The alkaline photo-sulfite system triggers Fe(IV/V) generation at hematite surfaces

The formation of high-valent iron-oxo species (i.e., Fe(IV) = O, Fe(V) = O) is of vital importance in iron-mediated advanced oxidation processes (AOPs) for the rapid removal of organic contaminants, and it is mainly derived from the reduction of ferrate(VI) or the oxidation of homogeneous Fe(II). In this study, we have shown Fe(III) in the hematite surfaces under light illumination in the presence of sulfite can generate high-valent iron-oxo species that efficiently degrade refractory organics under alkaline conditions. Interactions between hematite and sulfite under xenon lamp irradiation in aqueous solution were investigated by combination of quenching experiments, electron spin resonance (ESR), high-performance liquid chromatography coupled with mass spectrometer (HPLC-MS), and X-ray photoelectron spectroscopy (XPS) techniques, and a possible mechanism was proposed. Importantly, this work demonstrates a novel and fundamental breakthrough toward the design synthesis and understanding of the high-valent iron-oxo species, and also might provide potential applications in the treatment of alkaline wastewaters.