Plasma synthesis of various polymorphs of tungsten trioxide nanoparticles using gliding electric discharge in humid air: characterization and photocatalytic properties

Abstract

Gliding electric arc (glidarc) discharge generates a low temperature plasma at atmospheric pressure. When the discharge occurs in humid air as feeding gas, the chemistry of glidarc plasma consists of in-situ formation HO° and NO° as main primary chemical species. Tungsten trioxide (WO3) nanoparticles were successfully prepared by exposition of liquid precursor to glidarc plasma. The WO3 samples were calcined at three different temperatures (300 °C, 500 °C, and 800 °C), resulting to different pure polymorphs: γ-WO3 (at 300 °C), β-WO3 (at 500 °C) and α-WO3 (at 800 °C) according to X-ray diffraction analysis. The identification of WO3 compounds was also confirmed by ATR FTIR spectroscopy analysis. The increase of the calcination temperature of WO3 induced the decrease of its specific surface area according to the BET nitrogen physisorption analysis. The UV-vis results showed that the absorption bands of plasma-WO3 samples were more intense than those of WO3 samples obtained by precipitation route, a classical method used for comparison. Consequently, this parameter can improve the photocatalytic properties of WO3 under visible light. The photodegradation (in sunlight conditions) of gentian violet, chosen as pollutant model, confirmed the photocatalytic properties of plasma-WO3 samples. This novel synthesis method has a great potential to improve the efficiency of advanced tungsten trioxide-based functional material preparation, as well as for the pollution-reducing and energy-saving tungsten extractive metallurgy.