Stability of Aqueous Suspensions of Titanate Nanotubes

The long-term stability of titanate nanotubes, which were produced by alk. hydrothermal treatment of TiO2, was studied at room temp. in acidic, pure H2O, and basic aq. suspensions. In pure H2O and basic (0.1 mol dm-3 NaOH) solns., the nanotubes were stable and minimal morphol. changes occurred. In 0.1 mol dm-3 H2SO4, suspended titanate nanotubes slowly transformed to rutile nanoparticles of ca. 3 Nm size, which were agglomerated into ellipsoidal particles. The porosity, crystal structure, and morphol. of protonated titanates and TiO2 were studied for intermediate states during the transformation by nitrogen adsorption, XRD, Raman spectroscopy, SEM, and HRTEM. The rate of conversion of nanotubes to nanoparticles was related to the concn. of sol. Ti(IV) in soln., which depends on the nature of the acid. Thermodn. and kinetic aspects of the acid transformation are discussed. [on SciFinder (R)]