Synthesis, Characterization And Crystallization Of Nanosized Amorphous TiO₂ Powders

Materials can be classified into crystalline and amorphous materials according to the atom packing modes. Amorphous materials mainly include oxide glasses, macromolecule polymers, amorphous semiconductors and metallic glasses. Nanosized TiO₂ crystals exhibit unique characteristics such as large surface area, strong absorption of ultraviolet and oxidation capability, stable chemical properties and innocuity and attract attentions due to potential application in photoelectric conversion, heterogeneous photocatalysis, antifogging and self-cleaning materials. However, amorphous TiO₂ nanoparticles have not been systematically studied so far.In this work, nanosized amorphous titanium dioxide (TiO₂) powders have been synthesized by sol-gel method, using neutral inorganic material (tetrabutyl titanate) as a precursor. Structural characteristics were studied by powder X-ray diffraction (XRD), thermal analysis (TGA and DSC), Fourier transformed infrared spectra (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Crystallization of nanosized amorphous TiO₂ powders was studied on kinetics and thermodynamics.The results of XRD and FTIR indicated that the samples were amorphous without any organic residues after the thermal treatment at 320℃for 2 h. TEM and SEM observations showed that the particles were spherical in form with little agglomerated and the average particle size of about 30 nm.The apparent crystallization energy of the nanosized amorphous titania particles was 91.5 kJ/mol, and crystallization activation energy was about 42 kJ/mol at the initial stage of crystallization. The Avrami exponential (n) of the nanosized amorphous TiO₂ powders was between 2 and 3, indicating that crystallization of nanosized amorphous titania powders tended to two-dimensional nucleation and three-dimensional nucleation mixed-process; and n value decreased with crystallized fraction increase.The thermodynamic investigation suggested that the crystallization of nanosized amorphous TiO₂ tended to adopt the manner of non-uniform nucleation, and expanded from the free surface to the internal.