Porous Co3O4 nanocrystals derived by metal-organic frameworks on reduced graphene oxide for efficient room-temperature NO2 sensing properties

The combination of metal oxide and reduced graphene oxide (RGO) is a promising route but remains challenges to develop high-performance room-temperature nitrogen dioxide (NO2) sensors. The low gas sensitive properties of metal oxides-based sensors are mainly related to the poor surface activity of metal oxides at room temperature. Herein, a novel strategy for detecting ppm-level NO2 at room temperature is proposed. Highly porous Co3O4 nanoframeworks coated with polypyrrole (PPy) on RGO (Co3O4/PPy/RGO) are prepared by using metal-organic frameworks (MOFs) as precursors. Co3O4/PPy/RGO with Co3O4 nanocrystals (~5 nm) exhibit highly gas-accessible structure (pore size: 12.8 nm and surface area: 108.4 m2 g−1), which can serve as promising sensing materials for sensitive room-temperature NO2 gas sensors. As a result, the sensor based on Co3O4/PPy/RGO exhibits improved NO2 sensing properties with the sensitivity of 37.6% towards 3 ppm NO2, as compared with that of Co3O4/RGO (28.5%) and PPy/RGO (18.7%) at room temperature. In order to further investigate the mechanism of NO2 sensing, Brunauer-Emmett-Teller (BET), Current vs voltage (I-V) curves, In-situ X-ray photoelectron spectroscopy (XPS) and other characterizations are used to analyze the surface microstructure, surface chemistry and electrical properties of Co3O4/PPy/RGO, when the sensor is exposed to NO2.