Utilizing the oxygen-atom trapping effect of Co ₃ O ₄ with oxygen vacancies to promote chlorite activation for water decontamination

Abstract

Heterogeneous high-valent cobalt-oxo [≡Co(IV)=O] is a widely focused reactive species in oxidant activation; however, the relationship between the catalyst interfacial defects and ≡Co(IV)=O formation remains poorly understood. Herein, photoexcited oxygen vacancies (OVs) were introduced into Co₃O₄ (OV-Co₃O₄) by a UV-induced modification method to facilitate chlorite (ClO₂^-) activation. Density functional theory calculations indicate that OVs result in low-coordinated Co atom, which can directionally anchor chlorite under the oxygen-atom trapping effect. Chlorite first undergoes homolytic O-Cl cleavage and transfers the dissociated O atom to the low-coordinated Co atom to form reactive ≡Co(IV)=O with a higher spin state. The reactive ≡Co(IV)=O rapidly extracts one electron from ClO₂^- to form chlorine dioxide (ClO₂), accompanied by the Co atom returning a lower spin state. As a result of the oxygen-atom trapping effect, the OV-Co₃O₄/chlorite system achieved a 3.5 times higher efficiency of sulfamethoxazole degradation (~0.1331 min^-1) than the pristine Co₃O₄/chlorite system. Besides, the refiled OVs can be easily restored by re-exposure to UV light, indicating the sustainability of the oxygen atom trap. The OV-Co₃O₄ was further fabricated on a polyacrylonitrile membrane for back-end water purification, achieving continuous flow degradation of pollutants with low cobalt leakage. This work presents an enhancement strategy for constructing OV as an oxygen-atom trapping site in heterogeneous advanced oxidation processes and provides insight into modulating the formation of ≡Co(IV)=O via defect engineering.