Shape Modulation of Tungstic Acid and Tungsten Oxide Hollow Structures

Tungstic acid (H2W1.5O5.5·H2O) hollow structures, including hollow spheres, nanotubes, and hollow boxes, have been selectively synthesized by a nonaqueous and surfactant-free solvothermal method. The synthesis involves the alcoholeysis of WCl6 in the presence of urea. A series of experimental factors such as the urea amount, ethanol amount, reaction temperature, reaction time, and pH value have important influences on the morphology and size of the products on the basis of scanning electronic microscopy and X-ray powder diffraction characterizations. The subsequent slow annealing leads to the formation of tungsten oxide (WO3), the hollow morphology of which is well-retained. The most striking feature of these WO3 hollow structures is the resultant nanoporous walls or shells, which may lead to potential applications in many fields, including energy storage, catalysis, and biotechnology.