Abstract: TiO₂ nanometer thin films were prepared on soda-lime glass and pre-coated SiO₂ soda lime glass
via a sol-gel method, respectively. The as-calcined TiO₂ nanometer thin films were then treated by dipping them in 1mol/L HNO₃ aqueous solution.
The TiO₂ nanometer films before and after surface acid treatment were characterized by UV-VIS spectrophotometry, X-ray photoelectron spectroscopy
(XPS) and scanning electron microscopy (SEM), and photocatalytic activity of the thin films were evaluated by photocatalytic decoloration of methyl
orange aqueous solution. The results show that SiO₂ layer can effectively retard the diffusion of Na ions from glass substrates to TiO₂ films.
The photocatalytic activity of TiO₂ thin films is significantly enhanced after treated with HNO₃ solution. The enhancement of the
activity is ascribed to the reduction of sodium ions and the increase of the surfacehydroxyl content in the TiO₂ films.

Key words: TiO₂ nanometer thin films, photocatalytic activity, surface acid treatment