Preparation of TiO2 nanocrystallites by hydrolyzing with gaseous water and their photocatalytic activity

TiO2 nanocrystallites were prepared from precursors tetra-n-butyl titanate (Ti(OC4H9)4) and titanium tetrachloride (TiCl4). The precursors were hydrolyzed by gaseous water in autoclave, and then calcined at predetermined testing temperatures. The samples were characterized by X-ray diffraction (XRD), thermogravimetry–differential thermal analysis (TG–DTA), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectra (FT-IR), and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activities of the samples were evaluated by the photobleaching of methylene blue (MB) in aqueous solution and the photocatalytic oxidation of propylene in gas phase at ambient temperature. The results showed that the anatase phase nanocrystalline TiO2 could be obtained at relatively low temperatures (for precursor Ti(OC4H9)4 at 110 °C and for TiCl4 at 140 °C, respectively), and that the as prepared samples exhibited high photocatalytic activities to photobleach MB in aqueous solution. As the calcination temperatures increasing, the decolor ratio of MB increased and reached the maximum value of nearly 100% at 600 °C, and then decreased. The photobleaching of MB by all samples followed the pseudo-first-order kinetics with respect to MB concentration. The photodecomposition amount of propylene by TiO2 nanocrystallites calcined at 600 °C from precursor of Ti(OC4H9)4 is 21.6%, which is approaching to that by Degussa P25 TiO2 (24.9%).