Lamellar MXene Nanofiltration Membranes for Electrostatic Modulation of Molecular Permeation: Implications for Fine Separation

Nanofiltration membrane-based molecular separation has become an indispensable technology for fine sieving processes. However, the difficulty in regulating the separation performance restricts the applicability of these nanofiltration membranes in different separation systems. Herein, we will show that the separation performance of Ti3C2Tx–MXene lamellar nanofiltration membranes on certain dye molecules can be modulated by employing external electrostatic fields. Specifically, for cationic dyes, the negative voltage applied to Ti3C2Tx lamellar nanofiltration membranes can improve their sieving abilities on dyes but reduce their water flux at the same time. On the contrary, a positive electric field will cause a decline in the retention capacities but improve the water flux of the membranes. Interestingly, when using anionic dye molecules as solute models, the filtration performance of the Ti3C2Tx membranes exhibits completely opposite variations to that of filtering cationic dyes, whether the applied electric field is negative or positive. The regulation mechanisms for the filtration performance of Ti3C2Tx membranes have been discussed, which are probably ascribed to the changes in the electrostatic interactions between dyes and Ti3C2Tx induced by the external electric field. Our findings indicate that the filtration performance of MXene lamellar membranes on both cationic and anionic dyes can be modulated by applying an external electric field, opening up enormous opportunities to use such electrified nanofiltration membranes in the field of membrane-based molecular separations.