Photocatalytic Conversion of Carbon Dioxide Over Silver-Modified Lanthanide Titanate Under Photoirradiation Exceeding 300 nm

The photocatalytic conversion of CO2 into valuable chemicals is a promising approach for artificial photosynthesis. The photocatalytic conversion of CO2 over Ag-modified lanthanide titanates (Ln2Ti2O7) was investigated in this study under photoirradiation with wavelengths longer than 300 nm using 2-propanol as a hole scavenger. Among the various Ln2Ti2O7 materials tested, La2Ti2O7 exhibited superior photocatalytic performance. The activity was strongly dependent on the crystallinity and surface area of the La2Ti2O7 host, with the optimal sample obtained by calcination at 1423 K for 2 h. Furthermore, the Ag cocatalyst loading method significantly affected the CO production rate. Chemical reduction facilitated the formation of highly dispersed, small metallic Ag nanoparticles (2–10 nm), which were essential for efficient CO2 reduction. In contrast, the photodeposition and impregnation methods resulted in the formation of larger, aggregated Ag particles (20–50 nm), leading to lower photocatalytic activity. The optimised Ag/La2Ti2O7 photocatalyst achieved a CO formation rate of approximately 120 µmol h−1 with high selectivity (>90%). The stoichiometric formation of acetone and isotopic labelling experiments using 13CO2 confirmed that the reaction proceeded via the reduction of CO2 to CO, coupled with the oxidation of 2-propanol.