Self-Induced Oxygen Vacancies on Carboxyl-Rich MIL-121 Enable Efficient Activation and Oxidation of Benzyl Alcohol under Visible Light

The oxygen vacancies could efficiently drive the photocatalytic oxidation of aromatic alcohol through the activation of reactants. However, the activation between aromatic alcohol and O2 (oxidant) over oxygen vacancies is rarely studied. Herein, the ZnIn2S4/MIL-121 heterostructure with abundant surface uncoordinated carboxyl was rationally designed for benzyl alcohol (BA) oxidation under visible light. Oxygen vacancies on catalysts were self-induced after the surface complexation between the uncoordinated carboxyl and BA molecules. Based on the reaction results, it is concluded that the oxygen vacancy activation to BA is more effective than that to O2 for BA oxidation over ZnIn2S4/MIL-121 hybrids. Specifically, when the activation fully occurs on BA (reaction in N2), an admirable conversion of 93.9% (corresponding production rate of benzaldehyde: 2348 μmol·g-1·h-1) is achieved, which is 3.4 times that of pure ZnIn2S4, whereas an inferior conversion of 45.9% is obtained in O2 due to the competition effect between O2 and BA for oxygen vacancies.