Adsorption of Cu (II) and Ni (II) ions from metal solution using ...

INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 6, 2011 © 2011 Ramya.R et al., licensee IPA- Open access - Distributed under Creative Commons Attribution License 2.0 Research article

ISSN 0976 – 4402

Adsorption of Cu(II) and Ni(II) ions from metal solution using crosslinked chitosan-g-acrylonitrile copolymer Ramya R1, Sankar P2, Anbalagan S3, Sudha P.N4 1 - Part-Time Research Scholar, Department of Chemistry, Manonmanium Sundaranar University, Tirunelveli, Tamilnadu, India 2 - Part-Time Research Scholar, Department of Chemistry, Sathyabhama University, Chennai, Tamilnadu, India 3 - Part-Time Research Scholar, Department of Chemistry, Dravidian University, Kuppam, Andra Pradesh, India 4- Department of Chemistry, DKM College for Women, Vellore, Tamilnadu, India [email protected] doi:10.6088/ijes.00106020027

ABSTRACT A basic investigation on the removal of Cu(II) and Ni(II) ions from metal solution by crosslinked chitosan-g-acrylonitrile copolymer was conducted in a batch adsorption system. Graft copolymers of crosslinked chitosan (CLCS) with acrylonitrile (AN) were prepared by free radical polymerization using initiator ceric ammonium nitrate as redox system. Graft copolymerization was confirmed by FTIR, X-ray, DSC and SEM measurements. The influence of different experimental parameters such as pH, adsorbent dosage and contact time were evaluated. A pH 5.0 was found to be an optimum pH for Cu(II) adsorption, meanwhile pH 5.5 was an optimum pH for the adsorption of Ni(II) onto crosslinked chitosan-gacrylonitrile copolymer. The Langmuir adsorption isotherm model was applied to describe the isotherms and isotherm constants for the adsorption of Cu(II) and Ni(II) onto crosslinked chitosan-g-acrylonitrile (CLCS-g-AN). The maximum adsorption capacities of Cu(II) and Ni(II) ions onto crosslinked chitosan-g-acrylonitrile copolymer were 230.79 and 358.54 mg/g, respectively. Results showed that crosslinked chitosan-g-acrylonitrile copolymer is favourable adsorbents. Keywords: Crosslinked chitosan–g–acrylonitrile, graft copolymer, metal removal. 1. Introduction Several industrial and agricultural processes and mining activities have increased the concentration of toxic contamination in water and waste water around the world (GardeaTorresdey et al., 2004). Water is polluted in many ways like effluent of leather and chemical industries, electroplating industries and dye industries (Sudha, 2010). Heavy metals are classified into the following three categories: toxic metals (Hg, Cr, Pb, Zn, Cu, Ni, Cd, As, Co, Sn, etc.), precious metals (Pd, Pt, Ag, Au, Ru, etc.) and radionuclides (Ra, Am, etc.) (Bishop, 2002). The presence of heavy metal in environment is of major concern because of their transformation from relatively low toxic species into more toxic ones. Some metal ions such as Hg and Cd are highly toxic even in lower concentration 0.001-0.1 mg/L (Alkorta et al., 2004; Wang, 2002). The current physico-chemical processes for heavy metal removal like precipitation, reduction, ion-exchange, etc. are expensive and inefficient in treating large quantities. They also cause metal bearing sludges which are difficult to dispose of. More stringent rules by the government and media and public pressure regarding effluent discharges have necessitated the search for newer methods of treatment (Volesky, 2001; Received on March, 2011 Published on April 2011

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Adsorption of Cu(II) and Ni(II) ions from metal solution using crosslinked chitosan-g-acrylonitrile copolymer

Udaybhaskar et al., 1990). Therefore, there is a requirement for newer and effective methods which are also cost-effective. Biosorption is a feasible option because it is both efficient and cheap. Compared with conventional methods for removing toxic metals from effluents, the biosorption process has the advantages of low operating cost, minimization of volume of chemicals and biological sludge to be disposed off and high efficiency in detoxifying very dilute effluents. Biosorption, which involves active and non-active uptake by biomass, is a good alternative to traditional processes. Widely available biopolymers are also being used for sorption mainly because they are a cheap resource (Niu and Volesky, 2003). The advantage of biosorption is that the biomass used, could be a raw material which is either abundant, a waste from another industrial operation or could be cheaply available. There are certain broad range biosorbents which can collect all heavy metals from the solution with a small degree of selectivity. The biomaterials that are used for sorption are complex a number of mechanisms could be occurring simultaneously (Volesky, 2001). There are several chemical groups in biomass that could potentially attract and sequester metal ions: acetamido groups in chitin, amino and phosphate groups in nucleic acids, amino, amido, sulfhydryl and carboxyl groups in proteins and hydroxyls in polysaccharides (Volesky and Holan, 1995). Among the many other low cost absorbents identified (Olin et al., 1996; Bailey et al., 1999; Bailey et al., 1997), chitosan has the highest sorption capacity for several metal ions (Deshpande, 1986). Chitosan (2-acetamido-2-deoxy-β-D-glucose-(N - acetylglucosamine) is a partially deacetylated polymer of chitin and is usually prepared from chitin by deacetylation with a strong alkaline solution. The term “chitosan” refers to chitin that has been deacetylated to greater than 60%. Chitosan has many properties that have generated interest in its use such as biodegradability, biocompatibility and its nontoxic nature (Varma et al., 2004). The deacetylated product, chitosan, has an amine functional group, which is strongly reactive with metal ions. This has initiated research into the use of chitosan in metal uptake. The deacetylation degree will control the content of glucosamine and therefore the fraction of free amine groups available for metal binding. These groups are more reactive than the acetamide groups present on chitin. Also their solubility in acidic solutions differs, chitosan being soluble. The physico-chemical properties of chitosan depend on various parameters such as degree of deacetylation, polymer weight, etc. (Guibal, 2004). To improve chitosan’s performance as an adsorbent, cross-linking reagents such as glyoxal, formaldehyde, glutaraldehyde, epichlorohydrin, ethylene glycon diglycidyl ether and isocyanates have been used (Crini and Badot, 2008). Cross-linking agents do not only stabilize chitosan in acid solutions so that it becomes insoluble but also enhance its mechanical properties (Chiou et al., 2004). So the stability may be attained by chemical modifications. Chemical modifications that lead to the formation of chitosan derivatives, grafting chitosan and chitosan composites have gained much attention, extensively studied and widely reported in the literature. On the other hand, polyacrylonitrile (PAN) is one of the most important fiber-forming polymers and has been widely applied in textiles because of its excellent physical and chemical properties. To endue PAN textiles with antibacterial functions from chitosan, the methods of blending PAN with chitosan or its derivatives such as carboxymethyl chitosan have been widely investigated (Chang-Woo et al., 2001). However, these kinds of products are often accompanied with the problem of water stability, in which some of antibacterial Ramya R, Sankar P, Anbalagan S, Sudha P.N International Journal of Environmental Sciences Volume 1 No.6, 2011

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reagent may be released during laundering. Therefore, graft copolymerize of PAN with chitosan is a novel and promising attempt due to the chemical binding between macromolecules. Studies on the graft copolymerization of chitosan with various vinyl monomers have been conducted with different initiating systems and different mechanisms. There are mainly two kinds of initiating systems, i.e., chemical initiation and radiation initiation, to graft copolymerize different vinyl monomers such as vinyl acetate, acrylonitrile (AN), methacrylic acid (MA) and methylmethacrylate (MMA) (Shantha et al., 1995; Ren et al., 1993), onto chitosan. There are reports about graft copolymerization of vinyl monomers onto polysaccharides using both high energy (e.g. β, γ, χ-ray) and low energy (e.g. photo, UV light) (Singh et al., 2005; Yang et al., 1989). Although graft copolymerization with radiation initiation offers an economical and quick method, they are harder to handle under technical conditions. Graft copolymer of carboxymethyl chitosan with methacrylic acid (MA) was prepared by using the ammonium persulfate as the initiator and its water solubility was greatly improved (Sun et al., 2003). The graft copolymer of chitosan with polyacrylamide was successfully synthesized in the presence of nitrogen using ceric ammonium nitrate, nitric acid redox system with UV irradiation (Ansar Ali et al., 2011). The reaction of chitosangraft-polyacrylonitrile was carried out in a homogeneous acetic aqueous phase by using ceric ammonium nitrate as an initiator (Pourjavadi et al., 2003). In another work, graft copolymerization of AN and MMA onto chitosan using potassium persulfate as an initiator was studied (Prashanth and Tharanathan, 2003). Among the many vinyl monomers grafted, acrylonitrile (AN) has been the most frequently used one due to its high grafting efficiency and easy to hydrolyze to introduce varied subsequent derivatives (Pourjavadi et al., 2003). Ammonium persulfate or potassium persulfate was used as the initiator alone in most other literatures (Sun et al., 2003; Prashanth and Tharanathan, 2003; Retuert and Yazdani-Pedram, 1993; Hsu et al., 2002), which belongs to the peroxy initiator system. But the initiator of ammonium persulfate and sodium thiosulfate can consist of the redox system, which can generate two free radicals thus decrease the decomposition activation energy with faster polymerization rate. However, there are few reports about graft copolymerization for modification of crosslinked chitosan using the redox system of ammonium persulfate, sodium thiosulfate and ceric ammonium nitrate as the initiator. The aim of this study was to conduct a kind of chemical modification of chitosan by using the method of graft polymerization of acrylonitrile onto the backbone of crosslinked chitosan in presence of ceric ammonium nitrate as initiator. In the current work, the equilibrium of adsorption of Cu(II) and Ni(II) ions onto crosslinked chitosan-g-acrylonitrile copolymer from metal solution were investigated. Experiments were carried out as function of pH, adsorbent dosage and contact time. The adsorption capacity for the adsorption of Cu(II) and Ni(II) onto crosslinked chitosan-g-acrylonitrile (CLCS-g-AN) were determined using Langmuir equation. This information will be useful for further applications for the system design in the treatment of practical water effluents. 2. Materials and Method 2.1. Materials Chitosan was kindly gifted by India Sea food, Cochin, Kerala, India. Acrylonitrile, glutaraldehyde, ceric ammonium nitrate and the other chemicals used in the experiments were of analytical grade.

Ramya R, Sankar P, Anbalagan S, Sudha P.N International Journal of Environmental Sciences Volume 1 No.6, 2011

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2.2. Preparation of crosslinked chitosan copolymer A 2% W/V solution of chitosan was prepared in 2% aq. acetic acid. To 100 ml of chitosan solution 15 ml of glutaraldehyde was added and stirred for 20 minutes in a magnetic stirrer. To this crosslinked chitosan solution, a solution of 0.1 M ceric ammonium nitrate (CAN) in 10 ml of nitric acid was added followed by a known amount (1 g in 50 ml of water) of acrylonitrile drop by drop with continuous stirring with exposure to UV lamp. The temperature of reaction was maintained at 70 °C for 45 minutes, the product was precipitated by using sodium hydroxide solution with vigorous stirring. The precipitate was washed with distilled water several times to remove homopolymer formed and filtered. 2.3. Characterization of polymer The prepared crosslinked grafted copolymer of chitosan-g-acrylonitrile was analysed by FTIR in a wide range wavelength between 400 cm-1 and 4000 cm-1, and in solid state using KBr pelletisation. A Perkin – Elmer spectrophotometer was used. A DSC thermo gram was obtained by NET Z SCH – Geratebau GmbH thermal analyser. Samples were dried in vacuum desiccators and powdered in a standard aluminum pan. 2.0 mg of this sample was heated about 33 °C to 350 °C at a heating rate of 10 °K/min under constant purging of nitrogen. SEM study of the prepared graft copolymer was carried out by JSM – 640 Scanning Electron Microscope, JEOL at 20 MA and 15 KV. The dried sample film was cut and was sputter – coated with gold using a microscope sputter coater and viewed through the microscope. X-ray diffraction studies were performed using X-ray powder diffractometer (XRD – SHIMADZU XD – D1) using a Ni-filtered Cu Kα X-ray radiation. 2.4. Experimental process of removal of nickel and copper Batch studies were performed with different concentrations of nickel chloride and copper sulphate to investigate the extent of adsorption. The extent of removal of the two metals was investigated separately changing the adsorbent dose, pH of the solution and time of shaking the adsorbent metal solution mixture. The pH of each solution was adjusted to different values with either NaOH or HCl. The stoppered bottles were agitated at 30°C by orbital shaker at fixed speed, 160 rpm for various time intervals. The adsorbates were separated using Whattman filter paper and supernatant liquid was analyzed for residual concentration of the metals by atomic absorption spectrophotometer. Triplicate runs differing by less than 1% of all the tests were achieved assuring the reproducibility of the obtained data. 3. Results and Discussion 3.1. Characterisation of the grafted copolymer 3.1.1. FTIR Structural changes of crosslinked chitosan and its graft copolymer were characterized by FTIR spectroscopy. Figure 1 shows the FTIR spectrum of the CLCS-g-AN in comparison with original crosslinked chitosan. The strong peaks at around 2244 cm–1 appeared in spectra (b) was assigned to the stretching absorption of –CN, which proved the successful graft copolymerization of crosslinked chitosan and AN (Sun et al., 2003). Most of other peaks are related to the carbohydrate structure. The broad and strong absorption peak at around 3454 cm–1 (O–H and N–H stretching), peak at 2923 cm–1(C–H stretching), the three peaks at range


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of 1000–1157 cm–1 (C–O stretching) were common in spectra due to the crosslinked chitosan backbone.

Figure 1: FTIR spectra of (a) crosslinked chitosan, and (b) crosslinked CS-g-AN. 3.1.2. XRD The XRD pattern of crosslinked chitosan (a) and its graft copolymer (b) are showed in Figure 2. The crosslinked chitosan exhibited two diffraction peaks at 11° and 20°, which are characteristics of the hydrated crystalline structure of crosslinked chitosan, while the peak of (b) at around 42° was due to the overlapped diffraction peaks from the AN’s crystal.

Figure 2: XRD analysis of crosslinked chitosan (a) and crosslinked chitosan-g-acrylonitrile (b). In the XRD spectrum of (b), it is observed that diffraction intensity of the peak at around 20° was obviously weakened indicating that the crystallinity of the crosslinked chitosan decreased after modification. It illustrated that on copolymerization, the crystallinity of Ramya R, Sankar P, Anbalagan S, Sudha P.N International Journal of Environmental Sciences Volume 1 No.6, 2011

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crosslinked chitosan was disappeared. This phenomenon was due to the strong interaction (formation of covalent bond) between crosslinked chitosan and acrylonitrile. In other word, copolymerization improved the compatibility between crosslinked chitosan and acrylonitrile. 3.1.3. DSC DSC is an excellent tool to measure the thermal stability as a function of temperature. This technique provides a rapid, accurate and precise measurement of the thermal stability. The DSC provides a direct measurement for different heat flows between an inert reference and a sample. Two-stage heating process was conducted for the DSC analysis. The first-stage heating is used to decrease the water content in the films and release the stress. Since chitosan contains –NH2 and –OH functional groups, the hydrogen bonding force is strongly formed among molecules. The appearance of single Tg for copolymer confirms the formation of graft copolymer between crosslinked chitosan and acrylonitrile is shown in the Figure 3(a) and (b). Initial decomposition takes place at 330 °C for crosslinked chitosan and 248 °C for grafted crosslinked chitosan. The thermal degradation of crosslinked chitosan occurs at a highest temperature than that of the grafted crosslinked chitosan, which could indicate that graft thermal degradation occurs before the thermal degradation of the main crosslinked chitosan’s chain. Thus the thermal degradation rate related to grafted crosslinked chitosan copolymer is higher than the pure crosslinked chitosan. Also this result showed that the degree of crystallinity for the crosslinked chitosan-g-acrylonitrile was lesser than the pure crosslinked chitosan, which was consistent with the result of X-ray diffraction.

Figure 3: DSC thermograms of crosslinked chitosan (a) and crosslinked chitosan-gacrylonitrile (b) 3.1.4. SEM The surface morphology of the graft copolymer was examined by scanning electron microscopy. The scanning electron micrograph of crosslinked chitosan and crosslinked chitosan-g-acrylonitrile are shown in Figure 4(a) and (b), respectively. The copolymerization of acrylonitrile modified the surface morphology of crosslinked chitosan significantly making it useful for water treatment. SEM image of crosslinked chitosan was smooth and no pores or Ramya R, Sankar P, Anbalagan S, Sudha P.N International Journal of Environmental Sciences Volume 1 No.6, 2011

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semipores on the surface. Because of strong interactions between crosslinked chitosan and acrylonitrile, SEM image of crosslinked chitosan-g-acrylonitrile copolymer showed spherulites like structure, which provides larger surface area for better adsorption. Also it was revealed that uniform distribution of acrylonitrile onto the crosslinked chitosan which might be improving the characteristic nature of crosslinked chitosan as well as acrylonitrile. All these observations confirm that grafting acrylonitrile onto crosslinked chitosan allows better compatibility between crosslinked chitosan and acrylonitrile. This characteristic copolymer may responsible to allow water with greater adsorbing property.

Figure 4: Scanning electron micrographs of (a) crosslinked chitosan, and (b) crosslinked chitosan-g-acrylonitrile copolymer. 3.2. Factors influencing the adsorption of Cu(II) and Ni(II) ions The influences of several operational parameters such as dose of adsorbent, pH and contact time were investigated. 3.2.1. Effect of adsorbent dose The dependence of Cu(II) and Ni(II) adsorption was studied by varying the amount of adsorbents from 1 to 6 gms, while keeping other parameters (pH, and contact time) constant. From Figure 5, it can be observed that removal efficiency of the adsorbent generally improved by increasing its dosage. This is expected due to the fact that the higher dose of adsorbents in the solution, the greater availability of exchangeable sites for the ions. Results showed no further increase in adsorption after a certain amount of adsorbent was added (5-6 gms). The maximum % removal of Cu(II) was about 86% at the dosage of 6 gms, while for Ni(II) it was 81% at the dosage of 5 gms. This results also suggest that after a certain dose of adsorbent, the maximum adsorption sets in and hence the amount of ions bound to the adsorbent and the amount of free ions in the solution remain constant even with further addition of the dose of adsorbent.


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2+

% Ni 2+ % Cu

90

2+

85

% Removal of Ni and Cu

80 75

2+

70 65 60 55 50 45 1

2

3

4

5

6

Adsorbent dose in gms

Figure 5: Percentage removal of Cu(II) and Ni (II) ions using grafted copolymer with different dosages of adsorbents. 3.2.2. Effect of contact time Results (Figure 6) indicated that metal ions removal was increased with an increase in contact time before equilibrium was reached. Other parameters such as dose of adsorbent and pH of solution were kept constant. The results indicated that Ni (II) removal was increased from 15 to 62.5% with the contact time variation from 30 to 300 mins, respectively. From 300 to 400 mins, the percentage removal of Ni(II) remains constant (62.5%), which showed that equilibrium was reached at 300 mins itself. Similarly for the metal ion Cu(II), the rate of removal was increased with the increase in the contact time up to 325 mins and remained constant (72.5%) from 325 to 350 mins. Thus the results illustrated that the optimum contact time for maximum removal (62.5%) of Ni(II) was 300 mins and for maximum removal (72.5%) of Cu(II) was 325 mins. This result is important, as equilibrium time is one of the important parameters for an economical wastewater treatment system. 2+

% Ni 2+ % Cu

80

2+


2+

70

60

50

40

30

20

10 0

50

100

150

200

250

300

350

400

Time in mins

Figure 6: Percentage removal of Cu(II) and Ni (II) ions using grafted copolymer at different time interval.


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3.3.3. Effect of pH Figure 7 illustrated that pH obviously influenced the removal efficiency of the copper and nickel ions in the aqueous solution. The results indicated that Ni(II) and Cu(II) removal was increased to maximum and then decreased with pH variation from 4 to 8, respectively. The maximum % removal of Cu(II) was about 86% at pH 5. The dominant species of copper was free Cu(II) and was mainly involved in the adsorption process when the pH was lower than 5. When the pH greater than 5, copper ions started to precipitate as Cu(OH)2, this had been confirmed by Wang and Qin (2005). Similarly, the optimum % removal of Ni(II) was 85% at pH 5.5. Increases in metal removal with increased pH can be explained on the basis of the decrease in competition between proton and metal cations for same functional groups and by decrease in positive surface charge, which results in a lower electrostatic repulsion between surface and metal ions. Decrease in adsorption at higher pH (>pH 5) is due to formation of soluble hydroxy complexes (Meena et al., 2003). The adsorption of Cu(II) and Ni(II) ions was found mainly to be influenced by solution pH. 2+

% Ni 2+ % Cu

90

80 75

2+


2+

85

70 65 60 55 50 4

5

6

7

8

pH

Figure 7: Percentage removal of Cu(II) and Ni (II) ions using grafted copolymer at different pH. 3.3. Adsorption isotherm The application of biosorption process on the commercial scale requires proper quantification of the sorption equilibrium for process simulation. The Langmuir equation has been frequently used to give the sorption equilibrium (Koumanova et al., 2002). The Langmuir isotherm represents the equilibrium distribution of metal ions between the solid and liquid phases. The Langmuir model assumes that the uptake of metal ions occurs on a homogenous surface by monolayer adsorption without any interaction between adsorbed ions. To get the equilibrium data, initial metal concentrations were varied while the adsorbent mass in each sample was kept constant. The linearized Langmuir isotherm allows the calculation of adsorption capacities and Langmuir constant by the following equation: Ceq/Cads = bCeq/KL+ 1/KL

(1)

Cmax

(2)

= KL/b

where Ramya R, Sankar P, Anbalagan S, Sudha P.N International Journal of Environmental Sciences Volume 1 No.6, 2011

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Cads

= amount of metal ions adsorbed (mg g-1)

Ceq

= equilibrium concentration of metal ion in solution (mg dm-3)

KL

= Langmuir constant (dm3 g-1)

b

= Langmuir constant (dm3 mg-1)

Cmax

= maximum metal ion to adsorb onto 1 g adsorbent (mg g-1)

The constant “b” in the Langmuir equation is related to the energy or the net enthalpy of the sorption process. The constant KL can be used to determine the enthalpy of adsorption (Schmuchl et al., 2001). The constants “b” and “KL” are the characteristics of the Langmuir equation and can be determined from the linearized form of the Langmuir equation (1). A linearized plot of Ceq/Cads against Ceq gives “KL” and “b”. In a sorbent and solution system, a graph of the solute concentration in the solid phase Cads (mg/g) can be plotted as a function of the solute concentration in the liquid phase Ceq (mg/dm) at equilibrium. Since the data for the curve are obtained at a single temperature, the curve is an isotherm. In a solid-liquid system, positive sorption results in the removal of solute from the bulk solution and the concentration at the surface of the solid, until the remaining solute in the solution is in dynamic equilibrium with the solute on the solid surface. At equilibrium there is a defined distribution of the solute between the liquid and the solid phases, which can generally be expressed by one or more isotherms (Findon et al., 1993). Figures 8 and 9 show that the isotherm of the sorption of copper and nickel ions by crosslinked chitosan-g-acrylonitrile. The isotherm is characterized by the initial region, which is represented as being concave to the concentration axis. The isotherm is beginning to reach a plateau, which can typically be described by the Langmuir isotherm (Parfitt and Rochester, 1983).

Cads (mg/g)

150

100

50

0 0

100

200

300

400

500

Ceq (mg/dm3) Figure 8: Isotherm for the adsorption of Cu(II) ions onto crosslinked chitosan-g-acrylonitrile.


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Cads (mg/g)

150

100

50

0 0

100

200

300

400

500

Ceq (mg/dm3) Figure 9: Isotherm for the adsorption of Ni(II) ions onto crosslinked chitosan-g-acrylonitrile. The Langmuir equation was used to describe the data derived from the adsorption of Cu(II) and Ni(II) ions by crosslinked chitosan-g-acrylonitrile copolymer adsorbent over the entire concentration range studies.

Ceq/Cads (g/dm3)

5 4 3 2 1 0 0

100

200

300

400

500

Ceq (mg/dm ) 3

Figure 10: Langmuir plot for the adsorption of Cu(II) ions onto crosslinked chitosan-gacrylonitrile.

Ceq/Cads (g/dm3)

5 4 3 2 1 0 0

100

200

300

400

500

Ceq (mg/dm3) Figure 11: Langmuir plot for the adsorption of Ni(II) ions onto crosslinked chitosan-gacrylonitrile. Ramya R, Sankar P, Anbalagan S, Sudha P.N International Journal of Environmental Sciences Volume 1 No.6, 2011

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Table 1: Adsorption isotherm constants and Cmax Metal ions

Langmuir constants KL (dm /g) b (dm3/mg) Cmax (mg/g) 1.343 0.005819 230.79 1.915 0.005341 358.54 3

Cu(II) Ni(II)

A plot of Ceq/Cads vs. Ceq yielded a straight line (see Figures 10 and 11), confirming the applicability of the Langmuir adsorption isotherm. The calculated results of the Langmuir isotherm constants and Cmax are given in Table 1. It is found that the adsorption of Cu(II) and Ni(II) onto crosslinked chitosan-g-acrylonitrile copolymer correlates well with the Langmuir equation under the concentration studies. The essential features of a Langmuir isotherm can be expressed in terms of a dimensionless constant separation factor or equilibrium parameter, RL that is used to predict if an adsorption system is “favourable” or “unfavourable” (Ngah and Musa, 1998). The separation factor, RL is defined by: RL

=

1 --------------1 + bCf

(3)

where Cf is the final Cu(II) and Ni(II) concentration (mg/dm3) and b is the Langmuir adsorption equilibrium constant (dm3/mg). The parameter indicates the isotherm shape according to Table 2. The values of RL calculated for different initial Cu(II) and Ni(II) concentration are given in Table 3. If the RL values are in the range of 0 < RL < 1, it indicates that the adsorption of Cu(II) and Ni(II) onto crosslinked chitosan-g-acrylonitrile copolymer is favourable. Thus, crosslinked chitosan-g-acrylonitrile copolymer is favourable adsorbent. Table 2: Effect of separation factor on isotherm shape RL value RL > 1 RL = 1 0 < RL < 1 RL = 0

Type of isotherm Unfavourable Linear Favourable Irreversible

Table 3: RL values based on Langmuir adsorption Metal ions Cu(II) ion

Ni (II) ion

Initial concentration C0 (mg/dm3) 1000 500 200 100 50 1000 500 200 100 50

Final concentration Cf (mg/dm3) 440 155 55 25 10 465 195 70 30 12.5

RL values 0.2808 5.5263 0.7575 0.8733 0.9450 0.2871 0.4898 0.7279 0.8619 0.9374


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4. Conclusion The graft copolymerization of crosslinked chitosan with acrylonitrile has been done in the presence of CAN as redox initiator and by novel technique UV irradiation. The grafting was strongly confirmed by FTIR and DSC. The morphological structure by SEM revealed that copolymer is uniformly formed, which showed that the grafted copolymer has improved porosity and fractured structure, which can be responsible for adsorption of molecules. The results showed that the adsorbent dose, pH and the contact time had a pronounced effect on the removal of Cu(II) and Ni(II) ions from metal solution. The capacity of crosslinked chitosan-g-acrylonitrile copolymer to adsorb Cu(II) and Ni(II) ions from aqueous solutions was examined. The adsorption isotherms could be well fitted by the Langmuir equation. This adsorbent is found to be favourable in the removal the metal ions from the wastewater. It can be concluded that crosslinked chitosan-g-acrylonitrile copolymer is an effective and low cost adsorbent for the collection of metal ions. Hence the crosslinked chitosan-g-acrylonitrile can be used for waste water treatment at industrial level. Acknowledgement The authors thank the authorities of DKM college, Thiruvalluvar university, Vellore, Tamil nadu, India for the support. 5. References 1.

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