Heavy metal adsorptive application of hydrolyzed corn starch

Starch is an abundant natural and renewable carbohydrate polymer, with cation sorption deficiency due to its high crystallinity and amylose content which causes substantive mass transfer resistance during adsorption. Therefore, the present study synthesized polyacrylonitrile grafted starch (graft-starch) that was subjected to heat treatment and saponification reaction to facilitate a partial transformation of the available amide groups (due to copolymer grafting) into carboxylate groups. The reactions afforded the desired polyacrylonitrile-grafted starch hydrogel (‘ Poly-g-Hyd’) which was further utilized for zinc ion uptake. It was observed that the polar nitrile (CN) groups of the grafted polyacrylonitrile substantially improved the ‘ Poly-g-Hyd’ water absorption capacity and cation binding interaction, as well as entrenched stable network chains that are insoluble in water. The water absorption and zinc ion sorption capacities of 490 g water/g ‘Poly-g-Hyd’ and 508.85 mg/g, were respectively recorded. Furthermore, the optimum adsorption conditions were established at pH 5.0, 20 min and 0.3 g/L, while the Freundlich and pseudo-second-order models provided the best fit to the isotherm and kinetic data, respectively. The study, therefore, demonstrated the effectiveness of ‘ Poly-g-Hyd’ in the uptake of aqueous zinc ions.