Vacancy-engineered Co3O4@NC for enhanced peroxymonosulfate activation: mechanistic insights into dual N/C-vacancy synergy and 1O2-dominated bensulfuron-methyl degradation

Non-radical oxidation (e.g., singlet oxygen 1 O 2 ) is advantageous in wastewater treatment for its selectivity and interference resistance, but efficient 1 O 2 generation remains challenge. Herein, nitrogen‑carbon dual-vacancy Co₃O₄@NC catalysts were innovatively constructed via pyrolysis combined with KBH₄ reduction, successfully establishing a peroxymonosulfate (PMS)-based advanced oxidation system dominated by singlet oxygen ( 1 O₂). The proportional increase in nitrogen/carbon vacancy (V N/C ) concentration by tuning KBH₄ reducing agent dosage directly correlates with elevated 1 O₂ yield, thereby optimizing catalytic performance. 1 O₂, identified as the dominant reactive species in bensulfuron-methyl (BSM) degradation via steady-state concentration analysis, was predominantly generated through the reaction between V N/C and PMS, with minor contributions from vacancy-mediated dissolved oxygen activation and superoxide radical conversion. Under the optimized conditions, Co 3 O 4 @NC-800-1/PMS system could degraded 10 mg·L −1 BSM 100 % at a high k obs of 0.382 min −1 , which was 38.20-fold and 5.09-fold higher than those of vacancy-free Co 3 O 4 –800-1 and mono‑carbon-vacancy Co 3 O 4 @C-800-1, respectively. DFT results indicated the formation of V NC demonstrated enhanced thermodynamic stability, with a significantly lower formation energy (−2.82 eV) compared to single vacancies (V N : −2.01 eV, V C : −2.02 eV), favoring their preferential generation in the Co 3 O 4 @NC system. Theoretical calculations and experimental studies have confirmed that dual-vacancy catalysts are more easily generated and exhibit higher catalytic activity. The toxicity assessment of by-products through Ecological Structure Activity Relationships (ECOSAR) and Escherichia coli biotoxicity tests revealed a significant reduction in toxicity after degradation. This work offers new insights into the design of multifunctional vacancy catalysts and the regulation of non-radical pathways degradation. • Co 3 O 4 @NC rich in N/C-vacancies was prepared by thermal treatment and KBH 4 reduction. • 1 O₂-dominated Co₃O₄@NC-V NC /PMS system was produced by the interaction between V NC and PMS. • KBH₄-gradient reduction method modulated vacancy density, 1 O₂ yield, and degradation kinetics. • DFT confirmed V NC 's preferential formation enhances PMS adsorption/activation. • Significant toxicity reduction confirmed by ECOSAR prediction and E. coli viability tests.