| With the rapid development of economic in the society, the number of motor vehicles takes on an exponential increases, which leads to a sharp increase of NO2 emissions in the air. Due to its toxic effect on the environment and human health, it is of great significance to fabricate portable devices to monitor and detect the concentration of NO2 gases, and finally protect the human health and prevent the air pollution. WO3-based gas sensor is reported to be highly sensitive to NO2 gases, however, its sensing performance needs to be improved due to the high operation temperature and poor stability. In the modification study on the WO3, it has been found that forming composite with carbon nanomaterials could effectively lower the operation temperature, resulting in the research emphasis on the synthesis of WO3/carbonous nanocomposite.In this paper, we synthesized the WO3/graphene nanocomposite and studied its roomtemperature gas sensing properties. On the basis of preparing high-quality of graphene with the Stride's soverthermal method, we adopted the sodium tungstate, hydrochloric acid, grahene as the raw material and prepared the WO3/graphene nanocomposite via sol-gel method. The as-prepared WO3/GR nanocomposite was characterized by XRD, Raman, SEM, TEM, UV-vis, XPS to identify the crystal phase, morphology and structure. The measurement of sensing NO2 gases at room temperature was performed on the selfassembled gas sensing test platform. Room-temperature gas sensing results demonstrated that WO3/GR sensor possessed p-type gas sensing behavior and the response toward 56 ppm NO2 gases was 40.8%. However, neither the pure WO3 nor graphene based sensor demonstrated any obvious response to NO2 gases. We have confirmed the existence of CO-W bonds at the interfaces between WO3 and graphene sheets, which makes it possible for the charge transfer at the composites' s interface and finally endows superior gas sensing performance for the WO3/GR nanocomposite. Additionally, the distinct hierarchy structure including gauze-like graphene wrapping up WO3 nanosphere is conducive to the gas diffusing and enhancing the chemisorption reactions, contributing to the room-temperature gas sensing properties of nanocomposite.To improve the gas sensing performance of WO3/GR nanocomposite, we took N-doped GR as the starting material instead of graphene to form composite with WO3 under the same preparation process. N-doped graphene was obtained by dissolving the graphene precursor in the ammonium hydroxide. The as-prepared WO3/N-GR nanocomposite was characterized with the same methods as WO3/GR. Gas sensing results showed that the WO3/N-doped GR nanocomposite demonstrated a much higher response than WO3/GR nanocomposite. It can be attributed to the increased amount of defects in the graphene surfaces after N-doping, resulting in the conductivity improvement of graphene. C-N bonds have formed after N doped into the graphene, which facilitate the charge transfer with C-OW bonds and improves the charge trancfer efficiency rate greatly. Therefore, the synergistic effect from N-doped GR and chemical bonds have promoted the gas sensing properties of WO3/N-doped GR nanocomposite.In this current work, we prepared the WO3/GR and WO3/N-GR nanocomposite and studied their room-temperature gas sensing performances. Based on the distinct morphology and nanostructure, the mechanism of sensing NO2 gases was deeply discussed, which may give a new insight to fabricating room-temperature gas sensor with novel sensitive material. |
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