Photocatalytic Partial Water Oxidation Promoted by a Hydrogen Acceptor-Hydroxyl Mediator Couple.

Hydrogen peroxide (HO) is an important chemical in synthetic chemistry with huge demands. Photocatalytic synthesis of HO via oxygen reduction and water oxidation reactions (ORR and WOR) is considered as a promising and desirable solution for on-site applications. However, the efficiency of such a process is low due to the poor solubility of molecular oxygen and the rapid reverse reaction of hydroxyl radicals (OH) with hydrogen atoms (H). Here, a strategy is proposed to boost the HO evolution via oxidation of water by employing a H acceptor (A, nitrocyclohexane), an OH mediator (M, dioxane), and a photocatalyst (CdS nanosheets). While OH radicals are stabilized by dioxane to produce ketyl radicals prior to the formation of HO, H atoms are effectively utilized in the generation of cyclohexanone oxime, an important intermediate in the production of Nylon 6. The system displays a rapid kinetic accumulation of HO (0.13 min) to a high concentration (6.6 mM). At optimum reaction conditions, a high quantum efficiency (16.6%) and light-to-chemical conversion efficiency (4.9%) can be achieved under 410 nm irradiation.