Oxygen vacancies induced capture effect for enhancing peracetic acid activation and selective high-valent cobalt-oxo species formation

Abstract

High-valent cobalt-oxo species (Co^IV=O) is being increasingly investigated due to its anti-interference properties and selective degradability; however, overcoming the high occupancy of the Co 3d-orbitals to selectively form Co^IV=O remains a challenge. Herein, oxygen vacancies (OVs) were engineered on the surface of Co₃O₄ (OV-Co) via an acid etching strategy to enhance the activation of peracetic acid (PAA). The OV-Co-8/PAA system achieved complete degradation of sulfamethoxazole (SMX) within 60 min, with a k_obs value (0.07612 min⁻¹) 7 times higher than that of the pristine Co₃O₄ (CK-Co)/PAA system (0.01082 min⁻¹). Methyl phenyl sulfoxide (PMSO), used as a molecular probe, confirmed the OV-induced formation of Co^IV=O, which dominated the degradation process in the OV-Co-8/PAA system. Situ Raman spectroscopy and theory calculations indicated that OVs can induce the cleavage of the O–O bond in PAA adsorbed at Co sites through a capture effect, resulting in the co-coordination at Co sites (CH₃CO₂-Co-OH). Such co-coordination facilitated electron transfer from the Co sites via the Co d_z2–O p_z channel (CH₃CO₂-Co), stabilizing the previously unfavorable Co–O anti-bonding orbitals and promoting Co^IV=O formation. From a thermodynamic perspectives, OVs reduce the energy required for CH₃CO₂ release and facilitate the transfer of H through a proton-coupled electron transfer (PCET) pathway. Additionally, OV-Co-8 was loaded onto a carbon-felt membrane for water purification, achieving continuous SMX degradation with low cobalt leaching. This study advances the understanding of the molecular-level mechanism of surface defects in PAA activation and guides the rational design of efficient environmental catalysts.