Facile preparation of strontium tungstate and tungsten trioxide hollow spheres

A simple and low-cost technique was developed to produce unique SrWO4 and WO3 hollow spheres. The SrWO4 hollow spheres were prepared via a precipitation reaction between SrCl2 and Na2WO4 in the presence of polymethacrylic acid, and the synthesis of WO3 spheres used the as-prepared SrWO4 hollow spheres as both precursors and templates. After soaking in HNO3 and calcinations, the SrWO4 were completely transformed into WO3 while the hollow structures were perfectly retained. The "polymer-cation template" model was proposed to describe the formation of the SrWO4 hollow spheres. This technique is feasible in fabricating other inorganic hollow-structured materials.