Investigation of photocatalytic activity and UV-shielding properties for silica coated titania nanoparticles by solvothermal coating

Due to its excellent UV-rays shielding properties, titanium dioxide can be used in many sunscreen products. However, concerns have been raised about the possible photocatalytic decomposition of cosmetic formulation by titanium dioxide. Therefore, titania nanoparticles were encapsulated in silica shell by using solvothermal process. Both temperature and time parameters of the solvothermal process were optimized to produce silica shell with highest density (loss of micropores) and maximum shell thickness. The coated particles were characterized by X-ray diffraction (XRD), TEM, FTIR, XPS, zeta-potential, and porosity measurements. The photocatalytic activity of the coated samples was suppressed effectively by conducting solvothermal silica coating at 200 °C for 15 h where TEM observations revealed the gradual growth of silica shell around TiO₂ nanoparticles. On the other hand, UV-shielding properties were slightly reduced after silica coating which can be attributed to the loss of titania content.