Ionic liquid-assisted synthesis of tungsten oxide nanoparticles with enhanced NO2 sensing properties at near room temperature

Tungsten trioxide (WO3) nanoparticles were synthesized via a fancil hydrothermal method with the addition of small amount of ionic liquid 1-butyl-3-methyl tetrafluoroborate ([Bmim]BF4). The as-synthesized WO3 nanoparticles were calcined at various temperatures to yield final products, which were characterized by X-ray powder diffraction meter (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), Fourier transform infrared spectra (FT-IR) and N2 adsorption-desorption methods. The sensor based on WO3 nanoparticles that have been calcined at 500 °C for 2 h exhibits an excellent selective response to sub-ppm level NO2 at temperatures less than 50 °C. Its resistance to humidity and stability are also good at the same condition. Besides, the detection limit for the gas sensor towards NO2 is 100 ppb. The mechanism of NO2 sensing was characterized and the reasons for improved NO2 sensing performance in WO3 nanoparticles were also proposed.