Effects of HNO_3 Treatment on Photocatalytic Activity and Surface Microstructures of Sol-gel Derived TiO_2 Nanometer Thin Films

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.