Novel Fe7S8/C nanocomposites with accelerating iron cycle for enhanced heterogeneous electro-Fenton degradation of dyes

Fe3+/Fe2+ interconversion is one of the key factors for heterogeneous electro-Fenton degradation of organic pollutants. In this study, MIL-101Fe-derived carbon wrapping Fe7S8 nanocomposite (Fe7S8/C-1-600) exhibits outstanding rhodamine B (RhB) degradation ability with extremely low iron leaching and high recyclable degradability within 60 min in a wide pH range. Moreover, Fe7S8/C-1-600 presents a much higher activity for RhB degradation than Fe3O4 counterpart without sulfidation, which could be mainly attributed to the accelerated Fe3+/Fe2+ cycling by iron with both multiple valences (Fe0, Fe2+, and Fe3+) and sulfur species (S2− and S22−) of the catalyst. The enhancement of H2O2 adsorption and activation into OH on Fe7S8 surface is confirmed by density functional theory calculations with respect to that on Fe3O4. Interestingly, SO4·− can be generated by reacting S22− with dissolved O2 and subsequently converted into ·OH, which further facilitates RhB degradation. These findings may shed a new insight into the potential application of metal sulfides for wastewater treatment.