The highly dispersed TiO2 sols composed of anatase crystallites (ca.5 nm) were prepared by peptization of amorphous precipitates with trifluoroactic acid (TFA) during the synthesis. The size and crystallinity of the particles were tuned by the subsequent hydrothermal treatment. The prepared TiO2 nanocrystals were characterized by X-ray diffraction and transmission electron microscopy (TEM). The TEM results indicated that the growth of the crystallites could be inhibited by the increasing addition of TFA and the average sizes of TiO2 nanocrystals were all ultrafine. The degradation of phenol over the nanocrystals after calcination at 500 °C was investigated. The photocatalytic results showed that the sample with a high addition of TFA obtained a better photocatalytic property than that of the commercial TiO2

The transparent nanosized TiO2 film was fabricated by a layer-by-layer assembly method starting from the highly dispersed anatase oppositely charged TiO2 nanoparticles without using anypoly electrolytes. The positively charged TiO2 nanoparticles (ca.7 nm) and negatively charged TiO2 nanoparticles (ca.7 nm) were synthesized by a subsequently hydrothermal process. Field-emission scanning electron microscopy, UV-vis transmittance spectra and Contact angle measurement were employed to characterize TiO2films.By the treatment of 500°C for 2hrs, the nanostructured TiO2 film showed a water contact angle of below 10°andthe relative transmittance to quartz glass of over 90%.