Substrate-Assisted Crystallization and Photocatalytic Properties of Mesoporous TiO₂ Thin Films

Highly crystallized mesoporous TiO 2 thin films with enhanced photocatalytic activity were synthesized via a substrate-assisted strategy. Three types of substrates, namely, amorphous glass, polycrystalline Pt, and single-crystal Si(111) wafer, were employed to study their effects on the structure of TiO 2 films, by using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), X-ray diffraction (XRD), a Raman spectrometer, and a UV−vis spectrophotometer. When the substrate was changed from amorphous glass to polycrystalline Pt and then to single-crystal Si(111), a transition in the pore configuration took place from a cubical configuration to cagelike arrays, accompanied by an increase in nanocrystallinity. The observed transitions in pore configuration of mesoporous TiO 2 can be accounted for by the differences in nucleation behaviors and surface energy among the substrate systems involved. Mesoporous TiO 2 thin films of enhanced nanocrystallinity demonstrate improved photocatalytic activity for degradation of methylene blue (MB) under UV irradiation. They also show photoluminescence at room temperature, which is related to the radiative recombination of excitons.