Dual roles of MoS2 nanosheets in advanced oxidation Processes: Activating permonosulfate and quenching radicals

Peroxymonosulfate (PMS) based advanced oxidation processes (AOPs) have received increasing attention in wastewater treatment attributed to the high efficiency for organic pollutants removal. Our study reported that single layer MoS₂ exhibited greatly efficient PMS activation through one electron transfer and thus showed excellent orange II (OII) degradation performance. Sulfate radical (SO₄^∙−) and hydroxyl radical (∙OH) were detected as the primary reactive oxygen species (ROS) in the activation reaction system by radical quenching experiments and EPR spectroscopy. More importantly, we note that excessive dosage of 1T-dominated MoS₂ had a quenching effect on SO₄^∙− and ∙OH, which caused the decline of OII degradation efficiency. Compared to 1T-dominated MoS₂, 2H-MoS₂ nanomaterial was a weaker radical quencher and exhibited better organic dye pollutant degradation performance owing to its better chemical stability and adsorptive property. In addition, aligned stacks of MoS₂ nanosheets were prepared to preserve oxidation surface/edges, which weakened the ROS quenching effect and thus improved OII removal capacity. The dual roles of MoS₂ nanosheets, i.e. activating PMS and quenching free radicals, were systematically studied for the first time. Meanwhile, the protection of oxidation active sites proved to be a feasible way of suppressing ROS quenching effect to improve the degradation performance in PMS-AOPs, and thus providing a new sight for the activator design.