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

A gliding electric arc (glidarc) discharge generates a low-temperature plasma at atmospheric pressure. When the discharge occurs in humid air as the feed gas, the chemistry of a glidarc plasma consists of in situ formation of HO° and NO° as the primary chemical species. Tungsten trioxide (WO₃) nanoparticles were successfully prepared by exposure of a liquid precursor to glidarc plasma. The WO₃ samples were calcined at three different temperatures (300 ℃, 500 ℃ and 800 ℃), resulting in different pure polymorphs: γ-WO₃ (at 300 ℃), β-WO₃ (at 500 ℃) and α-WO₃ (at 800 ℃) according to x-ray diffraction analysis. The identification of WO₃ compounds was also confirmed by attenuated total reflection Fourier transform infrared spectroscopy analysis. Increase in the calcination temperature of WO₃ induced a decrease in its specific surface area according to Brunauer–Emmett–Teller nitrogen physisorption analysis. The UV-visible results showed that the absorption bands of plasma-WO₃ samples were more intense than those of WO₃ samples obtained by a 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 a model pollutant, confirmed the photocatalytic properties of plasma-WO₃ samples. This novel synthesis method has great potential to improve the efficiency of advanced tungsten trioxide-based functional material preparation, as well as in pollution-reducing and energy-saving tungsten extractive metallurgy.