Construction of ZnO/SnO2 Heterostructure on Reduced Graphene Oxide for Enhanced Nitrogen Dioxide Sensitive Performances at Room Temperature.

The employment of n-n homotypic heterogeneous junctions is an efficient method to improve sensitive performance of metal oxide-based gas sensors owing to the generation of charge accumulation regions. Herein, in order to further enhance nitrogen dioxide (NO2) sensing properties of the sensors based on reduced graphene oxide (RGO) at room temperature (RT), n-type ZnO nanoparticles (NPs) decorated n-type SnO2 NPs heterojunctions were successfully constructed on RGO nanosheets (NSs) by combination of the hydrothermal method and the wet-chemical deposition method. The formation of heterostructures between ZnO NPs and SnO2 NPs was confirmed by the nonlinear behavior of current versus voltage (I-V) curve of ZnO/SnO2-RGO. ZnO/SnO2-RGO based sensor displayed remarkably enhanced response (141.0%) for detecting 5 ppm of NO2 at RT, which is almost 4 and 3 times higher than that of SnO2-RGO (34.8%) and ZnO-RGO (43.3%), respectively. Moreover, as far as the ZnO/SnO2-RGO-based sensor is concerned, its response and recovery time (33 and 92 s) are also significantly decreased, compared to SnO2-RGO-based sensor (70 and 39 s) and ZnO-RGO-based sensor (272 and 1297 s). In this work, the improved NO2 sensing properties of the sensors based on RGO not only benefit from the effects of the heterostructures between SnO2 and ZnO, but also derive from the superior electrical characteristics of RGO. In particular, the n-n heterojunctions could offer facile access to effective electronic interaction and improve transfer efficiency of the charges at the interface to adsorbed oxygen. Meanwhile, the n-n heterojunctions can also provide additional reaction center for adsorbing gas.