Enhanced photocatalytic activity of nanotube-like titania by sulfuric acid treatment.

The TiO2 nanotube sample was prepared via a NaOH solution in a Teflon vessel at 150 degrees C. The as-prepared nanotubes were then treated with H2 SO4 solutions. The TiO2 nanotube has a crystalline structure with open-ended and multiwall morphologies. The TiO2 nanotubes before and after surface acid treatment were characterized by X-ray diffraction (XRD), scanning electron microscopy(SEM), transmission electron microscopy (TEM) and UV-VIS dispersive energy spectrophotometry (DRS). The photocatalytic activity of the samples was evaluated by photocatalytic degradation of acid orange II in aqueous solutions. It was found that the order of photocatalytic activity was as follows: TiO2 nanotubes treated with 1.0 mol/L H2SO4 solution (TiO2 (1.0M H2SO4) snanotubes) > TiO2 nanotubes treated with 0.2 mol/L H2SO4 solution (TiO2 (0.2M H2O4) nanotubes) > TiO2 nanotubes > TiO2 powder. This was attributed to the fact that TiO2 nanotubes treated with H2SO4 was composed of smaller particles and had higher specific surface areas. Furthermore, the smaller TiO2 particles were beneficial to the transfer and separation of photo-generated electrons and holes in the inner of and on the surface of TiO2 particles and reduced the recombination of photo-generated electrons and holes. Acid treatment was particularly effective for TiO2 nanotubes, this increase in activity was correlated with the concentration of H2 SO4 solution.