Zhihua Zhou

Metal oxide/reduced graphene oxide (RGO) heterojunctions have been widely used to fabricate room-temperature gas sensors due to large specific surface areas of RGO nanosheets and enhanced carrier separation efficiency at the interface. However, the sheet stacking of RGO nanosheets limits the full utilization of metal oxide/RGO heterojunctions. Herein, we demonstrate a high-performance room-temperature NO₂ gas sensor based on 3D Fe₃O₄@RGO p-n heterojunctions with a core-shell structure, which were synthesized by self-assembly method and further reduction. The effects of different Fe₃O₄/RGO ratios and the relative humidity on the sensing performances have been investigated. The experimental results suggest that the 3D Fe₃O₄@RGO sensor exhibits a good selectivity and high sensitivity of 183.1% for 50 ppm NO₂, which is about 8.17 times higher than that of the pure 2D RGO sensor. When exposed to 50 ppb of NO₂, the response value still reaches 17.8%. This enhanced sensing performance is mainly ascribed to the formed heterojunctions and the larger surface area of RGO nanosheets. This 2D to 3D heterostructure strategy provides a general route to fabricating ultrahigh-performance room-temperature RGO-based gas sensors.

Molybdenum selenide (MoSe ₂ ) has drawn significant interest due to its typical semiconductor properties. MoSe ₂ is a relatively novel material in the field of gas sensors especially at room temperature. Herein, we utilize a facile and efficient synthetic method of liquid-phase exfoliation to exfoliate bulk MoSe ₂ into nanosheets. Anhydrous ethanol is used as dispersant, so the low boiling point makes it easy to be removed from MoSe ₂ nanosheets, which does not affect the subsequent sensing performance. The exfoliated few-layered MoSe ₂ nanosheets shows significantly enhanced NO ₂ gas response (1500% to 10 ppm NO ₂ which is 18 times greater than pristine bulk MoSe ₂ ), a low detection concentration (50 ppb), an outstanding repeatability, a remarkable selectivity, and a reliable long-term device durability (more than 60 d) at room temperature (25 °C). The reason of the significant improvement in gas sensing performance can be attributed mainly to the higher surface-to-volume ratio of exfoliated MoSe ₂ nanosheets. It promotes the adsorption of gas molecules on the surface of the material, thereby facilitating the charge transfer process. The superior performance of this gas sensor makes MoSe ₂ nanosheets a potential candidate for room temperature NO ₂ detection.