Photocatalytic Activity of Sol−Gel TiO₂ Thin Films on Various Kinds of Glass Substrates:  The Effects of Na⁺ and Primary Particle Size

To study the effects of ions diffused from the glass substrate on TiO 2 photocatalysis, TiO 2 thin films were prepared on different kinds of glass substrates at different heating temperatures. The TiO 2 films were characterized using X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD), ellipsometry, and absorption spectroscopy. The photocatalytic activities of the TiO 2 thin films were evaluated using the degradation reaction of trichloroethylene (TCE). Diffused ions such as Na + and Si 4+ raised the anatase formation temperature and increased the particle size of TiO 2 thin films ( r c ). The photocatalytic activity of the thin films largely depended on the particle size of TiO 2; the reciprocal number of the half-life of the TCE degradation, t 1/2 -1, was roughly proportional to r c -1.8 . The conventional recombination center hypothesis for the Na + ions might not hold for the sol−gel TiO 2 films.