Encapsulating CuO quantum dots in MIL-125(Ti) coupled with g-C₃N₄ for efficient photocatalytic CO₂ reduction

Improving the stability of metallic oxide quantum dots (QDs) in a reaction system containing water is crucial for their practical applications in photocatalytic reduction of carbon dioxide. Herein, we use simple complexation-oxidation method to encapsulate CuO QDs in the pores of metal organic framework of MIL-125(Ti), and further combine it with g-C₃N₄ to form a composite photocatalyst, i.e., g-C₃N₄/CuO@MIL-125(Ti). Benefiting from the protection of the framework of MIL-125(Ti), the composite photocatalyst exhibits significantly improved stability in reaction systems containing water. In addition, due to the close contact of CuO QDs to the active catalytic site of Ti in MIL-125(Ti), the photogenerated electrons in the MIL-125(Ti) and g-C₃N₄ can be smoothly transferred to the confined CuO QDs, which remarkably enhances the photocatalytic activity of g-C₃N₄/CuO@MIL-125(Ti) for photocatalytic CO₂ reduction in the presence of water. An optimization of the photocatalyst has led to the yields of CO, methanol, acetaldehyde and ethanol up to 180.1, 997.2, 531.5 and 1505.7 μmol/g, respectively. This work provides an effective strategy for improving the stability and charge separation property of metallic oxide-QDs modified photocatalyst toward efficient photocatalytic CO₂ reduction.