WO3·nH2O Crystals with Controllable Morphology/Phase and Their Optical Absorption Properties

In this work, a one-step hydrothermal route is developed to prepare WO3·nH2O crystals with various morphology/phases, for which any surfactants, templates, or structure-directing agents are not used. Five types of WO3·nH2O crystals, including o-WO3·H2O nanoplates, rectangular m-WO3 nanosheets, o-WO3·0.33H2O microspheres, h-WO3 nanorods, and bundle-like h-WO3 hierarchical structures, are successfully obtained by adjusting the amount of H2SO4 and reaction temperature. According to the experimental results, the formation mechanism for various WO3·nH2O species is proposed. In addition, the optical absorption properties of these WO3·nH2O crystals are also investigated by UV–vis absorption spectra.