Sulphur vacancy derived anaerobic hydroxyl radical generation at the pyrite-water interface: Pollutants removal and pyrite self-oxidation behavior

We demonstrate that FeS2 possessing sulfur vacancies (SVs), under anaerobic water environment, can stabilize the H2O adsorption with a strong exothermic effect to compensate the apparent energy barrier of H2O oxidation on pyrite surface. Adsorbed H2O dissociates at SV site via π-back donation of localized electron, and thus breaks through thermodynamic restriction of H2O oxidation to generate bound hydroxyl radical through a one-electron transfer process of localized holes (Vs+). Meanwhile, the synergistic effect of surface Fe3+ and circumjacent H2O molecule can also promote the oxidation of H2O adsorbed at Fe3+ site to produce free hydroxyl radical via oxidation reaction. The generated hydroxyl radical on pyrite surface can induce the oxidation of different pollutants, and also contribute to the pyrite self-oxidation process. These findings clarify the in-depth mechanism of anaerobic hydroxyl radical generation at pyrite-water interface, and shed light on anaerobic environmental effect of pyrite and other natural iron sulfide minerals.