Photo-catalysis using titanium dioxide nanotube layers

Photo-degradation of acid orange 7 in aqueous solution was used as a probe to assess the photo-catalytic activity of titanium dioxide nanotube layers under UV irradiation. The nanotube layers were prepared by anodization of Ti foil in 0.4 wt% hydrofluoric acid solution and then annealed at different temperatures between 300 °C and 600 °C for 1 h. The nanotube layers were characterized using X-ray diffraction and scanning electron microscopy. After the 500 °C anneal, the anatase and rutile mass fractions were measured to be about 55% and 45%, respectively. After annealing at 500 °C, the anatase crystallite size was maximum while the size and shape of the nanotubes remain unaffected. Such TiO2 nanotube layers showed strong photo-catalytic activity. During UV irradiation, we measured the total disappearance of the organic carbon and the formation of anion species to confirm the total mineralization of the acid orange 7.