Preparation and Application of 2D MXene-Based Gas Sensors: A Review

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.

A Family of 2D-MXenes: Synthesis, Properties, and Gas Sensing Applications

“…Even though there are many research papers on MXenes, the key aspects have been summarized in informative review articles − and books . In addition, a few overviews of MXene-based gas sensors have been reported. ,− However, no comprehensive review has focused on recent developments in the MXene gas sensors for potential applications. This review systematically describes the summary of a diverse range of MXenes and their synthesis methods.…”

MXene Heterostructures as Perspective Materials for Gas Sensing Applications

“…PEDOT:PSS is another studied polymer for the fabrication of MXene/polymer-based gas sensors due to its simple production and high conductivity [ 22 ]. The combination of PEDOT:PSS with Ti 3 C 2 T x results in a synergetic effect with enhanced sensitivity to NH 3 in comparison to both pure PEDOT:PSS- and Ti 3 C 2 T x MXene-based sensors due to the large active sites on the MXene’s surface and direct charge transfer in PEDOT:PSS/Ti 3 C 2 T x composite structure [ 118 ].…”

“…Until now, MXene demonstrated great perspectives for the development of energy storage devices. Since the first investigation of Mxenes’ gas performance in 2015, the number of publications in this area increases each year (see Figure 1 b) by multiplying; however, the investigation of their sensing performance is still in the preliminary stage [ 22 ]. For instance, the selectivity of these systems still remains an issue, so further research efforts shall be applied to enhance and optimize their gas sensor performance, for example, by surface functionalization, coating or fabrication of hybrid materials [ 8 ].…”

Emergence of MXene–Polymer Hybrid Nanocomposites as High‐Performance Next‐Generation Chemiresistors for Efficient Air Quality Monitoring

“…These contaminants are released into the environment in the gaseous phase (ammonia (NH 3 ), nitrous oxides (NO x ), sulfur oxides (SO x ), carbon oxides (CO x ), vapor phase (alcohols, ketones, toluene(C 7 H 8 )), and solid phase (particulate matter) through numerous human activities, including industries, automobiles, urbanization, households, and farming. [1–3] Both outdoor (CO x , NO x , SO x , and NH 3 , ground‐level ozone) and indoor (volatile organic compounds (VOCs) like benzene (C 6 H 6 ), alcohols, ketones, C 7 H 8 ) contribute to air eminence degradation [ 1,2,4–16 ] as listed in Table 1 .…”