Latest developments in the design and fabrication of two-dimensional carbides and nitrides (MXenes)

MXenes (Mn+1XnTx) are a prospective family of two-dimensional (2D) nanomaterials. They possess properties that are advantageous in many fields, including mechanical strength, high thermal and electronic conductivities, high surface area, and strong absorption of electromagnetic waves. Since its first report in 2011, MXenes have grown to consist of a large variety of structures and have been developed for numerous purposes. Given this vast amount of research, a proper understanding of how MXenes can be fabricated is crucial for further innovation. This review highlights the evolution of MXenes structures and synthesis methods over the past decade. MXenes structures have grown to include not only single-metal, but also multi-metal and multi-X-element structures. These structures are affected by synthesis pathway with preferable conditions and precursors in each methods. This review addressed the laboratory scale synthesis method through top down and bottom-up strategies, followed by the application in industrial-based strategies. The general top-down (selective etching) synthesis approach has been improved using fluorine-free etching and sonication-free exfoliation, while newer bottom-up approaches such as chemical vapor deposition and direct synthesis have also been studied. Besides, the understanding on the first principles calculations of MXenes toward computational simulation also elaborated as the tools to determine the prospect structure with the desirable properties for MXenes application. The simulation is beneficial for conducting effective direct synthesis of MXenes with proper structure and performance on large scale. Finally, strategies for upscaling MXenes synthesis through new methods and reactor design are presented, and the outlook for MXenes synthesis prospect is also discussed.