In-situ grown hydrated tungsten oxide nanosheets for low temperature ppb-level NO2 detection with alleviated humidity interference

Abstract

Gas sensors operated at low temperature or room temperature are highly desirable from the point of view of low power consumption. Unfortunately, the senor performance is significantly affected by the environmental moisture due to the adsorption of water on the surface of the sensing materials at low temperature. Instead of employing a traditional oxide as the sensing material, monohydrate of tungsten oxide, WO3·H2O, is investigated for low temperature NO2 detecting. WO3·H2O thin films constructed from vertically aligned nanosheets are in-situ grown on the sensor chip. The electronic structure of WO3·H2O and the crystalline structure, morphology, thermal stability, optical properties of the thin films have been studied. The NO2 sensing performance of WO3·H2O is evaluated by operating at low temperatures (less than 150 °C) or at room temperature with intermittent UV irradiation. Effect of humidity on the sensor performance has also been elaborated. The results indicate that the nanostructured WO3·H2O thin films are highly sensitive to ppb-level NO2 and the sensor performance of WO3·H2O is less affected by humidity when compared with that of WO3. The crystalline hydrate WO3·H2O is found to reduce the adsorption of water and the interference of ambient moisture on sensor performance.