A multistep attachment process: Transformation of titanate nanotubes into nanoribbons

The mechanism of the conversion of titanate nanotubes into nanoribbons is of considerable interest. The details of the transformation processes involved when nanoribbons are produced from a P25 TiO₂ powder precursor by alkaline hydrothermal treatment have been investigated systematically by transmission electron microscopy. A multistep attachment model is proposed for the growth at the early stage of coarsening. The treatment duration has a strong effect on the change in product morphology from hollow nanotubes into nanoribbons, since the nanotubes cannot retain their morphology in the strong alkaline solution for extended periods of time. Most of the nanotubes were etched and dissolved, providing the nutrients for subsequent nanoribbon growth. Some stable nanotubes grew spirally internally to form nanowires or became connected together to form rafts which acted as the grains for nanoribbon growth. With increasing hydrothermal time, a large number of nanotubes and other fragments became attached to the grains which began to grow larger and eventually formed the nanoribbons, in a process in which the stepped faces and kinked faces became fused and were eliminated while the flat faces were retained in the nanoribbon morphology.