Competitive Removal of Cu(II) and Cd(II) from Water Using a

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Competitive Removal of Cu(II) and Cd(II) from Water Using a Bio-Composite Hydrogel Jayabrata Maity, and Samit Kumar Ray J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.7b08796 • Publication Date (Web): 07 Nov 2017 Downloaded from http://pubs.acs.org on November 7, 2017

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The Journal of Physical Chemistry

Competitive Removal of Cu(II) and Cd(II) from Water Using a Bio-Composite Hydrogel Jayabrata Maity, Samit Kumar Ray* Department of Polymer Science and Technology University of Calcutta, 92, A.P.C. Road, Kolkata-700009

* Corresponding author: Tel: 91-033-23508386, Fax: 91-033351-9755 Email address: [email protected], [email protected] (institution email)

1 ACS Paragon Plus Environment


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ABSTRACT: With an objective to improve the adsorption properties of a synthetic hydrogel, potato starch (PS) was incorporated in the ter-copolymer (TP) of acrylic acid (AA), acrylamide (AM) and bi-carboxylic itaconic acid (IA) during polymerization of the monomers. The resulting TP-PS composite hydrogels were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Nuclear magnetic resonance (NMR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) and rheological properties. These hydrogels were used for removal of Cu(II) and Cd(II) as single and binary competitive mixtures from water. The effect of PS as well as various physico-chemical parameters such as solution pH, adsorbent dosage, contact time of gel with metal ion in water and concentration of metal ion in water was studied in batch experiments. The adsorption results indicated that the gels could be used as an efficient adsorbent for removal of Cu(II) and Cd(II) from water as single as well as binary mixtures. The TP-PS4 gel containing 4 wt.% starch showed a removal % of 85.8 and 77.6 and adsorption capacity (mg/g gel) of 214.5 and 193.9 for Cu(II) and Cd(II), respectively from water containing 50 mg/L of each of these metal ions in a solution pH of 5.5 and a dose of only 0.2 g/L gel.


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1. INTRODUCTION Hydrogels can be obtained by crosslinking natural and/or semi-synthetic/synthetic hydrophilic polymers. In general, hydrogels prepared from natural polymers such as polysaccharides offer great advantages including excellent biocompatibility, biodegradability and low toxicity.1,2 However, many of these polysaccharide-based hydrogels possess poor mechanical property.3 In contrast, hydrogels prepared from synthetic polymers usually present favorable mechanical properties, good processing, easily tunable molecular weight and chemical compositions.4 Unfortunately, most of these gels require relatively long response times for external environment change due to slow diffusion of water.5 The drawbacks of hydrogels prepared from only natural or synthetic polymers may be eliminated by integration of these natural polymers such as polysaccharide with the synthetic polymers to form a mechanically stable composite type hydrogel.6-9 Among the various polysaccharides, starch is non-toxic, renewable and inexpensive.10,11 This carbohydrate obtained mainly from cereals, roots, tubers and legumes consists of two kinds of polymers, viz., branched amylopectin and linear amylose, both containing repeating anhydroglucose unit. Each anhydroglucose unit contains three hydroxyl (―OH) groups. Thus, because of these functionalities, starch and its derivatives are widely used as low-cost adsorbents.12 However, despite numerous functionalities, the application of native starch is limited since it is insoluble in cold water and has a tendency to retrograde. To widen the application areas of starch various functional groups such as carboxyl, acetyl, hydroxypropyl etc., are introduced into its backbone by chemical modifications such as crosslinking, esterification, graft and other copolymerization.13 Suwanmala et al.14 synthesized starch based metal adsorbent via radiation-induced graft copolymerization of methyl acrylate onto cassava starch. Guo et al.15 prepared cross-linked porous starch for the removal of methylene blue from



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aqueous solution. Among the various starches, PS extracted from potatoes tuber is a refined starch, containing minimal protein or fat. It is the third most important material used in food and non-food sector.16 It contains about 10 to 20% amylose and 80 to 90% amylopectin of long chain length.17 It also contains approximately 800 ppm phosphate on its amylopectin which contributes to its cation exchange properties.18 PS granules show strong intermolecular association via hydrogen bonding formed by the hydroxyl groups on its surface.19 Further, PS has good stability because of its high crystallinity.20 It is also blessed with excellent gelling capacity.21 Similar to other starches, potato starch (PS) and its derivatives have also been chemically modified and used as adsorbent for removal of synthetic dyes and heavy metal ions from water.22,19,21 Thus, in the present work PS was chosen as the natural polymer. As a synthetic monomer, a bicarboxylic acid such as IA would be more appropriate than the conventional mono carboxylic acrylic monomers with respect to adsorption properties of the resulting polymers. A very small amount of IA repeating unit in a polymer hydrogel render good pH sensitivity and increase the swelling capacity.23,24 However, due to low reactivity diprotic itaconic acid cannot homopolymerize on its own but it may be grafted to a natural polymer or copolymerized with other monomers to prepare functional adsorbents. Several adsorbents based on itaconic acid were reported for removal of heavy metal ions from water. A pH responsive composite gel was prepared by allowing copolymerization of methacrylic acid and its crosslinker in the network of chitosan crosslinked with bicarboxylic IA. This chitosan/methacrylic acid/IA composite gels were used for removal of Cd(II) and Cu(II) ions.25,26 Similarly, IA grafted chitosan crosslinked with glutaraldehyde and ethylene glycol showed good adsorption for Cd(II) from water while itaconic acid grafted starch was reported for removal of Pb(II), Ni(II), Cd(II) and Zn(II) ions from water. 27,28 Copolymer of


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IA with acrylamide loaded with nano sized zinc oxide was also used for removal of iron from contaminated water.29 It transpires from the above discussion that copolymer of IA or its graft copolymer with a natural polymer has been observed to be a good adsorbent for removal of heavy metal ions from water. The objective of the present work was to synthesize a functional hydrogel to be used as an effective adsorbent for removal of heavy metal ions from water. Accordingly, instead of only IA or its binary copolymer as reported elsewhere, in the present work a ter-copolymer of poly (AAco-AM-co-IA) (TP) was integrated with PS and crosslinked with N, N′-methylenebisacrylamide (MBA). These hydrogels were characterized and used for the removal of heavy metal ions from water by adsorption. Among the various heavy metal ions, special attention has been given to removal of Cu(II) and Cd(II) ions because of its toxic nature and detrimental effect on environments including plants and animals. The World Health Organization (WHO) has recommended a maximum permissible limit of 0.005 mg/L and 4.0 mg/L for Cd(II) and Cu(II), respectively in drinking water.30,31 Most of the reported works describe adsorption of single metal ions. However, the actual waste contains several metal ions and their mutual interaction also strongly influences the adsorption properties of the adsorbent. Thus, in the present work instead of only single Cu(II) or Cd(II) ions, binary mixtures of these two metal ions were also studied for adsorption at varied process conditions with the composite type hydrogels prepared from the tercopolymer and the PS.

2. MATERIALS AND METHODS



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2.1. Materials. PS (amylose content 20%, humidity content

Competitive Removal of Cu(II) and Cd(II) from Water Using a

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