The Synthesis of MXenes

The synthesis of MXenes

In this article, we summarize different synthesis routes of MXenes. MXenes are made by selective etching of certain atomic layers from their layered precursors, mostly MAX phases. The etching selectively removes the A-group element layers in the MAX phases while keeping the MX layers with two-dimensional structure. Wet-chemical etching is the most common method to make MXenes and hydrofluoric acid was the first etchant used to make MXenes. It is found that F− anion is vital in the etching process. Thus, fluoride salt mixed with hydrochloric acid was also used to make MXenes. The wet-chemical etching process for MXene synthesis is affected by environmental factors, such as temperature, pressure, and so on. Thus, by controlling these factors, more etching methods, such as hydrothermal etching and electrochemical etching, were used to synthesize MXenes effectively. Besides wet-chemical etching in aqueous solution, molten salt etching is also an important method to make MXenes with more terminations.