Coating Process and Kinetics of Rutile TiO2 with Silicon Oxide Film
In order to guide the optimization of the surface modification process of titanium dioxide, the work aims to study the preparation of silicon coated titanium dioxide (SiO2@TiO2) by liquid phase precipitation method and the deposition kinetics of silicon oxide film on the surface of sulfuric acid method titanium dioxide particles. The surface of TiO2 was coated with a silicon oxide film with sodium silicate as the coating reagent. To characterize the structure of SiO2@TiO2, the morphology of SiO2@TiO2 particles was observed by scanning electron microscopy, the specific surface area was measured by a specific surface area analyzer, and the isoelectric point was detected by Zeta potential analyzer. During the experiment, a single variable method was used to study the effects of process parameters (coating temperature, coating pH and aging time) on the structure of titanium dioxide film. Under the optimal process conditions, the silicon oxide film forming process and reaction kinetic fitting analysis were conducted. The mass concentration of silicate ions at different reaction temperature was measured by XRF, the surface silicon content of TiO2 during the reaction was calculated, and the film forming process of silicon oxide was divided into two stages according to its concentration change trend. In the first stage, the heterogeneous nucleation of silicon oxide was produced by sodium silicate on the surface of titanium dioxide particles, forming nucleation points. In the second stage, silicon oxide molecules were deposited around the nucleation point to form a dense and uniform surface film layer. The reaction kinetics model was used to fit the two reaction stages. Firstly, the first-order to third-order reaction was used to fit the change trend of the silicate mass of TiO2 particles, then the reaction rate constant was calculated by the fitted kinetic model, and finally the activation energy of the reaction was calculated by the Arrhenius equation. The experimental results showed that the SiO2@TiO2 prepared under the conditions of coating temperature of 368 K, reaction pH of 9, and maturation time of 180 minutes had excellent compactness with the specific surface area of 10.58 m2/g, the isoelectric point of 2.34, and the acid solubility of 14％. The results of experiment indicate that higher reaction temperature, weaker alkalinity and longer aging time can improve the compactness of silicon film of SiO2@TiO2. The variation of specific surface area and isoelectric point is highly correlated with the acid solubility of SiO2@TiO2. Therefore, these three indexes can be used together to characterize the density of silicon film. The deposition process of silicon oxide on the surface of titanium dioxide conforms to the characteristics of three-order reaction kinetics. The reaction activation energy in the first stage is 16.31 kJ/mol, and 25.80 kJ/mol in the second stage.
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