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Kinetics and Equilibrium Studies on the Removal of Victoria Blue Using Prosopis juliflora-Modified Carbon/Zn/Alginate Polymer Composite Beads Muthaiyan Kumar and Rengasamy Tamilarasan* Department of Chemistry, Anna University ChennaiUniversity College of Engineering Pattukottai, Rajamadam-614 701, India ABSTRACT: This article describes the removal of triarylmethane compound Victoria Blue (VB dye) from an aqueous medium using Prosopis julif lora-modified carbon/Zn/alginate polymer bead. The experimental conditions of the adsorption process chosen in this study are dye concentration (4·10−3 mg·kg−1 to 2.0·10 mg·kg−1), pH (3 to 10), adsorbent dose (0.5 g to 2.5 g), contact time (0.6 s to 5.4·103 s) and temperature (303 K to 343 K). The efficiency of the adsorption process was determined by kinetic, equilibrium, and thermodynamic parameters. The equilibrium uptake capacity of the adsorption process was obtained from Freundlich and Langmuir adsorption isotherm equations and the equilibrium uptake capacity of adsorption was compared with dimensionless separation factor (RL). The kinetics of adsorption process was estimated with pseudo-first-order and pseudo-second-order Lagergren’s equations. The diffusion of adsorption was confirmed using an intraparticle diffusion model. The feasibility of the adsorption process was ascertained from the thermodynamic parameters like standard enthalpy (ΔH°), standard entropy (ΔS°), and Gibbs free energy (ΔG°) utilizing the van’t Hoff plot. The alginate polymer composite bead was characterized with Fourier transform infrared spectroscopy and the morphological studies were done with scanning electron microscopy.

1. INTRODUCTION Environmental pollution has increased significantly due to the discharge of industrial effluents into the environment over the past decade. Most of these untreated industrial effluents affect the environmental matrices of water, air, and soil. The presence of dyes and pharmaceuticals in aquatic environments from the major polluters like the textile and pharmaceutical industries constitute severe environmental problems1 affecting the habitats of living organisms, humans and animals. Most of the industries use large quantities of basic dye for coloring their products that are anionic particles which tend to attract the cationic dyes. Even trace quantities ( pHZPC), then the alginate bead surface may attain negatively charged status thereby increasing the uptake capacity of the dye due to the electrostatic force of attraction.32 Figure 3 shows the pHZPC value of the alginate bead and the point of zero charge of the alginate polymer bead which is found to be 4.2. 3.2. Adsorbent Dose. From the standard adsorption pattern of an adsorbent, it could be observed that whenever the adsorbent dose increases, the percentage of adsorption also gets 519

dx.doi.org/10.1021/je3012309 | J. Chem. Eng. Data 2013, 58, 517−527

Journal of Chemical & Engineering Data

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Figure 5. Plot of percent removal vs time at different initial dye concentrations: filled square, 4.0·10−3 mg·kg−1; hollow circle, 8.0·10−3 mg·kg−1; crossed up-triangle, 1.2·10−2 mg·kg−1; half-filled left-triangle, 1.6·10−2 mg·kg−1; half-filled down-triangle, 2.0·10−2 mg·kg−1.

Figure 3. Plot of pHi vs pHf for the determination of pHZPC of alginate bead.

increased simultaneously. In the present study, the dose of adsorbent was varied as 0.5 g, 1.0 g, 1.5 g, 2.0 g, and 2.5 g with 1.2 × 10−2 mg·kg−1 concentration of 25 mL of VB dye. The removal of VB for a dosage value of 0.5 g shows low percentage removal of dye as compared to other dosages. Moreover 1 g of adsorbent dose shows prevailing removal of VB at 98 % (Figure 4) while higher adsorbent doses also show slightly enhanced removal but not much variation. Hence 1 g of adsorbent dose was found to be an optimum dosage in the entire experiment.

observed. The percentage removal of dyes was calculated from the following equation removal (%) =

C i − Cf 100 Ci

(1)

where Ci and Cf are initial concentration and final concentration of dye, before and after the sorption process. 3.4. Effect of Temperature on Adsorption. The adsorption processes are generally influenced by temperature which modifies the adsorption equilibrium capacity of the individual adsorbate. The effect of temperature for the VB dye onto the alginate bead was assessed at 303 K, 313 K, 323 K, 333 K, and 343 K and the experimental results were found to indicate that the increase of the experimental temperature does not favor the adsorption process; that is, the percentage removal of VB dye was found to decrease gradually (Figure 6). This decreasing percentage removal could be due to the

Figure 4. Plot of percent removal vs dose for the adsorption of VB on the polymer composite beads.

3.3. Effect of Agitation Time and Concentration of Dye. The agitation time highly alters the removal rate of dye in the adsorption processes. The effect of contact time was investigated by varying the initial dye concentration at (4·10−3, 8·10−3, 1.2·10−2, 1.6·10−2 to 2.0·10−2) mg·kg−1 for the adsorption of VB dye solution in 25 mL. The percentage removal of VB dye was found to be rapid at (0.6, 1.2 and 1.8·103) s of contact time and not rapid after attaining an equilibrium value. At a contact time of 2.4·103 s, a higher removal of VB as 98 % in 1.2·10−2 mg·kg−1 (Figure 5) was

Figure 6. Plot of percent removal vs temperature T for the adsorption of VB on the polymer composite beads: filled square, 4.0·10−3 mg·kg−1; hollow circle, 8.0·10−3 mg·kg−1; crossed up-triangle, 1.2·10−2 mg·kg−1; half-filled left-triangle, 1.6·10−2 mg·kg−1; half-filled down-triangle, 2.0·10−2 mg·kg−1. 520



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of linearized equations and their equilibrium constants were obtained by plotting 1/Ce vs 1/qe (Figure 8), qe vs qe/Ce (Figure 9) and qe/Ce vs qe (Figure 10).

reduction of the physical forces of attraction between dye and adsorbent. Moreover, the forces of attraction involved between the solute and the solvent matrices were predominant as compared to the solute and adsorbent matrices. Owing to the solute and solvent predominant part, the solute is more difficult to be adsorbed.33 The experiment results predict that the reduction in the dye removal with the increase in temperature on the adsorption of VB dye onto polymer bead is kinetically controlled by an exothermic process.34 Further the experimental results shows that a temperature value of 303 K was favorable for the adsorption process. 3.5. Adsorption Isotherms. The adsorption isotherms predict whether the adsorbate molecules combine with the adsorbent and also provide information about the nature of combinations. Several types of isotherms have been developed for the determination of adsorption equilibrium capacity of the adsorbent. In this study the standard isotherm models of Freundlich and Langmuir (four forms) were used. The Langmuir isotherm assumes that the adsorption involved in homogeneous sites involves intramolecular binding on the surface of the adsorbent and enhances specific site occupation of the dye molecules. Therefore on the occupied site no extension of adsorption is found. This states that the adsorption process is a monolayer process.35 The mathematical expression of the Langmuir equation is qe =

Figure 8. Plot of 1/qe vs 1/Ce for the adsorption of VB dye on the polymer composite beads: filled square, 4.0·10−3 mg·kg−1; hollow circle, 8.0·10−3 mg·kg−1; crossed up-triangle, 1.2·10−2 mg·kg−1; halffilled left-triangle, 1.6·10−2 mg·kg−1; half-filled down-triangle, 2.0·10−2 mg·kg−1.

qmK aCe 1 + K aCe

(2)

where Ce is equilibrium concentration, qe is amount of adsorbate adsorbed per unit mass of adsorbent at equilibrium, qm is the theoretical maximum adsorption capacity, and Ka is a Langmuir isotherm constant related to the energy of adsorption. The simplification of the eq 2 gives Ce 1 1 = Ce + qe qm K aqm

(3)

The parameters Ka and qm values are obtained from linear regression plot of slope and intercept of Ce/qe vs Ce (Figure 7). Moreover the Langmuir isotherm possesses three other forms

Figure 9. Plot of qe/Ce vs qe for the adsorption of VB dye on the polymer composite beads: filled square, 4.0·10−3 mg·kg−1; hollow circle, 8.0·10−3 mg·kg−1; crossed up-triangle, 1.2·10−2 mg·kg−1; halffilled left-triangle, 1.6·10−2 mg·kg−1; half-filled down-triangle, 2.0·10−2 mg·kg−1.

The Freundlich equation assumes that the adsorption involved in the heterogeneous site progression with a multilayer mechanism of adsorption with the capacity of adsorption process related with the equilibrium concentration of dye.36 The mathematical expression of the Freundlich equation qe = KFCe1/ nF

(4)

where qe is the amount of adsorbate adsorbed at equilibrium, Ce is an equilibrium concentration of the adsorbate, KF is a Freundlich adsorption constant related to the adsorption capacity of the adsorbent and 1/n is adsorption intensity.

Figure 7. Plot of Ce/qe vs Ce for VB dye on the polymer composite beads: filled square, 4.0·10−3 mg·kg−1; hollow circle, 8.0·10−3 mg·kg−1; crossed up-triangle, 1.2·10−2 mg·kg−1; half-filled left-triangle, 1.6·10−2 mg·kg−1; half-filled down-triangle, 2.0·10−2 mg·kg−1. 521



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and Langmuir-4, respectively). The Freundlich isotherm shows the correlation coefficient (r2) value 0.9853. These experimental values conclude that the adsorption process follows a unilayer adsorption process rather than a multilayer adsorption process. The characteristics of Langmuir adsorption isotherm can be represented in terms of dimensionless separation factor (RL) that is given by expression 6, RL =

(6)

The RL value determines the mode of isotherm process, that is, whether the process is unfavorable (RL > 1), or linear (RL = 1), or favorable (0 < RL < 1), or irreversible (RL = 0). From the experiments the RL values were calculated from the different concentrations of VB dye and are represented in Figure 15. The experimentally calculated values of RL lie in the range between 0 < RL < 1, thereby indicating that the process was favorable.37 Moreover, the low values of RL reveal that there is a strong interaction between the dye molecules and the polymer composite beads.38 3.6. Adsorption Kinetics. The kinetics of adsorption process was evaluated by the Lagergren’s equations of pseudofirst-order and pseudo-second-order, and the mode of diffusion was predicted from the intraparticle diffusion equation. The pseudo-first-order equation assumes that the rate of adsorption change of the solute with time may lead to the change in uptake capacity of the adsorbent. This phenomenon was directly proportional to the saturation concentration difference and the amount of solid uptake with time.39 The mathematical expression is the following

Figure 10. Plot of qe vs qe/Ce for the adsorption of VB dye on the polymer composite beads: filled square, 4.0·10−3 mg·kg−1; hollow circle, 8.0·10−3 mg·kg−1; crossed up-triangle, 1.2·10−2 mg·kg−1; halffilled left-triangle, 1.6·10−2 mg·kg−1; half-filled down-triangle, 2.0·10−2 mg·kg−1.

The linearized form of Freundlich isotherm is 1 log(qe) = log(KF) + log(Ce) nF

1 1 + bC0

(5)

The parameters of KF and 1/n were obtained with the linear regression of plot between Ce/qe vs Ce (Figure 11) from the intercept and slope, respectively. The different forms of the Freundlich and Langmuir equations are presented in Table 2.

log(qe − qt) = log qe −

k1t 2.303

(7)

where, k1 is pseudo-first-order rate constant, qe is the amount of dye adsorbed at equilibrium, and qt is the amount of dye adsorbed at time t. The value of k1 was calculated by plotting a graph between log (qe−qt) vs t. The plot was found to be a straight line suggesting the applicability of kinetic model of adsorption process. The qe and k1 were calculated from the intercept and slope, obtained from Figure 12. The pseudosecond-order model assumes that the rate limiting step involves chemical forces of attraction and resembles the whole adsorption process. The mathematical expression of the equation is40,41 t 1 t = + 2 qt qe k 2qe

(8)

where k2 is a pseudo-second-order adsorption rate constant, qe is the amount of dye adsorbed at equilibrium, and qe2 is the pseudo-second-order adsorption rate constant. The pseudosecond-order rate constant was obtained by plotting a graph of t/qt vs t, from which a straight line was obtained. The qe and k2 values were calculated using the slope and intercept in Figure 13. The experimental results of the kinetic data indicate that the pseudo-second-order kinetic model provides a best fit correlated value when compared with the pseudo-first-order kinetic equation. From Table 4 the pseudo-second-order kinetic model is found to give the value of correlation as r2 = 0.99634 when compared to the pseudo-first-order kinetic model correlation value as r2 = 0.6366. Hence, the adsorption

Figure 11. Plot of log qe vs log Ce for the adsorption of VB dye on the polymer composite beads: filled square, 4.0·10−3 mg·kg−1; hollow circle, 8.0·10−3 mg·kg−1; crossed up-triangle, 1.2·10−2 mg·kg−1; halffilled left-triangle, 1.6·10−2 mg·kg−1; half-filled down-triangle, 2.0·10−2 mg·kg−1.

The experimental isotherm parameters are summarized in Table 3. From the results it could be seen that the Langmuir-1 is a best fit isotherm model compared to other forms of Langmuir equations. Langmuir-1 shows the best matched coefficient values that are closer to unity (r2 = 0.99975), while other forms do not show such closer proximity values to unity (r2 = 0.9427, 0.9497, and 0.9497 for Langmuir-2, Langmuir-3, 522



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Table 2. Isotherms and Their Forms isotherms

nonlinear

linear

plot

ref

1 log(qe) = log(KF) + log(Ce) nF

log(qe) vs log(Ce)

Freundlich (39)

Ce 1 1 = Ce + qe qm K aqm

Ce vs Ce qe

Langmuir (35)

Langmuir-II

⎛ 1 ⎞1 1 1 ⎟⎟ = ⎜⎜ + qe K q C q ⎝ a m⎠ e m

1 1 vs qe Ce

Langmuir-III

⎛ 1 ⎞q qe = qm − ⎜ ⎟ e ⎝ K a ⎠ Ce

qe vs

qe

qe

Freundlich

qe =

Langmuir-I

qe =

KFCe1/ nF qmK aCe 1 + K aCe

Langmuir-IV

Ce

= K aqm − K aqe

Ce

qe Ce

vs qe

Table 3. Freundlich and Langmuir Isotherm Parameters for the Adsorption of VB on Alginate Bead C0/mg·kg−1 isotherm Langmuir-I

Langmuir-II

Langmuir-III

Langmuir-IV

Freundlich

parameter qm/mg·kg−1 Ka/kg·mg−1 r2 qm/mg·kg−1 Ka/kg·mg−1 r2 qm/mg·kg−1 Ka/kg·mg−1 r2 qm/mg·kg−1 Ka/kg·mg−1 r2 1/n KF/mg·kg−1/kg·g−1 r2

−3

−3

4·10

0.5421 ± 0.114 4.9254 ± 0.002 0.9828 0.5535 ± 0.275 4.9572 ± 0.012 0.8474 3.5590 ± 0.143 0.1615 ± 0.004 0.7937 4.420 ± 0.365 0.1365 ± 0.015 0.7937 0.2786 ± 0.062 1.9223 ± 0.715 0.9145

8·10

1.4269 ± 0.102 7.0893 ± 0.002 0.9944 1.4665 ± 0.42 8.0090 ± 0.024 0.8102 13.78 ± 0.352 0.1072 ± 0.006 0.7178 18.09 ± 0.442 0.0845 ± 0.024 0.7178 0.1415 ± 0.054 1.4647 ± 0.546 0.9062

1.2·10−2

1.6·10−2

2.0·10−2

2.4190 ± 0.076 12.133 ± 0.001 0.9963 2.4410 ± 0.42 11.782 ± 0.005 0.8332 27.19 ± 0.092 0.0891 ± 0.002 0.8542 30.91 ± 0.237 0.0794 ± 0.014 0.8542 0.0753 ± 0.035 0.847 ± 0.422 0.8571

3.3972 ± 0.181 12.51 ± 0.004 0.9992 3.4489 ± 0.42 15.4717 ± 0.026 0.8522 48.22 ± 0.132 0.0710 ± 0.005 0.8706 53.82 ± 0.532 0.0641 ± 0.035 0.8706 0.0742 ± 0.049 0.5613 ± 0.512 0.9617

4.3557 ± 0.215 12.224 ± 0.005 0.9997 4.3786 ± 0.42 13.2317 ± 0.030 0.9427 55.74 ± 0.156 0.0783 ± 0.004 0.9497 58.08 ± 0.681 0.0754 ± 0.053 0.9497 0.067 ± 0.059 0.391 ± 0.645 0.9853

Figure 13. Plot of t/qt vs time t for the adsorption of VB dye on the polymer composite beads: filled square, 4.0·10−3 mg·kg−1; hollow circle, 8.0·10−3 mg·kg−1; crossed up-triangle, 1.2·10−2 mg·kg−1; halffilled left-triangle, 1.6·10−2 mg·kg−1; half-filled down-triangle, 2.0·10−2 mg·kg−1.

Figure 12. Plot of log qe−qt vs time t for the adsorption of VB dye on the polymer composite beads: filled square, 4.0·10−3 mg·kg−1; hollow circle, 8.0·10−3 mg·kg−1; crossed up-triangle, 1.2·10−2 mg·kg−1; halffilled left-triangle, 1.6·10−2 mg·kg−1; half-filled down-triangle, 2.0·10−2 mg·kg−1.

The kinetic models do not provide enough information of an exact diffusion mechanism that is involved during the process and the rate controlling steps, which affect the nature of the

process follows chemisorptions (pseudo-second-order) rather than physisorption (pseudo-first-order). 523



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Table 4. Pseudo-first-order and Pseudo-second-order Kinetic Parameters for the Adsorption of VB Dye on Alginate Composite Beads pseudo-first-order kinetics K1

qe

mg·kg−1

s−1

mg·kg−1

4 8 12 16 20

0.0071 0.0125 0.0038 0.0023 0.0029

± ± ± ± ±

0.051 0.1513 0.073 0.143 0.256

0.7269 0.5502 0.4485 0.3320 0.2848

± ± ± ± ±

pseudo-second-order kinetics r2

C0

0.0001 0.0002 0.0003 0.0002 0.0004

0.6235 0.5004 0.6106 0.6366 0.6021

K2

calcd qe

mg·kg−1

s−1

mg·kg−1

0.69 1.59 2.94 3.69 4.49

adsorption process. Hence there is a need to explore a new method that provides information about the diffusion mechanism. The intraparticle diffusion model developed by the definition on the theory of Weber and Morris42 is applicable as a common method for all the adsorption processes, with the dye uptake capacity varying almost proportionally with t1/2 rather than with the contact time t, thereby providing an empirical functional relationship.43 The intraparticle diffusion equation is given as qt = K idt 1/2 + C

expt qe

0.8054 0.4009 0.6429 0.4887 0.3233

± ± ± ± ±

0.241 0.293 0.352 0.252 0.282

0.2672 0.3656 0.4574 0.2554 0.4406

± ± ± ± ±

0.019 0.028 0.031 0.025 0.29

r2 0.9965 0.9939 0.9818 0.9954 0.9963

Table 5. Intraparticle Diffusion Parameters for the Adsorption of VB on Alginate Bead C0 mg·kg

kid −1

4·10−3 8·10−3 1.2·10−2 1.6·10−2 2.0·10−2

mg·kg ·s 0.0098 0.0075 0.0107 0.0025 0.0097

± ± ± ± ±

r2

C

−1 1/2

0.015 0.018 0.008 0.014 0.023

mg·kg 0.3653 0.5401 0.8480 0.3733 0.7279

± ± ± ± ±

−1

0.534 0.657 0.263 0.446 0.713

0.6346 0.6498 0.6232 0.6963 0.5795

(9)

stage of the adsorption process. These results suggest that an intraparticle diffusion process is involved, and not only does that involvement happens at a rate controlled step but also there was also some unpredicted mechanism involved during the processes of diffusion.44 3.7. Effect of Thermodynamic Parameters. The prediction of thermal effect of the adsorption process using thermodynamic equations may contribute to the deliberation of the whole process mechanism and the changes in the permanently attributed energies that are associated with adsorption process. The parameters used in this study, such as change in Gibbs energy (ΔG°), isosteric heat of adsorption (ΔH°), and change in entropy (ΔS°), are predicted using equations.45 q Kd = e Ce (10)

where kid is an intraparticle diffusion rate constant and C is intercept. If the adsorption process follows the intraparticle diffusion model, the plot between qt vs t1/2 shows a straight line and the parameters of kid and C are calculated from the linear regression analysis of the slope and intercept. The experimental values are depicted in Figure 14, which shows the quantity of dye

ΔG = −RT ln Kd

ln Kd =

ΔS 0 ΔH 0 − R RT

(11)

(12)

where Kd is the distribution coefficient, T is temperature, and R is gas constant. From Figure 16, the thermodynamic parameters of ΔS° and ΔH° are calculated using the linear regression analysis of the van’t Hoff plot using the parameters ln Kd vs 1/ T. The experimentally predicted thermodynamic parameter values are presented in Table 6, for the adsorption of VB dye on the alginate bead. The negative value of ΔG° implies that the process is spontaneous in nature. The enhancement of higher negative values indicates the quantity of dye uptake from the equilibrium value may be increased and ΔH° provides a positive value from 303 K to 343 K which confirms the endothermic nature of adsorption process and there was a possibility of strong interaction between the dye molecule and alginate polymer beads. Moreover the adsorption processes involved in the liquid phase are complex in nature, arising due to the competition of solute and solvent particle involved on the solid surface of adsorbent. Hence there was a change in

Figure 14. Plot of qt vs t1/2 for the adsorption of VB on the polymer composite beads: filled square, 4.0·10−3 mg·kg−1; hollow circle, 8.0·10−3 mg·kg−1; crossed up-triangle, 1.2·10−2 mg·kg−1; half-filled left-triangle, 1.6·10−2 mg·kg−1; half-filled down-triangle, 2.0·10−2 mg·kg−1.

adsorbed vs t1/2 for various dye concentrations. The predicted plots do not show linearity at different time intervals, which denotes that the adsorption process may involve several modes of sorption, rather than a single mode. Table 5 shows the calculated values of the intraparticle diffusion model for an adsorption of VB dye onto alginate beads. The first portion of the plot indicates that the boundary layer affects the primary 524



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surface charges of adsorbent and adsorbate. If the surface of the adsorbent attains a negative charge, it adsorbs cationic dyes, and if it attains a positive charge it adsorbs anionic dyes. The functional groups of the adsorbent were analyzed using FTIR. The FTIR spectrum of alginate bead in Figure 17 shows peaks

Figure 15. Plot of RL vs C0 for VB dye on polymer composite beads: RL, dimentionless separation factor; C0, initial concentration of VB dye. Filled square, Langmuir-I; crossed circle, Langmuir-II; crossed uptriangle, Langmuir-III; half-filled down-triangle, Langmuir-IV.

Figure 17. FTIR spectrum of VB dye on alginate beads: solid line, Zn and alginate; dashed line, Zn, alginate, and VB dye.

at 3420 cm−1, 1608 cm−1, 1369 cm−1, 1221 cm−1, 1095 cm−1, and 551 cm−1. These peaks show the presence of an intermolecular hydrogen bond, primary with aromatic conjugation and CS bond respectively. The after adsorption curve of VB dye in Figure 17 bead shows FTIR peaks at 3430 cm−1, 1612 cm−1, 1393 cm−1, 1040 cm−1, and 627 cm−1 respectively. The shifted peaks and the reduced intensity are observed from the adsorption spectrum of FTIR, thus showing a well characterized dye adsorption on the surface of the alginate bead. The scanning electron microscopy (SEM) images of the polymer bead and dye loaded polymer bead indicate an adsorption of VB on alginate bead that possesses a well-defined structural variation in Figure 18a. The before adsorption alginate bead shows a very bright and porous structure, but the case of after adsorption (Figure 18b) shows that the porous structures are occupied with VB molecules and the bright nature was not seen.

Figure 16. van’t Hoff plot of Kid vs temperature T/K for the adsorption of VB on the polymer composite beads.

Table 6. Thermodynamic Parameters for the Adsorption of VB on Alginate Bead T

ΔG°

ΔH°

ΔS°

K

KJ·mol−1

KJ·mol−1

J·mol−1·K−1′

303 313 323 333 343

−0.23 −0.31 −0.34 −0.40 −0.53

20.61

66.53

their static energy levels of the adsorption process. The positive46−49 ΔS° value confirms the involvement of good affinity for the removal of VB dye toward alginate bead. 3.8. Characterization of Polymer Composite Beads. The adsorption process is mainly influenced by the presence of various functional groups in the adsorbent material when it comes into contact with the solution due to the changes in

Figure 18. (a) SEM image of Zn-alginate; (b) SEM image of Zn− alginate−VB dye. 525



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4. CONCLUSION From the experimental and statistical data obtained in the present study, it is concluded that the activated carbon/Zn/ alginate composite polymer bead may be used as an ecofriendly and latent adsorbent for the removal of dye from wastewater over other adsorbents. The batch mode study was conducted by varying adsorbent dose, concentration of dye, pH, agitation time, and temperature. The pH study helps the prediction of point of zero charge of the adsorbent material which was found to be pHZPC = 4.2. The adsorption data were evaluated by Freundlich and Langmuir isotherm equations and it was confirmed that the Langmuir was the best fitted model as compared to the Freundlich model. This shows that the adsorption process follows the monolayer process when compared to the multilayer. The performances of the kinetic equations and the experimental results of the kinetic data indicate that the pseudo-second-order kinetic model provides a best fit correlated value when compared with the pseudo-firstorder kinetic equation. It concluded that the adsorption process follows the pseudo-second-order kinetic model thereby the rate determining step governed by the chemical forces of attraction. The intraparticle diffusion model shows that the diffusion involvement happens not only in the rate controlling step but also some unpredicted mechanisms were also involved during the processes of diffusion. From the investigations of the thermodynamic parameters, a change in the Gibbs energy (ΔG°), isosteric heat of adsorption (ΔH°), and change in entropy (ΔS°) may reveal that the negative value of ΔG° implies that the process involved is spontaneous in nature and the ΔH° provides a positive value intimating that the process was endothermic in nature. The positive value of ΔS° confirms that a good affinity is involved for the removal of VB dye toward alginate bead. The FTIR study predicts the presence of various functional groups in the polymer bead and also the analytical evidence for an adsorption of VB on the alginate bead. The SEM images of VB on to alginate bead show welldefined morphological evidence for the adsorption process.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +91-4373293301. Notes

The authors declare no competing financial interest.

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REFERENCES

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