| TiO2 surface coating has become one of the most important and competitive technologies in TiO2 industry. In the present and also in the future, the competition of TiO2 surface coating technology will, to a large degree, represent the competition of the field. Although international competition is increasing rapidly, China has currently been much behind in TiO2 surface coating technology, making us much disadvantageous in the field. This study investigates the TiO2 surface coating mechanism of inorganic nano layers, the effects of coating morphology on pigmentary properties. And this present study also examines the use of naked and inorganically coated TiO2, both were organically modified, as catalysts in polyesterification reaction. We wish this present study can make some significant contributions to the field.This study examined the formation of SiO2 nano coating layers on the surface of TiO2 by a chemical liquid deposition method starting from Na2SiO3. The coating process and mechanism of SiO2-coated TiO2 were characterized by X-ray photoelectron spectroscopy, Zeta-potential analysis, Fourier transform infrared spectroscopy, and transmission electron microscopy. The dispersibility of SiO2-coated TiO2 in aqueous solution was analyzed by dynamic laser scattering (DLS) mode. The results showed when reaction temperature, reaction solution pH value, and SiO2 loading were low, the island-like SiO2 coating layer formed. With high reaction temperature, reaction solution pH value, and SiO2 loading, the continuous and uniform SiO2 coating layer was observed. The thickness of the coating layer was increased with the increase of the mole ratio of Na2SiO3 to TiO2. The SiO2 coating layers anchored on the TiO2 surface via the Ti-O-Si bonding. When the mole ratio of Na2Si03 to TiO2 was greater than 1:75, the Zeta potential of SiO2-coated TiO2 kept constant at-50mV, which was more negatively charged than the naked TiO2 whose Zeta potential was-24mV; this was advantageous for sample to disperse in aqueous solution under electrostatic repulsion. When the pH value of reaction solution was between 9 and 10, the dispersibility of SiO2-coated TiO2 was better than the naked TiO2. When the mole ratio of Na2SiO3 to TiO2 was 1:15, SiO2-coated TiO2 had the best dispersibility in aqueous solution. Coating TiO2 with SiO2 increased the whiteness, brightness, and its dispersibility in aqueous solution. The light scattering index was affected by the properties of SiO2 and TiO2, as well as by the dispersibility of SiO2-coated sample.This study investigated the formation of alumina nano coating layers on the surface of TiO2 by a chemical liquid deposition method starting from Al2(SO4)3. The morphology of the alumina coating surface was determined by transmission electron microscopy. The chemical structure and mechanism of the alumina coating surface were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and powder X-ray diffraction techniques. The dispersibility of the alumina-coated TiO2 powders in water was determined by dynamic laser scattering (DLS) mode. Results showed that alumina loading on TiO2 was affected by the pH value of reaction solution. Only when the pH value was between 8 and 9, alumina formed continuous and uniform coating layer on TiO2, in the form of thin boehmite. Alumina anchored at TiO2 surface via Ti-O-Al bonding. Alumina loading increased with increasing mole ratio of Al2(SO4)3 to TiO2. Coating TiO2 with alumina improved dispersibility which increased with the degree of alumina covering. The whiteness and brightness of alumina-coated TiO2 were greater than those of naked TiO2. Light scattering index was related to alumina loading.This study also examined the application of TiO2 as polyester catalysts. Metatitanic acid, an intermediate product in the production of pigment TiO2 by sulfuric acid method, was used as a raw material in manufacturing TiO2, by adjusting heating parameters. According to the results obtained in the first half of this study, the surface of TiO2 was coated with silica and alumina using Na2SiO3·9H2O and Al2(SO4)3, respectively. Using fatty alcohol as the organic modifier, we modified the surface of the naked and coated TiO2 and thus obtained the TiO2 catalysts which had excellent dispersibility in glycol. Then in a 70 L apparatus, the catalytic activity of the catalysts in polyesterification was examined. After analyzing the kinetics, we determined the catalytic activities of the catalysts in PET polyesterification reaction. Results showed that, the relativity of the catalytic activity in esterification and the catalyst calcination temperature had been the most obvious, the best calcination temperature of TiO2 was 600℃. The catalytic activity in esterification had also been related to the surface coating extent of TiO2 to some degree, SiO2-coated powder had the overally higher catalytic activity than alumina-coated and naked ones; this was possibly because of the cooperative activity between Si and Ti elements. When studying the catalytic activity in condensation reaction, the results showed that naked powders had significantly higher activity than both the SiO2-coated and alumina-coated samples, which acquired the highest catalyzing activity at 600℃. Therefore, it was believed that coating TiO2 powders with inorganic layers reduced its catalytic activity in the condensation reaction, and this activity had also shown some degree of relativity to calcination temperature. In comparison with the polyester sample made by using ethylene glycol antimony as a catalyst, the one manufactured using our catalysts showed similar general properties, higher thermal transition temperature, and better thermal stability. |
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