Light-induced coupling process of Fe redox cycling and natural dissolved organic matters oxidative decomposition at goethite surface: Key role of reactive oxidative species

Abstract

The interactions between widespread iron (oxyhydr)oxides (Fe oxides) and natural soil dissolved organic matters (DOM) are the dominant drivers in the geochemical behavior of Fe and the cycle of carbon in soil. Under visible light irradiation, their interactions become more complex due to the unique semiconducting structure of Fe oxides and complex components in DOM, which have not been deeply studied. In this study, the complex reactions occurred at the DOM-goethite interface under irradiation were investigated in detail. Fe2+(aq) from goethite reductive dissolution was accumulated at the DOM-goethite interface, along with the generation of reactive oxidative species (ROS). The reasons could be ascribed to the enhanced generation of photoelectron from the conduct band of goethite, ligand-to-metal charge transfer and photolysis of Fe(III)-carboxylate complexes. Moreover, the generated ROS were the main driving forces in the coupling process of Fe redox cycle and oxidative decomposition of DOM at goethite surface, inducing the formation of secondary Fe minerals and chemical composition change of DOM. This work provided new insights into the light-induced coupling process of Fe semiconducting minerals reductive dissolution and dissolved organic matters oxidation in top soil.