Autonomous Stepwise Process of Adsorption, Reduction, and Desorption of Chromium Ion Using Hydrogel Beads Having Poly(ethylene glycol) Chains

Abstract

Hydrogel beads were prepared by free-radical polymerization of acrylate having poly(ethylene glycol) (PEG) as the side chain, and applied to the detoxication of hexavalent chromium (Cr(VI)) in aqueous solutions in a batch mode. The beads adsorbed Cr(VI) and reduced the Cr(VI) to Cr(III) without adding any reducing agents, followed by spontaneous release of the resulting Cr(III) to the solution. Such behaviour is attributable to a difference in non-covalent interaction between the PEG chains and the two chromium species. The reduction time of Cr(VI) strongly depended on the solution acidity; it varied from 24 hours for 2N HCl and 10 weeks for pH 6. The gel beads could tolerate 20 cyclic uses at least.