Effect of Different Anions Upon the WO3 Morphology and Structure

In this study the effects of various anions (SO2-₄, ClO-₄ and PO3-₄) were investigated on the hydrothermal treatment of WO₃ from Na₂WO₄ and HCl at 180 and 200 °C. The products were analyzed by XRD and SEM. With the usage of SO2-₄ the obtained product was hexagonal (h-) WO₃ in the form of nanorods at both temperatures. Applying ClO-₄ resulted in a mixture of WO₃·0.33H₂O and small amount of m-WO₃ at 180 °C and pure WO₃·0.33H₂O at 200 °C. The morphology was consisted of cuboid shapes arranged into spherical structures at 180 °C and longitudinal ones at 200 °C. By the application of PO3-₄ no product formed at either temperature. Using the combination of SO2-₄, and ClO-₄ the product was h-WO₃ at both 180 and 200 °C with rod-like crystals; thus, the effect of ClO-₄ was overdominated by the SO2-₄ions. Utilization of PO3-₄ together with SO2-₄, and/or ClO-₄ resulted again in no product, meaning that adding PO3-₄ to the reaction mixture completely blocks the hydrothermal formation of solid products by forming water soluble phosphotungstic acids.