TiO2 nanorod films grown on Si wafers by a nanodot-assisted hydrothermal growth

We report the controlled hydrothermal growth of rutile TiO2 nanorods on Si wafers by using an anatase TiO2 nanodot film as an assisted growth layer. The anatase nanodot film was prepared on the wafer by phase-separation-induced self-assembly and subsequent heat-treatment at 500 degrees C. The nanodots on the wafer were then subjected to hydrothermal treatment to induce the growth of rutile TiO2 nanorod films. The size and dispersion density of the resulting TiO2 nanorods could be varied by adjusting the Ti ion concentration in the growth solution. The TiO2 nanorods were of the rutile phase and grew in the [001] direction. The growth mechanism reveals that the growth of the rutile nanorods was wholly dependent on the existence of rutile TiO2 seeds, which could be formed by the dissolution-reprecipitation of the anatase nanodots during hydrothermal treatment or under the high-temperature conditions of the subsequent heat-treatment of the as-prepared nanodots. In controlling the rutile nanorod growth, the anatase nanodots show more efficiency than a dense anatase film. Preliminary evaluations of the rutile nanorod films have demonstrated that the wettability changed from highly hydrophobic to superhydrophilic and that the photocatalytic activity was enhanced with increasing nanorod dispersion density. (C) 2011 Elsevier B.V. All rights reserved.