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

Abstract

Hydrogel beads were prepared by the free-radical polymerization of acrylates having poly(ethylene glycol) (PEG) as the side chain. These beads were used in a batch mode for the detoxication of hexavalent chromium (Cr(VI)) in aqueous solutions. The beads adsorbed Cr(VI) and reduced the Cr(VI) to Cr(III) without requiring any reducing agents to be added. The reduction was followed by the spontaneous release of the resulting Cr(III) in the solution. Such behaviour is attributable to a difference in non-covalent interactions between the PEG chains and the two chromium species. The reduction time for Cr(VI) strongly depended on the solution acidity; it varied from 24 h for a 2 N HCl aqueous solution to 10 weeks for a solution with a pH of 6. The gel beads could withstand a minimum of 20 cyclic uses.