Interface-induced built-in electric field breaks the oxo wall for efficient water purification: Directional generation and essential mechanism of Co(IV)=O species.

Faced with the growing threat of aquatic emerging contaminants, Co(IV)=O species exhibit great potential owing to their strong oxidation capacity and high selectivity, yet their efficient formation is constrained by the oxo wall that emphasizes considerable 3d antibonding electron occupancy destabilizing terminal Co-O bonds. Current studies focus on electron transfer regulation but neglect the vital role of proton transfer. In this study, the Co3O4/ZnOCN heterojunction catalyst was synthesized. The interface-induced built-in electric field drives electrons to spontaneously transfer from Co sites to Zn sites, reducing Co 3d anti-bonding occupancy to circumvent the oxo wall. Formed intramolecular hydrogen bonds facilitate proton transfer, thereby diminishing the high dissociation energy of OH bonds within PMS. Consequently, the catalyst has favorable thermodynamic and kinetic properties. It can completely degrade ciprofloxacin within 5 min (kobs= 1.11 min-1). Benefiting from high selectivity of Co(IV)=O species, the system resists real-water matrix interference, efficiently degrades electron-rich pollutants and maintains catalytic stability over 12 h continuous operation. In situ Raman spectroscopy successfully detected Co(IV)=O species and the key intermediate (HSO4-) along the coupled electron-proton transfer pathway (CEPT). DFT calculations indicate that there is strong electronic coupling between Co 3d (dxz and dz2) and O 2p (px and pz). Strengthened Co-O bonds and hydrogen bonds effectively facilitate generation of Co(IV)=O species via the CEPT pathway. This work offers novel mechanistic insights and theoretical support for the directional generation of Co(IV)=O species, as well as lays a foundation for developing stable and efficient catalytic systems for water pollution remediation.