Supercritical hydrothermal synthesis of titanium dioxide nanostructures with controlled phase and morphology

•A supercritical synthesis of controlled TiO2 nanostructures was carried out.•3D hierarchical spheres, 2D nanosheets, and 1D nanorods were obtained in 15 min.•NaOH solution pH and supercritical temperature were two determinant factors.•A dissolution–nucleation-growth mechanism was proposed.

A novel template- and organic-free synthesis of TiO2 nanostructures with controlled phase and morphology was realized through batch supercritical hydrothermal treatment (400 °C) of titanate nanotubes (TNTs) with H2O2 in NaOH aqueous solution. Well-defined 3D titanate hierarchical spheres (THSs), 2D multilayered titanate nanosheets (TNSs), and 1D monodisperse anatase nanorods (ANRs) exposing (0 1 0) facets were prepared in 15 min by slightly varying the NaOH solution pH. Specifically, the obtained Na/H-THSs (without/with HCl neutralization) exhibited highly porous structures with large specific surface area (109 m2 g−1 and 196 m2 g−1, respectively). Temperature-dependent phase and morphology evolutions of products under subcritical condition (200 and 300 °C) were investigated. The formation of the TiO2 nanostructures from TNTs was proposed mainly following a dissolution–nucleation-growth mechanism, suggesting that both supercritical temperature and NaOH solution pH were determinant factors governing the nucleation and growth process and thus the phase and morphology.

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