Research paper Micro- and nano-sized bentonite filled composite superabsorbents of chitosan and acrylic copolymer for removal of synthetic dyes from water Ruma Bhattacharyya, Samit Kumar Ray ⁎ Department of Polymer Science and Technology, University of Calcutta, 92, A.P.C. Road, Kolkata 700009, India abstract article info Article history: Received 29 April 2014 Received in revised form 12 September 2014 Accepted 13 September 2014 Available online xxxx Keywords: Chitosan Copolymer Bentonite Dye Isotherms Kinetics Bentonite clay, chitosan and acrylic copolymer gels have been separately reported for the adsorption of dyes. In the present work these three kinds of adsorbents were combined to make composite hydrogels. The hydrogels were characterized by FTIR, XRD, DTA–TGA and SEM. The swelling, diffusion and network parameters of the hydrogels were also evaluated. These composite hydrogels were used for the removal of malachite green and methyl violet dyes from water. The composite hydrogels showed high adsorption and removal% of both of these dyes. The mass transfer coefficient, diffusion coefficient and thermodynamic parameters of the dye adsorp- tion were also determined. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Chitin is the second most abundant biopolymer in nature after cellulose. It consists of unbranched chains of (1, 4)-2-acetamido-2- deoxy-D-glucose. Chitosan is obtained by deacetylation of chitin. Chito- san is widely used as an adsorbent for the removal of metal ions and dyes. The presence of amino, acetamide and hydroxyl functional groups in its structure serves as the active sites for adsorption (Wu et al., 2001). However, like most of the biopolymer based superabsorbents, the sta- bility of chitosan based superabsorbents or hydrogels is poor because of its extensive hydrophilicity and pH sensitivity (Wang et al., 2011). To overcome this limitation, chitosan has been modified by chemical crosslinking (Wan Ngah et al., 2011), making derivative of chitosan (Wan Ngah et al., 2011) or grafting a synthetic polymer to chitosan (Konaganti et al., 2010; Wang et al., 2011; Yang et al., 2013). Chitosan has also been modified by forming its semi and full IPN with synthetic polymers (Zhao et al., 2012; Maity and Ray, 2014) or making the com- posite hydrogels of chitosan (Wan Ngah et al., 2011). Composite hydrogels of chitosan may be obtained by incorporating inorganic filler (Wang et al., 2011; Nešic' et al., 2013; Auta and Hameed, 2014) in its matrix or incorporating chitosan in the matrix of a synthetic polymer (Zhao et al., 2012; Maity and Ray, 2014). In fact, in- tegration of various adsorbents to a single composite adsorbent results in increased mechanical strength, surface functionality, selectivity, re- generation and surface area (Auta and Hameed, 2014). Composite hydrogel may be prepared by impregnation, grafting, crosslinking, che- lation and in situ polymerization (Chang and Juang, 2004). During in situ polymerization the reactive monomers are allowed to polymerize in aqueous dispersion of inorganic fillers (Bhattacharyya and Ray, 2013). By this method the fillers are strongly impregnated in the matrix of the resulting polymer. The objective of the present study was to synthesize a strong adsorbent by integrating three different ad- sorbents, i.e., a natural polymer such as chitosan, a synthetic copolymer and inorganic clay such as bentonite. By this integration favorable ad- sorption properties of these different adsorbents will be synergistically combined in a single composite hydrogel. The novelty of the present work lies on the technique used for combining the synthetic copolymer with chitosan and clay. Instead of direct blending or grafting chitosan and clay were incorporated in situ during polymerization of the acrylic monomers. Thus, in the present work acrylic acid, acrylamide and MBA (crosslinker) were allowed to free radically polymerize in the presence of chitosan and clay in water. The monomers acrylic acid, acrylamide and crosslinker MBA were chosen since the copolymer gel obtained from these synthetic monomers was reported to be a good adsorbent for industrial dyes (Li et al., 2011). Accordingly, several hydrogels were prepared by varying molar ratio of acrylic acid and acrylamide, concentration of initiator and crosslinker. The chitosan incorporated copolymer gel (F0) showing the best swelling characteris- tics was identified and micro- and nano-sized bentonite clay was fur- ther incorporated during polymerization of F0 to produce composite hydrogels. Bentonite is an inorganic adsorbent. Its main component montmo- rillonite consists of two layers of tetrahedral silica sheets sandwiching Applied Clay Science xxx (2014) xxx–xxx ⁎ Corresponding author. Fax: +91 33 23508386. E-mail address: samitcu2@yahoo.co.in (S.K. Ray). CLAY-03162; No of Pages 11 http://dx.doi.org/10.1016/j.clay.2014.09.015 0169-1317/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Please cite this article as: Bhattacharyya, R., Ray, S.K., Micro- and nano-sized bentonite filled composite superabsorbents of chitosan and acrylic copolymer for removal of synthetic dyes f..., Appl. Clay Sci. (2014), http://dx.doi.org/10.1016/j.clay.2014.09.015