Structure and optical properties of mesoporous tungsten oxide

Mesoporous WO 3 was prepared by the sol–gel process and the structure and the optical properties have been investigated. Various techniques were used for characterization of mesoporous WO 3, including Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), N 2 adsorption–desorption isotherms and UV–vis spectroscopy. TEM and XRD analyses demonstrated that the mesoporous WO 3 was nanocrystalline. The estimated optical band gap ( E g) for the mesoporous WO 3 was 3.5 eV. We present evidence for a photoreduction of W 6+ into W 5+ following the irradiation with UV-light. The change in coloration is almost reversible as exposed in oxidation environment. These results suggest that the potential applications of mesostructured WO 3 with nanocrystals in the design of optical devices.