Synthesis of TiO2 nanoparticles coated with SiO2 for suppression of photocatalytic activity and increased dispersion stability

For its use as an absorber of UV light in cosmetic products, TiO2 was coated a with a SiO2 layer to suppress its photocatalytic activity and to increase its dispersion ability. Silica-coated TiO2 nanoparticles were prepared by a sol-gel process. High-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) analyses showed that hydrous silica was coated evenly on the surface of the TiO2 particles. The effect of heat-treatment on the products, i.e., increasing annealing time and temperature, was followed by X-ray powder diffraction (XRD) spectroscopy. To study the suppression of the photocatalytic effect, an manic compound was added to the silica-coated TiO2 sol and the solution was irradiated with UV light. The decrease in the photocatalytic activity and the UV shielding effect of the silica-coated TiO2 nanoparticles were confirmed by recording UV-vis spectra, which showed more than an 80% decrease in the photocatalytic effect. Improved dispersion of the silica-coated TiO2 nanoparticles, as compared with that of pure TiO2 was verified by the increased Zeta potential value, from -22 xi/mV for pure TiO2 to -47 xi/mV for the silica-coated TiO2, at pH 7 as measured using a Zeta potential analyzer.