Selective adsorption of Cr(III) over Cr(VI) by starch-graft-itaconic acid hydrogels

Abstract

This work investigates the applicability of starch-graft-itaconic acid hydrogels in the adsorption of Cr(III) and Cr(VI) in single- and binary-component systems. Batch adsorption studies were conducted at room temperature for 24 h using 0.1 g of hydrogels to explore the effect of pH, volume, and the binary system of Cr(III) and Cr(VI) solutions with a starting concentration of 100 mg/L. At pH 8.0, the adsorption of Cr(III) and Cr(VI) was up to 14.13 mg/g ± 0.42 mg/g and 1.11 mg/g ± 0.36 mg/g, respectively, validating that it is indeed possible to selectively adsorb one valence over another. This is mostly owing to the starch-graft-itaconic acid hydrogel functional groups (e.g., carbonyl, carboxyl), that depending on the pH, can become positively charged, negatively charged, or neutrally charged, contributing to this selectivity. Furthermore, because the stable ionic forms of Cr(III) are similarly pH dependent, the major adsorption mechanisms for Cr(III) by starch-graft-itaconic acid hydrogels may be through electrostatic interactions, ion exchange, and surface complexation.