Large-Scale Production of Tungsten Trioxide Nanoparticles

Tungsten trioxide (WO3) powder has been used to produce filaments and tungsten carbide. As more characteristics are discovered, WO3 powder has been widely used in electrochromic displays, semiconductor gas sensors, photocatalysts and other devices due to its excellent electrochromic, gastrochromic, thermochromic and photochromic properties. WO3 powders with nanostructures are believed to have the enhanced properties because of their larger surface area and unique physical properties.

Conventional routes to prepare tungsten trioxide nanoparticles include wet chemical methods (sol-gel chemistry, hydrothermal method, colloidal method, and ion exchange method), thermal evaporation, and irradiation methods. New nanomaterials with controllable morphology and stoichiometry but are complex and time-consuming. Irradiation and thermal evaporation technologies have been performed under low pressure conditions using complex equipment, which limits their use in industrial applications. Therefore, it is still challenging to produce WO3 nanoparticles in large quantities using simple methods, short processing times, and reduced material and process costs. Therefore, a simple solid evaporation route to large-scale, well-crystalline WO3 nanoparticles from ammonium paratungstate is introduces as below:

Ammonium paratungstate (APT) has been applied as raw material. APT was firstly dispersed on a quartz plate, which was then located in the central area of the horizontal tube furnace. Upon reaching the reaction temperature (1350 °C), Ar gas was introduced and kept flushing for 30 min. A carbon-cloth bag was connected to the outlet of the glass tube, serving as powder collector. The as-synthesized particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The average diameter (da) of the particles was calculated, where corresponds to the diameter of approximately 1000 randomly sampled particles in the SEM images.

In summary, a facile solid evaporation route to prepare tungsten trioxide particles in large quantity. The morphology and size of the resulting tungsten oxide particles can be altered by simply varying the carrier gas flow rate. Single-crystalline quasi-spherical nanoparticles with an average diameter of 60 nm could be obtained when the carrier gas flow rate was 6 L/min. The adsorption activity of the tungsten trioxide particles increased with decreasing particle size.

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