CO2 photoconversion using photocatalyst of TiO2 thin films deposited by sputtering technique

TiO₂ thin films were used as photocatalysts in CO₂ photoconversion to solar fuels under UV irradiation. The films were deposited via sputtering while varying the working pressure for each deposition and could produce CH₂O₂ and CH₃OH. According to Raman results, the films Ti-1 (3.87 Pa) and Ti-2 (3.73 Pa) deposited at high working pressure have a higher contribution of brookite phase compared with the films Ti-3 (3.47 Pa) and Ti-4 (3.33 Pa) obtained at low working pressure. Likewise, a higher presence of the brookite phase increases the atomic concentration of C–O bonds and ⁻OH groups on the film surface, which reaches the CO₂ photoconversion, as the TiO₂ capacity to adsorb CO₂ on the surface is determined by the O and C species present in the film. Therefore, the films Ti-1 and Ti-2, deposited at high working pressures and significantly contributing to the brookite phase, can produce 0.56 and 0.94 μmol of CH₃OH, respectively. Meanwhile, according to the Raman and XPS results, the highest formic acid production was obtained from the Ti-3 and Ti-4 films, which show a less brookite phase presence and a higher contribution of O²⁻ ions in TiO₂.