Water assisted crystallization, gas sensing and photo-electrochemical properties of electrochemically synthesized TiO2 nanotube arrays

Abstract

We report a simple water assisted crystallization process for electrochemically synthesized TiO₂ nanotube (TNT) arrays at room temperature (30 °C) and near-room temperature (50 °C). The TNT array samples kept immersed in de-ionized water at room temperature for durations from 1 day to 6 days show a distinct anatase phase confirmed by both X-ray diffraction and transmission electron microscopy. When the process is repeated at an elevated temperature of 50 °C, the crystallization is accelerated with the appearance of an anatase phase within 8 h of treatment. Interestingly, addition of 0.05 M HCl or HNO₃ to the DI water during treatment helped in forming the rutile phase of TiO₂, along with the dominant anatase phase. By carefully choosing the nanotube parameters (length and diameter) it has been possible to retain the nano-tubular morphology, which is advantageous for applications such as solar cells and gas sensing. Finally, we show the gas sensing and photo-electrochemical characteristics of the DI water crystallized TNT arrays. The samples show good sensitivity and appreciable values of photo-current under the given experimental conditions.