Boosting peroxodisulfate activation by MIL-68(Fe) derived magnetic Fe3S4 nanosheets: Key role of sulfur vacancy

Abstract

The peroxodisulfate (PDS) activation promoted by iron-based catalysts has captured ever-increasing attention in degrading organic contaminants. However, the difficulty in converting Fe(Ⅲ) to Fe(Ⅱ) greatly limits the generation of Fe(Ⅱ) and greatly inhabits the practical use of iron-based catalysts for PDS activation owing to the low reactivity between Fe(Ⅲ) and PDS. In this contribution, the magnetic Fe3S4 nanosheets with sulfur vacancy (SV) were synthesized by sulfuring MIL-68(Fe) with thioacetamide (TAA). Various characterizations, such as SEM, XRD, and XPS were employed to confirm the Fe3S4 catalyst, which was subsequently applied to activate PDS to degrade Rhodamine B (RhB). Fe3S4/PDS system exhibited superhigh RhB degradation performance without extra energy involvement, resulting in complete degradation in 5 min with 0.15 g/L Fe3S4 and 0.4 mM PDS. The enhanced RhB degradation performance could be attributed that the S-vacancy significantly promoted Fe(Ⅲ)/Fe(Ⅱ) cycle and nanosheet structure enabled well-exposure of active catalytic sites. EPR tests and quenching experiments proved that the Fe3S4 promoted the PDS activation in generating SO4•−, •OH, Fe(Ⅳ), and 1O2 to degrade RhB. We proposed possible RhB degradation pathway according to DFT calculations and HR-MS. T.E.S.T. analysis showed that most intermediates were less toxic than RhB, demonstrating that Fe3S4/PDS system was beneficial for RhB degradation.