Comparison of photochemical properties of brookite and anatase TiO2 films

Abstract

The photocatalytic oxidation activity and photoinduced hydrophilicity of brookite-rich TiO₂ film were compared to those of anatase TiO₂ film under ultraviolet (UV) light irradiation. The photocatalytic oxidation activities were evaluated by the initial photodegradation rates of methylene blue and cis-9-octadecenoic acid. The rates for the methylene blue bleaching were nearly identical (−2.2 × 10⁻³ Abs min⁻¹) for the brookite-rich and anatase films, and the rate for cis-9-octadecenoic acid decomposition on the brookite-rich film was slightly less than that on the anatase one (−0.08 ± 0.01 μg cm⁻² min⁻¹ and −0.10 ± 0.01 μg cm⁻² min⁻¹, respectively). However, the rate constants for photoinduced hydrophilicity, which were evaluated by the changes in water contact angles (θ) under rather weak UV light irradiation (5 μW cm⁻²), were better for the brookite surface than the anatase one. Moreover, the brookite-rich film became more hydrophilic (θ = 10°) than the anatase one (θ = 18°) after long time exposure to weak UV light irradiation, and showed a good ability for the photoinduced hydrophilicity.