Understanding the Role of Dual Zinc and Indium Vacancies in ZnIn2S4 for the Visible-Light-Driven Photocatalytic Air-Oxidation of 5-Hydroxymethylfurfural

Defect engineering is an effective strategy to enhance the photocatalytic performance of ZnIn₂S₄ (ZIS), but it remains a formidable challenge to manipulate the cationic defects in the catalyst because of their high formation energies. Herein, dual Zn and In defects have been successfully created in the ZnIn₂S₄ (ZIS-5) with a facile cetyltrimethylammonium chloride (CTAC)-assisted hydrothermal method. The resulting ZIS-5, rich in cation vacancies, achieved a 3.6-fold higher 2,5-diformylfuran (DFF) yield (92.0%) than the pristine ZIS (25.8%) for the visible-light-driven photocatalytic air-oxidation of 5-hydroxymethylfurfural (HMF). Especially, ZIS-5 delivers a high DFF productivity of 1600 μmol g^–1 h^–1, significantly surpassing the previously reported catalysts (75–953 μmol g^–1 h^–1) for the photocatalytic oxidation of HMF to DFF in air. Density functional theory (DFT) simulations revealed that the presence of dual Zn and In defects endows the catalyst with defect states that intersect the Fermi level and lower work function. These enhance the migration and separation of photogenerated carriers in ZIS-5, significantly promoting O₂ activation and resulting in the generation of more reactive oxygen species (·O₂^– and ¹O₂) for the catalytic oxidation of HMF. This study offers valuable insights for guiding the design of photoredox reaction systems through cationic-defect-engineering strategies, enabling the efficient valorization of biomass-derived platform chemicals.