Characterization and Mechanism of Nanotubular TiO₂ Formation

Nanotubular titanates, with an external diameter of 8nm and a wall thickness of about 1nm, were prepared by hydrothermal processing.The thermal stability of the products was tested,and their morphology and phase structures were analysed by means of transmission electronic microscopy (TEM)、X-ray diffraction (XRD) and thermal analysis (TG) respectively. The experimental results indicated that the formation of nanotubular products was due to hydrothermal treatment, rather than washing processes. However, pH values of washing solutions determined the composition of products. Na₂TiO₃, H₂TiO₃ and TiO₂ nanotubes were synthesised by controlling the conditions of washing process and heat-treatment. The nanotubes may be formed from nanosheets through curling in the primary stage, and grew longer by dissulation-reprecipitation processing with the increase of reaction time. The nanotubes remained in their shape at 400℃, fused together at 600℃, and completely lost their nanotubular shape to give aggregated anatase nano-particles at 800℃.