Synthesis and characterization of graft copolymers of chitosan with NIPAM and binary monomers for removal of Cr(VI), Cu(II) and Fe(II) metal ions from aqueous solutions

To develop pH responsive hydrogels, N-isopropylacrylamide (NIPAM) has been grafted on to chitosan by free radical initiation method using azoisobutrylnitrile (AIBN) as an initiator. The optimum grafting conditions were worked out for grafting of NIPAM onto 1 g of chitosan by varying one reaction parameter at a time and keeping all other parameters constant. Binary monomers were grafted for five different concentrations of comonomers acrylic acid (AAc), acrylamide (AAm) and acrylonitrile (AN) at optimum grafting conditions evaluated for GMA alone onto chitosan. The grafted copolymers were analyzed by FTIR, TGA/DTA, XRD and SEM. The swelling studies for the grafted samples were performed at various pH in order to explore their end use in sorption of Cr(VI), Fe(II) and Cu(II) ions from water system. Metal ion sorption behaviour of polymeric samples was studied as function of time, temperature and pH. Various metal ion sorption parameters such as percent uptake (Pu), partition coefficient (Kd) and retention capacity (Qr) were discussed. Chitosan grafted with binary monomers NIPAM-co-AAc and NIPAM-co-AAm showed best results for sorption of all three metal ions.