Studies On Preparation Of TiO₂/SiO₂ Nanocompsite By Adsorption Layer Reactor Technology

In this dissertation, Synthesis of TiO₂/SiO₂ nanocomposite materials in a nanoreactor formed by the water-rich adsorption layer on the surface of SiO₂ was studied. First, the research, characteristic and application of TiO₂ nanoparticles and nanocomposite materials were reviewed. According to whether nanoreactor was used in the preparation process of nanoparticles, the author divided the preparation methods of nanocomposite materials into two kinds: traditional methods and the micro scale reaction technology. The author divided micro scale reaction technology into soft constraint and hard constraint in terms of boundary properties, and independently generalized its principle, characteristic and application.The advantage and disadvantage microscale reaction technology were also generalized contrasted with traditional methods. Based on the generalization of abroad literatures and research findings, the principle and characteristic of adsorption phase nanoreactor technology were represented detailed, and pointed out the formation of adsorption layer and reaction place were the two most important factors in this technology. The latest development and the former works of our research group were summarized in three points of view for adsorption, reaction and particle growth. Then the research orientation and experiment strategies were proposed based on research findings which had been achieved.SiO₂ with homogeneous external surface was employed as support in pre-experiments for further researches. Comparing with the results of former works, it is found that adsorption on both SiO₂ surface was similar, but the characteristic and evolution of adsorption layer changed with different surface. Because of homogeneous surface and high dispersibility, SiO₂ with external surface was suitable to use as supports in further studies on adsorption layer reaction.Aimed at SiO₂ support with homogeneous external surface, adsorption experiments under different water concentration and temperature were designed. The adsorption rate and change of adsorption layer were determined by GC and Thermal Analyzer. The results shows that the adsorption rate of SiO₂ was quick and changed little with different conditions, but the evolution of water content in adsorption layer was in relation to the nature of adsorption layer. Chemical-adsorption and physical-adsorption are two forms of adsorption on SiO₂ surface. Water molecular is combined stably by chemical bonds in the chemical-adsorption layer, so water content in this layer changed little with temperature increasing. Whereas because the physical-adsorption layer formed by weaker molecular force, there was a sharp decrease in change of water content in layer with temperature increasing.Based on adsorption experiments, first three models which were used widely in researches of solid-liquid adsorption were employed in adsorption system in paper. According to the advantages and disadvantages of the three models, competitive adsorption monolayer model has been built and solved aiming to the change of the chemical-adsorption and physical-adsorption with different conditions. And it is found that the dependences of adsorption amount on conditions calculating by model can explain well the change of adsorption and results in pre-experiments.According to the results of adsorption experiments and model calculation, the experiments were designed to research the feature and evolution of reaction of tetrabutyl titanate in adsorption layer. Comparing the reaction mechanism of tetrabutyl titanate, the results of spectrophotometry, EDAX and TEM show that three feature of reaction in nanoreactor: (1) Similar to the reaction mechanism of tetrabutyl titanate, the reaction in adsorption can also be divided into hydrolysis and condensation; (2) Water concentration in adsorption layer is much higher than one in alcohol bulk, so the reaction of tetrabutyl titanate in adsorption layer is quicker than reaction in bulk, and Ti concentration on SiO₂ surface after reaction by APRT is also higher; (3) With water concentration in bulk increasing, the reaction cite of tetrabutyl titanate transfer from SiO₂ surface to adsorption layer, then into alcohol bulk.The crystallization of TiO₂ was studied combining with calcination. Only a few TiO₂ particles agglomerated after sintering at different temperature, so the results after sintering can also reflect the change of TiO₂ particles with reaction conditions changing. The results analyzed by XRD show that there was pure anase TiO₂ in all samples prepared by adsorption layer reaction technology. The grain size of all TiO₂ particles was below 10 nm and changed little with different reaction conditions.The photocatalytic activity of TiO₂/SiO₂ nanocomposites was characterized by photodegradation of methyl orange aqueous solution. It is found that photocatalytic activity of TiO₂ by adsorption layer reaction technology was much higher than those by impregnation method under same reaction conditions. The grain size and content of anase of TiO₂ are the two factors which affected photocatalytic activity the most.At last, the work in the dissertation was generalized, and the problems which still need to discuss in paper were represented.