Two-dimensional layered MoS₂ recently demonstrates great potentials in water purification via adsorption and catalysis. The structure-catalysis relationship of MoS₂ has not been well addressed. Herein, we investigated the mechanistic difference of 1 T-2H MoS₂ homojunctions in catalytic activation of peroxymonosulfate (PMS) and peroxydisulfate (PDS) for degrading butyl paraben (BPB). PMS/1 T-2H MoS₂ attains higher performance in BPB removal compared to PDS/1 T-2H MoS₂. 1 T phase in MoS₂ primarily contributed to PMS activation to produce SO₄^-, OH and ¹O₂, while the defects in MoS₂ coordinated the PDS activation to generate OH, ¹O₂ and O₂^-. Nevertheless, OH-induced BPB removal was the top priority for PMS/1 T-2H MoS₂ and PDS/1 T-2H MoS₂. The different activation pathways and reactive species resulted in the varying BPB removal, by-product distributions and toxicity. This work provides new insights into the different functions of MoS₂ in persulfates activation and the guidance in rational design of oxidant-oriented MoS₂ composites for sewage purification.