Self-Crosslinked MXene (Ti₃C₂T_x) Membranes with Good Antiswelling Property for Monovalent Metal Ion Exclusion

A 2D membrane-based separation technique has been increasingly applied to solve the problem of fresh water shortage via ion rejection. However, these 2D membranes often suffer from a notorious swelling problem when immersed in solution, resulting in poor rejection for the monovalent metal ion. The design of the antiswelling 2D lamellar membranes has been proved to be a big challenge for highly efficient desalination. Here a kind of self-crosslinked MXene membrane is proposed for ion rejection with an obviously suppressed swelling property, which takes advantage of the hydroxyl terminal groups on the MXene nanosheets by forming Ti-O-Ti bonds between the neighboring nanosheets via the self-crosslinking reaction (-OH + -OH = -O- + H₂O) through a facile thermal treatment. The permeation rates of the monovalent metal ions through the self-crosslinked MXene membrane are about two orders of magnitude lower than those through the pristine MXene membrane, which indicates the obviously improved performance of the ion exclusion by self-crosslinking between the MXene lamellae. Moreover, the excellent stability of the self-crosslinked MXene membrane during the 70 h long-term ion separation also demonstrates its promising antiswelling property. Such a facile and efficient self-crosslinking strategy gives the MXene membrane a good antiswelling property for metal ion rejection, which is also suitable for many other 2D materials with tunable surface functional groups during membrane assembly.