Effect of Different Anions Upon the WO3 Morphology and Structure.

ABSTRACT

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.