Synchronously engineering Co single atoms with oxygen vacancies on TiO2 for boosting selective photocatalytic benzyl alcohol oxidation

The selective photocatalytic oxidation of benzyl alcohols towards benzaldehyde has aroused the vital potential for high-value-added organics with a lower energy consumption to cope with the ever-increasing energy crisis. However, this reaction is usually hindered by a limited number of active sites, which makes it difficult to activate benzyl alcohol molecules. Herein, a facile pyrolytic transformation strategy is conducted to simultaneously engineer Co single atom and oxygen vacancies (V_O) on TiO₂ (Co₁/TiO₂) for promoting the selective photocatalytic oxidation of benzyl alcohol to benzaldehyde. The existence of the single Co single atom on Co₁/TiO₂ is verified by X-ray absorption fine structure (XAFS) and electron microscopy. The electronic structure and coordination condition of the Co single atom and the synchronic formation of oxygen vacancies can be resolved via XAFS and X-ray photoelectron spectroscopy (XPS) characterizations. A series of optical and electrochemical experiments demonstrate that introduced Co single atom can improve the light-harvesting for generating electron-hole pairs as well as the following charge separation and transfer. The prepared Co₁/TiO₂ photocatalyst is capable of converting benzyl alcohol to benzaldehyde with high conversion and selectivity when suitable amount of water exists. The cycling test and corresponding structural characterization demonstrate the excellent catalytic stability of the Co₁/TiO₂ catalyst. The controlled experiments and in-situ infrared experiments confirm that the introduction of Co single atomic sites and the adjacent Vo can accelerate the water splitting towards hydroxyl and oxygen molecular to superoxide radicals, and improve the selective photocatalytic oxidation of benzyl alcohol performance.