A room-temperature NO2 gas sensor based on CuO nanoflakes modified with rGO nanosheets

Conventional gas-sensing materials for detecting trace NO2 gas are suffering from limitations such as low selectivity, high operation temperature and an agglomerated tendency during synthesis. In this work, uniform CuO nanoflakes modified with rGO nanosheets (CuO/rGO) were synthesized via an ultra-low-cost hydrothermal process with a thermal treatment. The gas sensor based on the as-synthesized CuO/rGO was fabricated by spincoated method and applied to detect ppb-level NO2 gas at room temperature (23?C). Remarkably, the CuO/rGObased sensor maintained an ultrahigh response behavior of approximately 400.8 % towards 5 ppm NO2 gas with ultrafast response time of 6.8 s at 23?C, and the limit of detection was down to 50 ppb (S = 20.6 %). In addition, the gas sensor had outstanding consistency, reliable repeatability, and long-term stability (30 days). The improved gas-sensing response was attributed to the synergetic effects of CuO and rGO. Specifically, the porous flake-like nanostructures of CuO and high surface areas of CuO/rGO may provide additional active adsorption sites for NO2 gas and accelerate the redox reaction on the surface of CuO/rGO, leading to the ultrahigh response. On the other hand, the rGO nanosheets with excellent transport capability may serve as highly conductive channels to accelerate carrier transfer, which dramatically reduced the response and recovery time. Furthermore, abundant surface defects of CuO/rGO were also conducive to surface reactions in the gas-sensing process. Undoubtedly, the scientific study of the present work will promote potential applications of ppb-level NO2 detection at room temperature.