One-dimensional WO3 and its hydrate: One-step synthesis, structural and spectroscopic characterization

We report on a one-step hydrothermal growth of one-dimensional (1D) WO3 nanostructures, using urea as 1D growth-directing agent and a precursor free of metals other than tungsten. By decreasing the pH of the starting solution, the size of the nanostructures was reduced significantly, this development being accompanied by the realization of phase pure hexagonal WO3 nanorods (elimination of monoclinic impurity phase) and a red shift in optical absorption edge. Surface analyses indicated the presence of reduced tungsten species in the WO3 nanostructures, which increased two-fold in a hydrated WO3 phase obtained with further decrease in pH. We suggest that oxygen vacancies are responsible for this defect state in WO3, while protons are responsible or contribute significantly to the same in the hydrated phase.