Preparation of TiO₂-based powders with high photocatalytic activities

TiO₂-based powders doped with a small amount of SiO₂ were prepared by a sol-gel method and subsequently were heated to precipitate fine anatase crystals. Although the obtained powders have large specific surface areas (≈200 m² · g⁻¹), they showed poorer activity in a photocatalytic property than the undoped TiO₂ powders which have the area of 50 m² · g⁻¹. The SiO₂-doped TiO₂ powders were treated chemically with aqueous NaOH. Infrared reflection spectra showed that the treatment reduced the amount of SiO₂ in the powders. The photocatalytic property of the powders was extremely improved by the treatment, and the powders showed higher activity than the undoped TiO₂ powders.