The porous NiO nanoplates modified with rGO nanosheets and SnO2 nanoparticles are developed for accurate and rapid ppb-level NO2 detection. The developed SnO2/NiO/rGO sensor towards 50 ppm NO2 gas demonstrates an excellent gas-sensing response of 14.8 at 23 °C, which is 3.03 times that of NiO/rGO sensor (4.89) and 6.49 times that of NiO sensor (2.28), respectively. The developed SnO2/NiO/rGO sensor exhibits faster response/recovery speed (12.7/32.8 s @5 ppm), with extra-low theoretical detection limit of 0.15 ppb at room temperature. More fascinatingly, our sensors indicate great sensitivity, outstanding repeatability and long-term stability for longer than 7 weeks. Additionally, it also suggests that 1 °C and 1 % relative humidity have the same effect on the SnO2/NiO/rGO sensor signal as approximately 13 ppb and 7.0 ppb NO2 gas change, respectively. Such excellent properties are mainly attributed to the large surface-to-volume ratio, which provides active sites to NO2 gas spread, adsorption and diffusion on material surface in redox reaction. Moreover, the ternary heterojunctions formed by NiO, rGO and SnO2 may serve as highly conductive channels to accelerate carrier transfer and abundant oxygen vacancies to reduce the adsorption energy for O2 and NO2 gas, thus further improving performance of the sensors.
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