N-Doped Graphene Quantum Dot-Decorated Three-Dimensional Ordered Macroporous InO for NO Sensing at Low Temperatures.

Nitrogen dioxide (NO) detection is of great importance because the emission of NO gas profoundly endangers the natural environment and human health. However, a few challenges, including lowering detection limit, improving response/recovery kinetics, and reducing working temperature, should be further addressed before practical applications. Herein, a series of N-doped graphene quantum dot (N-GQD)-modified three-dimensional ordered macroporous (3DOM) InO composites are constructed and their NO response properties are studied. The results show that compared to pure 3DOM InO, reduced graphene oxide (rGO)/3DOM InO, and N-doped graphene sheets (NS)/3DOM InO, the N-GQDs/3DOM InO sensing materials exhibit higher NO responses with fast response and recovery speed and low working temperature (100 °C). In addition, the detection limit of NO response for the optimal N-GQDs/InO sensor is as low as 100 ppb. Upon exposure to CO, CH, NH, acetone, ethanol, toluene, and formaldehyde, only very weak responses could be observed, indicating good selectivity for the synthesized material. More attractively, the responses of the optimized N-GQDs/InO sensor exhibit no obviously big fluctuation over 60 days, implying good long-term stability. We suggest that the formation of heterojunctions between 3DOM InO and N-GQDs and the doping N atoms in N-GQDs play crucial roles in improving the NO sensing properties.