Electric Field-Assisted Ion Separation Using Ceramic-Based Thermally Cross-Linked MXene Membranes

Highly efficient separation of monovalent/divalent cations from seawater and brines of salt lakes remains a major challenge primarily because such ions exhibit similar physical and chemical properties. Two-dimensional (2D) MXene (Ti3C2Tx) nanochannels are considered one of the most promising membranes for ion separation because of their remarkable electronic properties and regular interlayer spacing. Herein, a tubular ceramic-based MXene membrane was prepared through thermal cross-linking; the membrane was then employed for precisely separating Na+/Mg2+ with the assistance of an electric field. According to the cross-linking action (Ti-OH + Ti-OH = H2O + Ti-O-Ti) between MXene layers, interlayered nanochannels between MXene nanosheets can be fixed by decreasing the interlayer spacing, thereby exhibiting robust stability suitable for ion separation. Under an electric field of 1.5 V, the prepared membrane substantially improved the mixed-ion selectivity of Na+/Mg2+, achieving approximately complete separation through size sieving, ion dehydration, and Mg2+ enrichment on the membrane surface. Benefiting from the robust structure, the membrane retained long-term stability over eight cycles (up to 1000 min) of electric field-assisted ion separation for an acidic solution containing Na+ and Mg2+. Overall, this study provides a viable solution for constructing tube-based 2D membranes with highly robust nanochannels for efficient ion sieving.