Spin-selection-favored peroxymonosulfate activation on reaction-induced Co–N1O2 sites enables 1O2-biased yet radical-parallel oxidation

ABSTRACT Transformations in metal coordination environments, particularly their impact on spin-state transitions, remain underexplored in peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs). In this study, we synthesize a Co1/C3N5 single-atom catalyst using a coordination–recrystallization strategy followed by argon pyrolysis. The Co–N2O1 sites evolve to Co–N1O2 upon PMS activation, enabling spin-selection-favored activation and efficient pollutant degradation. The evolved site enables spin-selection-favored PMS activation that co-generates sulfate radicals (·SO4⁻) and singlet oxygen (1O2), operating in a 1O2-biased yet radical-parallel regime. Within this regime, Co1/C3N5 achieves a 5.3-fold increase in the pseudo-first-order rate constant (kapp) for oxytetracycline degradation relative to pristine C3N5 under identical conditions, and it consistently outperforms more than 30 state-of-the-art PMS-based catalysts. The catalyst further exhibits broad-spectrum activity toward structurally diverse antibiotics and dyes, while maintaining durability in matrix-rich water and under continuous-flow operation. Overall, this work links reaction-induced single-site evolution to spin-aware oxygen transfer, providing concise design guidance for selective and robust PMS-activated AOP catalysts.