The once reported Ag-modified CaTiO3 photocatalyst was reexamined by optimizing the Ag loading amount and using a conventional photochemical reactor. This revealed that the Ag-modified CaTiO3 photocatalyst actually showed both high production rate of CO (54 µmol h −1) and excellent selectivity toward CO formation (94%) by suppressing the H2 production via water splitting. It is suggested that the high photocatalytic performance originates from not only the optimized amount of cocatalyst and the high irradiation light intensity but also the high concentration of dissolved CO2 that was achieved by a bubbling flow of CO2 at the lower reaction temperature. These reaction conditions provided ca. 40 times higher CO formation rate. It was proposed that the deposited small Ag nanoparticles are the selective active sites for CO formation and the CaTiO3 crystal surface produces H2 preferably.

Flux method was applied to prepare sodium hexatitanate (Na 2 Ti 6 O 13) photocatalysts for reduction of carbon dioxide with water. The preparation conditions were examined, such as the starting material, the flux, the composition in the molten mixture, the holding temperature, and the cooling rate of the molten mixture, so as to obtain several sodium hexatitanate samples consisting of the crystals with various morphologies and sizes. These samples were loaded with 0.1 wt% of Ag cocatalyst nanoparticles (Ag/Na 2 Ti 6 O 13) and examined for photocatalytic reduction of carbon dioxide with water, where carbon monoxide, hydrogen and oxygen were formed as products. It was found that the photocatalytic production rate of carbon monoxide varied with the morphology and the size of the sodium hexatitanate crystals. Among the prepared samples, thick rod-like crystals exhibited high photocatalytic activity for the reduction of carbon dioxide.