From POMs To Tungsten Oxide Ceramics

K₄SiW₁₂O₄₀ microtubes were prepared in aqueous solution without using any template or organic reagent in the whole process;the obtained tubes indicated a faceted hexagonal shape, and all the tubes showed cluster shape. These tubes were characterized with IR, SEM, XRD, HRTEM, SAED cyclic voltammogram and NMR. All of them proved that the tubes are composed of single-crystal Keggin structural K₄SiW₁₂O₄₀. The growth mechanism of the K₄SiW₁₂O₄₀ microtubes was studied in detail;microtubes were the coalescence of neighboring microrods. The growth of the tubular crystals of K₄SiW₁₂O₄₀ depends on the concentration of starting materials, the crystallization time and the roughness of the glass substrate. The formation process of the tubes results from a dynamical match of the transformation of the Keggin-type 11-series to 12-series and the crystal growth of the 12-series K₄SiW₁₂O₄₀. This is a new phenomenon observed for the first time. The formation mechanism of the tubules is hoped to apply to fabricating other POM tubes. The newly discovered tube structure of the POM in our present work is believed to be promising for use in templates, composites and precursor of tungsten oxide ceramic microtubes (see Figure S10). Further studies are underway on the possibility of preparing POM tubes in nanoscale by this simple method, the assembly of hollow array from the tubes and the exploring application of the POM microtubes.We calcining K₄SiW₁₂O₄₀ microtubes at 700 ℃ and treating the product with HF. EDS, XRD and SEM were used for the characterization of the obtained microtubes. The result showed that the obtained product was tungsten oxide microtubes containing Potassium.