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INTRODUCTION
Synthetic dyes are employed in many industries like printing, plastic, textile, paper and food. Because of the harmful effects of dyes on both humans and the environment, the industries’ effluent must be treated (Liu et al. 2010). Various methods have been developed so far for treating industrial wastewater, including membrane separation (Tahri et al. 2012), electro coagulation (Merzouk et al. 2010) and adsorption (Salama et al. 2014). Among the several techniques for removal of dyes, adsorption has been found as a facile, economical, cheap and effective method (Kaplan & Kasgoz 2011). Many efforts have been made to find an appropriate adsorbent. Polymeric adsorbents enable to adsorb anionic and cationic pollutants such as dyes and metal ions. Polymeric hydrogels are crosslinked, hydrophilic, three-dimensional networks with functional groups that can adsorb wastewater pollutions. Due to their abundant resources, biodegradability, low cost, low toxicity, and environmentally friendly natures, they have attracted special research attention (Bao et al. 2011; Pourjavadi et al. 2015). Generally, hydrogels are obtained from biopolymers such as chitosan (CTS) (Moussout et al. 2016), starch (Guclu et al. 2010), collagen (Kurdtabar et al. 2015), guar gum (Sharma et al. 2015) and cellulose (Liu et al. 2010). CTS is a linear biopolymer, which is prepared by deacetylation of chitin, and is the second most abundant polymer in the world after cellulose. CTS is an effective adsorbent for removal of dye and metal ions due to the presence of hydroxyl and amino functional groups. The pollution adsorption property of CTS, along with its non-toxicity and biodegradability, has made it useful for environmental applications (Auta & Hameed 2014). Nowadays, grafting functional groups like carboxyl and sulfonic groups on the polysaccharide backbone can improve adsorption capacity and adsorption rate; this is done by grafting acrylamide (AM) (Yang & Ni 2012), acrylic acid (AA) (He et al. 2012) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) (Bao et al. 2011). Because of double carboxylic acid groups of itaconic acid, it can be used to improve adsorption capacity in removal of cationic dyes from aqueous solutions (Kaplan & Kasgoz 2011). Thus, special attention has been paid to hydrogels due to their different functional groups and high adsorption capacity.
Lately, because of the poor mechanical strength of polymeric hydrogels, an inorganic component like smectite group...