The effect of the hydrothermal treatment with aqueous NaOH solution on the photocatalytic and photoelectrochemical properties of visible light-responsive TiO2 thin films

The effect of the hydrothermal treatment with aqueous NaOH solution on the photoelectrochemical and photocatalytic properties of visible light-responsive TiO2 thin films prepared on Ti foil substrate (Vis-TiO2/Ti) by a radio-frequency magnetron sputtering (RF-MS) deposition method has been investigated. The hydrothermally treated Vis-TiO2/Ti electrodes exhibited a significant increase in their photocurrent under UV and visible light irradiation as compared to untreated Vis-TiO2/Ti electrode. SEM investigations revealed that the surface morphology of Vis-TiO2/Ti are drastically changed from the assembly of the TiO2 crystallites to the stacking of nanowires with diameters of 30–50 nm with increasing hydrothermal treatment time (3–24 h), accompanying the increase in their surface area. The separate evolution of H2 and O2 from water under solar light irradiation was successfully achieved using the Vis-TiO2/Ti/Pt which is hydrothermally treated for 5 h, while the H2 evolution ratio was 15 μmol h−1 in the early initial stage, corresponding to a solar energy conversion efficiency of 0.23%.