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.