UC Davis

Herein, we systematically investigated the mechanisms of OH production and arsenic (As(III)) oxidation induced by sulfur vacancy greigite (Fe₃S₄) under anoxic and oxic conditions. Reactive oxygen species analyses revealed that sulfur vacancy-rich Fe₃S₄ (SV-rich Fe₃S₄) activated molecular oxygen to produce hydrogen peroxide (H₂O₂) via a two-electron reduction pathway under oxic conditions. Subsequently, H₂O₂ was decomposed to OH via the Fenton reaction. Additionally, H₂O was directly oxidized to OH by surface high-valent iron (Fe(IV)) resulting from the abundance of sulfur vacancies in Fe₃S₄ under anoxic/oxic conditions. These differential OH-generating mechanisms of Fe₃S₄ resulted in higher OH production of SV-rich Fe₃S₄ compared to sulfur vacancy-poor Fe₃S₄ (SV-poor Fe₃S₄). Moreover, the OH production rate of SV-rich Fe₃S₄ under oxic conditions (19.3 ± 1.0 μM•h^-1) was 1.6 times greater than under anoxic conditions (11.8 ± 0.4 μM•h^-1). As(III) removal experiments and X-ray photoelectron spectra (XPS) showed that both OH production pathways were favorable for As(III) oxidation, and a higher concentration of As(V) was immobilized on the surface of SV-rich Fe₃S₄ under oxic conditions. This study provides new insights concerning OH production and environmental pollutants removal mechanisms on surface defects of Fe₃S₄ under anoxic and oxic conditions.