Investigation of Microstructure Effect on NO₂ Sensors Based on SnO₂ Nanoparticles/Reduced Graphene Oxide Hybrids

The microstructures of metal oxide-modified reduced graphene oxide (RGO) are expected to significantly affect room-temperature (RT) gas sensing properties, where the microstructures are dependent on the synthesis methods. Herein, we demonstrate the effect of microstructures on RT NO2 sensing properties by taking typical SnO2 nanoparticles (NPs) embellished RGO (SnO2 NPs-RGO) hybrids as examples. The samples were synthesized by growing SnO2 NPs on RGO through hydrothermal reduction (SnO2 NPs-RGO-PR), which display the advantages such as high reactivity of the SnO2 surface with NO2, more oxygen vacancies (OV) and chemisorbed oxygen (OC), close contact between SnO2 NPs and RGO, and large surface area, compared to the samples prepared by one-pot hydrothermal synthesis from Sn4+ and GO (SnO2 NPs-RGO-IS), and the assembly of SnO2 NPs on RGO (SnO2 NPs-RGO-SA). As expected, the SnO2 NPs-RGO-PR-based sensor presents high sensitivity towards 5 ppm NO2 (65.5%), but 35.0% for the SnO2 NPs-RGO-IS-based sensor and 32.8% for the SnO2 NPs-RGO-SA-based sensor at RT. Meanwhile, the corresponding response time and recovery time calculated by achieving 90% of the current change of the SnO2 NPs-RGO-PR-based sensor for exposure to NO2 is 12 s and to air is 17 s, respectively, whereas 74/42 s for the SnO2 NPs-RGO-IS-based sensor and 77/90 s for the SnO2 NPs-RGO-SA-based sensor. The results can prove the tailoring sensing behavior of the gas sensor according to different structures of materials