Alkaline hydrothermal kinetics in titanate nanostructure formation

In this study, the mechanism of precursor dissolution and the influence of kinetics of dissolution on titanate nanotube formation were investigated. This comparative study explored the dissolution kinetics for the case of commercial titania powders, one composed of predominantly anatase (>95%) and the other rutile phase (>93%). These nanoparticle precursors were hydrothermally reacted in 9 mol L⁻¹ NaOH at 160 °C over a range of reaction times of between 2 and 32 h. The high surface area nanotube-form product was confirmed using X-ray diffraction, FT-Raman spectroscopy, and transmission electron microscopy. The concentration of nanotubes produced from the different precursors was established using Rietveld analysis with internal and external corundum standardization to calibrate the absolute concentrations of the samples. Interpretation of the dissolution process of the precursor materials indicated that the dissolution of anatase proceeds via a zero-order kinetic process, whereas rutile dissolution is through a second-order process. The TiO₂ nanostructure formation process and mechanism of TiO₂ precursor dissolution was confirmed by non-invasive dynamic light scattering measurements. Significant observations are that nanotube formation occurred over a broad range of hydrothermal treatment conditions and was strongly influenced by the order of precursor dissolution.