A Lamellar MXene (Ti3 C2 Tx )/PSS Composite Membrane for Fast and Selective Lithium-Ion Separation.

A two-dimensional (2D) laminar membrane with Li+ selective transport channels is obtained by stacking MXene nanosheets with the introduction of poly(sodium 4-styrene sulfonate) (PSS) with active sulfonate sites, which exhibits excellent Li+ selectivity from ionic mixture solutions of Na+ , K+ , and Mg2+ . The Li+ permeation rate through the MXene@PSS composite membrane is as high as 0.08 mol m-2  h-1 , while the Li+ /Mg2+ , Li+ /Na+ , and Li+ /K+ selectivities are 28, 15.5, and 12.7, respectively. Combining the simulation and experimental results, we further confirm that the highly selective rapid transport of partially dehydrated Li+ within subnanochannels can be attributed to the precisely controlled interlayer spacing and the relatively weaker ion-terminal (-SO3 - ) interaction. This study deepens the understanding of ion-selective permeation in confined channels and provides a general membrane design concept.