Synthesis And Characterization Of Nanometer Titania-coated Silica Fine Particles

In this paper, two methods for preparation of the SiO2/TiO2 particles were investigated. The first method is microemulsion method, which used SiO2 particles as the corn, and coated nanometer TiO2 phase on it. The second method is sol-gel process, in which titania gels were developed on silica gel particles dried 24 hours. The effect factors of those two processes were studied in the text, experimental results show that many process conditions influence the formation of SiO2/TiO2 particles, such as SiO2/EtOH, H2O/TBOT, temperature, pH of solution, Ti/Si, deposited time, dispersant and so on. The ratio of SiO2/EtOH determines disperse of SiO2 particles; temperature effects the formation rate of coated TiO2 layer, PH values of solution influences the hydrolysis of TBOT, the ratio of Ti/Si effects the TiO2-coated thickness on SiO2 particles. The coated layer is also influenced by H2O/TBOT. The dispersant added into solution have not remarkable effect on the dispersion of SiO2 particles. Moreover, deposited time for the first process gives the SiO2/TiO2 particles enough time to disperse and ripen; Coated particles make ripe during gels time from sols to gels in sol-gel process. The prepared samples of the SiO2/TiO2 particles have been characterized by powder X-ray diffraction (XRD), FT-IR spectroscopy, TEM, UV-VIS spectroscopy and X-ray photoelectron spectronscopy (XPS). The results show that coated-TiO2 layer could be transformed anatase-phase TiO2 by annealing in air at 550℃, and the Ti-O-Si bond could be formed at the particles interfaces. The nanometer titania-coated silica particles have strong absorption-light ability, especially to UV light. The SiO2/TiO2 particles prepared by the first method are spheric, the coated-TiO2 layers are uniform and homodisperse, the average thickness of TiO2 layers are 20~40nm. The SiO2/TiO2 particles prepared by Sol-Gel method are anomalous, the coated-TiO2 layers are uneven, the average thickness of TiO2 layers are 20~50nm. According to experimental data, the optimum conditions for synthesis of the SiO2/TiO2 particles are as follows: for the microemulsion method, temperature is at 20℃, SiO2/EtOH is 2g/L, the mole ratio of Ti/Si is 1/4, pH value of solution is 7, the mole ratio of H2O/TBOT is 100, deposited time is 24 h, annealed at 550℃. For the Sol-Gel method, the cores selected are the gels particle of silica dried at room temperature for 24 h; the mole ratio of H2O/TBOT is 1/4, pH value of solution is controll at 1~2, SiO2/EtOH is 0.1g/L, the mole ratio of Si/Ti is 4/1.The coating mechanisms of the SiO2/TiO2 particles prepared by two methods were studied in the text. At initiative stage, the reaction principle is the same, which should interact between the hydroysis offspring of TBOT and –OH groups adsorbed on silica core, and format Ti-O-Si chemically bonds. Then at followed stage, deposited time for the first process gives the SiO2/TiO2 enough time to disperse and ripen; and gels time from sols to gels in sol-gel process make particles ripe gradually.