Preparation of TiO₂ Nanotube Array on the Pure Titanium Surface by Anodization Method and Its Hydrophilicity

In this work, a highly ordered TiO₂ nanotube array on pure titanium (Ti) was prepared by anodization. The effects of the applied voltage and anodization time on the microstructure of the TiO₂ nanotube arrays were investigated, and their hydrophilicity was evaluated by the water contact angle measurement. It was found that a highly ordered array of TiO₂ nanotubes can be formed on the surface of pure Ti by anodized under the applied voltage of 20 V and the anodization time in the range of 6-12 h, and the nanotube diameter and length can be regulated by anodization time. The as-prepared TiO₂ nanotubes were in an amorphous structure. After annealing at 550°C for 3 h, the amorphous TiO₂ can be transformed to the anatase TiO₂ through crystallization. The anatase TiO₂ array exhibited a greatly improved hydrophilicity, depending on the order degree of the array and the diameter of the nanotubes. The sample anodized at 20 V for 12 h and then annealed at 550°C for 3 h exhibited a superhydrophilicity due to its highly ordered anatase TiO₂ nanotube array with a tube diameter of 103.5 nm.