A room-temperature chemiresistive NO2 sensor based on one-step synthesized SnO2 nanospheres functionalized with Pd nanoparticles and rGO nanosheets

Abstract A high-performance and cost-effective NO2 gas sensor operating at room temperature was realized from synthesized SnO2 nanospheres functionalized with Pd nanoparticles and rGO nanosheets (Pd-SnO2/rGO) by a facile one-step hydrothermal route. The as-synthesized materials were characterized by SEM, TEM, XRD, Raman, XPS, TGA and BET techniques. The Pd-SnO2/rGO composites have unique porous structure, large specific surface area and good thermal stability, as well as abundant oxygen vacancies on material surface. Importantly, the obtained gas-sensing results indicate that the optimal response of the Pd-SnO2/rGO sensor to 100 ppm NO2 gas at room temperature is 7.92 with the response/recovery times of 56.9/22.1 s, and the response/recovery times to 10 ppm NO2 gas are 54.3/24.2 s with the theoretical detection limit of 37.8 ppb, ensuring the real-time detection at relative low concentration of NO2 gas. The Pd-SnO2/rGO sensor performs better than other sensors (including SnO2, Pd-SnO2 and SnO2/rGO sensors) in response and response/recovery times. Besides, our sensor exhibits excellent repeatability, high selectivity for NO2 gas relative to other gases and long-term stability. The enhanced performance of the Pd-SnO2/rGO sensor to trace NO2 gas may benefit from the unique porous structure and large specific surface area, which can provide rich active centers for redox reaction. Also, hybrid heterostructure between SnO2 and rGO can provide more channels for electron transfer, and thus increase the free electron. Catalytic effects of Pd nanoparticles help to produce more oxygen vacancies and chemisorbed oxygen for accelerating the process in redox reaction. It is speculated that our work will provide a superior strategy for realizing ppb-level NO2 gas sensor at room temperature.