Synthesis of tungsten trioxide nanoparticles by microwave plasma in liquid and analysis of physical properties

Tungsten trioxide nanoparticles were synthesized from a tungsten wire by plasma generated in water by 2.45 GHz microwaves. The effect of synthesis pressure, power and wire diameter on the formation of nanoparticles and the production rate was investigated. The character of the produced nanoparticles was determined by XRD, absorption spectrum, TEM and particle size distribution. The method proposed in this paper allows control of the nanoparticle size and shape and the optical properties through pressure alone without any additives. In one specific experiment, spherical nanoparticles with a peak diameter of 7 nm were synthesized from a tungsten wire with a diameter of 1 mm by 200 W at 20 kPa at a high production rate of 4 mg/s. Whereas, rhombic cylindrical nanoparticles together with spherical nanoparticles were synthesized with a peak diameter of 13 nm at 101 kPa. In addition, plasma and bubble behavior was observed by high-speed camera. Use of a plate to control the updraft of the bubbles caused the gap between the plate and the coaxial electrode to remain consistently filled with bubbles, and plasma generation continued without pause.

► Tungsten trioxide nanoparticles are synthesized by microwave plasma in water.
► The nanoparticles are produced through erosion of tungsten wire.
► The nanoparticles size increases with an increase of pressure.
► The production rate becomes 4.5 mg/s.
► Plasma and bubble behavior during the synthesis was observed by high-speed camera.