Aggregation Behavior and the Resulting Morphology of Nanocrystalline Titania in Peptization and Hydrothermal Process

During the process of peptization and hydrothermal crystallization, the aggregation behavior and the resulting morphology of nanocrystalline titania (TiO2) were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), and dynamic light scattering (DLS) techniques. The results show that during peptization process the mixture of rutile-type and anatase-type primary particles with 10-15nm in diameter formed by peptizing the precipitated amorphous titania are transformed into rod-like secondary crystalline grains with sizes of (30-50)nm×(80-100)nm through an oriented aggregation mechanism, which obey a crystal face-matching rule. In the process of hydrothermal crystallization under 180℃, however, the rod-like secondary crystalline grains are first broken into nanoparticles with diameter in the range of 10-15nm (namely the same sizes as those of the primary particles), and the formed nanoparticles then grow in hydrothermal solution. The finally resulting particles with the sizes of 10-30nm (spherical anatase) and 20-60nm (rod-like rutile) are found to have a higher crystallization degree than the primary particles formed in the process of peptization.