activate carbon biocomposite for removal of hexavalent chromium from aqueous solution

Journal Pre-proof Synthesis of a chitosan/polyvinyl alcohol/activate carbon biocomposite for removal of hexavalent chromium from aqueous solution

Raziye Nowruzi, Maryam Heydari, Vahid Javanbakht PII:

S0141-8130(19)34134-0

DOI:

https://doi.org/10.1016/j.ijbiomac.2020.01.044

Reference:

BIOMAC 14348

To appear in:

International Journal of Biological Macromolecules

Received date:

3 June 2019

Revised date:

31 December 2019

Accepted date:

5 January 2020

Please cite this article as: R. Nowruzi, M. Heydari and V. Javanbakht, Synthesis of a chitosan/polyvinyl alcohol/activate carbon biocomposite for removal of hexavalent chromium from aqueous solution, International Journal of Biological Macromolecules(2018), https://doi.org/10.1016/j.ijbiomac.2020.01.044

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© 2018 Published by Elsevier.

Journal Pre-proof Synthesis of a chitosan/polyvinyl alcohol/activate carbon biocomposite for removal of hexavalent chromium from aqueous solution Raziye Nowruzi, Maryam Heydari, Vahid Javanbakht* ACECR Institute of Higher Education (Isfahan Branch), Isfahan, 84175-443, Iran *Corresponding author: Address: ACECR Institute of Higher Education (Isfahan Branch), Isfahan, 84175-443,

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Tel: +98-3133667264

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Iran

Fax: +98-3133667266

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E-mail: [email protected]

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Abstract

In this study, a biocomposite of chitosan/poly vinyl alcohol/activated carbon was

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synthesized and used for hexavalent chrome removal from aqueous solution. The

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synthesized adsorbent was characterized by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) analysis. The effect of important variables such as pH, concentration, contact time, temperature, and adsorbent dosage was investigated. The value of pHPZC for the adsorbent was evaluated at 4.9. Results showed that adsorption of chrome onto the adsorbent follows the Langmuir isotherm model and has a pseudo-second-order kinetic model. The maximum capacity of chrome adsorption was determined 109.89 (mg/g) according to the Langmuir isotherm model. According to adsorption results, the removal percentage of chrome increases with increasing the activated carbon content in the biocomposite, the adsorbent dosage, and decreasing the initial chrome concentration, pH, and temperature. The results showed that the

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Journal Pre-proof synthesized adsorbent can be used as an effective adsorbent for chrome removal from aqueous solutions. Keywords: Chitosan; Poly vinyl alcohol; Activated Carbon 1. Introduction Water pollution with heavy metals is a major global problem. Heavy metals have a high atomic weight between 63.5 and 200.6 and a density of at least five times greater than

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that of water [1-6]. These non-biodegradable metals accumulate in living organisms.

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Heavy metals are released into the wastewater from industries such as metal- plating,

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dyeing operations and pigment production [7-12]. Chromium is one of the most toxic pollutants which cause severe environmental and public health problems. The most

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common forms of chromium are Cr(0), Cr(III), and Cr(VI). The hexavalent form is more

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toxic than trivalent and requires more concern. Strong exposure to Cr(VI) causes cancer

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in the digestive tract and lungs and may cause epigastric pain, nausea, vomiting, severe diarrhea and hemorrhage [12-16]. It is very soluble and can easily accumulate in the

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human and other creature's bodies [17]. According to the world health organization (WHO) the maximum permissible amount of hexavalent chrome in potable water is 0.05mg/L [18]. There are several methods for heavy metal removal from an aqueous solution such as membrane separation, chemical precipitation, adsorption and ion exchange [19]. These methods have some disadvantages like high energy and reagent requirement, generation of toxic sludge or waste product which need to be treated. But adsorption is a much more effective method used extensively for heavy metal removal.it has low cost and chemical stability. Activated carbon, biological material, fly ash and chitosan are conventional adsorbents for the adsorption process [20]. Activated carbon (AC) has a porous structure with a big surface area it is abundant and economical. It has also high adsorption capacity, functional groups and chemical stability. Activated carbon 2

Journal Pre-proof is very effective in removing organic and mineral compounds from water due to its inexpensiveness, high surface area, and high porosity. Activated carbon is far more important than other adsorbents such as functionalized polymers like resins in organic dyes removal due to their disadvantages such as low surface area or low adsorption capacity [10]. However, it is a non-biodegradable adsorbent and has a hard regeneration process [21]. Susmita et al. studied the hexavalent chrome removal from aqueous solution by microporous activated carbon from Aegle Marmelos shell. According to the results,

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the maximum removal percentage was 82.3% at pH=2 [22]. Wenmi et al. used

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AC/CoFe2O4 composite for hexavalent chrome adsorption from wastewater. Results

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showed that the adsorption capacity of AC/CoFe2O4 is much better than activated carbon.

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In addition, the magnetic property of AC/CoFe2O4 revealed that this adsorbent can be separated easily with a magnet [23]. Yang et al. used activated carbon prepared from

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Longan seed in order to remove hexavalent chromium from aqueous solution. According

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to the results equilibrium data follows second-order kinetic and also Langmuir isotherm. This was an effective adsorbent for hexavalent chromium removal from aqueous solution.

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In recent years, the use of cheaper adsorbents like chitosan has been paid more attention. Chitosan (CS) is a nontoxic and biodegradable polymer produced from chitin extracted from shrimp and crab shell [8, 24]. CS, as one of the most naturally abundant and cheapest biopolymers, has been broadly investigated as an adsorbent for pollutant removal. It is a natural adsorbent with high selectivity and lots of functional groups such as amin groups (-NH2) and hydroxyl groups (-OH) which has good chelation with ions and provides enough active sites for capturing of pollutants. It can interact with pollutant ions of the solution by ion exchange or other complexation reactions due to the presence of amino groups on the polymer matrix [8]. Sun et al. used the nanoparticles of magnetic silica with chitosan for hexavalent chrome removal from acidic aqueous solution. Results

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Journal Pre-proof showed that this adsorbent has a good capability for chrome removal [25]. Higher pH values are more favorable for adsorption of heavy metals such as Cu2+, Cd2+, Pb2+ on chitosan, while adsorption of hexavalent chrome will be favorable at lower pH values. It is attributed to anionic forms of chrome in aqueous solution which contain CrO42-, HCrO4-, HCr2O7-, Cr2O72-. This means that chitosan is not suitable for chrome adsorption because it has low acidic resistance and also is soluble in dilute acid solutions [26]. Chitosan also forms a gel in acidic condition making hydroxyl and amine groups non-

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accessible for metal bonding [27]. Therefore, the material should be added to improve

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chemical stability in acidic condition. In this research, Poly Vinyl Alcohol (PVA) is

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added to the chitosan structure overcome this limitation. PVA is a cheap and nontoxic

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polymer used for immobilization of microorganisms in wastewater treatment. In addition, it has well mechanical strength with active hydroxyl groups which easily modified with

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different functional groups [28]. PVA forms hydrogen bonds with amin groups in

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chitosan and strengthen it by making extra active sites. The main objective of the present study is to evaluate the use of Chitosan/Poly Vinyl

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Alcohol/Activated Carbon beads for chrome removal from aqueous solutions. Further, the synthesized adsorbent was characterized by Scanning Electron Microscopy and Fourier Transform Infrared analysis. In addition, the effect of different parameters such as pH, chrome concentration, contact time, temperature and adsorbent dosage on chrome adsorption was investigated. Kinetics, isotherms, and thermodynamics of the adsorption process were studied to evaluate the performance of the synthesized adsorbent for chrome removal.

2. Experimental procedure 2.1. Materials

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Journal Pre-proof Poly Vinyl Alcohol (C2H4O) and chitosan (C6H11NO4) with medium molecular weight purchased from Sigma-Aldrich. Sodium hydroxide (NaOH), sulfuric acid (H2SO4), potassium nitrate (KNO3), potassium dichromate (K2Cr2O7), and activated carbon (with particle size<100 µm) were Merck analytical grade and were used without further purification.

2.2. Synthesis of Chitosan/Poly Vinyl Alcohol (CS/PVA) biocomposite

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First, 4 gr chitosan was solved in 100 ml of acidic acid 3% (v/v) and was stirred for 2 hr

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in 65 0C. Then, the PVA solution was prepared by adding 4 gr PVA powder into 100 ml

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of deionized water and refluxing for 5 hr in 70 0C. Finally, CS/PVA adsorbent prepared

C.

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0

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with mixing of two mentioned precursor in the ratio of 2:1 under stirring for 1 hr in 70

biocomposite

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2.3. Synthesis of Chitosan/Poly Vinyl Alcohol/activated carbon (CS/PVA/AC)

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At first, 1.33gr of AC was added to CS/PVA solution prepared based on the procedure described before and was stirred for 1 hr. Then this solution was kept at room temperature for 24 hr in order to provide a homogenous solution. After that, this solution was injected into the 0.5M NaOH solution by a syringe to form a bead and was stirred for 1 hr at room temperature in order to solidify the beads. These beads were filtered from the NaOH solution and were washed with deionized water to neutral pH. Finally, the beads were dried at room temperature (Fig. 1).

Fig. 1. The schematic of the synthesis of Chitosan/Poly Vinyl Alcohol/activated carbon biocomposite

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Journal Pre-proof 2.4. Adsorption procedure The removal of chrome (VI) from a 60ppm dichromate potassium aqueous solution was done and the effect of parameters like pH, AC percentage, initial solution concentration, contact time, the adsorbent dosage was investigated. The solution pH was adjusted by 0.1M NaOH and 0.1M H2SO4. After that, the pH of the solutions was measured to determine the pHPZC. After the experiments the adsorbent was separated from the solution by a filter paper and a UV- spectrophotometer (Sanjesh-Sp2000UV- spectrophotometer)

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was used to specify the concentration of a solution by measuring its absorbance value at

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λ=390nm. The amount of chrome adsorbed on the adsorbent surface and the removal

% Re moval 

C0  Ce  100 C0

(1)

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C0  Ce V m

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qe 

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percentage was determined by equations (1) and (2), respectively:

(2)

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Where, qe is the equilibrium chrome value (mg/g), V is the volume of the solution (lit), m

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is the weight of adsorbent and C0 and Ce are initial and final concentrations (mg/L) of the solution, respectively.

For the investigation of the effect of contact time on adsorption and kinetic study, a series of experiments were carried out in which 0.1gr adsorbent come in contact with 125ml of potassium dichromate with a concentration of 60ppm at different contact times. For the investigation of isotherms, thermodynamics, and the effect of temperature on the adsorption process, the adsorption experiments were performed at different temperatures ranges from 25 0C to 55 0C. The effect of activated carbon percentage in the adsorbent was performed by conducting a set of experiments at different percentages of activated carbon (4%, 7%, and 10%). To study the effect of pH, some experiments are performed at different pH levels from 2-6. For the investigation of the Effect of potassium dichromate 6

Journal Pre-proof concentration on adsorption, 0.1gr adsorbent was contacted with a potassium dichromate solution at different concentrations. For the determination of pHPZC, a KNO3 solution (0.1M) was used to determine the pHPZC point [29]. Then 0.1gr of adsorbent (CS/PVA/AC) was added to the aforementioned solution and agitated more than equilibrium contact time.

3. Result and discussion

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3.1. FTIR results

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FTIR results for chitosan/Poly Vinyl Alcohol, activated carbon and chitosan/ Poly Vinyl

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Alcohol/activated carbon are shown in Fig. 2a, 2b, and 2c, respectively. Amino and

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hydroxyl are very important functional groups in the chitosan structure. As demonstrated in Fig. 2a the peak in 3386 cm-1 shows stretching vibration of O-H. Peaks also at 1376

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cm-1 can be related to the -NH vibration in –NH2. Adsorption peaks at 2920.6 and 2852.2

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cm-1 shown in Fig. 2b are due to C-H aliphatic stretching and O-CH3 aldehyde group respectively. Peaks in 1549 and 1417 cm-1 also show stretching vibration of C=O in

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carbonyl group and vibration deformation of C-O and O-H in carboxylic acid respectively. Fig. 2c shows the FTIR spectrum of chrome adsorbed On CS/PVA/AC composite. The peak in 1073 cm-1 shows N-H scissoring from amines and amides groups and reveals that the CS/PVA is covered by activated carbon successfully.

Fig. 2. FT-IR spectra of (a) CS/PVA, (b) AC, and (c) CS/PVA/AC

3.2. SEM results Morphology and surface characteristics of synthesized adsorbents before and after the adsorption process were determined with SEM images. Fig. 3 shows SEM images for

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Journal Pre-proof internal surface area for spherical CS/PVA and CS/PVA/AC biocomposites. As can be seen from Figs. 3a, b CS/PVA has a smooth surface area without any pores in its structure that can’t be effective for adsorption. Figs. 3c, d show the surface morphology of chitosan/poly vinyl alcohol)/AC. According to these figures, the surface of adsorbent has been a more porous structure with the presence of activated carbon providing more opportunity for adsorbate.

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Fig. 3. SEM images for (a, b) CS / PVA, (c, d) CS / PVA / AC

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3.3. Adsorption procedure results

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3.3.1. Effect of contact time on adsorption and kinetic study Contact time is a factor should be inevitably considered for economic treatments of

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wastewater. As demonstrated in Fig. 4, equilibrium was approached within about 225min.

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There are high concentrations of chrome in solution and also a large number of vacant adsorption sites in the initial adsorption stages resulting in a more effective collision

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between chrome ions and adsorption sites. Therefore, chrome is more rapidly adsorbed at the early hours. After that with the saturation of surface adsorption sites, the adsorption process continues slowly through the deeper positions within the adsorbent structure. This will cause the rate of adsorption to become slow and the adsorption rate decreases gradually over time until reaches the equilibrium point.

Fig. 4. Effect of contact time on chrome removal percentage and equilibrium adsorption of chrome (qe) , (pH=2, volume=125ml ,potassium dichromate concentration =60ppm, amount of adsorbent =0.1gr, temperature=250C)

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Journal Pre-proof The kinetic data evaluation can provide useful information about an adsorption mechanism. Here, three kinetic models including, pseudo-first-order and pseudo-secondorder kinetic equations and intraparticle diffusion examined to describe the chrome ion adsorption process. The liner form of the Pseudo -First-order kinetic is given by equation (3).

log( qe  qt )  log qe 

k1 t 2.303

(3)

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k1 is kinetic constant (min-1),qe is equilibrium metal uptake (mg/g), qt is metal uptake in

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time t (mg/g). k1 and qe can be obtained from intercept and slope of diagram log(qe -qt)

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versus t as shown in Fig. 5a. As seen in this figure kinetic doesn’t have good

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compatibility with experimental data. The calculated values also are given in Table 3.

t 1 t   2 qt k 2 qe qe

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The pseudo-second-order kinetic is described as equation (4). (4)

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k2 is kinetic constant (mg-1min-1), qe is an equilibrium amount of metal adsorbed (mg/g)

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which determines from intercept and slope of the equation t/qt versus t. qt is also metal adsorbed in time t (mg/g) which shown in Table 1. The linear fit for this model in Fig. 5b. shows that chromium removal by this adsorbent can be approximated by pseudo-secondorder kinetic.

The intraparticle diffusion model uses to investigate diffusion mechanism and given by equation (5) [30]. 1 2

qt  k p t  C

(5)

qt is the amount of metal adsorbed per minute(mg/g), kp is intra-particle diffusion constant, C is intercept related to the thickness of the boundary layer. The values of k p

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Journal Pre-proof and C can be calculated from the slope and the intercept of the plot of qt versus t0.5. The diagram of this model shown in Fig. 5. As shown in Table 1 pseudo-second-order kinetic has the highest correlation coefficient (R2=0.998) confirming the better compatibility of this model with experimental data. Fig. 5. The plot of adsorption kinetic (a) pseudo-first-order kinetic, (b) pseudo-secondorder kinetic, (c) intraparticle diffusion

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3.3.2. Adsorption isotherm

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Isotherm studies describe the behavior of adsorbent and express a relationship between

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the amount of adsorbate taken up by adsorbent and the adsorbate concentration in

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solution at equilibrium. Langmuir and Freundlich isotherms are mostly employed to describe the adsorption process behavior. The linear forms of Langmuir and Freundlich

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isotherms are as equations (6) and (8), respectively. (6)

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Ce Ce 1   qe q m bqm

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Where Ce (mg/L) is equilibrium concentration and qe (mg/g) is equilibrium capacity .b (L/mg) and qm (mg/g) are Langmuir constants related to the adsorption energy and maximum adsorption capacity of adsorbent respectively and determined from intercept and slope of diagram Ce/qe versus Ce. The results are shown in Fig. 6. The characteristic of the Langmuir model can be described with the dimensionless separation factor (RL) based on equation (4). RL 

1 1  bC0

(7)

In this equation, b is Longmuir constant and C0 is initial concentration (mg/l). Values of RL >1 suggest that isotherm is undesirable, RL =1 corresponds to linear isotherms and 0 < RL <1 shows that isotherm is desirable. In this study, as can be seen from Table 2, the 10

Journal Pre-proof calculated values of RL at different concentrations confirm that the Langmuir isotherms are desirable. Freundlich assumes a heterogeneous surface with different adsorption energies. According to equation (8), KF and n are also Freundlich constants determining the adsorption capacity and adsorption intensity, respectively. These constants can be obtained from intercept and slope of diagram log qe versus Ce respectively as shown in Fig. 6. The calculated values of these constants are given in Table 3. (8)

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1 log Ce n

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log qe  log K F 

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According to the data reported in Table 3, a higher correlation coefficient obtained from

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comparison with the Freundlich model.

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Langmuir isotherm reveals that there is good compatibility with experimental data

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Fig. 6. Plot of adsorption isotherm (a) Langmuir model, (b) Freundlich model

3.3.3. Thermodynamic studies

The values Gibbs energy (∆G), entropy (∆S) and enthalpy (∆H), can be obtained by equations (9) to (11), respectively [11].

G   RT ln k d ln k d  

(9)

H S  RT R

(10)

G  H  TS

(11)

In these equations kd is distribution factor, T is temperature (K) and R is universal gas constant (8.314 kJ/mole.K).

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Journal Pre-proof The values of enthalpy and entropy obtained from the slope and intercept of the plot of Ln K vs. 1/T as shown in Fig. 7. Then Gibbs energy can be calculated from equation (11). The values of these parameters are shown in Table 4. The negative values for Gibbs energy and enthalpy reveal that the adsorption is spontaneous and exothermic. Entropy is the degree of disorder. The negative value of entropy means that there is a decrease in disordering.

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Fig.7. The plot of the adsorption process thermodynamic

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3.4. Effect of activated carbon percentage in the adsorbent

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This effect was investigated by conducting a set of experiments at different percentages of activated carbon. Results have been shown in Fig. 8. Removal percentage increases

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with an increase in the amount of activated carbon which may be related to the increase

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was 10wt%.

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in the surface porosity [15]. Therefore, the activated carbon used for adsorbent synthesis

Fig. 8. Effect of activated carbon percentage on chrome removal percentage (pH= 2, volume= 125mL, initial potassium dichromate concentration= 60ppm, temperature = 25 0C,time =180 min)

3.5. Effect of pH on adsorption Solution pH is one of the most important factors affecting adsorption behavior. To study the effect of pH, some experiments are performed at different pH levels. As demonstrated in Fig. 9, chrome adsorption decreases when pH increases from 2 to 6. In acidic conditions, the anionic form of hexavalent chrome (HCrO4-) is predominant. Because of

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Journal Pre-proof electrostatic forces between adsorbent and adsorbate ions removal percentage is better in acidic condition [31]. There are a lot of H+ ions in acidic pH neutralizing negative charges on the adsorbent surface so that chromate ions (HCrO4-) can penetrate to the adsorbent bulk easily. Thus, pH=2 is chosen as an optimum pH for other experiments. Fig. 9. Effect of pH on removal percentage and equilibrium adsorption of chrome (qe) ,(volume= 125ml , ,potassium dichromate concentration =60ppm, amount of adsorbent=0.1 gr , temperature=250C ,time=180min

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3.5.1. pHPZC

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pHPZC is a point in which the surface charge of adsorbent is zero. At pH,>.pHPZC the

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surface charge of the adsorbent is negative and at pH<.pHPZC the charge is positive.

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According to the results shown in Fig. 10. pHPZC =4.9 obtained for this adsorbent. It means that at pH lower than 4.9 the adsorbent surface charge is positive which bonds

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with hydrogen chromate ions. At pH larger than 4.9 the negative surface charge of the

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[32].

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adsorbent repulses the hydrogen chromate ions and adsorption decreases significantly

Fig. 10. Determination of pHPZC (KNO3 solution= 0.1M, volume =125 ml, amount of adsorbent=0.1 g, temperature=25 °C, time=more than equilibrium contact time)

3.6. Effect of potassium dichromate concentration on adsorption The adsorbent was contacted with a potassium dichromate solution at different concentrations. Results have been shown in Fig. 11. The removal percentage of chrome depends on initial concentration. The amount of chrome adsorbed increases with solution initial concentration. Primary, adsorption progresses quickly and then its rate decreases gradually until it became constant at an equilibrium point. At high ion concentrations, the

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Journal Pre-proof decrease in the number of active sites leads to a decrease in removal percentage [33]. As shown in Fig. 7 the amount of chrome adsorbed increases from 69mg/g to 106 mg/g when initial concentrations increase from 60ppm to 110ppm, respectively. The equilibrium reaches 110ppm. Increasing initial concentration increases the driving force of adsorption of chrome and leads to an increase in adsorption capacity [34].

Fig. 11. Effect of initial concentration on chrome removal percentage and equilibrium

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3.7. Effect of temperature on adsorption

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temperature=250C)

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adsorption of chrome (qe), (pH=2, volume=125ml, amount of adsorbent =0.1gr,

Adsorption experiments were performed at optimum conditions at different temperatures

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ranges. The results are shown in Fig. 12. Adsorption and removal percentage decreases

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with an increase in temperature. At high temperatures, kinetic energy is more than the electrostatic attraction between adsorbent and chrome ions resulting in a decrease in

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adsorption capacity [35]. According to the results, the adsorption process is exothermic for this adsorbent.

Fig. 12. Effect of temperature on chrome removal percentage and equilibrium adsorption of chrome (qe) , (pH=2, volume= 125ml , ,potassium dichromate concentration =60ppm, amount of adsorbent=0.1 gr, time=225min)

3.8. Effect of adsorbent dosage on the adsorption process For this experiment, all of the effective parameters, except adsorbent dosage, kept constant at pre-determined optimum condition. According to Fig. 13, the removal

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Journal Pre-proof percentage increases with adsorbent dosage. It can be related to an increase in surface area of adsorbent resulting from the increase in the number of active sites in comparison with the number of chrome ions. However, the adsorption capacity decreases due to an increase in saturated adsorption sites [30].

Fig. 13. Effect of adsorbent dosage on removal percentage and equilibrium adsorption of chrome (pH=2, volume= 125ml , ,potassium dichromate concentration =60ppm,

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temperature=250C,time=225min)

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3.9. Comparison of another adsorbent with present adsorbent

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In this section different adsorbents compared with CS/PVA / AC for chrome adsorption. According to Table 5, the adsorption capacity for present adsorbent is 109.89 (mg/g)

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4. Conclusion

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removal from aqueous solution.

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which is the highest one than the others. So it can be used extensively for chrome

Synthesis of the CS/PVA/AC adsorbent was performed and the adsorbent was used to hexavalent chromium removal from aqueous solution. SEM images showed that the adsorbent surface of CS/PVA/AC has a lot of pores resulting in an increase in adsorption. Based on FTIR results CS/PVA/AC has special peaks in 1073 cm-1 for N-H scissoring from amines and amides. Adsorption experiment results revealed that using activated carbon in CS/PVA adsorbent structure improves its adsorption performance. In the initial stages, the chrome adsorption rate was very fast. In this study, the highest adsorption occurred at pH=2. The value of pHPZC for this adsorbent was 4.9, as well. The negative charge of the adsorbent surface at the pH values higher than pHPZC confirm that the lower

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Journal Pre-proof pH is favorable for adsorption. In addition, an increase in solution concentration from 60ppm to 110ppm caused an increase in adsorption capacity. Adsorption rate also gradually decreased over time and became constant after equilibrium time (225min). The removal percentage increases with the adsorbent dosage. It can be related to an increase in surface area of adsorbent resulting from the increase in the number of active sites in comparison with the number of chrome ions. Kinetic and isotherm studies also conducted. According to the results, Langmuir isotherm and pseudo-second-order kinetic

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had good compatibility with experimental data. The maximum amount of chrome

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adsorbed was 109.89 (mg/gr) based on Langmuir isotherm. Thermodynamic studies

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reveal that the adsorption process is exothermic and spontaneous as well. According to

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the results, this adsorbent is effective for hexavalent chrome removal from aqueous

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Conflict of interest

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solution.

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The authors have no conflict of interest to declare.

Acknowledgment

Financial support of this work by ACECR Institute of Higher Education (Isfahan Branch) is gratefully appreciated.

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Journal Pre-proof [16] P. Singh, D. Tiwary, I. Sinha, Starch-functionalized magnetite nanoparticles for hexavalent chromium removal from aqueous solutions, Desalination and Water Treatment 57(27) (2016) 12608-12619. [17] J. Yang, M. Yu, W. Chen, Adsorption of hexavalent chromium from aqueous solution by activated carbon prepared from longan seed: Kinetics, equilibrium and thermodynamics, Journal of industrial and engineering chemistry 21 (2015) 414-422. [18] J. Zhou, Y. Wang, J. Wang, W. Qiao, D. Long, L. Ling, Effective removal of

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hexavalent chromium from aqueous solutions by adsorption on mesoporous carbon

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microspheres, Journal of colloid and interface science 462 (2016) 200-207.

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[19] W. Wang, X. Wang, X. Wang, L. Yang, Z. Wu, S. Xia, J. Zhao, Cr (VI) removal

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from aqueous solution with bamboo charcoal chemically modified by iron and cobalt

1726-1735.

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with the assistance of microwave, Journal of Environmental Sciences 25(9) (2013)

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[20] K. Padmavathy, G. Madhu, P. Haseena, A study on effects of pH, adsorbent dosage, time, initial concentration and adsorption isotherm study for the removal of

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hexavalent chromium (Cr (VI)) from wastewater by magnetite nanoparticles, Procedia Technology 24 (2016) 585-594.

[21] A. Maleki, B. Hayati, M. Naghizadeh, S.W. Joo, Adsorption of hexavalent chromium by metal organic frameworks from aqueous solution, Journal of Industrial and Engineering Chemistry 28 (2015) 211-216. [22] R. Gottipati, S. Mishra, Preparation of microporous activated carbon from Aegle Marmelos fruit shell and its application in removal of chromium (VI) from aqueous phase, Journal of Industrial and Engineering Chemistry 36 (2016) 355-363.

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Journal Pre-proof [23] W. Qiu, D. Yang, J. Xu, B. Hong, H. Jin, D. Jin, X. Peng, J. Li, H. Ge, X. Wang, Efficient removal of Cr (VI) by magnetically separable CoFe2O4/activated carbon composite, Journal of Alloys and Compounds 678 (2016) 179-184. [24] A. Adamczuk, D. Kołodyńska, Equilibrium, thermodynamic and kinetic studies on removal of chromium, copper, zinc and arsenic from aqueous solutions onto fly ash coated by chitosan, Chemical Engineering Journal 274 (2015) 200-212. [25] X. Sun, Q. Li, L. Yang, H. Liu, Chemically modified magnetic chitosan

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microspheres for Cr (VI) removal from acidic aqueous solution, Particuology 26

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(2016) 79-86.

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[26] F. Shen, J. Su, X. Zhang, K. Zhang, X. Qi, Chitosan-derived carbonaceous

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material for highly efficient adsorption of chromium (VI) from aqueous solution, International journal of biological macromolecules 91 (2016) 443-449.

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[27] Q. Liu, B. Yang, L. Zhang, R. Huang, Adsorptive removal of Cr (VI) from

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aqueous solutions by cross-linked chitosan/bentonite composite, Korean Journal of Chemical Engineering 32(7) (2015) 1314-1322.

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[28] Z. Jia, Z. Li, S. Li, Y. Li, R. Zhu, Adsorption performance and mechanism of methylene blue on chemically activated carbon spheres derived from hydrothermallyprepared poly (vinyl alcohol) microspheres, Journal of Molecular Liquids 220 (2016) 56-62.

[29] M.O. Omorogie, J.O. Babalola, E.I. Unuabonah, W. Song, J.R. Gong, Efficient chromium abstraction from aqueous solution using a low-cost biosorbent: Nauclea diderrichii seed biomass waste, Journal of Saudi Chemical Society 20(1) (2016) 4957.

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Journal Pre-proof [30] A. Ali, K. Saeed, F. Mabood, Removal of chromium (VI) from aqueous medium using chemically modified banana peels as efficient low-cost adsorbent, Alexandria Engineering Journal 55(3) (2016) 2933-2942. [31] R. Dubey, J. Bajpai, A. Bajpai, Green synthesis of graphene sand composite (GSC) as novel adsorbent for efficient removal of Cr (VI) ions from aqueous solution, Journal of Water Process Engineering 5 (2015) 83-94. [32] S. Kahu, A. Shekhawat, D. Saravanan, R. Jugade, Two fold modified chitosan

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for enhanced adsorption of hexavalent chromium from simulated wastewater and

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industrial effluents, Carbohydrate polymers 146 (2016) 264-273.

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[33] R. Nithya, T. Gomathi, P. Sudha, J. Venkatesan, S. Anil, S.-K. Kim, Removal of

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Cr (VI) from aqueous solution using chitosan-g-poly (butyl acrylate)/silica gel nanocomposite, International journal of biological macromolecules 87 (2016) 545-

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[34] X. Wang, C. Wang, Chitosan-poly (vinyl alcohol)/attapulgite nanocomposites for copper (II) ions removal: pH dependence and adsorption mechanisms, Colloids and

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Surfaces A: Physicochemical and Engineering Aspects 500 (2016) 186-194. [35] S. Sugashini, K.M.M.S. Begum, Preparation of activated carbon from carbonized rice husk by ozone activation for Cr (VI) removal, New Carbon Materials 30(3) (2015) 252-261.

[36] V.K. Gupta, I. Ali, T.A. Saleh, M. Siddiqui, S. Agarwal, Chromium removal from water by activated carbon developed from waste rubber tires, Environmental Science and Pollution Research 20(3) (2013) 1261-1268. [37] M. Arulkumar, K. Thirumalai, P. Sathishkumar, T. Palvannan, Rapid removal of chromium from aqueous solution using novel prawn shell activated carbon, Chemical Engineering Journal 185 (2012) 178-186.

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Journal Pre-proof

Table 1. Kinetic parameters of different models for chrome adsorption onto CS/PVA/AC Pseudo-second-order

Pseudo- first -order

R2

C

KP

R2

qe

K2

R2

qe

K1

0.95

45.5

1.65

0.998

76.33

0.0006

0.84

3.88

1.008

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Intraparticle Diffusion

60

70

RL

0.04

0.033

80

90

100

110

0.033

0.029

0.027

0.024

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C(ppm)

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Table 2. The values of RL factor at different concentrations

Adsorption system CS/PVA/AC

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Table 3. Isotherm parameters for hexavalent chrome adsorption onto CS/PVA/AC

R2

n

KF (mg/g)

0.87

4.36

5.37

Freundlich isotherm

Langmuir isotherm R2 0.98

b(L/mg) 0.36

Table 4. Thermodynamic parameters for hexavalent chrome adsorption onto CS/PVA/AC with 60 mg/L concentration of the solution T(K)

ΔG(KJ/mole)

22

ΔH(KJ/mole)

ΔS(J/mole)

qm (mg/g) 109.89

Journal Pre-proof 298

-8.1

308

-6.82

318

-5.5

328

-4.2

-46.55

-129.1

Table 5. Comparing the amount of adsorption by different adsorbent and present adsorbent in chrome removal

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Amount of

Adsorbent

reference

89.13

[27]

52.13

[35]

12.08

[36]

Novel prown shell activated carbon

100.00

[37]

Chitosan/Poly Vinyl Alcohol /activated carbon

109.89

This study

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Cross-link chitosan/bentonite composite

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adsorption (mg/g)

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Activated carbon from rice husk

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Activated carbon/from waste rubber tire

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Journal Pre-proof Figure captions: Fig. 1. The schematic of the synthesis of Chitosan/Poly Vinyl Alcohol/activated carbon biocomposite Fig. 2. FT-IR spectra of (a) CS/PVA, (b) AC, and (c) CS/PVA/AC Fig. 3. SEM images for (a, b) CS / PVA, (c, d) CS / PVA / AC Fig. 4. Effect of contact time on chrome removal percentage and equilibrium

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adsorption of chrome (qe) , (pH=2, volume=125ml ,potassium dichromate

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concentration =60ppm, amount of adsorbent =0.1gr, temperature=250C) Fig. 5. The plot of adsorption kinetic (a) pseudo-first-order kinetic, (b) pseudo-

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second-order kinetic, (c) intraparticle diffusion

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Fig. 6. Plot of adsorption isotherm (a) Langmuir model, (b) Freundlich model

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Fig.7. The plot of the adsorption process thermodynamic Fig. 8. Effect of activated carbon percentage on chrome removal percentage (pH= 2,

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25 0C,time =180 min)

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volume= 125mL, initial potassium dichromate concentration= 60ppm, temperature =

Fig. 9. Effect of pH on removal percentage and equilibrium adsorption of chrome (qe) ,(volume= 125ml , ,potassium dichromate concentration =60ppm, amount of adsorbent=0.1 gr , temperature=250C ,time=180min Fig. 10. Determination of pHPZC (KNO3 solution= 0.1M, volume =125 ml, amount of adsorbent=0.1 g, temperature=25 °C, time=more than equilibrium contact time) Fig. 11. Effect of initial concentration on chrome removal percentage and equilibrium adsorption of chrome (qe), (pH=2, volume=125ml, amount of adsorbent =0.1gr, temperature=250C)

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Journal Pre-proof Fig. 12. Effect of temperature on chrome removal percentage and equilibrium adsorption of chrome (qe) , (pH=2, volume= 125ml , ,potassium dichromate concentration =60ppm, amount of adsorbent=0.1 gr, time=225min) Fig. 13. Effect of adsorbent dosage on removal percentage and equilibrium adsorption of chrome (pH=2, volume= 125ml , ,potassium dichromate concentration =60ppm,

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temperature=250C,time=225min)

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Journal Pre-proof International Journal of Biological Macromolecules, Vahid Javanbakht

Activated Carbon Poly Vinyl Alcohol Chitosan

Chitosan

Activated Carbon

+

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Fig. 1.

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Poly Vinyl Alcohol

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Chitosan

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Chitosan/Poly Vinyl Alcohol/Activated Carbon Bead

Journal Pre-proof International Journal of Biological Macromolecules, Vahid Javanbakht

(a)

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(b)

3500

3000

2500

2000

lP

4000

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(c)

Fig. 2.

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Wavenumber (cm-1)

27

1500

1000

500

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(b)

(c)

(d)

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(a)

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International Journal of Biological Macromolecules, Vahid Javanbakht

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Fig. 3.

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Journal Pre-proof International Journal of Biological Macromolecules, Vahid Javanbakht

100

80 70

80

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40

20

0 0

50

100

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equilibrium adsorption

150

200

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Time(min)

Fig. 4.

29

30 20

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removal percentage

40

10 0 250

300

qe (mg/g)

50

60

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Removal percentage (%)

60

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International Journal of Biological Macromolecules, Vahid Javanbakht

Fig. 5.

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Journal Pre-proof International Journal of Biological Macromolecules, Vahid Javanbakht

0.3

(a)

0.2 0.15 0.1

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Ce /qe(gr/l)

0.25

0.05

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0 0

10 Ce(mg/l) 20

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2.05

(b)

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2

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1.95 1.9

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logqe

30

1.85

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1.8

0

0.5

logCe

Fig. 6.

31

1

1.5

Journal Pre-proof International Journal of Biological Macromolecules, Vahid Javanbakht

3.5 3

2

of

1.5

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1

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0.5

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0 0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325 0.0033 0.00335 1/T (1/K)

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Fig.7.

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Ln KC

2.5

32

Journal Pre-proof International Journal of Biological Macromolecules, Vahid Javanbakht

110 90 80 70 60 50 40 30

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Removal percentage (%)

100

20

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10 0 2

4 6 8 10 Activated carbon percentage (%)

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0

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Fig. 8.

33

12

Journal Pre-proof International Journal of Biological Macromolecules, Vahid Javanbakht

100

80

60

40

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40 removal percentage 20

20

0 0

2

4

6

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pH

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equilibrium adsorption

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Fig. 9.

34

0 8

qe (mg/g)

60

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Removal percentage (%)

80

Journal Pre-proof International Journal of Biological Macromolecules, Vahid Javanbakht

2

of

1

0 2

4

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0

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0.5

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-0.5

-1

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pHi

Fig. 10.

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pH i - pH f

1.5

35

6

8

Journal Pre-proof International Journal of Biological Macromolecules, Vahid Javanbakht

94

120 100

90

86

60

84

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40

82

20

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removal percentage

80

equilibrium adsorption 50

70 90 110 Inital concentration (ppm)

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78

na

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Fig. 11.

36

0

qe (mg/g)

80

88

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Removal percentage (%)

92

Journal Pre-proof International Journal of Biological Macromolecules, Vahid Javanbakht

qe (mg/g)

80 60 40

equilibrium adsorption

20 0 20

30

40

of

removal percentage

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Removal percentage (%)

100

50

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Temperature

(0C)

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Fig. 12.

37

60

Journal Pre-proof International Journal of Biological Macromolecules, Vahid Javanbakht

100

100

98

90 80 60

92

50

90

40 30

of

removal percentage equilibrium adsorption

88 86 84 0.07

0.09

0.11

0.13

0.15

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0.05

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Amount of adsorbent(gr)

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Fig. 13.

38

20 10 0

0.17

qe (mg/g)

70

94

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Removal percentage (%)

96

Journal Pre-proof Contributor Roles Taxonomy: Raziye Nowruzi: Conceptualization Maryam Heydari: Supervision

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Vahid Javanbakht: Writing- Reviewing and Editing

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