Heat treated titanate nanotube is based on the hydrothermally synthesized titanate nanotube having an average diameter of 5-8 nm and length upto 100-500 nm depends on the preparation parameters. Heat treated nanostructure is obtained by thermal annealing at 600 °C for 24 hours. During the thermal treatment the raw ionic trititanate structure going through a recrystallization process to anatase TiO2. The tubular morphology is ruined but the anisotropic nanostructured morphology is remained. The transformation from trititanate to anatase is complete as shown in fig. 1.
Fig. 1. XRD patterns of TiO2-NT. Black line shows the raw trititanate structure; purple line shows the heat-treated sample with anatase
Heat stability of titanate nanotube’s morphology lags behind the titanate nanowires. While TiO2-NW product keep stable upto 800 °C, the titanate nanotube’s tubular morphology ruined at the required 600 °C. Morphology of the raw and the heat treated nanotubes are shown in fig. 2.
Fig. 2. Typical TEM images of titanate nanotubes before (left) and after (right) thermal treatment at 600°C
TEM images of TiO2-NT shows the absence of holes, tubular morphology but the presence of elongated one dimensional nanoparticles. Average diameter of the nanoparticles is 20 nm. The aspect ratio compared to the pristine titanate nanotube decreased from 20 to 3.
In summary, TiO2-NT product having a crystal structure of anatase are nanoparticles formed from tubular nanotubes resulted in an anistrope morphology with elongated length. TiO2-NT product can be widely used in industrial stages with a need of anatase. There is a promising possibility in filling of the tubular morphology before thermal treatment resulted in new way of materials. During the annealing procedure the filler material can be embeded into the anatase structure arisen a new, functionalized TiO2-NT-based nanomaterials.