MXenes: 2D Materials that Can Reach Far beyond Graphene
Dr. Yury Gogotsi
Department of Materials Science and Engineering, and A. J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, PA 19104, USA
Abstract: Two-dimensional (2D) materials with a thickness of a few nanometers or less can be used as single sheets due to their unique properties or as building blocks, to assemble 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 BN and transition metal dichalcogenides, have been produced as 2D sheets. By combining various 2D materials, unique combinations of properties, which are not available in any bulk materials, can be achieved. The family of two-dimensional (2D) transition metal carbides and nitrides, MXenes, has been expanding rapidly since the discovery of Ti3C2 in 2011 . About 30 different MXenes have been synthesized, and the structure and properties of numerous other MXenes have been predicted using density functional theory calculations . The availability of solid solutions on M and X sites, control of surface terminations, and a recent discovery of multi-element layered MXenes (e.g., Mo2TiC2) offer a potential for synthesis of dozens of new distinct structures. MXenes’ versatile chemistry renders their properties tunable for a large variety of applications. Oxygen or OH terminated MXenes, such as Ti3C2O2, have redox capable transition metals layers on the surface and offer a combination of high electronic conductivity with hydrophilicity, as well fast ionic transport. This makes them promising candidates for energy storage and related electrochemical applications, but their applications in optoelectronics, electromagnetic interference shielding, plasmonics, sensors, water purification and desalination, electrocatalysis, medicine and other fields are equally exciting .