Morphology evolution of tungsten trioxide nanorods prepared by an additive-free hydrothermal route

Tungsten trioxide nanorods were prepared at 453 K by the hydrothermal treatment of aqueous tungstic acid sol, which was obtained by sodium tungstate solution passing through a strongly acidic ion-exchange resin in its proton form. The composition and morphology evolution of the nanorods were investigated by means of scanning electron microscopy, transmission electron microscopy, selected area electron diffraction and X-ray diffraction. The results show that all as-prepared samples mainly consist of hexagonal tungsten trioxide and tungsten trioxide one-third hydrate. With the extension of treatment time, the sample morphology will undergo an evolution in the sequence of nanorod, bundle-like and irregular shapes.