InP-Quantum Dot Surface-Modified TiO2 Catalysts for Sustainable Photochemical Carbon Dioxide Reduction

In this study, an InP-cored quantum dot (InP-QD) material was prepared and physically immobilized on TiO2 particles functionalized with an archetypical reduction catalyst, (4,4-Y2-bpy)ReI(CO)3Cl (ReP, Y = CH2PO(OH)2), to form a new type of InP quantum dot-sensitized hybrid photocatalyst (InP-QD/TiO2/ReP) and evaluated as a lower-energy photosensitizer in this hybrid system. It was found that the TiO2 heterogenization of the InP-QD material promotes the photoexcited electron transfer process from the photoexcited InP-QD* to the inorganic TiO2 solid with rapid electron injection (by ∼25 ps) through oxidative quenching, resulting in efficient charge separation at the InP-QD/TiO2 interface. With such an effective photosensitization, the stabilization of the structurally vulnerable InP-cored QDs by TiO2 heterogenization resulted in highly efficient and durable photochemical CO2-to-CO conversion of the InP-QD/TiO2/ReP hybrid in a 10 times-repeated photolysis, giving a turnover number of ∼51,000 over a 420 h period without any damage to the InP-QD photosensitizer. The stability of TiO2-bound InP-QDs was confirmed by the comparative analysis of their photophysical and chemical structures before and after long-term photoreaction. This catalytic performance is the highest reported for QD-sensitized photocatalytic CO2 conversion systems using sacrificial organic electron donors. This study provides useful design guidelines for photocatalysts using QD materials as photosensitizing components.