Solvent-free aerobic photocatalytic oxidation of alcohols to aldehydes over ZnO/C3N4

Abstract

It is attractive but challenging to develop a non-noble metal-based photocatalytic system for the selective oxidation of benzyl alcohol to benzaldehyde under solvent-free conditions. Herein, a Z-scheme heterojunction photocatalyst of ZnO/C₃N₄ was designed and prepared. Under solvent-free irradiation conditions, benzyl alcohol can be exclusively oxidized to benzaldehyde with a yield of 99.8% and a formation rate of 16 633 μmol g⁻¹ h⁻¹ at room temperature. To the best of our understanding, the photocatalytic activity and selectivity of this oxidation process are much better than those reported for noble and non-noble metal-based photocatalyses. The water generated in the solvent-free oxidation process is revealed to disfavor the activity and selectivity. In addition, the mechanism of the title reaction is proposed. The present solvent-free photocatalytic system can be applied for the oxidation of benzylic, allylic, heterocyclic, and aliphatic alcohols to their corresponding aldehydes.