At present, researchers' research on black phosphorene-based gas sensors mainly focuses on the following aspects:
1.The gas sensing performance of a black phosphosphaene-based gas sensor is calculated theoretically.
Zhang et al. calculated the possibility of preparing a high-sensitivity gas sensor by doping black phosphorus with elements such as B, N, Si and S according to first principles. According to the calculation results, it can be seen that when the N element is doped with the black phosphorene sheet, the physical adsorption capacity of the material for NO2 can be significantly improved, and a high-performance NO2 gas sensor can be prepared. The chemisorption capacity of the material for NO2 and NH3 can be significantly improved by using B element doped with black phosphorene nanosheets. When Si is doped with black phosphorene nanosheets, the chemical adsorption capacity of the material for O2, NO2 and NH3 can be significantly improved. Moreover, the work function of the composites increases with the doping of b and si elements, and decreases with the doping of n and s elements. Sar**Anan et al. calculated the adsorption performance of black phosphosphamine in the form of nanotubes for trimethylamine (TMA) and dimethylamine (DMA) by first principles. According to the results, TMA and DMA are attached to the surface of the material in the form of physical adsorption, but electrons can be transferred from TMA and DMA to black phosphorene in the form of nanotubes, which proves that nanotube-based black phosphorene is a good material for chemical resistance gas sensors (Figure 1). Using first-principles (DFT), Kou et al. theoretically demonstrated that the black phosphoene nanosheet layer has a strong adsorption energy for NO2 gas. The results show that compared with the two-dimensional materials (GO and MOS2) that have been widely reported by previous researchers, black phosphatene has the largest adsorption energy of NO2 and is a new sensitive material that can be applied to gas sensing. At the same time, there are also related studies that show that the specific surface area of black phosphorus is 2400m2 g. The large specific surface area helps to provide a large number of active contact sites on the surface of the sheet and improve the gas sensitivity performance of the black phosphoene nanosheet. 
Fig.1. Schematic diagram of the composite structure of TMA and DMA materials with black phosphorus.
2.FET-type black phosphosphoene-based gas sensor.
Abbas researchers have found that high-performance FET gas sensors can be fabricated by suspending a layer of black phosphoene nanosheets on the top of the electrode pillar. Compared with the traditional support structure, the black phosphorene suspension structure has a larger specific surface area, which can provide more adsorption sites, and the gas sensing performance is improved by about 23% (200ppm NO2), which provides a new idea for the fabrication of FET-based gas sensors.
Abbas et al. reported a high-performance NO2 gas sensor with a lower detection limit as low as 5ppb. Its structure, characterization and performance are shown in Figure 2, a FET black phosphorene gas sensor with SiO2 as the base material, Ti Au as the two ends of the electrode, and black phosphorene nanosheet layer as the sensitive material. For the first time, it was experimentally demonstrated that a FET gas sensor with black phosphoene nanosheet as a sensitive material can have good gas sensing performance for NO2. In addition, through stress testing, we can find that the black phosphoene nanosensor has good stability. Kim et al. fabricated a high-performance FET-based NO2 gas sensor by stacking layers of black phosphoene nanosheets directly on metal electrodes. The NO2 gas molecule is regarded as chemical doping, and the change in the resistance of the NO2 gas molecule after the reaction with the surface of the material is understood. It provides a new idea of gas sensing mechanism.
Fig.3 Schematic diagram of the structure of black phosphorene nanosheets.
As shown in Figure 3, Donarelli et al. found that the stripped black phosphorene nanosheet layer was drop-cast on a Si3N4 substrate with PT as the electron fork wrapped in N2 atmosphere. The lower detection limit for NO2 gas in 25 environment is as low as 20ppb, and it has excellent sensitivity characteristics. Shi et al. constructed a new type of FET sensor by using the black phosphorene nanosheet layer (BP), boron nitride (BN) and molybdenum disulfide (MOS2) as the top deleting electrode, and the dielectric layer and conduction channel. By separating the sensitive material from the conduction channel, the lower detection limit of NO2 gas can be significantly increased to 33 ppb。However, these efforts ignore the fact that black phosphorene is susceptible to degradation due to air oxidation. In the outermost shell of the black phosphorene material there is a group of lone electron pairs whose chemical valence state is shown as +3 valence. When black phosphorene comes into contact with air, the outermost lone electron pair will be oxidized by H2O and O2 in the air, and the chemical valence state will change to +5 valence, and its electrical properties will also change. FET-type sensors, which are sensitive materials with black phosphorene nanosheets, have excellent sensitivity characteristics such as high sensitivity and room temperature operation. However, the lack of continuous environmental stability of the device is one of the biggest difficulties in the practical application of FET-based gas sensors.
3.Gas sensor prepared by black phosphorene and semiconductor metal oxide composites.
Liu et al. first prepared BP-PEI composites in batches by non-covalent bond polymerization (Fig. 4), and then prepared co3o4@bp-PEI composites by traditional hydrothermal methods. It is possible to quickly detect a certain amount of NO2 gas at 25 levels. The sensitivity to 100 ppm NO2 is 838, the response rate can be as fast as 067s。
Fig.5 Schematic diagram of BP-pei@co3o4 synthesis.
Li et al. successfully prepared BP-ZNO composites by ultrasonic treatment of ZNO and black phosphorene nanosheets (Fig. 6), and the prepared composites stabilized the environmental structural stability of black phosphorene according to the XPS results. According to the gas sensing test data, at 160, the response value to 100 ppb NO2 can reach 20, and the lower detection limit can be as low as 1 ppb. However, the high operating temperature is not conducive to the integration and miniaturization of devices, which is not in line with the development trend of green and energy-saving sensors today.
Fig.6 (a) Schematic diagram of BP-ZNO structure (b) Schematic diagram of ZNO structure (c) Schematic diagram of BP structure (d) Schematic diagram of the reaction between BP-ZNO and NO2 (e) Schematic diagram of the reaction between ZNO and NO2 (f) Schematic diagram of the reaction between BP and NO2.
In addition to the above reports of black phosphosphone-based gas sensors, the combination of black phosphatene and ***, and the combination of black phosphatene and optical fiber to detect gases have also achieved fruitful scientific research results.