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

Tungsten trioxide (WO 3 ) nanoparticles were synthesized via a fancil hydrothermal method with the addition of small amount of ionic liquid 1-butyl-3-methyl tetrafluoroborate ([Bmim]BF 4 ). The as-synthesized WO 3 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 N 2 adsorption-desorption methods. The sensor based on WO 3 nanoparticles that have been calcined at 500 °C for 2 h exhibits an excellent selective response to sub-ppm level NO 2 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 NO 2 is 100 ppb. The mechanism of NO 2 sensing was characterized and the reasons for improved NO 2 sensing performance in WO 3 nanoparticles were also proposed.