Effect of the temperature and concentration of NaOH on the formation of porous TiO2

The influence of the temperature and concentration of NaOH on the formation of porous TiO2 was investigated. The porous TiO2 was obtained only after a 24-h immersion in 5 M NaOH at 353 K. The X-ray diffraction pattern indicated that the porous layer consisted of a mixture of anatase and rutile types of TiO2. During immersion in the NaOH solution, the anodic and cathodic reactions proceed at the same time on the titanium. From the cathodic polarization measurements, the cathodic reaction proceeded mainly the hydrogen evolution reaction. Therefore, a part of the adsorbed hydrogen penetrated into the titanium. The penetration of hydrogen confirmed with a glow discharge optical emission spectroscopy. The hydrogen evolution reaction continues during immersion in the 5 M NaOH solution at 353 K. However, the hydrogen evolution did not proceed in the low concentration of NaOH solution or at below 283 K. In addition, although the hydrogen evolution continues during immersion in 5 M NaOH solution at 303 or 333 K. As a result, the content of hydrogen in the titanium is insufficient to form the porous TiO2 layer so that the porous layer is not produced on the titanium.