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.