Comparison of photochemical properties of brookite and anatase TiO2 films

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 x 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 mug cm(-2) min(-1) and -0.10 +/- 0.01 mug cm(-2) min(-1), respectively). However, the rate constants for photoinduced hydrophilicity, which were evaluated by the changes in water contact angles (theta) under rather weak UV light irradiation (5 muW cm(-2)), were better for the brookite surface than the anatase one. Moreover, the brookite-rich film became more hydrophilic (theta = 10degrees) than the anatase one (theta = 18) after long time exposure to weak UV light irradiation, and showed a good ability for the photoinduced hydrophilicity.