Influence of valence state, radius of ion and molar ratio of directing salt on WO3·0.33H2O crystal morphology

WO3·0.33H2O networks were prepared by using structure-directing agent under a hydrothermal condition. The influences of the valence state (Na+, Ca2+), radius of ions (Ca2+ < Sr2+ < Ba2+), molar ratio of W to Ca, and reaction time on the crystal structure and morphology of the products have been investigated systematically. It was found that higher ion valence state (2 + ), smaller ion radius (Ca2+), 1:1 molar ratio of W to Ca and 15 h reaction time at 180 °C were the optimal experimental condition for the growth of well-defined three- dimensional networks. The proposed growth mechanism of the nanostructures can provide important information for structure design and morphology-controlled synthesis of WO3·0.33H2O and other oxides.