Cu/TiO2 Derived from Cu-Doped MIL-125 for Enhanced Photocatalytic CO2-to-CH4 Conversion

Photocatalytic CO2reduction into CH4is a promising route for solar fuel production, but its efficiency is still limited by poor charge separation, insufficient CO2activation, and sluggish multi-electron transfer kinetics. Herein, Cu-modified TiO2(Cu/TiO2) was prepared by calcining a Cu-modified defective MIL-125(Ti) precursor, denoted as Cu-MIL-125, through a temperature-controlled calcination strategy. The effects of calcination temperature on the structural evolution, surface chemical states, interfacial charge transport, and CO2photoreduction performance were examined. These results indicated that the Cu/TiO2was successfully prepared, while the crystallinity, porous structure, and interfacial electronic properties of Cu/TiO2were strongly dependent on the calcination temperature. Among the obtained samples, the Cu/TiO2sample obtained by calcining Cu-MIL-125 at 450 °C (450 Cu/TiO2) exhibited the highest CH4formation rate, reaching 15.90 μmol g−1h−1, corresponding to an approximately 9.8-fold enhancement over TiO2calcined from defective MIL-125(Ti) at 450 °C, together with a high CH4selectivity of 93.05%. Control experiments and13CO2isotope-labeling tests confirmed that the detected carbon-containing products were generated from CO2under photocatalytic conditions. In situ diffuse reflectance infrared Fourier transform spectroscopy measurements further revealed the formation of carbonate, bicarbonate and hydrogenated carbon-containing intermediates during the reaction. This work offers a practical route for constructing metal–organic framework-derived Cu/TiO2photocatalysts for selective CH4production from CO2.