Enhanced Cr(VI) stabilization by terrestrial-derived soil protein: Photoelectrochemical properties and reduction mechanisms

Abstract

Glomalin-related soil protein (GRSP) is a stable iron-organic carbon mixture that can enhance heavy metal sequestration in soils. However, the roles of GRSP in the transformation and fate of Cr(VI) have been rarely reported. Herein, we investigated the electrochemical and photocatalytic properties of GRSP and its mechanisms in Cr(VI) adsorption and reduction. Results showed that GRSP had a stronger ability for Cr(VI) adsorption and reduction than other biomaterials, with the highest adsorption amount of up to 0.126 mmol/g. The removal efficiency of Cr(VI) by GRSP was enhanced (4–7%) by ultraviolet irradiation due to the hydrated electrons produced by GRSP. Fe(II) ions, persistent free radicals, and oxygen-containing functional groups on the GRSP surface as electron donors participated in the reduction of Cr(VI) under dark condition. Moreover, Cr(III) was mainly adsorbed on the –COOH groups of GRSP via electrostatic interactions. Based on 2D correlation spectroscopy, the preferential adsorption occurred on the GRSP surface for Cr(VI) in the sequential order of CO → COO– → O–H → C–O. This work provides new insights into the Cr(VI) adsorption and reduction mechanism by GRSP. Overall, GRSP can serve as a natural iron-organic carbon for the photo-reduction of Cr(VI) pollution in environments.