Room temperature NO2-sensing properties of hexagonal tungsten oxide nanorods

Hexagonal WO3nanorods were synthesized through a facile hydrothermal method. The nanorods properties were investigated by scanning electron microscope(SEM), transmission electron microscope(TEM), energy dispersive spectroscopy(EDS), and x-ray diffraction(XRD). The NO2-sensing performances in terms of sensor response, response/recovery times and repeatability at room temperature were optimized by varying the heat treatment temperature of WO3nanorods. The optimized NO2sensor(400-℃-annealed WO3nanorods) showed an ultra-high sensor response of 3.2 and short response time of 1 s to 5-ppm NO2. In addition, the 400-℃-annealed sample exhibited more stable repeatability.Furthermore, dynamic responses measurements of annealed samples showed that all the annealed WO3nanorods sensors presented p-type behaviors. We suppose the p-type behavior of the WO3nanorods sensor to be that an inversion layer is formed in the space charge layer when the sensor is exposed to NO2at room temperature.Therefore, the 400-℃-annealed WO3nanorods sensor is one of the most energy conservation candidates to detect NO2at room temperature.