Fluorine-free MXenes via molten salt Lewis acidic etching: Applications, challenges, and future outlook

MXenes, a family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, have garnered a global attention for their diverse applications in energy storage, electromagnetic interference shielding, sensing, catalysis, biomedicine, and more. Traditionally, MXenes have been prepared by dissolving Al from the MAX phase using fluorine-based etching solutions. However, a greener alternative approach, that is, Lewis acidic etching via molten salt has recently emerged which avoids the use of harmful fluorine-based etchants and allows for the production of MXenes with tunable surface functionalities. In this comprehensive review article, the authors delve into the drawbacks of traditional fluorine-based MXene fabrication methods and showcase the advantages of the greener and more efficient approach of Lewis acid etching via molten salt. The chemical processes involved in the conventional and Lewis acid etching methods are discussed and a special emphasis is given on the structure–property relationship that can be tuned by using the later approach. This article is expected to be a valuable resource for researchers interested in the MXene fabrication and to inspire further development and innovation in this exciting and rapidly evolving field.