Sulfur vacancy-mediated selective S-O bond scission dictates dominant singlet oxygen evolution in PMS activation

Molybdenum disulfide (MoS₂) is a promising candidate for peroxymonosulfate (PMS) activation; however, its practical application is constrained by the trade-off between selectivity and activity, as well as the unresolved role of transient intermediates. Specifically, the catalytic function of metastable Mo(V) species and their modulation by sulfur vacancies (Sv) remain contentious. Herein, we address these challenges by demonstrating that engineered Sv sites dictate selective S-O bond scission during PMS activation. Combining in situ low-temperature electron paramagnetic resonance (LT-EPR) and density functional theory (DFT) calculations, we reveal that the activated Sv centers drive the targeted cleavage of the S-O bond (elongated to 1.83 Å) while preserving the intact peroxo motif. Subsequently, these engineered vacancies serve as deep thermodynamic traps, specifically stabilizing a surface-confined Mo^(V)-∗OO^• intermediate via internal valence tautomerism within a closed Mo(IV)/Mo(V)/Mo(VI) redox cycle. This dynamic electron transfer steers the reaction towards dominant singlet oxygen (¹O₂) evolution. This ¹O₂-dominated pathway synergizes with a minor branch of auxiliary radicals to achieve deep pollutant mineralization (>70% TOC removal). Meanwhile, the kinetic accumulation of these metastable intermediates accounts for the reversible deactivation, which can be effectively restored via periodic thermal treatments, ensuring sustained catalytic activity. Enhanced by an intrinsic pH self-buffering capability and robust matrix adaptability, this defect-mediated targeted cleavage strategy establishes a mechanistic foundation for designing precision environmental catalysts.