Porous MXenes: Synthesis, Structure, and Applications

【Research Background】
    Thanks to the controllable complex composition and surface functional groups, MXenes has been widely used in many applications, such as energy storage, electromagnetic shielding, sensors, and biomedicine. With the introduction of porous structures, MXenes has unique advantages in the control of electrical conductivity and permittivity, the adjustment of electromagnetic wave transmission, and the loading and distribution of other functional materials. Therefore, porous MXenes have great potential in improving performance. Recently, the team of Academician Zhao Dongyuan of Fudan University published a review article on Nano Today, an internationally renowned academic journal, titled Porous MXenes: Synthesis, structures and applications. The article summarized the main synthesis methods of porous MXenes in the past three years, as well as porous MXenes in rhenium capacitors and lithium Applications in the fields of sodium / ion batteries, lithium-sulfur batteries, electromagnetic shielding and absorption, piezoresistive sensors, and cancer treatment are summarized, and the formation mechanism of porous structures in different fields is analyzed.

[Picture and text guide]
    According to different synthesis methods and formation mechanisms, porous MXenes can be divided into four categories:
    i) Assembly of MXenes
    ii) Deposition or insertion of MXenes in porous substrates
    iii) Load or cover functional porous materials on the surface of MXenes
    iv) Construction of in-plane pores in MXenes

Figure 1. Schematic diagram of the synthetic routes and formation mechanisms of four porous MXenes.

Figure 2. Formation mechanism and macroscopic and microscopic images of C12E6 surfactant modified layered structure MXLLC film. Composite process and micro-morphology of hollow MXene sphere and 3DMXene membrane.

Figure 3. MXene sponge formation process and MXene / rGO aerogel synthesis method.

Figure 4. In-situ growth of ultra-thin FeNi-LDH nanosheets on the surface of MXene after peeling to form a porous structure; Ti3C2 @ mMSNs-RGD porous composite synthesis mechanism and morphology.

Figure 5. Method of chemically etching Ti3C2Tx to obtain a porous MXene structure and its transmission image. (Mo2 / 3Sc1 / 3) 2AlC etching principle and image after etching.

Figure 6. Ti3C2MXene aerogel as a lithium metal anode material. The wrinkled N-Ti3C2Tx / S composite material is used in lithium-sulfur batteries.

Figure 7. SEM image and absorption properties of MXene foam.

Figure 8. MXene @ rGO aerogel applied to a piezoresistive sensor.

Figure 9. Application of Ti3C2 @ mMSNs-RGD porous complex in the field of cancer treatment.
 
[Summary and Prospect]
      Although MXenes has made some progress in the research areas discussed above, for future research directions, challenges and opportunities coexist.
     i) How to prepare ordered porous MXenes with highly controlled pore size and structure?
    ii) How to simultaneously optimize the composition and structure of porous MXenes?
   iii) The rich defects and functional groups on the surface of MXenes nanosheets make the porous structure an ideal substrate for supporting other functional materials, such as monoatomic catalysts. Therefore, MXene-based porous composites still need further research
   iv) Explore the possibilities of other potential applications for porous MXenes.
 
Literature link:
https://doi.org/10.1016/j.nantod.2019.100803

Source: WeChat public account MXene Frontier