Sorption of Pb(II), Cu(II), Fe(II) and Cr(VI) metal ions onto cross-linked graft copolymers of chitosan with binary vinyl monomer mixtures

Novel adsorbents for sorption of Pb(II), Cu(II), Fe(II) and Cr(VI) metal ions from waste water were synthesized by simultaneous cross-linking and graft copolymerization of chitosan (Ch) with N-isopropyl acrylamide (NIPAM) and its binary comonomers acrylic acid, acrylamide and acrylonitrile in presence of azo-bis(isobutyronitrile) (AIBN) as free radical initiator and N,N′-methylene bisacrylamide (MBA) cross-linker. FTIR, XRD, SEM and TGA/DTA techniques were used to describe the structural aspects of cross-linked graft copolymers. The improvement in swelling properties of the synthesized hydrogels was utilized to explore their potential for sorption of toxic metal ions from aqueous solutions. Metal ion sorption by synthesized cross-linked adsorbents was studied as a function of the change in contact time, pH, temperature and concentration of metal ions from a solution of individual metal ions. Selective sorption of metal ions was performed by immersing polymeric samples in a solution containing four metal ions in the same concentration. Candidate polymers showed preferential sorption of metal ions in order of Cu(II) > Pb(II) > Fe(II) > Cr(VI) ions. Cross-Ch-g-poly(NIPAM-co-AAc), Cross-Ch-g-poly(NIPAM-co-AAm) and Cross-Ch-g-poly(NIPAM), showed best results for sorption of all ions from single and four component solutions.