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.