Abstract
Structural, optical, and chemical properties of the WO k -ZrO 2 nanometric system were investigated using Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and UV-visible diffuse reflectance. From diffuse reflectance spectroscopy, the absorption profile of the species in which WO x was present (layers and small clusters) on the surface of ZrO 2 crystals was obtained. This study shows three main energetic regions for optical absorption. As tungsten (W) concentration diminished, which corresponded with a decrease in WO x layer thickness, the absorption edge showed a blue shift, and the band gap increased. The analysis of such behaviors suggests that they are due to quantum confinement produced by 0- or 1-dimensional WO x species. Local chemical analyses and HRTEM observations allowed determination of the presence of an irregular thin coating, a small cluster, and a crystalline thin film formation over the ZrO 2 for samples with loadings of 6, 10, and 20 wt % of W, respectively. The results obtained from different techniques were used to propose a chemical approach to the relationship between structure and electronic behavior of the active surface as a function of W concentration.
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