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Layered titanate nanotubes (TTNT) with a general formula Na x H 2-x Ti 3 O 7 ‚nH 2 O were synthesized by hydrothermally reacting TiO 2 -anatase with NaOH at 120 °C. Detailed TGA and XRD characterization indicated that the as-synthesized material rich in sodium as an interlayer cation contained intercalated water (n), which was reduced substantially after nearly complete proton exchange (x ) ∼0), while the interlayer distance decreased approaching the interlayer distance d 200 of H 2 Ti 3 O 7 . Chemical composition and crystal structure of TTNT as well as their dependence on sodium content were not affected by the crystallite size of the starting anatase. On the other hand, TEM examination and N 2 adsorption measurements revealed distinct morphology at the nanometer scale and different textural properties depending on the precursor TiO 2 . Such dependence was rationalized based on a dissolutionrecrystallization mechanism.

H-trititanate nanotubes obtained by alkali hydrothermal treatment of TiO(2) followed by proton exchange were compared to their bulk H(2)Ti(3)O(7) counterpart with respect to their thermally induced structural transformation paths. As-synthesized and heat-treated samples were characterized by XRD, TEM/SAED, DSC and spectroscopy techniques, indicating that H(2)Ti(3)O(7) nanotubes showed the same sequence of structural transformations as their bulk counterpart obtained by conventional solid state reaction. Nanostructured H(2)Ti(3)O(7) converts into TiO(2)(B) via multistep transformation without losing its nanotubular morphology. The transformation occurs between 120 and 400 degrees C through topotactic mechanisms with the intermediate formation of nanostructured H(2)Ti(6)O(13) and H(2)Ti(12)O(25), which are more condensed layered titanates eventually rearranging to TiO(2)(B). Our results suggest that the intermediate tunnel structure H(2)Ti(12)O(25) is the final layered intermediate phase, on which TiO(2)(B) nucleates and grows. The conversion of nanostructured TiO(2)(B) into anatase is completed at a much lower temperature than its bulk counterpart and is accompanied by loss of the nanotubular morphology.

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