Snapshots of the Formation of NaTi3O6(OH)·2H2O Nanowires: A Time-Resolved XRD/HRTEM Study

Layered titanates are important intermediates during the formation of TiO2-related nanostructures in hot concentrated base solution. Microwave-assisted hydrothermal techniques allow a time-resolved ex-situ analysis of the reaction in one-minute intervals by rapid heating and quenching followed by separation and structure analysis of the intermediates. By a combination of powder X-ray diffraction, high resolution electron microscopy (HRTEM), and selected area electron diffraction (SAED) the individual stages of the reaction could be identified. Sodium titanate nanosheets are formed within several minutes by digesting the crystalline TiO2-P25 precursor in NaOH. These nanosheets with a low sodium content form flake-like aggregates. Subsequently, these nanosheet intermediates form nanoscrolls and/or nanotubes, which transform in the next step to NaTi3O6(OH) ·2H2O nanowires by reaction with NaOH via an oriented attachment of nanotubes from solution. The NaTi3O6(OH) ·2H2O nanowires grow at the expense of the nanotubes and form an ordered structure via dissolution-recrystallization equilibria between solid NaTi3O6(OH)·2H2O and soluble titanate species. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.