The evolution of morphology and crystal form of titanate nanotubes under calcination and its mechanism

Titanate nanotubes with an outer diameter of ca. 9 nm were obtained with hydrothermal method followed by an ion exchange reaction. The as-prepared sample was composed of H2Ti2O4(OH)2, which was thermally unstable. The effect of calcination temperature on its morphology and crystal form was investigated. Based on the results, especially the appearance of lotus-root-like structures, the transformation mechanism was proposed, which involved the dehydrations of intralayered and interlayered OH groups. The decrease in the interlayer distance and the transformation from titanate to anatase were ascribed to the interlayered dehydration, while the destruction of nanotubes into particles was caused by the intralayered one.