Metastable Nature of Titanate Nanotubes in an Alkaline Environment

A systematic analysis of the effect of the composition and temperature of a NaOH/KOH binary aqueous mixture on the morphological properties of titanate nanostructures formed during alkaline hydrothermal transformation of TiO2 under atmospheric conditions has been performed using high-resolution transmission electron microscopy techniques. All observed nanostructures, including nanosheets, nanotubes, nanofibers, and nanoparticles, have been mapped over a wide range of compositions (from pure NaOH to pure KOH) and temperatures (from 50 to 110 degrees C). Attempts to intensify the TiO2, transformation via addition of titanate nanotube seeds or agitation of the reaction mixture have resulted in formation of thermodynamically stable nanofibers rather than nanotubes. The effects of kinetic and thermodynamic control of the reaction are discussed with regard to the transformation of TiO2 to nanosheets, nanotubes, and nanofibers.