Mxene Nanosheets Preparation Sensitive Film for QCM Humidity Sensor

Abstract

Fast, sensitive and stable detection of humidity is essential. In this paper, a 2D ultra-thin nanosheet Mxene was used as the material to form a sensitive film to construct the quartz crystal microbalance (QCM) humidity sensor by drop coating method. The element A in the MAX phase was dislodged by a simple liquid phase etching method. The morphology and composition of Mxene were studied by means of a series characterization methods, it was found the sample take on a ultrathin grapheme-like nanosheet. The test results show that the humidity sensor has 12.8Hz/% RH sensitivity, 6s and 2s (@ 90%)response/recovery time, maximum humidity hysteresis of 1.16%RH, good stability and selectivity. Finally, the adsorption enthalpy of water molecules on the surface of Mxene was explored by DFT calculation. It was found that residual F- played an important role in humitity sensing Introduction: The new two-dimensional (2D) material Mxene has been widely used in energy storage , battery , catalysis , electromagnetic shielding and other directions since it was discovered by the research team of Professor Yury Gogotsi of Drexel University in 2011.Ti3C2Tx has good electronic conductivity and hydrophilicity, it is the most widely studied and mature of all Mxenes. This work combines Mxene-Ti3C2Tx with the QCM test platform to further enhance the application of Mxene materials on humidity sensors.By optimizing the method in the previous literature, the Ti3AlC2 powder was etched in LiF / HCl solution to remove the Al element, some post-treatment such us ultrasonic was carry out to obtain a single-layer Ti3C2Tx solution that can be used to directly prepare the device. The obtained samples were characterized by XRD, SEM, TEM, EDS, XPS and BET, etc, it was found that Mxene with a large specific surface area has a good single-layer sheet structure, and the surface contains a large number of -OH, -O, -F functional groups. This single-layer sheet structure with large specific surface area and abundant active sites is more conducive to the adsorption of water molecules. By detecting the relative humidity of 11.3% - 97.3% shows that the sensor with the best performance has excellent sensitivity of 12.8Hz/% RH, 6s and 2s (@ 90%) rapid response/recovery time, maximum humidity hysteresis of 1.16%RH, good short-term repeatability, long-term stability, and excellent cross-sensitivity. Through characterization and simulation, it is found that -F functional group plays a certain role in the excellent humidity sensitivity. This not only provides a new possibility for the application of 2D materials in humidity sensor, but also widens the application of Mxene materials in sensor field. Figure 1