A rapid transformation of titanate nanotubes into single-crystalline anatase TiO2 nanocrystals in supercritical water

• The transformation of titanate nanotubes in supercritical water is investigated.
• Single-crystalline anatase nanocrystals are prepared in just 10 min.
• Two simultaneous processes take place during the transformation.
• An in situ nucleation mechanism of titanate into anatase is proposed.

The present study was aimed to investigate the morphological and phase transformations of hydrothermally prepared titanate nanotubes (TNTs) in supercritical water (SCW). We found that single-crystalline anatase nanocrystals including rhombic nanoparticles with the ends faceted with (1 0 1) facets and spindle-shaped nanorods mainly exposing (0 1 0) facets were rapidly generated in 10 min, of which the thicknesses were less than 5 nm. The morphologies and crystal forms of products treated for 6 and 8 min were investigated, showing that the outside nanotube walls were gradually decomposed meanwhile the inside tubular structures underwent a local shrinkage, followed by spontaneous phase transformations. We proposed that TNTs were transformed into anatase nanocrystals by two simultaneous processes. One is a dissolution-nucleation and crystal growth while the other is an in situ nucleation and crystal growth, resulting in the formation of rhombic and spindle-shaped morphologies, respectively.

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