A band structure framework for understanding sorption processes : the role of Mn (III) in Cr (III) oxidation

Abstract

In the natural environment, manganese oxide is known for its excellent adsorption properties and strong oxidation ability. The interaction between Cr and Mn oxides is complex, which is not only due to the absorption and oxidation of Cr, but also due to the reduction and acid dissolution of the surface Mn cations. One of unusual property of certain phases of Mn oxide mineral is its ability to oxidize less toxic Cr (III) to more toxic Cr (VI). Oxidation of Cr (III) to Cr (VI) can significantly increase the mobility and toxicity of chromium, thus exacerbating its potential threat to the environment and water quality. Our results indicate that the high affinity of birnessite mineral (MnO2) for Cr (III) oxidation is due to its unusually large work function and electron affinity, which promotes electron injection from chemical species such as Cr (III) into the conduction band of the oxide.