Heterogeneous activation of peroxymonosulfate by sulfur-doped Fe_xMn_3-xO₄ (x=1, 2) for trichloroethylene degradation: Non-radical and radical mechanisms

The sulfurized spinels (S-FexMn3-xO4 (x = 1, 2)) were synthesized with the aim to enhance the internal electron transfer process (ETP) when used as a heterogeneous catalyst. A peroxymonosulfate (PMS) based heterogeneous catalytic oxidation (HCO) system was constructed based on the sulfurized spinels with dithionite (DNT) as a reductant to accelerate the redox cycle of surface metal, and trichloroethylene (TCE) was chosen as the target pollutant. The synthesized S-FexMn(3-x)O(4) featured with faster electron transfer and shorter ion transport path compared with the original spinel, especially S-Fe2MnO4 with cubic spinel structure, the activation energy for PMS decomposition significantly decreased via the mediated electron transfer from Fe-S and Mn-S bonds to PMS molecules. In addition, the formation of peroxo species bonding to the surface metal sites (metal-PMS*) was also involved in the formation of high-valent metal species (HVMS) in S-Fe2MnO4/PMS/DNT system, which could directly decompose organics in a non-radical manner via direct electron transfer due to their high redox po-tentials. Both the radical and non-radical mechanisms contributed to the degradation of TCE, and the contri-bution of different species followed the order of O-1(2) (30.4 %) > metal-PMS* (26.1) > O-2(center dot-) (21.3) > HVMS (8.0 %) > center dot HO (7.9 %) > SO4 center dot- (6.3 %). This study dedicates to deepening the understanding of ETP in PMS-HOC system that was based on the spinel catalyst, and provided a new strategy for the synthesis of spinel catalysts.