adsorption of 6.66  104 and 2.51  105 (g mg1 min1) for CAS and COP, respectively. Results showed that Langmuir isotherm model is better fitted for adsorption data quite reasonably than Freundlich model (R2 > 97). The maximum adsorption capacity from Langmuir equation was 166.7 mg g1 and 288.57 mg g1 for COP and CAS, respectively. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Keywords: Activated carbon Adsorption Almond shell 2-Picoline Orange peel

1. Introduction Adsorption is commonly considered as an effective method for quickly lowering the concentration of pollutants such as organic compounds, metal ions and dissolved dyes in an effluent. Sorption is relatively useful and economical for removal of organic pollutants [1–7]. Adsorption method is regarded as one of the most competitive methods, because it is a simple method and does not need a high operation temperature [8–10]. Several materials have been tested to adsorb organic compounds and dyes from water solutions [11–18]. Activated carbon is the most commonly used adsorbent, because it has great capacity for adsorbing diverse organic compounds such as dyes, heavy metals, pharmaceutical and surfactants [19]. However, the price of activated carbon is relatively high. Due to its relatively high cost, attempts have been made to utilize low cost, naturally occurring sorbents to remove trace contaminants from wastewater. Many researchers have worked on production of activated carbon from renewable resources, using low cost methods and materials and emphasis also on to decontaminated water in an environmental friendly manner. Agricultural and industrial waste materials were used as activated carbons source by different researchers [20–24]. The agricultural and forestry waste products represent unused resources and also they are widely available and

* Corresponding author. Tel.: +98 351 8117572; fax: +98 351 7266560. E-mail address: [email protected] (S. Hashemian).

environmentally friendly so they have a great potential to be used as adsorbents. Almond is one of the important agricultural materials. The shells of almond are waste materials and generally discarded as a waste. It can be collected on community basis for reuse. Almond shells are abundant, inexpensive and readily available lignocellulosic material. Almond shells can be used as sorbent. The cell walls of almond shell consist of cellulose, silica, lignin and carbohydrates which have hydroxyl groups in their structures [25–27]. Orange, as a kind of biological resources is available in large quantities in many parts of the world. Dried orange peel was previously investigated to adsorb acid violet 17, and Direct Red 23 and 80 [28,29]. The moisture content of the almond shell and orange peel are 25% and 38.5%, respectively. The ash content of almond shell and orange peel are 16.5% and 22%, respectively [25,28]. 2-Pic is a colorless liquid and has an unpleasant odor similar to pyridine. 2-Picoline is a derivative of pyridine. It is also used as a solvent and a raw material for various chemicals used in the manufacture of various polymers, textiles, fuels, agrochemicals and colorants. It is used in a variety of agrochemicals and pharmaceuticals. 2-Pic is considered to be a hazardous chemical. Various industrial units manufacturing pyridine and its derivatives, pharmaceutical units, etc. discharge 2-pic-bearing wastewaters. Different treatment techniques are suggested for the treatment of 2-pic-bearing wastewaters, which include concentration followed by biodegradation and adsorption. Adsorption can be a preferred treatment technique, provided that the adsorption process is cost-effective [7].

1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.09.009

S. Hashemian et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1892–1900

In this paper is reported the preparation of carbon almond shell and carbon orange peel. The prepared carbons were used for adsorption of 2-picoline for aqueous solutions. Effect of adsorption parameters such as contact time, pH, adsorbent concentration and initial concentration of pollutant (2-picoline) was studied. 2. Experimental 2.1. Adsorbent preparation Almond shells (AS) were collected from a local center of preparation of shell-removed almond (IRAN-Yazd). Orange peels were collected from a local fruit field in the south of IRAN. Almond shells and orange peels were cut into small pieces and, after drying and crushing, washed thoroughly with doubledistilled water to remove adhering dirt. Then, they were dried in oven at 100 8C for 24 h and were sieved. After sieving the particle size of materials was remained between 1 and 5 mm. Steel tube was filled with the shells powder and placed into the oven. The N2 gas was passed through the tube in order to prevent the burning of the shells. Almond shells and orange peels were carbonized at different temperatures such as 200, 300, 500, 700, 900, and 1200 8C under nitrogen atmosphere in an oven for 1 h. They were activated by carbon dioxide gas for 1 h. Adsorbent obtained in this series is expression as activated carbon almond shell (CAS) and activated carbon orange peel (COP). 2.2. Adsorbate preparation All chemicals were analytical grade reagents and were purchased from Merck. 2 picoline (2-pic) as a pollutant model was used. A stock solution of 1000 mg L1 in double distillated water was prepared. It subsequently whenever necessary, diluted. 2.3. Adsorption experiments In order to study the effect of different parameters like; the contact time, pH and sorbent dosage on the sorption capacity of 2pic, various experiments have been carried out by agitation of known amount of COP and CAS (0.1 g) in 50 mL of 2-pic solution with an initial concentration 100 mg L1 on rotary shaker at a constant speed of 150 rpm at room temperature (25 8C). Samples were withdrawn at appropriate time intervals and centrifuged at 1000 rpm for 10 min and the absorbance of the 2-pic was measured using a UV–Vis spectrophotometer. The effect of pH was studied by adjusting the pH of the solutions in the range of 2– 12 with 0.1 M NaOH or HCl solutions. IR measurements were performed by FTIR tensor-27 of Burker Co., using the KBr pellet. UV-Vis spectrophotometer 160 A Shimadzu was used for determination of concentration of 2-pic. All pH measurements were carried out with an ISTEK-720P pH meter. Scanning electron microscopy was performed using a Philips SEM model XL30 electron microscope. The powder X-ray diffraction studies were made on Philips PW3719 X-ray diffractometer by using Cu-Ka radiation of wave length 1.54060 A˚. The specific surface area was measured by N2 adsorption–desorption isotherm and was obtained with an ASAP-2010 instrument (Micromeritics). The percent removal of 2-pic by the hereby adsorbent is given by:

%RemovalðpicÞ ¼

ðC 0  C e Þ  100 C0

1893

where C0, Ce is denoted the initial and equilibrium concentration (mg L1) of 2-pic respectively. The amount of 2-pic adsorbed (qe) was determined by using the following equation:

qe ¼

ðC 0  C e ÞV m

V is the volume of the solutions (mL) and m is the amount (mg) of adsorbent. 3. Results and discussion 3.1. Characterization of samples (CAS and COP) FTIR spectra of almond shell (AS), CAS and activated carbon (Merck) is shown in Fig. 1. In AS spectrum (Fig. 1A) the broad peaks at around 3367 cm1 correspond to O–H stretching vibrations due to inter and inter-molecular hydrogen banding of polymeric compounds, such as alcohols, phenols and carboxylic acids, as in pectin, cellulose groups on the adsorbent surface. The peaks at 2928 cm1 are attributed to the symmetric and asymmetric C–H stretching vibration of aliphatic acids. The peak observed at 1730 cm1 is the stretching vibration of bond due to non-ionic carboxyl groups (–COOH, –COOCH3), and may be assigned to carboxylic acids or their esters. Broad peak at 1066 cm1 may be due to stretching vibration of C–OH of alcoholic groups and carboxylic acids. The peaks around 1440 cm1 are due to the symmetric bending of CH3 [25]. Fig. 1B shows the prepared activated carbon from almond shell. Fig. 1C shows the activated carbon from Merck. Comparing the Fig. 1B and C confirmed the preparation of activated carbon from almond shell (CAS). FTIR spectra of orange peel (OP), COP and activated carbon (Merck) are shown in Fig. 2. The broad and intense adsorption peaks at around 3413 cm1 correspond to O–H stretching vibrations. The peaks at 2824 cm1 are attributed to the symmetric and asymmetric C–H stretching vibration of aliphatic acids. The peak observed at 1751 cm1 is the stretching vibration of bond carboxyl groups and may be assigned to carboxylic acids or their esters. The peak observed at 1618 cm1 is due to C5 5C stretching that can be attributed to the aromatic C–C bond. The peak observed at 1077 cm1 is attributed to C–H in plane. Fig. 2B shows the prepared activated carbon from OP. Fig. 2C shows the activated carbon from Merck. Comparing the Fig. 2B and C confirmed the preparation of activated carbon from orange peel (COP). SEM image of CAS before and after adsorption of 2-pic are shown in Fig. 3. SEM image of COP before and after adsorption of 2pic are also shown in Fig. 4. The SEM images obviously are shown the porous nature of prepared carbons from ASs and Ops. The COP

Fig. 1. FTIR spectra of (A) AS, (B) CAS and (C) activated carbon.

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S. Hashemian et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1892–1900

stacked nearly parallel and equidistant, with each layer having a random orientation. The value of d002 is comparable with those reported by Kumar et al. on activated carbon cloth [31]. 3.2. Effect of carbonisation temperature

Fig. 2. FTIR spectra of (A) OP, (B) COP and (C) activated carbon.

has cylindrical porous shape and homogeneous distribution. After adsorption of 2-pic, a significant change is observed in structure of the carbons. The SEM images of CAS and COP (Figs. 3 and 4) are shown the formation of homogeneous pores structure. However, this is not the case after adsorption. After adsorption, a significant change is observed in structure of the peels. The peels appear to have a rough surface with crater-like pores because they are partially covered by 2-pic molecules. X-ray diffraction patterns for activated carbon (Merck), CAS and COP are shown in Fig. 5. The positions of the peaks due to d002 and d100 reflections are attributed to 2u = 25.18 and 458, respectively [30]. These diffraction peaks are evidence that the samples have a turbostratic structure. This turbostratic model assumes that the samples is made of graphite-like microcrystallites, bounded by cross linking network, consisting of several graphite-like layers,

Orange peel and almond shell samples were carbonized at different temperatures (200, 300, 500, 700, 900, and 1200 8C) under nitrogen atmosphere in an oven for 1 h to produce COP and CAS, respectively. Fig. 6 indicates the effect of carbonisation temperature of shell on the adsorption of 2-pic by CAS. It was shown that the 2-pic removal increased with increasing temperature up to 700 8C, and then decreased at higher temperatures. In the adsorption experiments carried out by CAS prepared at 300 8C, the 2-pic removal was 27.6%. At 700 8C, the 2-pic removal by CAS increased up to 90%. The best results have been obtained with CAS by adding 10% H2SO4 at the carbonisation temperature of 700 8C. Surface area of ACs is increased from carbonization temperature 200–700 8C, but it is decreased from carbonization temperature 700–1200 8C. Therefore the adsorption capacity of CAS increased to carbonization temperature of 700 8C. The adsorption capacity of CAS decreases for temperature 900–1200 8C (Table 1). In addition, a maximum porous structure develops in the material at temperature of 700 8C, and creates a larger internal surface area. Therefore the optimum carbonization temperature of 700 8C was selected. A similar result was obtained for COP. 3.3. Effect of contact time Contact time is inevitably a fundamental parameter in all transfer phenomena such as adsorption. The effect of contact time

Fig. 3. SEM image of AAS (A, B) before adsorption and (C, D) after adsorption of 2-pic.

S. Hashemian et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1892–1900

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Fig. 4. SEM image of COP (A, B) before adsorption and (C, D) after adsorption of 2-pic.

than COP. FTIR spectra results also show the 2pic adsorbed onto CAS and COP. Appearance the bands at 1500–1700 cm1 and 3400– 3500 cm1 confirm the adsorption of 2-pic onto CAS and COP after 120 min of contact time. 3.4. Effect of pH Point zero charge (PZC) is a very useful parameter in sorption studies that allows one to hypothesise on the ionization of functional groups and their interactions with adsorbates. The pHzpc (pH of zero net proton charge) is defined here as the pH value at which the net surface charge is equal to zero. The point of zero

% Adsorption

on the adsorption of 2-pic by CAS and COP are shown in Fig. 7. The adsorption of 2-pic increased rapidly with time up to 120 min. It can be seen from Fig. 7, the amount of the absorbed 2-pic onto CAS and COP initially, increase with time and at some point of time, it reaches a constant value beyond which no more is removed from solution. The amount of 2-pic adsorbed at the equilibrium time reflects the maximum adsorption capacity of the adsorbent under those operating conditions. It is evident that the CAS and COP are efficient in absorbing equilibrium gradually. It is obviously the rate of adsorption and adsorption capacity of 2-pic onto CAS is more

100 90 80 70 60 50 40 30 20 10 0 0

Fig. 5. XRD patterns of (A) Activated carbon, (B) COP and (C) CAS.

30

60

a

b

c

d

e

f

90 120 Time (m min)

150

180

Fig. 6. Effect of carbonisation temperature for CAS on adsorption of 2-pic ((a) 200, (b) 300, (c) 500, (d) 700, (e) 900 and (f) 1200 8C).

S. Hashemian et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1892–1900

1896 Table 1 Characterization of COP and CAS.

700

Carbonization temperature (8C)

Mean pore diameter (nm)

Total pore volume (cm3 g?1)

Surface area (m2 g?1)

CAS

500 700 1200

8–12 10 15–25

19.5 16.92 15.5

322 385 342

500 700 1200

7–14 10 12–14

14.5 15 13.5

225.6 248 240

COP

600 500 qe

Sample

400 300 COP

200

CAS

100 charge of COP and CAS were measured. Both of COP and CAS showed the point of zero charge between 4.2 and 5.0. It is well known that adsorption process depends on pH of aqueous solution. The sorption capacity of the CAS and COP was studied by varying the pH in the range of 2–12. The effect of solution pH on the adsorption of 2-pic by CAS and COP was shown in Fig. 8. 2-pic behaves like a base (pKa 5.96). The solution pH affects the surface charge of the adsorbents and, therefore the adsorption proceeds through dissociation of functional groups, viz. surface oxygen complexes of acid character such as carboxyl and phenolic groups or basic character such as pyrones, on the active sites of adsorbent. At low pH (pH < 4), the 2-pic is converted to 2picH. At pH < 5.0, surface of sorbent may get positively charged due to the adsorption of H+. This could be explained by the fact that at low pH, more protons will be available to protonate hydroxyl groups, reducing the number of binding sites for the adsorption (electrostatic repulsive). At higher pH (pH > 5), p–p dispersion interactions also take place and electrostatic interactions become important and 2-pic molecules are sorbed onto the adsorbents [32]. When solution pH increases, high –OH ions accumulate on the adsorbent surface. Therefore, electrostatic interaction between negatively charge adsorbent surface and 2-pic molecule increases. Hence, pH > 5 is more favorable for adsorption of 2-pic by CAS and COP. 3.5. Effect of initial concentration of 2-pic The effect of initial 2-pic concentration on the adsorption process was investigated at constant concentration of CAS and COP and different initial 2-pic concentrations (10–60 mg L1). High percentage removal of 2-pic was observed for lower concentration of 2-pic for both adsorbents. Fig. 9 indicated the effect of initial concentration of 2-pic on CAS and COP. The decrease in qe, with increasing of C0 is attributed to the increase in the mass transfer driving force.

0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 pH Fig. 8. Effect of pH on the adsorption of 2-pic by CAS and COP (0.1 g sorbent, 120 min contact time and 50 mL of 2-pic100 mg L1).

3.6. Adsorbent dosage effect Adsorbent dosage is one of the important parameter of adsorption. It can be seen that the adsorption increases with the increase in the amount of the adsorbents. This can be explained by a greater availability of the exchangeable sites or surface area at higher amount of the adsorbent. The adsorption percentage increases from the doses of 0.1–1 g/50 ml rapidly. But no significant adsorption was found beyond 1.0 g/50 ml. Table 2 is shown the effect of adsorbent dosage on the adsorption of 2-pic. The increase in adsorption capacity is probably because of the creation of some new active sites on the surface of adsorption [24]. 3.7. Kinetic of adsorption The kinetic data of the adsorption of 2-pic onto CAS and COP was evaluated using pseudo-first order and pseudo-second-order kinetic models. The pseudo-first order model assumes that the rate of change of solute uptake with time is directly proportional to difference in saturation concentration and amount of solid uptake with time [33]. lnðqe  qt Þ ¼ ln qe  k1 t

where qe and qt are the amounts of dye adsorbed per unite mass of the adsorbent (mg g1) at equilibrium and time t, respectively and k1 is the rate constant of adsorption (min1). When ln (qe  qt) was plotted against time, a straight line should be obtained with a slope of k1, if the first order kinetics is valid.

600

qe(mgg¯¹)

500 qe(mg g¯¹)

400 300 200

COP

CAS

100 0 0

50

100 150 200 250 300 350 400 t(min)

Fig. 7. Effect of contact time on the removal of 2-pic by CAS and COP (0.1 g sorbent, 50 mL of 2-pic100 mg L1).

(1)

500 450 400 350 300 250 200 150 100 50 0

COP 0

10

20

CAS

30 40 C(mg L¯1)

50

60

Fig. 9. Effect of initial concentration of 2-pic by CAS and COP (0.1 g sorbent, 100 min contact time and 50 mL of 2-pic100 mg L1).

S. Hashemian et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1892–1900 Table 2 Effect of adsorbent dosage on the adsorption of 2-pic. Adsorbent dosage (g/50 mL)

Table 3 Kinetics parameters for the removal of 2-pic onto CAS and COP.

Percentage of adsorption CAS

First order

Sample

R

COP

46 51 65 77 84 91 91.3 91.5 92 92.3 92.7 93 93

0.05 0.1 0.3 0.5 0.7 1.0 1.5 2.0 2.5 3.0 3.5 4.0 5.0

55 59 64 78 83 94 94.2 94.7 95 95.5 95.7 95.9 96

The pseudo-second order model as developed by Ho and McKay [34] has the following form: t t 1 ¼ þ qt qe ðk2 q2e Þ

lnqe - qt]

ln[qe- qt]

0.2 0 80 100 120

t(min)

CAS b

60

7.0  10 6.0  103

R2

K2 (g mg1 min1)

0.988 0.991

6.66  104 2.51  105

1 ln C e n

(3)

2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0

0.8

40

3

where, kF(L g1) and n are Freundlich constants related to adsorption capacity and adsorption intensity, respectively (Fig. 11). The intercept KF obtained from the plot of log qe versus ln Ce is roughly a measure of the sorption capacity and the slope (1/ n) of the sorption intensity (Table 4). It was indicated by that magnitude of the term (1/n) gives an indication of the favorability and capacity of the adsorbent/adsorbate systems [35]. The Langmuir isotherm assumes a surface with homogeneous binding sites, equivalent sorption energies, and no interaction

1

20

)

The Freundlich and Langmuir models are the most frequently used models to describe the experimental data of adsorption isotherms. Here, both models were used to investigate how 2-pic interacts with adsorbents. The Freundlich isotherm is an empirical equation based on an exponential distribution of adsorption sites and energies. It is represented as:

a 1.2

0.4

K1 (s

3.8. Adsorption isotherms

ln qe ¼ ln kF þ

0.6

Second order 1

kinetics of 2-pic fitted well the pseudo-second-order kinetic model.

1

where qe and qt represent the amount of dye adsorbed (mg g ) at equilibrium and at any time. k2 in the rate constant of the pseudosecond order equation (g mg1 min1). A plot of t/q versus time (t) would yield a line with a slope of 1/qe and an intercept of 1/(k2qe2), if the second order model is a suitable expression. The plot between ln(qe  qt) versus time t shows the pseudo first order model and the plot of t/q versus time t shows the pseudo second order model (Fig. 10a, b), respectively. The kinetic model with a higher correlation coefficient R2 was selected as the most suitable one (Table 3). The results show that adsorption

2

0.870 0.923

CAS COP

(2)

0

1897

0

20

40

60 80 100 120 t(min)

0

20 40 60 80 100 120 t(min)

COP 0.5

0.35 0.3

0.4

0.25 t/q

t/q

0.2 0.15

0.3 0.2

0.1 0.1

0.05 0 0

CAS

20

40

60 80 100 120 t(min)

0

COP

Fig. 10. a. Pseudo-first-order kinetic model for adsorption of 2-pic onto CAS and COP. b. Pseudo-second-order kinetic model for adsorption of 2-pic onto CAS and COP.

S. Hashemian et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1892–1900

1898

6.6

8

6.4 6.2 Lnqe

Lnqe

6 4

6 5.8

2

5.6 5.4

0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 LnCe CAS

0

0.2

0.4

0.6

0.8

1

1.2

LnCe

COP

Fig. 11. Freudlich isotherm for adsorption of 2-pic using CAS and COP.

Table 4 Langmuir and Freundlich isotherm parameters for adsorption of 2-pic onto CAS and COP. Sample

CAS COP

Freundlich

Langmuir

KF

n

R2

qmax (mg g1)

KL (L mg1)

R2

4.3 2.07

0.14 0.157

0.935 0.940

166.7 288.5

42.3 24.4

0.990 0.973

between adsorbed species. Its mathematical form is written as:

and these were determined using the following equations [7]:

Ce 1 Ce þ ¼ qe ðK L qmax Þ qmax

DG ¼ RT ln K C

(4)

where, qmax and kL represent the maximum adsorption capacity for the solid phase loading and the energy constant related to the heat of adsorption respectively (Fig. 12). A plot of 1/qe versus Ce gives KL and qmax if the isotherm follows the Langmuir equation. Based on the correlation coefficient (R2) shown in Table 3, the adsorption isotherms of CAS and COP can be slightly better described by the Langmuir equation. The fit of the data to the Freundlich equation may indicate the heterogeneity of the adsorbent surface. The Langmuir type isotherm hint towards surface homogeneity of the adsorbent [36]. This leads to the conclusion that the surfaces of CAS and COP is made up of small homogeneous adsorption patches. 3.9. Thermodynamic studies

0.0035 0.003 0.0025 0.002 0.0015 0.001 0.0005 0

where, DG8 is the standard free energy change, T the absolute temperature, R the universal gas constant (8.314 J mol1 K1) and KC the equilibrium constant. The apparent equilibrium constant of the sorption, KC, is obtained from: KC ¼

CA CS

ln K C ¼ 

Ce

D G RT

¼

DH RT

þ

DS

(7)

R

DH8 and DS8 were calculated the slope and intercept of van’t Hoff plots of ln KC versus 1/T. The results of thermodynamic parameters of 2-pic adsorption onto CAS and COP are given in Table 5.

0.009 0.008 0.007 0.006 0.005 0.004 0.003 0.002 0.001 0 0

0 0.40.81.21.6 2 2.42.83.2

CAS

(6)

where KC is the equilibrium constant, CA is the amount of CR adsorbed on the adsorbent of solution at equilibrium (mg L1); CS is the equilibrium concentration of CR in the solution (mg L1). KC values calculated at different temperature to allow the determination of the thermodynamic equilibrium constant (KC) [7]. The free energy changes are also calculated by using the following equations:

1/qe

1/qe

The amount of 2-pic adsorbed at equilibrium at different temperatures 20–50 8C, have been examined to obtain thermodynamic parameters for the adsorption system. The thermodynamic parameters, change in the standard free energy (DG8), enthalpy (DH8) and entropy (DS8) associated with the adsorption process

(5)

1

2

3 Ce

COP

Fig. 12. Langmuir isotherm for adsorption of 2-pic using CAS and COP.

4

5

6

S. Hashemian et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1892–1900

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Table 5 Thermodynamic parameters for adsorption of 2-pic by adsorption onto CAS and COP. S8 (J mol1 K1)

H8 (KJ mol1)

G8 (KJ mol1)

Kc

T (K)

Sorbent

25.40

6.4

2.18 3.28 4.15 4.95

2.45 3.68 4.92 6.5

293 303 313 318

CAS

14.5

3.85

3.15 3.58 4.84 5.22

3.65 4.15 6.43 7.2

293 303 313 318

COP

Table 6 Comparison of maximum adsorption capacities of CAS and COP with different sorbents. Sorbent

qmax (mg g1)

References

Sorbent

qmax (mg g1)

References

Hazelnut shell Sawdust Walnut shell Almond shell carbon Palm pressed fibers Rice straw Carbon orange peel

8.28 1.5 8.01 10.6 14.0 3.15 166.7

[36] [37] [36] [38] [39] [40] This study

Ground nut shell Rice husks Bagasse Spent activated clay Oak pine Orange peel Carbon almond shell

2.3 0.6 13.4 1.42 0.47 33.78 288.5

[41] [42] [43] [44] [45] [28] This study

Table 7 Comparison of maximum adsorption capacities of orange peel with different dyes. Name of pollutant

Maximum adsorption (mg L1)

References

Name of pollutant

Maximum adsorption (mg L1)

References

Methyl orange Methylene blue Rhodamine B Congo red 14.0 Acid violet 17

20.5 18.6 14.3, 3.23 14.0, 22.4 19.88

[46] [46] [47,48] [47,48] [46,48]

Methyl violet Amido black Direct red 80 Direct red 23 Direct blue-86

11.5 7.9 21.05 10.72 33.78

[46] [46] [49,50] [49,50] [28]

The overall standard free energy change during the adsorption process was negative for the experimental range of temperatures and the system did not gain energy from an external source. It becomes more favorable when temperature increased [7]. 3.10. Comparison of CAS and COP with other adsorbents The adsorption capacity of 2-pic onto CAS and COP was compared with several low cost adsorbents and they are reported in Table 6. The comparison of maximum adsorption capacities of some dyes with orange peel is shown in Table 7. CAS and COP in this study possess reasonable adsorption capacity in comparison with other sorbents. 4. Conclusion Activated carbon from AS and OP adsorbents were successfully prepared by physical method. The present investigation shows that CAS and COP have capable low-cost adsorbent. Results show that low-cost, easy obtained, high efficiency and eco-friendly adsorbents have been prepared for adsorption of 2-picolin (2-pic) from aqueous solution. The adsorption process was attained equilibrium within 120 min of contact time and pH > 5. Equilibrium and kinetic studies were made for the adsorption of 2-pic from aqueous solutions onto CAS and COP. The kinetic was found to be best-fit pseudo-second- order equation [51].

[3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30]

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