Influence of Pretreatment of Titanium Substrate on Long-Term Stability of TiO2 Film

TiO2 films coated on titanium substrates pretreated using different methods were prepared and characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, and electrochemical impedance spectroscopy. The results indicated that the TiO2 film coated on the substrate pretreated with oxalic acid (TiO2/Ti-OC) was tight, whereas the film coated on the substrate pre-treated with sodium carbonate solution (TiO2/Ti-SC) was loose. The catalytic activity of the TiO2/Ti-OC film for the degradation of ben-zamide remained up to 70% even after being dipped in deionized water for 280 d, whereas the TiO2/Ti-SC film lost its photoactivity after being dipped in water for 60 d. The deactivation of the catalyst was attributed to the flaking of the coated TiO2, which was caused by the continuous growth of the passive film between the substrate and the coated catalyst. Oxalic acid pretreatment could largely prevent the passive film from growing on the substrate and therefore greatly increased the stability of the catalyst during a long-term running. In a 35-d test of continuous decolorization of an aqueous reactive brilliant red X-3B solution, TiO2/Ti-SC exhibited very high photocatalytic activity and stability.