Stabilizing MXene membranes via metal ion cage strategy for high-performance ion sieving

The separation of salts and heavy metal ions from wastewater is crucial for environmental protection and resource recovery. Lamellar membranes assembled from 2D nanoflakes have emerged as promising candidates due to their high selectivity and permeability. Here, we reported the fabrication of Metal Ion Cage MXene membranes with enhanced anti-swelling properties using a dual-modification strategy involving K + intercalation and polyethyleneimine (PEI) functionalization. The resulting membranes exhibited excellent structural stability in aqueous solutions, along with outstanding separation performance. The membranes achieved a maximum CR rejection rate of 98.7%, with divalent ions such as Ca 2+ , Cu 2+ , and Pb 2+ being rejected at rates exceeding 80%, alongside a water flux of ∼38.22 L m −2  h −1 . Mechanistic analysis revealed that K + intercalation enhanced interlayer interactions and limited swelling, while PEI modification strengthened electrostatic repulsion and stabilized the membrane structure. This synergistic strategy provided new insights into the structural design of stable 2D membranes and broadens their applicability in sustainable water treatment technologies.