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.