Optical properties of TiO2 thin films deposited by DC sputtering and their photocatalytic performance in photoinduced process.

TiO 2 thin films were deposited by DC Sputtering varying the deposit time. These films were characterized by XRD, AFM, photoluminescence, UV–Vis, ellipsometry and XPS. The optical properties of TiO 2 thin films with different thickness, influenced their photocatalytic behavior in two photoinduced process. When TiO 2 thin films were irradiated with a UV light, midgap states were generated and the electrons were placed in lower energies than its band gap, favoring the photocatalytic hydrogen production and CO 2 photoreduction. From PL technique analyses it was observed that electrons occupied midgap states between the bands, with lower energies than the band gap. With these results it was possible to propose an energy diagram in order to correlate with photoinduced processes results. The presence of Ti3+ species was reconfirmed by means of XPS analyses. These species could be found in the midgap states, generated by the interaction between the UV irradiation and the film surface, which contributed to the photocatalytic activity of the films. The hydrogen production was similar for all the thin films studied (33–35 μmol) associated to the presence of similar energy midgap states. In the case of CO 2 photoreduction, all films produced CH 2 O (8951 and 6252 μmol/g) and the films with a thickness of 330 and 420 nm generated CH 3 OH (970 and 292 μmol/g). The extinction coefficient confirmed the XRD results for the film with greatest deposited time, which exhibited the highest crystallinity. All photocatalytic results did not show any dependence with the thin film thickness. Image 1 • Thin films optical properties influenced activity of TiO 2 in photoinduced process. • Ti3+ species, located in midgap states, promoted the generation of 35 μmol of H 2. • Ti3+ species contributed to the photoreduction of CO 2 in formaldehyde and methanol. • Both photoinduced processes performance are independent on the thin film thickness. [ABSTRACT FROM AUTHOR]