Microwave effect for synthesis of TiO2 particles by self-hydrolysis of TiOCl2

TiO2 nanoparticles were synthesized by self-hydrolysis of TiOCl2 using conventional and microwave heating methods. By XRD analysis, rutile and anatase phases were detected at the early stage of reaction. In conventional heating method, the XRD peaks of rutile became stronger with time and the roundish agglomerates surrounded by acicular particles were observed by SEM. The initial product was confirmed by TEM to consist of small acicular particles assigned to rutile and fine nanoparticles assigned to hydrous TiO2 sol having anatase-like structure. As the reaction time was longer, the amount of acicular particles increased. These results suggest that TiO2 Sol formed at the early stage by hydrolysis of TiOCl2 and the crystal growth of rutile progressed by dissolution-reprecipitation of TiO2 sol. In order to synthesize TiO2 nanoparticles, microwave was applied to this system. The microwave irradiation shortened the period of the precipitation because microwave can quickly heat up the aqueous solution, but retarded the crystal growth of rutile, leading to size reduction of TiO2 particles identified a hydrous TiO2 phase.