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

Abstract

Nano-sized tungsten oxide (WO₃) particles, each of which was encapsulated as a core in a hollow silica sphere (WO₃@SiO₂), 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 WO₃ by heat treatment to obtain WO₃@SiO₂. A hollow space was formed in WO₃@SiO₂ between the WO₃ core and the SiO₂ shell as a result of shrinkage of WO₃ during the heat treatment. The thus-obtained WO₃@SiO₂ was 40 nm in diameter, the WO₃ core was 10 nm in diameter, and the silica shell, which was permeable to gas and liquid, was 10 nm in thickness. WO₃@SiO₂ absorbed visible light to the wavelength of 454 nm, which enabled photocatalytic reaction under visible light; Pt was loaded on the WO₃ cores in the photocatalytic reactions. In contrast to Pt-loaded bulk WO₃ photocatalysts without an SiO₂ shell, Pt-loaded WO₃@SiO₂ showed continuous and complete decomposition of gaseous acetic acid in air under visible as well as UV irradiation.