Rutile TiO2 films with 100% exposed pyramid-shaped (111) surface: photoelectron transport properties under UV and visible light irradiation

Abstract

In this work, a facile hydrothermal method was employed to directly grow the rutile TiO₂ film with 100% exposed pyramid-shaped (111) surface onto a FTO conducting substrate, and the resulting rutile TiO₂ film was used as the photoanode after annealing at 450 °C for 2 h in argon (Ar) to investigate photoelectrocatalytic properties under UV and visible light irradiation. The photoelectrocatalytic activities of the resultant photoanode under UV (main wavelength of 365 nm) and visible light (λ > 400 nm) irradiation were evaluated using water as the probe compound. The photoelectrocatalytic activity of the UV light illuminated photoanode was found to be 0.144 mA mW⁻¹, significantly higher than that obtained from the visible light illuminated photoanode (0.102 μA mW⁻¹). Despite this, the determined value of 0.102 μA mW⁻¹ represents an excellent visible light photoelectrocatalytic activity of the photoanode. The origin of visible light activity could be attributed to the doped Ti³⁺ in the bulk TiO₂. The superior photoelectrocatalytic activity could be due to the high reactivity of the exposed high-energy (111) surface and the superior photoelectron transport property. A photoelectrocatalytic method was used to manifest the photoelectron transport properties inside the rutile TiO₂ film and concurrently quantify the inherent resistances (R₀) of UV and visible light illuminated photoanodes. The determined R₀ values were 93.5 and 91.3 Ω for UV and visible light illuminated photoanodes, respectively. The similar R₀ values imply a similar photoelectron transport resistance inside the rutile TiO₂ film under UV and visible light irradiation, confirming that the measured R₀ is an inherent property of the photocatalyst film. This also implies that the rate of charge recombination is similar under UV and visible light irradiation. To our knowledge, this is the first time the electron transport properties of a rutile TiO₂ photoanode have been concurrently investigated under UV and visible light irradiation.