MXenes is a new class of two-dimensional materials, including two-dimensional transition metal carbides, nitride and carbides. MXenes has shown potential applications in gas/humidity sensing, energy storage systems, water purification, and electromagnetic interference shielding. According to the reported gas sensing work, the signal-to-noise ratio of the gas sensor based on the pure TWO-DIMENSIONAL MXene nanosheet is higher than that of other two-dimensional gas sensing materials, such as graphene, transition metal dishalide compounds and black phosphorus. However, MXene causes severe aggregation after drying and loses a large specific surface area. Therefore, the response and selectivity of gas sensors based on pure 2D MXene nanosheets are very poor, and further improvement is needed to improve their practicability.

Recently, Professor Lu Geyu from Jilin University has published a paper on the tiny and Actuators: B. Chemical, an internationally renowned academic journal: Flexible resistive NO2 gas sensor of three - dimensional crumpled MXene Ti3C2Tx/ZnO the spheres for room temperature application of research, the method of using ultrasonic spray pyrolysis demonstrated resistance to gather 3 d ruffle MXene Ti3C2Tx ball, provides the high specific surface area of MXene, make the target gas adsorption on the surface. In addition, ZnO nanoparticles were combined with three-dimensional folded MXene Ti3C2Tx spheres to create more activated adsorption sites. The above improvements greatly improved the NO2 sensitivity, selectivity, responsiveness and recovery of the MXene sensor. In addition, polyimide (PI) substrate was used to realize NO2 room temperature sensing of flexible devices, and the sensing process between MXene and NO2 was deeply discussed. Based on the above sensing performance, a new sensing strategy and a flexible gas sensing device are proposed.

FIG. 1 schematic diagram of preparation of 3D MXene fold sphere and 3D MXene fold sphere /ZnO and flexible gas sensing device.

Figure 2. Morphology and element distribution of MXene three-dimensional folded spheres.

Figure 3. Morphology and element distribution of THREE-DIMENSIONAL MXene sphere /ZnO.

Figure 4. The structure, phase characterization and surface analysis of MXene lamellae, THREE-DIMENSIONAL folded MXene sphere and three-dimensional folded MXene sphere /ZnO were studied.

Figure 5. The selectivity, concentration sensitivity and recovery characteristics of flexible gas sensors based on MXene sheet, 3D MXene sphere and 3D MXene sphere /ZnO are studied.

Figure 6. Flexible NO2 sensing performance of the folded MXene/ZnO flexible gas sensor, the influence of humidity on NO2 sensing, and the difference between ammonia sensing and NO2 sensing.

FIG. 7. Schematic diagram of gas adsorption.

Figure 8. Density Functional Theory (DFT) simulates the adsorption of NO2 molecules on different materials.

To sum up, this paper introduces the preparation and modification of MXene Ti3C2Tx THREE-DIMENSIONAL fold sphere by reliable and effective ultrasonic spray pyrolysis method, and other two-dimensional materials can also be modified by similar methods. The 3d folded MXene not only maintains the high specific surface area of MXene sheet, but also provides a stable and uniform way for composite with other materials. High specific surface area, the possibility of increasing response sites and high gas sensitive materials make it possible to apply three-dimensional folded MXene spheres to gas sensors in this paper. Compared with the MXene sheet and the 3D folded MXene sphere, the 3D folded MXene sphere /ZnO realized the reversible perception of NO2 and significantly improved the selectivity and response to NO2. The response to 100ppm NO2 increased from 27.27% to 41.93%, and the recovery rate increased from 30% to 100%. MXene sphere /ZnO has high NO2 sensing performance, which is due to the defects of MXene sphere and ZnO nanoparticle caused by the folding of its surface and the appearance of PN heterojunction. The THREE-DIMENSIONAL folded MXene sphere structure provides a new idea for chemical sensing of MXenes, further promotes the application of MXenes in gas sensors, and thus provides a reference for exploring the gas sensing mechanism of MXene.

Literature link:

https://doi.org/10.1016/j.snb.2020.128828.

Source: MXene Frontie

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