Structure-transport relationships in MXene-based membranes: from synthesis to selective water treatment.

Two-dimensional laminar membranes with precisely controlled nanochannels have attracted significant attention for overcoming the permeability selectivity trade-off in water purification. Among them, MXene-based membranes exhibit unique advantages arising from their hydrophilic surfaces, rich surface terminations, and tunable interlayer spacing. This review presents MXene synthesis routes, including direct and in situ etching, hydrothermal processing, and emerging green approaches, with emphasis on their influence on flake morphology, surface chemistry, and stacking behavior. Membrane fabrication strategies, such as vacuum-assisted filtration, mixed-matrix integration, and interlayer engineering, are analyzed to establish correlations between structural features and separation performance. Particular attention is given to transport mechanisms within MXene nanochannels, where size sieving, electrostatic interactions, and confined transport collectively govern ion and molecule selectivity. Recent advances in crosslinking and nanoparticle intercalation are highlighted for effectively suppressing swelling and stabilizing angstrom-scale channels under aqueous conditions. MXene membranes demonstrate high rejection efficiencies with enhanced water permeance and antifouling properties across desalination, heavy metal removal, and organic contaminant separation. The remaining challenges, including scalable fabrication, structural stability, and defect control, are discussed to guide future development toward practical membrane applications.