Metastable nature of titanate nanotubes in an alkaline environment

A systematic analysis of the effect of composition and temperature of a NaOH/KOH binary aqueous mixture on the morphological properties of titanate nanostructures formed under alkaline hydrothermal transformation of TiO2 at atmospheric conditions has been performed using HRTEM techniques. All observed nanostructures, including nanosheets, nanotubes, nanofibres and nanoparticles, have been mapped over a wide range of composition (from pure NaOH to pure KOH) and temperature (from 50 ºC to 110 ºC). Attempts to intensify the TiO2 transformation by addition of titanate nanotubes seeds or agitation of the reaction mixture have resulted in formation of thermodynamically stable nanofibres rather than nanotubes. The effects of kinetic and thermodynamic control of the reaction are discussed regarding the transformation of TiO2 to nanosheets, nanotubes and nanofibres