engleski

Thermal evolution of hydrothermally-derived titanate nanotubes

Titanate nanotubes were prepared by hydrothermal treatment of TiO2 powder in 10 M NaOH aqueous solution at reaction temperature of 135 °C for 72 h, followed by HCl rinsing. Scanning electron microscope (SEM) analysis revealed the presence of strongly aggregated nanotubes. According to X-ray diffraction (XRD) data, the crystal structure of the nanotubes is analogous to that of H2Ti2O5×H2O. The differential thermal analysis (DTA) curve shows a series of endothermic peaks in a range between room temperature and 250 °C, which represent the release of adsorbed and interlayer water followed by the release of structural water up to 400 °C. Small exothermic peak at approximately 500 °C is attributed to the transformation to anatase. The thermo-gravimetric analysis (TGA) curve showed a mass loss in the interval from room temperature to 400 °C of about 18% encompassing the removal of adsorbed, intercalated and crystal water. The thermal treatment of titanate nanotubes was interrupted at various temperatures between 135 and 1000 °C and the obtained samples were analyzed using XRD and Fourier-transformed infra-red (FTIR) spectroscopy. Slight shift of the XRD interlayer peak towards a higher 2θ value after thermal treatment was attributed to dihydroxylation. The transformation of titanate nanotubes to anatase begins above 400 °C and it is almost complete at 500 °C, rutile appears at 700 °C, while the conversion of anatase to rutile is completed at 900 °C. FTIR spectra in the 400-800 cm-1 region exhibit bands at 440, 415 and 465 cm-1 that can be assigned to Ti-O-Ti skeletal vibrations. Considering XRD data it is quite obvious that those bands could be attributed to Ti-O-Ti vibrations in titanate nanotubes, anatase and rutile, respectively. 1D morphology is retained to some extent even in the sample heated to 900 °C, which consists of short thick rods.

titanate nanotubes ; hydrothermal synthesis ; thermal treatment ; sodium hexatitanate

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