Synthesis of nano-sized tungsten oxide particles encapsulated in a hollow silica sphere and their photocatalytic properties for decomposition of acetic acid using Pt as a co-catalyst.

Nano-sized tungsten oxide (WO 3 ) particles, each of which was encapsulated as a core in a hollow silica sphere (WO 3 @SiO 2 ), were synthesized using calcium tungstate particles as the starting material. The calcium tungstate particles, each of which was covered with a silica shell, were converted to tungstic acid by nitric acid treatment and then to WO 3 by heat treatment to obtain WO 3 @SiO 2 . A hollow space was formed in WO 3 @SiO 2 between the WO 3 core and the SiO 2 shell as a result of shrinkage of WO 3 during the heat treatment. The thus-obtained WO 3 @SiO 2 was 40 nm in diameter, the WO 3 core was 10 nm in diameter, and the silica shell, which was permeable to gas and liquid, was 10 nm in thickness. WO 3 @SiO 2 absorbed visible light to the wavelength of 454 nm, which enabled photocatalytic reaction under visible light; Pt was loaded on the WO 3 cores in the photocatalytic reactions. In contrast to Pt-loaded bulk WO 3 photocatalysts without an SiO 2 shell, Pt-loaded WO 3 @SiO 2 showed continuous and complete decomposition of gaseous acetic acid in air under visible as well as UV irradiation.