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 pi-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.

Automated summary

In anaerobic water environments, FeS2 with sulfur vacancies stabilizes H2O adsorption to compensate for the energy barrier of H2O oxidation on pyrite surfaces. The presence of surface Fe3+ and nearby H2O molecules promotes the oxidation of adsorbed H2O, generating free hydroxyl radicals. These results shed light on the mechanism of anaerobic hydroxyl radical generation on pyrite surfaces and its environmental implications.