Flame volume synthesis of carbon-coated WO3 nanoplatelets and nanorods
This paper reports the flame synthesis of WO3/C organic/inorganic octagonal nanoplatelets and nanorods. A high-purity tungsten wire inserted into the oxygen-rich region of the flame was used as a material source. The growth of the formed nanostructures starts with the oxidation of the metal probe, and evaporation of the oxide layer which is followed by the transport of the tungsten oxide vapors from the oxygen-rich to the hydrocarbon-rich zone of the flame. In the oxygen-rich zone, tungsten oxide vapors are crystallized into well-defined single crystal octagonal nanoplatelets. The continuous vapor deposition leads to the nanoplatelet growth in a preferred direction resulting in elongated rod-like nanostructures. The tungsten oxide structures entering the hydrocarbon-rich zone of the flame are coated with carbon layers forming hybrid WO3/C nanomaterials. The ideal conditions for the rapid and direct formation of these novel nanostructures are attributed to the synergy of the strong thermal and chemical gradients present in the flame volume. The entire process takes only a few seconds. A proposed mechanism of the hybridization process of the WO3 nanorods and nanoplatelets to WO3/C is described.