Abstract
H-trititanate nanotubes obtained by alkali hydrothermal treatment ofTiO2 followed by proton exchange were compared to their bulkH2Ti3O7 counterpart with respect to their thermally induced structural transformationpaths. As-synthesized and heat-treated samples were characterized byXRD, TEM/SAED, DSC and spectroscopy techniques, indicating thatH2Ti3O7 nanotubes showed the same sequence of structural transformations as their bulkcounterpart obtained by conventional solid state reaction. NanostructuredH2Ti3O7 convertsinto TiO2(B) viamultistep transformation without losing its nanotubular morphology. The transformation occurs between120 and 400 °C through topotactic mechanisms with the intermediate formation of nanostructuredH2Ti6O13 and H2Ti12O25, which are more condensed layered titanates eventually rearranging toTiO2(B). Our results suggest that the intermediate tunnel structureH2Ti12O25 is the final layered intermediate phase, on whichTiO2(B) nucleates and grows. The conversion of nanostructuredTiO2(B) into anatase is completed at a much lower temperature than its bulk counterpart and isaccompanied by loss of the nanotubular morphology.
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