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The preparation and characterization of titanate nanotubes

Due to unique one-dimensional structures, nanotubes have become one of the most important research subjects in nanotechnology. Among the nanotubular materials that have been prepared, titanate nanotubes have attracted a lot of attention due to cheap fabrication, advantageous properties and potential usage in a wide variety of applications. In this work various properties of titanate nanotubes prepared in our laboratory were characterized. Titanate nanotubes were prepared from TiO2 powder (P25) via hydrothermal processing in 10 M NaOH at reaction temperature of 135 °C for 72 h, followed by HCl rinsing. The properties of prepared nanotubes were investigated in detail by various analytic techniques such as X-ray diffraction (XRD), Fourier transformed infra- red spectroscopy (FTIR), differential thermal analysis combined with thermo-gravimetric analysis (DTA/TGA), field emission scanning electron microscopy (FESEM), adsorption- desorption N2 isotherms and UV-Vis diffuse reflectance spectroscopy (DRS). Although for hydrothermally synthesized nanotubes hydrogen trititanate (H2Ti3O7) structure is usually reported, XRD data revealed the crystal structure of the nanotubes is analogous to that of H2Ti2O5×H2O (ICDD PDF No. 47-0124). The broad and weak diffraction peaks reveal the nanoscale character of obtained material. The peak at 9.75 °2θ corresponding to d = 906 nm could be attributed to nanotubes interlayer spacing. The nanotubes FTIR spectrum exhibit bands due to hydroxyl groups and water molecules as well as Ti–O vibrations. TGA curve showed mass loss in interval from room temperature to 200 °C of about 18 % comprising removal of adsorbed, intercalated and molecular water. FESEM images displayed strongly aggregated nanotubes with approximate diameter of 10 nm. Specific surface area and pore structure of the prepared material were determined from the N2 desorption isotherm. It was established that the material is mesoporous having specific surface area of 84.89 m2 g–1. The nanotubes band-gap energy of 3.4 eV was determined on the basis of DRS data using Tauc’s plot. This value is blue shifted in comparison to the band-gap value usually reported for anatase, which is probably caused by quantum size effects.

Titanate nanotubes ; structure ; band gap

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