A step towards length control of titanate nanotubes using hydrothermal reaction with sonication pretreatment.

It was experimentally confirmed that the average length of titanate nanotubes (TNTs) can be increased and controlled to a certain degree by applying sonication pretreatment to their titania precursors prior to hydrothermal synthesis. Without sonication, the average length of the TNTs synthesized by the hydrothermal process was much shorter due to constricted diffusion of the hydroxyl ion (OH(-)) and the sodium ion (Na(+)) through the narrow interparticle space of agglomerated titania precursors, thereby retarding the TNT formation mechanism. On the other hand, much longer TNTs with an average hydrodynamic size of 490-1760 nm were produced when the sonication pretreatment was applied. Based on microscopic observations on the transformation of the present precursors and the reported nanotube formation phenomena during the hydrothermal process, a mechanism contributing to length control is proposed.