Stable TiO2 nanotube arrays with high UV photoconversion efficiency

This work is intended to define an optimal methodology for preparing highly ordered TiO2 nanotube arrays by a 60-V anodization in a glycol ethylene solution. In order to obtain a mechanically stable structure with a high UV photoconversion efficiency, it is necessary to carefully control the growth mechanism through the anodization process. For this reason, the nanotube arrays have to be formed upon a compact titanium dioxide layer with well-defined thickness. Besides, both the fluoride concentration and anodization time are strictly correlated, because elevated concentrations and/or a long anodization time produce unstable structure with low photoconversion efficiency. The best result in the terms of reproducibility has been obtained previously for a three-minute galvanostatic oxide growth on the pickled titanium sheet, and anodic growth in ethylene glycol solution containing 1 wt.% H2O and 0.20 wt.% NH4F for a period lower than 4.5 h. The UV photoconversion efficiency was measured and a maximum value of 28.3% has been obtained, which is the highest result in the literature.