Controlled Formation And Charaterization Of Titania Microspheres

Titania is characteristic of high whiteness, lightening power and hiding power. It has been widely applied in paints, photocatalysts, chemical fibers, ceramic pigments and inorganic filler. Titania in the form of microspheres could have better mobility and dispersion and thus improved application effects. The sol - gel route based on the hydrolysis and condensation of titanium alkoxides is widely used to prepare titania powders. However, titanium alkoxides are easily hydrolyzed,making it difficult to control the morphology and dispersion of titania powders. Adjusting the of hydrolysis rate of titanium alkoxides is a key issue in the preparation of titania microsphere. Methods including using non-aqueous solvent, titanium source with low reactivity or the water generated from the esterification reaction are among the measures to reduce the hydrolysis rate of titanium alkoxides.Using tetrabutyl titanate and tetraisopropyl titanate as the titanium sources, TiO₂microspheres were synthesized via the solvent evaporation. The influence of the type and amount of alcohol, water/Ti ratio on the formation, morphology and crystalline phase of TiO₂ microspheres was studied by scanning electron microscopy, X-ray diffraction, and differential thermal - thermogravimetric analysis, respectively. The formation mechanism of TiO₂ microspheres was discussed. The photocatalytic degradation of organics with the obtained TiO₂ microspheres was tested.Synthesis media of tetrabutyl titanate- ethanol-water with different reactant ratios were stirred followed by natural evaporation, drying, calcination. Anatase or rutile titania microspheres sized 0.5 1μm in diameter were obtained. Scanning electron microscopy analysis confirmed the microspheres are assembled by particles with a size about tens of nanometers. The results show that, the size of microspheres is reduced with the increase in water/Ti molar ratio. The dispersion of microspheres increases when this ratio is increased from 0.3 to 0.5. However, the obtained titana microspheres are highly aggregated when the ration is more than 0.8. It was found that amount of ethanol has a major impact on the formation of titania microspheres. Titania microspheres were formed when the alcohol/water ratio is increased to 168 or 280. Study on the influence of the concentration of NaCl solution on the formation of titania microspheres shows that when Nacl solution concentration is less than 1mol/ L, the ability of dispersion of titanium dioxide can be improved. However, when the concentration is increased to 4mol/L, spheres can not be generated. Photocatalytic tests suggest that titanium dioxide microspheres with good dispersion exhibit enhanced efficiency in the degradation of methyl orange.Experimental results show that the type of alcohol has a significant impact on the hydrolysis and condensation of isopropyl titanate and thus the formation of titanate microspheres. Microspheres can not be formed when methanol and ethanol were used as solvents. Only aggregated titanate microspheres are formed in propanol and isopropanolDispersed titanate microspheres are successfully obtained in butanol and pentanol.In the case of isopropanol, the size of titania microspheres decreases with the water/Ti ratio. When water/Ti ratios is increased to 4, titania microspheres can not be not produced. In contrast, increasing the amount of alcohol has the opposite effect.In the cases of butanol and pentanol, increasing the water/Ti ratios benefits the formation of titania microspheres. As the water/Ti ratios increases, more small titania microspheres are found among the products. XRD results indicate that the crystallization of the hydrolysis products of tetrabutyl titanate in butanol increases with raising the calcination temperature increases. Comparison shows that rutile type titania microspheres have higher photocatalytic efficiency in the degradation of rhodamine 6G than the anatase phase.