Graphene-based gas/vapor sensors have attracted much attention in recent years due to their variety of structures, unique sensing performances, room-temperature working conditions, and tremendous application prospects, etc. Herein, we summarize recent advantages in graphene preparation, sensor construction, and sensing properties of various graphene-based gas/vapor sensors, such as NH3, NO2, H2, CO, SO2, H2S, as well as vapor of volatile organic compounds. The detection mechanisms pertaining to various gases are also discussed. In conclusion part, some existing problems which may hinder the sensor applications are presented. Several possible methods to solve these problems are proposed, for example, conceived solutions, hybrid nanostructures, multiple sensor arrays, and new recognition algorithm.

We report the synthesis of a two-dimensional enamine-linked covalent organic framework (COF) using a rapid microwave-assisted solvothermal method in significantly less time and high yield under a relatively low temperature. This COF was found to have a high crystallinity, high stability, high BET surface area, and a high CO2 capacity and adsorption selectivity of CO2/N2.

Here we present a useful ammonia (NH 3 ) gas sensor based on reduced graphene oxide (RGO)polyaniline (PANI) hybrids. PANI nanoparticles were successfully anchored on the surface of RGO sheets by using RGO-MnO 2 hybrids as both of the templates and oxidants for aniline monomer during the process of polymerization. The resultant RGO-PANI hybrids were characterized by transmittance electron microscopy, infrared spectroscopy, Raman spectroscopy, UV-Vis spectroscopy, and scanning electron microscopy. The NH 3 gas sensing performance of the hybrids was also investigated and compared with those of the sensors based on bare PANI nanofibers and bare RGO sheets. It was revealed that the synergetic behavior between both of the candidates allowed excellent sensitivity and selectivity to NH 3 gas. The RGO-PANI hybrid device exhibited much better (3.4 and 10.4 times, respectively, with the concentration of NH 3 gas at 50 ppm) response to NH 3 gas than those of the bare PANI nanofiber sensor and bare graphene device. The combination of the RGO sheets and PANI nanoparticles facilitated the enhancement of the sensing properties of the final hybrids, and pave a new avenue for the application of RGO-PANI hybrids in the gas sensing field.

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Molybdenum disulfide (MoS), as a promising gas-sensing material, has gained intense interest because of its large surface-to-volume ratio, air stability, and various active sites for functionalization. However, MoS-based gas sensors still suffer from low sensitivity, slow response, and weak recovery at room temperature, especially for NO. Fabrication of heterostructures may be an effective way to modulate the intrinsic electronic properties of MoS nanosheets (NSs), thereby achieving high sensitivity and excellent recovery properties. In this work, we design a novel p-n hetero-nanostructure on MoS NSs using interface engineering via a simple wet chemical method. After surface modification with zinc oxide nanoparticles (ZnO NPs), the MoS/ZnO hetero-nanostructure is endowed with an excellent response (5 ppm nitrogen dioxide, 3050%), which is 11 times greater than that of pure MoS NSs. To the best of our knowledge, such a response value is much higher than the response values reported for MoS gas sensors. Moreover, the fabricated hetero-nanostructure also improves recoverability to more than 90%, which is rare for room-temperature gas sensors. Our optimal sensor also possesses the characteristics of an ultrafast response time of 40 s, a reliable long-term stability within 10 weeks, an excellent selectivity, and a low detection concentration of 50 ppb. The enhanced sensing performances of the MoS/ZnO hetero-nanostructure can be ascribed to unique 2D/0D hetero-nanostructures, synergistic effects, and p-n heterojunctions between ZnO NPs and MoS NSs. Such achievements of MoS/ZnO hetero-nanostructure sensors imply that it is possible to use this novel nanostructure in ultrasensitive sensor applications.