Adsorption of phenol from aqueous solutions by Luffa ... - CyberLeninka

0 downloads 0 Views 723KB Size Report
on LC. It was found that the Langmuir isotherm model best fits the phenol adsorption onto LC. ... Analytical grade of phenol (C6H5OH) was used for the prepa-.
Egyptian Journal of Aquatic Research (2013) 39, 215–223

National Institute of Oceanography and Fisheries

Egyptian Journal of Aquatic Research http://ees.elsevier.com/ejar www.sciencedirect.com

Adsorption of phenol from aqueous solutions by Luffa cylindrica fibers: Kinetics, isotherm and thermodynamic studies O. Abdelwahab a b

a,*

, N.K. Amin

b

Environmental Division, National Institute of Oceanography and Fisheries, Alexandria, Egypt Chemical Engineering Department, Faculty of Engineering, Alexandria University, Alexandria, Egypt

Received 19 November 2013; revised 28 December 2013; accepted 28 December 2013 Available online 4 February 2014

KEYWORDS Phenol; Luffa cylindrica; Adsorption; Kinetics; Isotherm

Abstract The present study is concerned with the removal of phenol from aqueous solution by adsorption onto low cost adsorbent. Luffa cylindrica fibers, LC, were investigated as an adsorbent for the removal of phenol. Batch adsorption experiments were performed as a function of pH, contact time, phenol concentration, adsorbent dose and temperature. The optimum conditions for maximum adsorption were attained at pH 7, LC dose of 3 g/L. Langmuir, Freundlich, Tempkin and Dubinin–Radushkevich isotherm models were selected to evaluate the adsorption of phenol on LC. It was found that the Langmuir isotherm model best fits the phenol adsorption onto LC. The pseudo-second-order rate equation as well as the micropore diffusion model described the kinetic data well. The adsorption process was found to be an exothermic process. Thermodynamic parameters of phenol adsorption were calculated. The FT-IR analysis confirms that the adsorption of phenol on LC has a good and favorable adsorptive capacity. ª 2014 Production and hosting by Elsevier B.V. on behalf of National Institute of Oceanography and Fisheries.

Introduction Phenolic compounds naturally occur in fossil fuels or are produced by the microbial decomposition of proteins, humic compounds and lignin. Phenolic compounds are common raw * Corresponding author. Tel.: +20 1221093161; fax: +20 3 4801553. E-mail address: [email protected] (O. Abdelwahab). Peer review under responsibility of National Institute of Oceanography and Fisheries.

Production and hosting by Elsevier

materials for manufacturing a great variety of chemical products such as petrochemicals, plastics, pesticides, pharmaceuticals and dyes. Besides, they are also used to produce phenolic, epoxy and polyamide resins (Ocampo-Perez et al., 2011). Phenolic compounds are toxic and mutagenic at high concentrations and may be absorbed by the human body through the skin. The elimination of phenol is thus a major necessity for environmental protection. Different techniques have been developed to remove phenol from polluted water, including chemical oxidation (Chedeville et al., 2009; Amin et al., 2010), electrocoagulation (Abdelwahab et al., 2009; ElAshtoukhy et al., 2013), solvent extraction (Burghoff et al., 2009; Yu et al., 2009), membrane separation (Shen et al., 2009; Bo´dalo et al., 2009) and adsorption (Liu et al., 2010).

1687-4285 ª 2014 Production and hosting by Elsevier B.V. on behalf of National Institute of Oceanography and Fisheries. http://dx.doi.org/10.1016/j.ejar.2013.12.011

216 Among all of these methods adsorption has been preferred due to its cheapness and the high-quality of the treated effluents especially for well-designed sorption processes. Adsorption by agricultural by-products used recently as an economical and realistic method for removal of different pollutants has proved to be efficient at removing of phenol (Srivastava et al., 2007; Henini et al., 2012). Luffa cylindrica, LC, mainly consists of cellulose, hemicelluloses and lignin; of composition (60%, 30% and 10% by weight, respectively) (Rowell et al., 2002). Cellulose structure consists of monomeric unit of a b-D-glucopyranose linked through 1,4-glucosidic linkage. Cellulose is renewable, cheap and low in density, exhibits better processing flexibility and is a biodegradable material. Cellulose is a highly functionalized, linear stiff chain homopolymer, characterized by its hydrophilicity, chirality, biodegradability and broad chemical modifying capacity (Gupta et al., 2013). Because of its unique structure, LC, has been used as an efficient adsorbent or as a carrier for immobilization of some microalgal cells for the removal of water pollutants (Tanobe et al., 2005; Demir et al., 2008). In this study, LC fibers were investigated as an alternative adsorbent for removing of phenol from aqueous solutions. The adsorbed amounts of phenol were measured in equilibrium. Kinetic parameters were investigated to determine the ratio of reaction time versus adsorbed amounts. The optimum process temperature was also investigated.

O. Abdelwahab, N.K. Amin the concentrations less than 40 mg/L. Two replicates per sample were done and the average results are presented. The pH of the solution was adjusted with HCl or NaOH solution by using a pH meter. All reagents were of AR grade. Batch studies The batch studies were performed to study the removal of phenol from aqueous solution. A predetermined amount of adsorbent was added to 100 mL solution of known concentration in 250 mL Erlenmeyer flasks at temperature 20 C and agitated at 150 rpm on thermostatic orbital shaker (Scigenics Biotech ORBITEK) for 120 min. At predetermined time interval, the adsorbent was separated by centrifugation at 4000 rpm for 10 min. The residual phenol concentration in the supernatant was determined as stated before. The phenol removal percent was calculated for each run by the following equation: Removal % ¼

Adsorbent preparation Luffa cylindrica (LC) was purchased from a local specialty shop in Alexandria, Egypt. It was washed with tap water to remove the adhering dirt followed by distilled water. Then it was dried in an oven until constant weight. After drying it was cut into small pieces, fractionated by sieving for obtaining particles of an average size of 0.5 mm. After then, it was stored in closed bottles. FT-IR analysis using (FTIR-8400S), Shimadzu, Japan in solid phase was performed before and after use of LC to get qualitative and preliminary information of the main functional groups that might be involved in phenol uptake. Reagents and analytical measurements Analytical grade of phenol (C6H5OH) was used for the preparation of the synthetic adsorbate solutions of various initial concentrations in the range of 5–40 mg/L. A stock solution was prepared by dissolving the required amount of phenol in distilled water without pH adjustment. It was stored in a brown colored glass reservoir to prevent photo-oxidation. Working solutions of the desired concentrations were obtained by successive dilutions. The initial concentration of phenol was ascertained before the start of each experimental run. The concentration of phenol in the solutions was determined by 4AAP (4-amino antipyrin and red potassium prussiate) spectrophotometry by 722SP visible spectrophotometer (Shanghai Lengguang Instrument Co. Ltd) at 510 nm (Eryomin et al., 2006). The calibration plot of absorbance versus concentration for phenol showed a linear variation up to 40 mg/L concentrations. Therefore, the concentrations of phenol greater than 40 mg/L were diluted with distilled water, to bring down to

ð1Þ

where C0 and Cf are the initial and final concentrations of phenol in the solution in mg/L. The phenol uptake loading capacity (mg/g) of LC for each concentration of phenol at equilibrium was determined as follows: qe ¼

Experimental part

C0  Cf  100 C0

ðC0  Ce Þ W

ð2Þ

where Ce is the equilibrium concentrations of the phenols (mg/ L) in solution, W is the dose of adsorbent (g/L). The kinetic studies were performed following a similar procedure at 20 C, the initial phenol concentration was set (5– 40 mg/L), and the samples were separated at predetermined time intervals. The uptake of the adsorbate at time t, qt (mg/g), was calculated by the following equation: qt ¼

ðC0  Ct Þ W

ð3Þ

Results and discussion Characterization of adsorbent FTIR spectra of Luffa cylindrica (LC) and phenol sorbed LC are presented in Fig. 1. A band at about 3418 cm1 could be assigned to OH stretching vibrations. The peak at about 2916 cm1 was attributed to the asymmetric and symmetric stretching vibrations of CH2 and CH3. The band around 1638 cm1 was associated with C‚C and C‚O stretching in the aromatic ring (Tanobe et al., 2005). The peak at 1056 cm1 may be due to C–O stretching vibrations (Gupta et al., 2013). Also it is important to notice that the band intensities decreased in the FTIR spectrum of phenol loaded LC because the functional groups of the LC surface have been occupied with phenol (Senturk et al., 2009). This study demonstrated that phenol was adsorbed and penetrated into the interlayer space of the LC. Optimization of adsorption parameters The optimization of different adsorption parameters such as pH of solution, phenol concentration, dose of LC and

Phenol Removal, %

Adsorption of phenol from aqueous solutions by Luffa cylindrica fibers

217

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

2

4

6

8

10

12

14

pH

Figure 1 FTIR spectra of (a) raw LC fiber and (b) LC loaded phenol sample.

temperature at different time intervals was carried out for phenol onto Luffa cylindrica fibers. Effect of dosage of adsorbent The effect of the adsorbent dose on percentage of phenol removal was studied at 20 C and pH 7. Fig. 2, shows the influence of LC dosage on phenol removal percent and adsorption capacity, to find the minimum dosage for the maximum phenol removal. It can be observed that the percentage of phenol removal increased with increasing adsorbent dose. When the adsorbent dose increases, the number of sorption sites at the adsorbent surface will increase, as a result increasing the percentage of phenol removal from the solution (Mohd Salleh et al., 2011; Ofomaja, 2008). On the other hand, the increase in the LC doses promotes a remarkable decrease in the amount of phenol uptake per gram of adsorbent, qe, (Fig. 2). This effect that can be mathematically explained by Cardoso et al., by the following equation (Cardoso et al., 2011) qe ¼

%R  C0 100  W

ð4Þ

As observed in the Eq. (4), the amount of phenol uptake, qe, and the adsorbent dosage, W, are inversely proportional. For a fixed phenol percentage removal, sorbent doses lead to

12

100

10

Phenol Removal, %

80 70

8

60 6

50 40

4

30 20

% Remaoval

10

Capacity

2

0

Adsorpon Capacity, mg/ g-

90

0 1

2

3

4

5

Dose of Adsorbent, g/ L

Figure 2 Effect of absorbent dosage on the phenol adsorption onto LC at the given conditions (pH = 7, C0 = 20 mg/L, temp = 20 C).

Figure 3 Effect of pH on the percent removal of phenol by LC (initial concentration = 20 mg/L, dose of LC = 1 g/L, contact time = 2 h, temp = 20 C).

a decrease in qe values, since the initial phenol concentration (C0) is always fixed. These results clearly indicate that the LC dosages must be fixed at 3 g/L, which is the dosage that corresponds to the minimum amount of adsorbent that leads to constant phenol removal. LC dosages were therefore fixed at 3 g/L for the entire experiments. Effect of solution pH on dye adsorption The pH has an important effect on phenol adsorption since the pH of the medium will control the magnitude of the electrostatic charges that are imparted by ionized phenol molecules. As a result the rate of adsorption will vary with pH of an aqueous medium (Senturk et al., 2009). Fig. 3 shows the influence of solution pH on phenol removal by LC in the pH range from 2.0 to 12.0. The phenol removal increases with pH from 2.0 to 4.0 and remains constant from 4.0 to 9.0, then sharply decreases at pH >9. The maximum adsorption is attained at pH of 4.0. At pH 2.0, there are many positive charges on the surface of LC, which give a large static repulsion force. As pH increases from 2.0 to 4.0 the static repulsion force decreases and the phenol adsorption increases. At pH >9, the decrease of phenol adsorption may have resulted from the following reasons. (i) The negative charges on the surface of adsorbent increase with pH and phenol changes from molecular state to ionic state, which makes the repulsion force between phenol ions and the activated carbon significant. (ii) The phenol ions adsorbed by LC also have a repulsion force between themselves. (iii) The negative charges on the surface of LC are repulsive that represses the disaggregation of phenol ions and phenol adsorption (Guocheng et al., 2011). Since removal percent got small variations in the range 4–9, therefore pH 7, the normal pH of phenol solution, was selected as an optimum pH value for further adsorption experiments. Effect of initial phenol concentration Fig. 4 shows the effect of the initial concentration on the percentage removal of phenol and adsorption capacity of LC for each concentration at 20 C and pH 7. The amount of phenol adsorbed decreased with increasing initial phenol concentration. This may be due to the saturation of the adsorption sites at higher phenol concentrations. Meanwhile, the amount of phenol adsorbed per the same dose of LC increased with increasing initial phenol concentration. The initial phenol

218

O. Abdelwahab, N.K. Amin

80

8

60

6

40

4 % Removal

20

2

Capacity

active sites on the sorbent and the phenol species, and also between adjacent phenol molecules on the adsorbed phase. Adsorbent Capacity, mg/ g

10

Phenol Removal, %

100

0

0 0

5

10

15 20 25 30 35 Inial Concentraon, mg/ L

40

45

Figure 4 Effect of phenol concentration on percentage phenol removal and adsorption capacity of LC (pH = 7, LC dose = 3 g/L, temp = 20 C).

concentration provides an important driving force to overcome all mass transfer resistance. Hence a higher initial concentration of phenol tends to enhance the adsorption capacity. A similar phenomenon was observed for the adsorption of phenol onto organobentonite (Ocampo-Perez et al., 2011) and lignite activated carbon (Guocheng et al., 2011). Effect of temperature Temperature is an indicator for the adsorption nature whether it is an exothermic or endothermic process. As mentioned by Senthilkumaar et al. (2006), if the phenol percentage removal increases with increasing temperature then the adsorption is an endothermic process. This may be due to increasing the mobility of the phenol and an increase in the number of active sites for the adsorption with increasing temperature (Senthilkumaar et al., 2006). Increasing temperature may decrease the adsorptive forces between the phenol species and the active sites on the adsorbent surface as a result of decreasing adsorption efficiency (Ofomaja and Ho, 2007). The effect of temperature on the removal percent of phenol was studied in the temperature range of 20–50 C as shown in Fig. 5. The maximum removal was observed at 20 C, further increase in temperature leads to the decrease in removal percent. According to Ofomaja and Ho (2007), the decrease in the percentage removal of phenol with increasing temperature is due to the weakening of the sorptive forces between the

100

The Langmuir (Langmuir, 1916), Freundlich (Freundlich, 1906), Tempkin (Tempkin and Pyozhev, 1940) and Dubinin– Radushkevich (Dubinin, 1960) isotherm models were selected in this study to evaluate the adsorption of phenol on LC. The Langmuir isotherm (Eq. (5)) used single component adsorption model. qe ¼

qm KL Ce 1 þ KL Ce

ð5Þ

where qe (mg/g) is the amount adsorbed at equilibrium; qm (mg/g) is the maximum adsorption capacity; and KL (L/mg) is the Langmuir constant related to the energy of adsorption. The Freundlich expression is an equation based on heterogeneous surfaces suggesting that binding sites are not equivalent and/or independent (Holan et al., 1993). The Freundlich equation is given by, qe ¼ Kf C1=n e

ð6Þ

where Kf [mg/g (L/mg)1/n] and n are Freundlich isotherm constants. The constant Kf is the measure of adsorption capacity, and 1/n is the measure of adsorption intensity. Tempkin isotherm, assumes that the heat of adsorption decreases linearly with the coverage due to adsorbent–adsorbate interaction (Vijayaraghavan et al., 2006). The Tempkin isotherm has generally been applied in the following linear form: qe ¼ B ln A þ B ln Ce B¼

ð7Þ

RT b

ð8Þ

where A (L/g) is Tempkin isotherm constant, b (J/mol) is a constant related to heat of sorption, R is the gas constant (8.314 J/mol K) and T the absolute temperature (K). A plot of qe versus ln Ce enables the determination of the isotherm constants A, b from the slope and intercept. Dubinin–Radushkevich (D–R) isotherm is another isotherm equation that was proposed by Dubinin (Dubinin, 1960). He assumed that the characteristics of the sorption curves are related to the porosity of the adsorbent. The linear form of the isotherm can be expressed as follows: ln qe ¼ ln QD  BD e2

Temp.,°C

80

phenol Removal,%

Adsorption isotherm

where QD is the theoretical maximum capacity (mol/g), BD is the D–R model constant (mol2/kJ2), e is the Polanyi potential and is equal to   1 ð10Þ e ¼ RT ln 1 þ Ce

20 30 40

60

ð9Þ

50

40

The mean energy of sorption, E (kJ/mol), is calculated by 1 the following equation E ¼ pffiffiffiffiffiffi :

20

2BD

0 0

20

40

60

80

100

120

Time, min.

Figure 5 Effect of temperature on percent removal of phenol by LC (pH = 7, LC dose = 3 g/L, phenol conc. = 20 mg/L).

Fig. 6, shows the adsorption isotherms of phenol on LC at an initial solution pH of 7. The uptake of phenol increased with increasing equilibrium concentration. The isotherm parameters and the regression values are listed in Table 1. The adsorption equilibrium data fitted well to the Langmuir

Adsorption of phenol from aqueous solutions by Luffa cylindrica fibers 9

qe ¼

8 7 6

qe

5 Langmuir

4

Freundlich

3

Tempkin

2 Dubinin

1 Experimental

0 0

5

10

15

r2 ¼ 0:9667

ð12Þ

Adsorption capacity was found to be 10.35 mg/g of adsorbent which is comparable to that of other adsorbents used in the literature (Senturk et al., 2009; Liao et al., 2008; Vazquez et al., 2007; Shen et al., 2009). The adsorption capacity varies and depends mainly on the initial phenol concentration and characteristics of the individual adsorbent. Nevertheless, the current experiments were carried out to find the technical applicability of the cheaply available adsorbents to treat phenol.

20

Ce

Figure 6 LC.

1:74Ce ; 1 þ 0:168Ce

219

Adsorption kinetics

Equilibrium isotherms for the removal of phenol onto

Table 1 Values of isotherm constants for phenol adsorption onto LC. Isotherm model

Parameters

Langmuir

qm KL r2 % Error

Values 9.250694 0.198167 0.9921 6.69349

Freundlich

KF nF r2 % Error

1.770517 1.897173 0.9454 10.23879

Tempkin

b A r2 % Error

2.1141 1.838429 0.951 9.43757

D–R

QD E r2 % Error

5.9263 5.00E-07 0.8416 16.16281

model. Value of n in the Freundlich model between 2 and 10 shows good adsorption (Erdem et al., 2005). Percentage error function of non-linear regression basin was used to measure the isotherm constants and compare them with the less accurate linearized analysis values (r2 values). Percentage error is calculated as follows: 1 Xm ðqexp;i  qcalc;i Þ %Error ¼ ð11Þ i¼1 qexp;i m where the subscripts ‘‘exp’’ and ‘‘calc’’ show the experimental and calculated values (Table 1) and m is the number of measurements. By comparing the values of % error, it was found that the Langmuir isotherm model shows best fit of the phenol adsorption onto LC. The model shows high correlation coefficient and low% error value. Meanwhile Fig. 6 shows plots comparing different isotherm equations with experimental data. The figure shows an excellent fit of Langmuir model with experimental data for the removal of phenol onto LC, which confirms the results obtained by error analysis. The adsorption capacity of LC for phenol can be expressed as a function of initial phenol concentration as follows:

In the kinetic models, it is normally assumed that the overall rate of adsorption is exclusively controlled by the adsorption rate of the solute on the surface of the adsorbent, and the intraparticle diffusion and external mass transport can be neglected. Moreover, it is considered that the adsorption rate of a solute on the surface can be represented in the same manner as the rate of a chemical reaction (Ocampo-Perez et al., 2011). The adsorption kinetics is commonly modeled with the pseudo-first-order (Lagergren, 1898) and pseudo-secondorder (Ho, 1995). The equations of the two kinetic models are described next. The Lagergren equation, a pseudo-first-order equation, describes the kinetics of adsorption process for the boundary conditions t = 0 to t = t and qt = 0 to qt = qt as follows: qt ¼ qe ð1  expðk1 tÞÞ

ð13Þ

where qe is the amount of phenol adsorbed at equilibrium (mg/g), qt is the amount of phenol adsorbed at time t (mg/g) and k1 is the rate constant of pseudo-first order adsorption (min1). On the other hand, the pseudo-second-order model can be expressed in the following form for boundary conditions t = t and qt = 0 to qt = qt qt ¼

q2e k2 t 1 þ qe k2 t

ð14Þ

where k2 is the rate constant of pseudo second order adsorption (g/(mg min)). The experimental results of the phenol uptake, qt, versus time were fitted to the above mentioned models by the method of nonlinear regression. The results are shown in Table 2 and Fig. 7a and b. It is obvious from the plots of qt versus t that an increase in initial concentration leads to the increase in adsorption capacity, qe this indicates that the initial phenol concentration is an important parameter in determining the adsorption capacity of phenol uptake onto LC. It is observed from Fig. 7a that the adsorption data were well represented by Lagergren’s model only for low initial phenol concentrations (5–10 mg/L phenol concentrations) while, higher phenol concentrations deviate from theory. The values of theoretical adsorption capacity, qe, calculated from Lagergren’s model are lower than the values observed experimentally, qexp, for adsorption of phenol onto LC. Meanwhile, the values of the coefficient of determination, r2, decrease with the increase in initial phenol concentration for adsorption of phenol on LC which means that it is not appropriate to use Lagergren’s

220

O. Abdelwahab, N.K. Amin

Table 2

Kinetic and diffusion parameters for adsorption of phenol onto LC at different initial phenol concentrations.

Phenol conc. (mg/L)

qe (exp) mg/g

5 10 15 20 25 30 40

First order

1.584 3 4.26 5.608 5.5 6.48 8.384

Second order

k1 (min1)

r2

qe,cal.

k2 (g/(mg min))

r2

ki (mg/(gmin))

r2

1.497 2.794 4.149 4.976 5.27 6.093 7.793

0.02418 0.02234 0.0304 0.0182 0.02649 0.02349 0.02211

0.9315 0.9632 0.9223 0.9762 0.9666 0.9453 0.9004

1.498 2.837 4.204 5.560 5.499 6.383 8.116

0.01140 0.00560 0.00270 0.00100 0.00015 0.00088 0.00056

0.9952 0.9933 0.9709 0.9724 0.9787 0.9619 0.9674

0.1488 0.2856 0.4411 0.5672 0.6398 0.7508 0.9537

0.9961 0.9939 0.9955 0.9881 0.9868 0.9882 0.9971

assumption in the model that chemisorption plays a major role in this adsorption system.

9 8 7 6 5 4 3 2 1 0

Conc., mg/L 5 10 15 20 25 30 40

0

50

100

150

Time, min

(b) 9 8 7 6 5 4 3 2 1 0

Conc., mg/L 5 10 15 20 25 30 40

0

50

100

150

Time, min

Figure 7 The fitting of (a) pseudo first order model and (b) pseudo second order model for adsorption of phenol on LC, at different initial concentrations.

model for the prediction of the kinetics of phenol adsorption on LC for phenol concentrations higher than 10 mg/L. The kinetic data were further analyzed using the pseudo second order model of Eq. (14). It is obvious from Fig. 7b that the pseudo second order model fits the experimental data better than Lagergren’s model for the entire adsorption period of phenol concentrations up to 40 mg/L. Moreover, it was noticed from the regression data in Table 2 that the values of qe,calc, obtained from the pseudo second order model, are closer to the experimental results than qe,cl, obtained from Lagergren’s model. Furthermore, for different concentrations of phenol, the constants calculated from the plots are given in Table 2. The r2 values are excellent and calculated qe values match well with experimental ones. Therefore, the sorption of phenol by LC follows the second-order reaction kinetics. Thus supporting the basic

Diffusional model It is well documented in the literature that the overall adsorption rate in a porous adsorbent must consider the three following steps: external mass transport, intraparticle diffusion and adsorption on an active site inside the pores. The overall rate of adsorption is controlled by either film or intraparticle diffusion, or a combination of both mechanisms (Ocampo-Perez et al., 2011). The intraparticle diffusion parameter, ki, is defined by the following equation (Weber and Morris, 1963): qt ¼ ki t0:5 þ c

ð15Þ

where ki is the intraparticle diffusion constant (mg/(g min0.5)), and c is the intercept. The intraparticle diffusion plots of the experimental results, qt versus t0.5 for different initial phenol concentrations at 20 C and LC dose of 3 g/L are shown in Fig. 8. The values of ki, and the correlation coefficients r2 obtained from intraparticle diffusion plots are given in Table 2. In Fig. 8, it can be seen that there are mainly three linear regions. The second linear region is related to intraparticle diffusion. In general, ki was found to increase while increasing the initial phenol concentration, which can be due to the greater concentration driving force (O¨zer and Dursun, 2007). Fig. 8, shows that the linear plot did not pass through the origin which indicated that the intraparticle diffusion was not the only rate controlling step and the boundary layer diffusion controlled the adsorption to some degree (Cheung et al.,

qt

qt

(a)

qt

Intraparticle diffusion

qe,cal.

9 8 7 6 5 4 3 2 1 0

Conc., mg/L 5 10 15 20 25 30 40

0

2

4

6 t0.5

8

10

12

Figure 8 Intraparticle diffusion plots for adsorption of phenol on LC at different initial concentrations.

Adsorption of phenol from aqueous solutions by Luffa cylindrica fibers 4

221

Table 3 Thermodynamic parameters of adsorption of phenol onto LC.

3

Bt

2

Temp.

DG0 (J/mol)

DS0 (J/mol)

DH0 (J/mol)

20 30 40 50

1866.47 666.724 515.70 102

126.47

32749.7

1 Conc., mg/L

0

5

10

15

20

25

30

entropy change (DS0) can be calculated using the following equation (Liu et al., 2012):

40

ln Kc ¼ 

-1 0

50

100

150

Time, min

Figure 9

Boyd plots for the adsorption of phenol onto LC.

2007). This deviation may be due to the difference in mass transfer rate in the initial and final stages of adsorption. In order to determine the actual rate controlling steps of adsorption of phenol onto LC, the experimental data were further analyzed by the expression of Boyd et al. (1947). If the rate-determining step is diffusion through the adsorbent, then the following equation is valid. F¼1

6 expðBtÞ p2

ð16Þ

where F is the extent of exchange at time t, which has been determined as ðqqet Þ and B is the time co-ordinate of Boyd’s equation and is expressed in terms of the effective diffusion coefficient Di and particle radius rp as: B¼

p2 Di r2p

ð17Þ

According to the Eq. (16), F is a function of B and t only and is thus independent of the concentration of the external solution. Eq. (16) can be rearranged to Bt ¼ 0:4977  lnð1  FÞ

ð18Þ

The values of Bt were calculated from Eq. (18). Then a plot of t versus Bt is used to find whether the process is film or particle diffusion controlled. The value of Bt is calculated for each qt value and then plotted against t. From this plot, it is achievable to find out whether intraparticle diffusion or external transport controls the rate of adsorption. The rate controlling step is pore diffusion if this plot is linear and passes through the origin. Otherwise surface (film) diffusion is the rate controlling step (El-Khaiary, 2007). The t versus Bt plots are presented in Fig. 9. The plots are only linear in the initial period of adsorption and do not pass through the origin, indicating that external mass transfer is the rate limiting process in the beginning of adsorption for LC. Thermodynamic study Thermodynamic parameters such as standard free energy change (DG0), standard enthalpy change (DH0) and standard

DG0 DS0 DH0 ¼ ¼ RT R RT

ð19Þ

where, Kc is equilibrium constant resulting from the ratio of the equilibrium concentrations of the phenol on an adsorbent in the solution. DG0, DH0 and DS0 can be calculated from a plot of ln (Kc) versus 1/T. The thermodynamic parameters of the phenol adsorption onto LC are given in Table 3. The standard Gibbs free energies (DG0) of adsorption were negative at all investigated temperatures. The negative values of DG0 of the adsorption confirmed that the adsorption of phenol onto LC was feasible and spontaneous (Fu et al., 2009). In addition, the DG0 values increased as the temperature increased, suggesting that adsorption might be more spontaneous at lower temperature. Generally, the range of free energy values (DG0) for physisorption is between 20 and 0 kJ/mol, while chemisorption is between 80 and 400 kJ/mol (Su et al., 2011). This further indicated that the adsorption of the phenol onto LC was by physisorption. The change in adsorption standard enthalpy (DH0) for phenol adsorbed onto LC was 32.7 kJ/mol, indicating loose bonding between the phenol and LC since phenol was adsorbed and penetrated into the interlayer space of adsorbent, indicating that the adsorption process was exothermic (Su et al., 2011). The adsorption of phenol onto modified LC can be concluded to be via physicosorption since the change in the standard enthalpy is less than 40.0 kJ/mol (Canizares et al., 2006). The standard entropy change (DS0) for phenol adsorbed onto LC was 126.47 J/mol. The negative value of DS0 suggested a decrease in degree of freedom of the adsorbed phenol (Fu et al., 2009). Similar results were reported in the literature for the adsorption of phenol by organomontmorillonit (Fu et al., 2009) and adsorption of phenol onto chemically modified activated carbon (Canizares et al., 2006). Conclusions The adsorption of phenol using Luffa cylindrica fibers was investigated. The adsorption of phenol was found to be dependent on the pH solution, initial phenol concentration, contact time and temperature. The maximum removal of phenol was attained at pH 7, LC dose of 3 g/L using phenol concentration of 20 mg/L. The equilibrium adsorption data were best represented by the Langmuir isotherm, indicating monolayer adsorption on a homogenous surface and the adsorption capacity was found to be 10.37 mg/g at 20 C. The adsorption kinetic was described well by the pseudo-second-order model, while the intraparticle diffusion was not the only rate controlling step of the adsorption process. The adsorption is more

222 spontaneous at lower temperatures, tends to be exothermic. The FT-IR analysis indicates that after adsorption the pores of the adsorbent are covered with phenol. Thus, local raw materials could be used to prepare an adsorbent with a good and favorable adsorptive capacity. References Abdelwahab, O., Amin, N.K., El-Ashtoukhy, E.-S., 2009. Electrochemical removal of phenol from oil refinery wastewater. J. Hazard. Mater. 163, 711–716. Amin, N.A.S., Akhtar, J., Rai, H.K., 2010. Screening of combined zeolite-ozone system for phenol and COD removal. Chem. Eng. J. 158, 520–527. Bo´dalo, A., Go´mez, E., Hidalgo, A.M., Go´mez, M., Murcia, M.D., Lo´pez, I., 2009. Nanofiltration membranes to reduce phenol concentration in wastewater. Desalination 245, 680–686. Boyd, G.E., Adamson, A.W., Myers Jr., L.S., 1947. The exchange adsorption of ions from aqueous solutions by organic zeolites, II: kinetics. J. Am. Chem. Soc. 69, 2836–2848. Burghoff, B., de Haan, A.B., 2009. Liquid–liquid equilibrium study of phenol extraction with Cyanex 923. Sep. Sci. Technol. 44, 1753– 1771. Canizares, P., Carmona, M., Baraza, O., Delgado, A., Rodrigo, M.A., 2006. Adsorption equilibrium of phenol onto chemically modified activated carbon F400. J. Hazard. Mater. 131, 243– 248. Cardoso, N.F., Lima, E.C., Pinto, I.S., Amavisca, C.V., Royer, B., Pinto, R.B., Alencar, W.S., Pereira, S.F.P., 2011. Application of cupuassu shell as biosorbent for the removal of textile dyes from aqueous solution. J. Environ. Manage. 92, 1237–1247. Chedeville, O., Debacq, M., Porte, C., 2009. Removal of phenolic compounds present in olive mill wastewaters by ozonation. Desalination 249, 865–869. Cheung, W.H., Szeto, Y.S., McKay, G., 2007. Intraparticle diffusion processes during acid dye adsorption onto chitosan. Bioresour. Technol. 98, 2897–2904. Demir, H., Top, A., Balkose, D., Ulku, S., 2008. Dye adsorption behaviour of Luffa cylindrical fibers. J. Hazard. Mater. 153, 389– 394. Dubinin, M.M., 1960. The potential theory of adsorption of gases and vapors for adsorbents with energetically non-uniform surface. Chem. Rev. 60, 235–266. El-Ashtoukhy, E.-S.Z., El-Taweel, Y.A., Abdelwahab, O., Nassef, E.M., 2013. Treatment of petrochemical wastewater containing phenolic compounds by electrocoagulation using a fixed bed electrochemical reactor. Int. J. Electrochem. Sci. 8, 1534–1550. El-Khaiary, M.I., 2007. Kinetics and mechanism of adsorption of methylene blue from aqueous solution by nitric-acid treated waterhyacinth. J. Hazard. Mater. 147, 28–36. Erdem, E., C¸o¨lgec¸en, G., Donat, R., 2005. The removal of textile dyes by diatomite earth. J. Colloid Interface Sci. 282, 314–319. Eryomin, A.N., Semashko, T.V., Mikhailova, R.V., 2006. Cooxidation of phenol and 4-aminoantipyrin, catalyzed by polymers and copolymers of horseradish root peroxidase and Penicillium funiculosum 46.1 glucose oxidase. Appl. Biochem. Microbiol. 42, 399– 408. Freundlich, H.M.F., 1906. U¨ber die adsorption in lo¨sungen. Zeitschrift fu¨r Physikalische Chemie 57, 385–470. Fu, Q.L., Deng, Y.L., Li, H.S., Liu, J., Hua, H.Q., Chen, S.W., Sa, T.M., 2009. Equilibrium, kinetic and thermodynamic studies on the adsorption of the toxins of Bacillus thuringiensis subsp. kurstaki by clay minerals. Appl. Surf. Sci. 255, 4551–4557. Lu¨, Guocheng, Hao, Jiao, Liu, Liu, Ma, Hongwen, Fang, Qinfang, Limei, W.U., Wei, Mingquan, Zhang, Yihe, 2011. The adsorption of phenol by lignite activated carbon. Chin. J. Chem. Eng. 19 (3), 380–385.

O. Abdelwahab, N.K. Amin Gupta, V.K., Agarwal, S., Singh, P., Pathania, D., 2013. Acrylic acid grafted cellulosic Luffa cylindrical fiber for the removal of dye and metal ions. Carbohydr. Polym. 98, 1214–1221. Henini, G., Laidani, Y., Souahi, F., Hanini, S., 2012. Study of static adsorption system phenol/Luffa cylindrical fiber for industrial treatment of wastewater. Energy Procedia 18, 395–403. Ho, Y.S., 1995. Adsorption of Heavy Metals from Waste Streams by Peat (Ph.D. thesis). University of Birmingham, Birmingham, UK. Holan, Z.R., Volesky, B., Prasetyo, I., 1993. Biosorption of cadmium by biomass of marine algae. Biotechnol. Bioeng. 41, 819–825. Lagergren S., 1898. Zur theorie der sogenannten adsorption geloster stoffe 591. Kungliga Svenska Vetenskapsakademiens, Handlingar, 24 (4), 1–39. Langmuir, I., 1916. The constitution and fundamental properties of solids and liquids. J. Am. Chem. Soc. 38, 2221–2295. Liao, Q., Sun, J., Gao, L., 2008. The adsorption of resorcinol from water using multi-walled carbon nano tubes. Colloids Surf. A 312, 160–165. Liu, Q.-S., Zheng, T., Wang, P., Jiang, J.-P., Li, N., 2010. Adsorption isotherm, kinetic and mechanism studies of some substituted phenols on activated carbon fibers. Chem. Eng. J. 157 (2–3), 348–356. Liu, Z., Zeng, Z., Zeng, G., Li, J., Zhong, H., Yuan, X., Liu, Y., Zhang, J., Chen, M., Liu, Y., Xie, G., 2012. Influence of rhamnolipids and Triton X-100 on adsorption of phenol by Penicillium simplicissimum. Bioresour. Technol. 110, 468–473. Mohd Salleh, M.A., Mahmoud, D.K., Wan AbdulKarim, W.A., Idris, A., 2011. Cationic and anionic dye adsorption by agricultural solid wastes: a comprehensive review. Desalination 280, 1–13. Ocampo-Perez, R., Leyva-Ramos, R., Mendoza-Barron, J., GuerreroCoronado, R.M., 2011. Adsorption rate of phenol from aqueous solution onto organobentonite: Surface diffusion and kinetic models. J. Colloid Interface Sci. 364, 195–204. Ofomaja, A.E., 2008. Sorptive removal of methylene blue from aqueous solution using palm kernel fibre: effect of fibre dose. Biochem. Eng. J. 40, 8–18. Ofomaja, A.E., Ho, Y.S., 2007. Equilibrium sorption of anionic dye from aqueous solution by palm kernel fibre as sorbent. J. Dyes Pig. 74, 60–66. O¨zer, A., Dursun, G., 2007. Removal of methylene blue from aqueous solution by dehydrated wheat bran carbon. J. Hazard. Mater. 146, 262–269. Rowell, R.M., James, S.H., Jeffrey, S.R., 2002. Characterization and factors effecting fiber properties. In: Frollini, E., Leao, A.L., Mattoso, L.H.C. (Eds.), Natural Polymers and Agrofibres Based Composites. Embrapa Instrumentacao Agropecuaria, SanCarlos, Brazil, p. 115. Senthilkumaar, S., Kalaamani, P., Subburaam, C.V., 2006. Liquid phase adsorption of crystal violet onto activated carbons derived from male flowers of coconut tree. J. Hazard. Mater. 136, 800– 808. Senturk, H., Ozdesa, D., Gundogdu, A., Duran, C., Soylak, M., 2009. Removal of phenol from aqueous solutions by adsorption onto organomodified Tirebolu bentonite: equilibrium, kinetic and thermodynamic study. J. Hazard. Mater. 172, 353–362. Shen, S.F., Smith, K.H., Cook, S., Kentish, S.E., Perera, J.M., Bowser, T., Stevens, G.W., 2009. Phenol recovery with tributyl phosphate in a hollow fiber membrane contactor: experimental and model analysis. Sep. Purif. Technol. 69, 48–56. Srivastava, V.C., Mall, I.D., Mishra, I.M., 2007. Adsorption thermodynamics and isosteric heat of adsorption of toxic metal ions onto bagasse fly ash (BFA) and rice husk ash (RHA). Chem. Eng. J. 132, 267–278. Su, J., Lin, Hong-fu, Wang, Qing-Ping, Xie, Zheng-Miao, Chen, Zuliang, 2011. Adsorption of phenol from aqueous solutions by organomontmorillonite. Desalination 269, 163–169. Tanobe, V.O.A., Sydenstricker, T.H.D., Munaro, M., Amico, S.C., 2005. A comprehensive characterization of chemically treated Brazilian sponge-gourds (Luffa cylindrica). Polym. Test. 24, 474–482.

Adsorption of phenol from aqueous solutions by Luffa cylindrica fibers Tempkin, M.J., Pyozhev, V., 1940. Acta Physicochim. USSR 12, 327–352. Vazquez, I., Rodrıguez- Iglesias, J., Maranon, E., Castrillon, L., Alvarez, M., 2007. Removal of residual phenols from coke wastewater by adsorption. J. Hazard. Mater. 147, 395–400. Vijayaraghavan, K., Padmesh, T.V.N., Palanivelu, K., Velan, M., 2006. Biosorption of nickel(II) ions onto Sargassum wightii:

223

application of two-parameter and three-parameter isotherm models. J. Hazard. Mater. B133, 304–308. Weber, W.J., Morris, J.C., 1963. Kinetics of adsorption on carbon from solution. J. Sanit. Eng. Div. ASCE 89, 31–59. Yu, P., Chang, Z., Ma, Y., Wang, S., Cao, H., Hua, C., Liu, H., 2009. Sep. Purif. Technol. 70, 199–206.