2D Copper-Porphyrin Metal-Organic Framework Nanosheet-Photosensitized TiO₂ for Efficiently Broadband Light-Driven Conversion of CO₂ to CH₄

The effective utilization of light is crucial in the use of the solar energy for CO2 conversion into valuable fuels and chemicals, in which improving the photocatalytic materials' capacity to absorb light is a key. Herein, a 2D copper-porphyrin metal-organic framework (MOF)-photosensitized titania, TiO2/Zn-CuTCPP, is reported, which can absorb wide range of light and photoreduce CO2 with high efficiency under full spectrum irradiation. Fluorescence spectral analysis elucidates the relationship between the photocatalytic activity and the electron-hole separation efficiency. In addition, mechanistic information obtained from electron paramagnetic resonance and in situ infrared analyses demonstrates that the presence of Cu-N-4 site in the MOF structure is conducive to the generation of hydrogen free radicals (center dot H), which plays a key role in the formation of intermediates, thus facilitating the hydrogenation in the reaction process. Consequently, TiO2/Zn-CuTCPP significantly enhances the photocatalytic conversion of CO2 into CH4 with a yield 14 times higher than that of P25.