Crystallization peculiarities of titania nanotube films under hydrothermal and solvothermal conditions

We report on the peculiarities of crystallization of amorphous TiO2 nanotube (TNT) films produced by Ti anodization in ethylene glycol solution containing some NH4F and H2O. We note that in contrast to the traditional thermal crystallization, carried out usually at 400 °C and higher temperatures, the hydrothermal treatment in water, ethanol, water–ethanol or their vapor environments even at 100 °C results in the formation of crystalline hydrous anatase, O–Ti–OH. The content of chemically attached water molecules depend on the composition of solution applied. Besides, the autoclaving of TNT films in the solutions containing strong reducing agent, such as hydrazine hydrate, leads to the formation of brookite. These findings were confirmed by Raman spectroscopy, thermo gravimetrical, and X-ray diffraction results.

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