Electronic Structure Control of Oxidizing Capacity in Birnessite Minerals

Abstract

Birnessite, a layered manganese oxide, shows strong oxidation ability, but the main factor that controls its reactivity remains unclear. In this study, ten natural and synthetic birnessite samples with different interlayer cations and Mn(III)/Mn(IV) ratios were used to study the effect of electron affinity on oxidation behavior. The electron affinity measured by ultraviolet photoelectron spectroscopy ranged from 5.55 to 6.10 eV. Oxidation of Fe(II) and As(III) followed a pseudo-second-order model, with rate constants increasing from "1.1×1" "0" ^"-3"  "to5.6×1" "0" ^"-3"  g mg⁻¹ min⁻¹ for Fe(II) and from "6.8×1" "0" ^"-4"  "to3.3×1" "0" ^"-3"  g mg⁻¹ min⁻¹ for As(III). A clear positive relation was found between electron affinity and oxidation rate, showing that a higher electron affinity gives stronger oxidation ability. Surface analysis showed that Mn(IV) was partly reduced to Mn(III) and Mn(II), and hydroxyl groups formed after the reaction, which caused surface passivation and lower activity over time. Theoretical calculations supported these results and linked the conduction band position with electron affinity. The study proves that electron affinity directly affects oxidation ability and provides a useful guide for developing manganese oxide catalysts for pollutant control and environmental use.