Room temperature gas sensor based on porous NiO nanoplates modified with rGO nanosheets and SnO2 nanoparticles for accurate and rapid ppb-level NO2 detection

The porous NiO nanoplates modified with rGO nanosheets and SnO 2 nanoparticles are developed for accurate and rapid ppb-level NO 2 detection. The developed SnO 2 /NiO/rGO sensor towards 50 ​ppm NO 2 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 SnO 2 /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 SnO 2 /NiO/rGO sensor signal as approximately 13 ​ppb and 7.0 ​ppb NO 2 gas change, respectively. Such excellent properties are mainly attributed to the large surface-to-volume ratio, which provides active sites to NO 2 gas spread, adsorption and diffusion on material surface in redox reaction. Moreover, the ternary heterojunctions formed by NiO, rGO and SnO 2 may serve as highly conductive channels to accelerate carrier transfer and abundant oxygen vacancies to reduce the adsorption energy for O 2 and NO 2 gas, thus further improving performance of the sensors.