Photoexcited Hole-Enabled Synthesis of Surface High-Valent Cobalt-Oxo Species with Water as the Oxygen Atom Source for Water Purification

Abstract

High-valent cobalt-oxo species (Co^IV═O) are key intermediates in catalytic chemistry but suffer a great challenge in their efficient and mild synthesis due to the strong electronic repulsion between the cobalt center and the oxygen ligand. Herein, we report a new approach to synthesizing surface Co^IV═O on the Co₃O₄/BiVO₄ (CoBi) catalyst via a photoexcited hole-induced process using water as the oxygen atom source. The interfacial Co²⁺─O─Bi³⁺ bonds act as the atomic-level channels to directionally transport photoexcited holes driven by the internal electric field effect. It has been found that H₂O was photolyzed to cobalt-coordinated hydroxyls that were turned to Co^IV═O via a photoexcited hole-induced deprotonation. The isotopic labeling experiments confirmed that the oxygen atom source of Co^IV═O was derived from water rather than chlorite. A synergistic effect was formed between photocatalysis and transition metal-catalyzed chlorite activation, which enhanced the degradation of sulfadiazine (SDZ) and elevated the conversion ratio of chlorite to chlorine dioxide (ClO₂) from 40% to 60%. The present work has elucidated the essential role of H₂O and photoexcited holes in the formation of Co^IV═O and provides a viable strategy to synthesize surface high-valent metal species utilizing ubiquitous water and sunlight for water purification.

Keywords: High‐valent cobalt‐oxo species; Internal electric field; Oxygen atom transfer; Synergistic effect; Water purification.