Ultrasonication-Assisted Hydrothermal Synthesis of Ultralong TiO2 Nanotubes

Ultralong titanate nanotubes were synthesized by treating general anatase TiO2 in alkaline solution using a facile sonication-assisted hydrothermal method. The as-synthesized products via sonication and sonication-hydrothermal treatment were characterized by SEM, TEM, OM and XRD. The effects of sonication power, sonication frequency and sonication temperature on the morphology and the crystal structure of the products were investigated. The results show that in the range of ultrasonic power (200, 300, 400, 500 W) and frequency (20, 40, 80 kHz), titanium dioxide particles were swelled in alkali aqueous solution to get the hedgehog flocculent intermediate products by ultrasonic irradiation when the ultrasonic temperature was equal or higher than 60 °C; several tens of microns long titanate nanotubes were achieved using the intermediate products as raw materials under the mild hydrothermal conditions of 90 °C and 5 h. The possible formation mechanism for ultralong titanate nanotubes was also discussed. The hedgehog floccules synthesized by sonication play an important role to synthesize the several tens of micrometers long nanotubes.