Multi-functional amorphous TiO2 layer on ZIF-67 for enhanced CO2 photoreduction performances under visible light

Multi-functional amorphous TiO2 (a-TiO2) layer is uniformly decorated on ZIF-67 through a simple hydrothermal and low temperature calcination methods, which promotes the conversion efficiency and selectivity in the photoreduction of CO2 under visible light. The optimized ZIF-67@a-TiO2 demonstrates high CO production of 43.8 mu mol after 4 h irradiation with high CO selectivity of 67.2%, which are substantially enhanced compared with that of pristine ZIF-67. State and transient optical and electrochemical tests indicate that the multi-functional a-TiO2 layer not only leads to enhanced utilization of incident light by the effective light scattering effect, but also serves as blocking layer to suppress the charge recombination by restraining the backwards photoelectron flow without interrupting the photoelectron transfer from the photosensitizer to ZIF-67. In addition, the a-TiO2 layer introduces abundant mesoporous characteristics in the catalyst, which facilitates the mass diffusion without scarifying the overall CO2 absorption capacity. Meanwhile, it is tentatively believed that the H3O+ is more likely adsorbed on the hydrophilic a-TiO2 with highly polarized surface, which inhibits the H-2 generation and results in the pleasant CO selectivity. Furthermore, the a-TiO2 shell effectively suppresses the photo-corrosion of ZIF-67, which finally leads to the superior photocatalytic performances along with the high stability.