Abstract
Nanoparticles of calcia doped ceria coated with amorphous silica were prepared for UV shielding via soft solution chemical routes at 40-90°C. About 20mol% of CaO could be alloyed with ceria. Doping with calcia resulted in extremely decreasing the particle size (2-4nm), and consequently increasing UV light (λ<400nm) absorbing capacity and transparency in the visible ray region (λ >400 nm). Coating ceria with less than 20 mass% amorphous silica resulted in the decrease in the ceria content, but no noticeable decrease in the UV-shielding ability probably because of the depression of the powder agglomeration. The oxidation catalytic activity of ceria was effectively depressed by both doping with calcia and coating with amorphous silica. The photocatalytic activity of undoped and doped CeO2 was much lower than that of TiO2 and ZnO. The generation of singlet oxygen on CeO2 with UV irradiation in air was also lower than that on TiO2 and ZnO and was greatly decreased by doping with CaO. There was a clear advantage with CaO doped CeO2 coated with amorphous silica compared with other inorganic UV filters because of its excellent UV-absorption capacity, high transparency in visible light and low photocatalytic activity which may safely supply high sun protection factor (SPF) with natural appearance.
