Ultrathin MoS2 nanosheet-wrapped Fe3O4 nanocrystals synergistically activate peroxymonosulfate for enhanced removal of organic pollutants

In peroxides-based advanced oxidation technologies (AOPs) using Fe-based catalysts, the low efficiency of Fe-ions cycling hinders their industrial applications. Recently, MoS2 has been validated to be a promising co-catalyst that can effectively promote the dynamic cycling of Fe-ions during the reaction. However, the activities of the reported MoS2-loaded Fe-based catalysts still decreased significantly after 3-5 cycling reactions, so it is necessary to develop a catalyst with high activity and stability. A series of MoS2 @Fe3O4-x (MF-x) catalysts were successfully constructed to trigger peroxymonosulfate (PMS) to eliminate the refractory organics. Ultrathin MoS2 nanosheets (similar to 5.7 nm) were uniformly and firmly coated on the surface of Fe3O4 nanoparticles via Fe-S bridging interaction. Pure MoS2 made little contribution to the climbazole (CBZ) degradation. Compared to the Fe3O4/PMS system, the adsorption and degradation efficiencies of the CBZ by MF-x/PMS system were improved by 7.5 and 4 times, respectively. The Fe-II/Fe-III and Mo-IV/Mo-VI redox cycles on the MF-x surface could interact and work in synergy during the catalytic activation of PMS to degrade pollutants. MF-0.23 was an effective and stable catalyst for application over a wide pH range (2.0-9.8). Moreover, it efficiently dealt with other representative refractory contaminants with different pKa values, such as fluconazole (FZ), phenol, and rhodamine B (RhB). The primary active free radicals in MF-0.23/PMS system were detected to be O-2(center dot-) and SO4 center dot-. Specifically, the generated O-2(center dot-) not only participated in the degradation of contaminants but also contributed to the MoIV regeneration. With outstanding catalytic activity, broad applicability, excellent reusability, and long-term stability, the MoS2 nanosheet-wrapped Fe3O4 nanocrystals should be an ideal heterogeneous catalyst for PMS-based AOPs.