Abstract
Since MXene (a two-dimensional material) was discovered in 2011, it has been favored in all aspects due to its rich surface functional groups, large specific surface area, high conductivity, large porosity, rich organic bonds, and high hydrophilicity. In this paper, the preparation of MXene is introduced first. HF etching was the first etching method for MXene; however, HF is corrosive, resulting in the development of the in situ HF method (fluoride + HCl). Due to the harmful effects of fluorine terminal on the performance of MXene, a fluorine-free preparation method was developed. The increase in interlayer spacing brought about by adding an intercalator can affect MXene’s performance. The usual preparation methods render MXene inevitably agglomerate and the resulting yields are insufficient. Many new preparation methods were researched in order to solve the problems of agglomeration and yield. Secondly, the application of MXene-based materials in gas sensors was discussed. MXene is often regarded as a flexible gas sensor, and the detection of ppb-level acetone at room temperature was observed for the first time. After the formation of composite materials, the increasing interlayer spacing and the specific surface area increased the number of active sites of gas adsorption and the gas sensitivity performance improved. Moreover, this paper discusses the gas-sensing mechanism of MXene. The gas-sensing mechanism of metallic MXene is affected by the expansion of the lamellae and will be doped with H2O and oxygen during the etching process in order to become a p-type semiconductor. A p-n heterojunction and a Schottky barrier forms due to combinations with other semiconductors; thus, the gas sensitivities of composite materials are regulated and controlled by them. Although there are only several reports on the application of MXene materials to gas sensors, MXene and its composite materials are expected to become materials that can effectively detect gases at room temperature, especially for the detection of NH3 and VOC gas. Finally, the challenges and opportunities of MXene as a gas sensor are discussed.
Highlights
In recent years, due to the development of industrial production and the emission of automobile exhaust, environmental pollution has become serious
The preservation, use and yield of MXene are of great significance to the practical application, so the synthesis methods which can improve the dispersion of MXene and carry out large-scale production are discussed
Su et al [72] studied the effect of reaction temperature and ball milling time on the synthesis of Ti3 C2, and found that high etching temperature and longer ball milling duration resulted in faster conversion of Ti3 C2 MXene
Summary
Due to the development of industrial production and the emission of automobile exhaust, environmental pollution has become serious. The goal of the development of gas sensors is to produce sensors that possess high sensitivity, fast response and recovery speed, selectivity, and low working temperature in order to realize real-time monitoring of gas concentration and to avoid irreversible consequences. The prepared gas sensor showed an excellent response to CO2 (The response of 500 ppm CO2 at room temperature was 50% Hz/μg and response time and recovery time was 26/10 s). Due to the porosity of the ZIF-8 nanostructure and the high free charge carrier density, when the ZIF-8 sensor was exposed to 100 ppm NO2 at 350 ◦ C, the sensor showed a high gas response (118.5%) and a rapid response and recovery time was observed (113.5 s and 111.5 s, respectively). We aim to introduce MXene and gas sensors in detail and to contribute to the body of research relative to MXene in gas sensors
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