The TiO 2 nanotube sample was prepared via a NaOH solution in a Teflon vessel at 150℃. The as-prepared nanotubes were then treated with H 2SO 4 solutions. The TiO 2 nanotube has a crystalline structure with open-ended and multiwall morphologies. The TiO 2 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: TiO 2 nanotubes treated with 1.0 mol/L H 2SO 4 solution (TiO 2(1.0M H 2SO 4) nanotubes)>TiO 2 nanotubes treated with 0.2 mol/L H 2SO 4 solution (TiO 2(0.2M H 2SO 4) nanotubes)>TiO 2 nanotubes >TiO 2 powder. This was attributed to the fact that TiO 2 nanotubes treated with H 2SO 4 was composed of smaller particles and had higher specific surface areas. Furthermore, the smaller TiO 2 particles were beneficial to the transfer and separation of photo-generated electrons and holes in the inner of and on the surface of TiO 2 particles and reduced the recombination of photo-generated electrons and holes. Acid treatment was particularly effective for TiO 2 nanotubes, this increase in activity was correlated with the concentration of H 2SO 4 solution.
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