Nanocrystalline TiO 2 has been studied extensively in recent years as photocatalysts to deal with environmental pollutions, such as water purification, wastewater treatment and air purification. Here a novel sonochemical method for directly preparing anatase nanocrystalline TiO 2 has been established. Nanocrystalline TiO 2 were synthesized by the hydrolysis of titanium tetrabutyl in the presence of water and ethanol under a high intensity ultrasonic irradiation(20 kHz, 100 W/cm 2) at 363 K for 3 h. The structure and particle sizes of the product were dependent upon the reaction temperature, the acidity of the medium and the reaction time. Characterization was accomplished by using various different techniques, such as powder X ray diffraction(XRD), transmission electron microscopy(TEM), thermogravimetry differential thermal analysis(TG DTA) and Fourier transform infrared(FTIR) spectroscopy. The TEM images showed that the particles of TiO 2 were columnar in shape and the average sizes were ca. 3 nm×7 nm . The formation mechanism of nanocrystalline TiO 2 under a high intensity ultrasonic irradiation was also investigated. The hydrolytic species of titanium tetrabutyl in water condensed to form a large number of tiny gel nuclei which aggregated to form larger clusters. Ultrasound irradiation generated a lot of local hot spots within the gel and the crystal structural unit was formed near the hot spots with the decrease of the gel nuclei, which lead to form nanocrystal particles.
