Effect of silica addition on crystallinity and photo-induced hydrophilicity of titania-silica mixed films prepared by sol-gel process

Effect of silicon dioxide (silica) addition into titanium oxide (titania) films on crystallinity and photo-induced hydrophilicity was investigated. Titania films and titania-silica mixed films with 20% or 50% silica were prepared by spin-coating deposition. For the titania films, photo-induced hydrophilicity is only observed in the films with anatase polycrystalline structure. For the titania-silica mixed films, however, despite these films showing no obvious anatase polycrystalline structure, very strong photo-induced hydrophilicity is observed. Particularly, even super-hydrophilicity where the contact angle shows 0° is easily observed for the titania-silica mixed films with 20% silica. The hydrophilicity of the titania films correlates closely with anatase crystalline structure. In the titania-silica mixed films, the synergistic effects of anatase polycrystalline structure of titania and water-trapping effect of silica are important for their strong photo-induced hydrophilicity.