Ultrasensitive and selective sensing material of ultrafine WO3 nanoparticles for the detection of ppb-level NO2

WO₃ nanoparticles were successfully deposited onto SiO₂/Si substrates equipped with a pair of interdigitated Pt electrodes by heating tungsten filaments in a vacuum chamber. The morphology and structure of the obtained WO₃ nanoparticles were characterized by means of field emission scanning electron microscopy (FESEM) and X-ray diffractometer (XRD). The results revealed that these nanoparticles show a sphere-like structure and their sizes depend on deposing pressure. Furthermore, the NO₂ sensing properties of WO₃ nanoparticles were studied. The intrinsic WO₃ nanoparticles with small size exhibit surprisingly high response to ppb-level NO₂, low detection limit, excellent selectivity, and good stability at a very low operating temperature, demonstrating their potential in monitoring ppb-level NO₂ at low power consumption. In addition, an in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurement was carried out to propose the NO₂ sensing mechanism, which demonstrates that adsorbed nitrate and nitrite species are the main species on WO₃ surface. Furthermore, the intensity and the sensing response show the same trend with respect to the temperature, indicating that nitrate and nitrite species play a joint role in NO₂ sensing behavior on WO₃ surface.