Visible-Light-Responsive Photocatalysts and Photoelectrodes Using WO3 Semiconductors for Degradation of Organics and Water Splitting

Abstract

Visible-light-responsive photocatalysts have been extensively investigated for indoor or in-vehicle applications. Conventional TiO2 photocatalysts are responsive in the UV region and hence cannot be utilized under fluorescent light through acrylic plate, LED light, or sunlight through UV-cut glass, as the intensity of UV is negligible. However, there are large total photon numbers in the visible region from these light sources, and therefore the activity of visible-light-responsive photocatalysts is high compared with that of TiO2. Tungsten oxide (WO3) is a visible-light-responsive photocatalyst, which absorbs light up to ca. 480 nm. Compared with mixed metal oxides and doped oxides, WO3 is easy to prepare, modify, and coat onto substrates. The absorption coefficient of WO3 is very high due to the direct photon transition, and the amount of absorbed photons under fluorescent and sunlight is 10 and 3 times higher than that of TiO2, respectively. WO3 also is non-toxic and is stable in acidic and oxidative conditions. Considering these advantages, WO3 semiconductors are of interest for further studies for use as photocatalysts. Here, the development of various WO3 photocatalysts for degradation of various organic compounds and for water splitting is reported. Moreover, WO3 particles have been used to fabricate porous and nanocrystalline photoelectrodes for water splitting. The charge separation of e− and h− occurs in the semiconductor nanoparticles; therefore, the nanocrystalline photoelectrodes are called “photocatalytic photoelectrodes.” The development of various WO3 nanocrystalline photoelectrodes with other semiconductors such as BiVO4 is also reported.