Novel synthesis of hexagonal WO₃ nanostructures

This paper discusses the synthesis and characterization of a new form of WO₃ nanostructures based on the hexagonal WO₃ (h-WO₃) polymorph. This typically “metastable” phase was synthesized from a substoichiometric metal alkoxide precursor-tungsten (V) isopropoxide, by a novel colloidal synthesis method. Nanowires of h-WO₃ were obtained upon heat-treating the sol–gel precursor at 400 °C. Further processing at elevated temperatures (515 °C) resulted in coarsening of the nanowires and the formation of nanowire bundles with polytypic character. Hexagonal WO₃ differs from the other tungsten oxide polymorphs in that it possesses unique structural features such as long, hexagonal prism channels parallel to the c-axis and layered oxygen octahedra. This makes it a very attractive host matrix for metal ion intercalation for rechargeable batteries and for the selective gas sensing of amines.