In this study, sol-gel-derived amorphous TiO2 powders have been demonstrated to exhibit superior photocatalytic activity over the anatase TiO2 crystals for CO2 reduction. The reduced species of CO2 in the water medium by the sol-gel-derived photocatalysts included CH4, CO, C2H4, and C2H6 species, and the CH4 was the majority. After 10-hour irradiation, the accumulated CH4 yield and the total quantum efficiency for hydrocarbons was 11.23 µmol/g and 2.2 % in the amorphous TiO2-based system, which was respectively 15 and 14 times higher than the corresponding values in the anatase-TiO2-based system. The high surface area (327 m2/g) and abundant surface OH groups (18.67/nm2) were responsible for the high activity of the amorphous TiO2 photocatalyst. According to FTIR, CO2-TPD, and EPR, the surface OH groups were able to transform adsorbed CO2 molecules into covalent-bonded carbonate/bicarbonate species, which facilitated electron transfer from the TiO2 surface to the C-species through the Ti-O-C bonding. In addition, the surface OH groups also trapped holes to form Ti-O-O-Ti species, which promoted O2 evolution from H2O and released H+ ions for hydrocarbon formation. These functions effectively improved surface charge utilization and thus contributed to high photoactivity of the amorphous surface even though severe charge recombination still took place inside the bulk lattice.

Roles of surface properties of amorphous TiO2 in photocatalytic CO2 reduction

2019 Fall National Meeting

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