Evaluation of Bi–W‐oxides for visible light photocatalysis

Photocatalytic solar water splitting has the potential to become a low‐carbon source of hydrogen fuel over the coming decades if the issue of low visible light absorption can be addressed without sacrificing chemical stability. We report on an investigation into the potential of the Bi–W‐oxides, Bi 2 WO 6 and Bi 6 WO 12 , as visible light photocatalysts. X‐ray diffraction and Raman spectroscopy have been used to assess the structure of the oxides, whilst UV–vis diffuse reflectance spectroscopy analysed with the Kubelka–Munk function has been used to identify their optical band gaps. It has been revealed that Bi 6 WO 12 shows significantly higher optical absorption in the region above 440 nm than either Bi 2 O 3 or WO 3 , raising the possibility of enhanced photocatalytic activity under solar illumination. Bi 2 WO 6 has a marginally lower band gap at 2.59 eV than Bi 2 O 3 or WO 3 but the results reported herein raise doubts concerning its chemical stability under aqueous, illuminated conditions for protracted periods of time. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)