Yury Gogotsi

Department of Materials Science and Engineering, and A. J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, PA 19104, US
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http://nano.materials.drexel.edu

Two-dimensional (2D) materials with a thickness of a few nanometers or less can be used as single sheets, or as building blocks, due to their unique properties and ability to assemble into a variety of structures. Graphene is the best-known example, but several other elemental 2D materials (silicene, borophene, etc.) have been discovered. Numerous compounds, ranging from clays to boron nitride (BN) and transition metal dichalcogenides, have been produced as 2D sheets. By combining various 2D materials, unique combinations of properties can be achieved which are not available in any bulk material. The family of 2D transition metal carbides and nitrides (MXenes) has been expanding rapidly since the discovery of Ti₃C₂ in 2011 [1,2]. Approximately 30 different MXenes have been synthesized, and the structure and properties of numerous other MXenes have been predicted using density functional theory (DFT) calculations [3]. Moreover, the availability of solid solutions on M and X sites, control of surface terminations, and the discovery of ordered double-M MXenes (e.g., Mo₂TiC₂) offer the potential for synthesis of dozens of new distinct structures.

This paper will describe the synthesis of MXenes by selective etching of layered ceramic precursors, including various MAX phases. Delamination into single-layer 2D flakes and assembly into films and 3D structures will be discussed.

The versatile chemistry of the MXene family renders their properties tunable for a large variety of applications. Oxygen or hydroxyl- terminated Menes, such as Ti₃C₂O₂, have been shown to have redox capable transition metals layers on the surface and offer a combination of high electronic conductivity with hydrophilicity, as well as fast ionic transport. This, among many other advantageous properties, makes the material family promising candidates for energy storage and related electrochemical applications, but applications in optoelectronics, plasmonics, electromagnetic interference shielding, electrocatalysis, medicine, sensors, water purification/ desalination and other fields are equally exciting [4].

References

1. M. Naguib, et al., Two-Dimensional Nanocrystals Produced by Exfoliation of Ti₃AlC₂, Advanced Materials, 23, 4248 (2011)
2. A. Alhabeb, et al., Guidelines for Synthesis and Processing of Two-Dimensional Titanium Carbide (Ti₃C₂T_x MXene), Chemistry of Materials, 29, 7633 (2017)
3. B. Anasori, et al., 2D Metal Carbides and Nitrides (MXenes) for Energy Storage, Nature Reviews Materials, 2, 16098 (2017)
4. K. Hantanasirisakul, et al., Fabrication of Ti₃C₂T_x MXene Transparent Thin Films with Tunable Optoelectronic Properties, Advanced Electronic Materials, 2, 1600050 (2016)