Chitosan‑g‑maleic acid for effective removal of copper and nickel ions from their solutions

Pollution of the environment associated with discharging the toxic heavy metals in water makes us focus the light to solve this problem. In continuation of our efforts, we aim in this work to utilize the graft copolymer (chitosan‑g‑maleic acid) to purify water from copper and nickel ions. The graft copolymer has been synthesized using gamma radiation and the grafting conditions have been optimized by studying the influence of acetic acid concentration (0.5-10% V/V), monomer concentration (5-17.5% w/v), chitosan concentration (0.25-2.5% w/v) and absorbed dose (0.5-5 kGy). FT-IR and TGA have been employed to characterize the graft copolymer. The metal ions uptake by the prepared graft copolymer was investigated and the influence of contact time, solution pH, polymer concentration, and metal ion concentration was studied. Adsorption kinetic models (pseudo-first-order, pseudo-second-order, and intra-particle diffusion equations) and adsorption isotherms (Langmuir, Freundlich, and Temkin equations) were also studied. It was found that the adsorption kinetics and isotherm agreed well with pseudo-second-order and Langmuir equations, respectively, indicating that the adsorption was chemisorption. The adsorption capacities of CTS‑g‑MA were 312.4 mg g^-1 and 70.1 mg g^-1 for Cu²⁺ and Ni²⁺, respectively. Effect of co-existence of other cationic ions on the adsorption capacity was also investigated.