Linking mineral reactivity to its semiconducting band structure

Abstract

Certain transition metal oxides are known to readily reduce chromium ion from its highly toxic +VI oxidation state to its +III state, which is an important nutrient for human biological functions. Herein, the factors which govern the reduction of Cr (VI) to Cr (III) by five selected Fe and Mn based metal oxides were investigated in order to better understand the mechanism driving the reduction. Results show that of the five metal oxides (hematite, hollandite, magnetite, manganite, and Romanechite), only Romanechite displayed the capability of reducing the concentration of Cr (VI) in isolation. This distinctive capability is likely related to their differences in their electronic properties, namely the differing band alignment with respect to Cr (VI) / Cr (III) redox couple in the aqueous environment.