The multi-staged formation process of titanium oxide nanotubes and its thermal stability

The multi-staged formation process of titanium oxide nanotubes was investigated in detail under a hydrothermal treatment. During the synthesis procedure, an intermediate stage (tree-like structures) was observed before the formation of the titanium oxide layered structures. The layered structure of titanium oxide generally was considered to exfoliate directly from raw TiO2 materials through the alkaline hydrothermal treatment. The rolling process of the layered structures of titanium oxide was confirmed by TEM observation after the alkaline hydrothermal treatment for the raw TiO2 materials, followed by washing with 4 M HNO3 aqueous solution. The thermal stability of the tube products was investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The result showed that both the morphology and crystal phase of titanium oxide nanotubes could be retained even after calcination at 650 °C.