Influence of synthetic conditions in the hydrothermal preparation of TiO₂ nanotubes

Abstract: TiO₂ nanotubes have been synthesized using a 2-step strategy that involves the hydrothermal preparation of intermediate titanates followed by a subsequent thermal/hydrothermal treatment of these species to produce the desired oxide. In the first step the influence of parameters such as temperature, pH or reaction time on the composition, structure and morphology of the intermediate species has been studied. We have then examined how temperature and the presence of surfactants affect the composition, structure, morphology and particle size of the titanium dioxide obtained in the second thermal/hydrothermal treatment. In particular, we have studied the effects that the presence of CTAB has upon the morphology of the final product. Both intermediate and final species have been studied by means of X-ray diffraction, transmission electron microscopy, IR spectroscopy and thermogravimetric analysis. This way we have been able to identify NaTi₃O₆(OH).2H₂O and (TiO₂)_x(H₂O)_y as the intermediate titanate species and rutile and anatase as the final TiO₂ polymorphs. Finally, it is worth mentioning the preparation of spindle- or oval-shaped anatase, obtained via hydrothermal synthesis in the presence of CTAB.