Positively charged Ti3C2Tx membrane for enhanced Li+/Mg2+ sieving

Lithium extraction from salt lake is important for carbon neutrality, while obtaining both high Li + /Mg 2+ selectivity and high water permeance is still challenging. The burgeoning two-dimensional (2D) material membranes in decade show enormous potential to solve above problem due to its highly designable lamellar structure. In this work, a kind of positively charged laminated membranes using MXene nanosheets as building blocks with decoration of poly (diallyl dimethyl ammonium chloride) (PDDA) were proposed. Benefiting from the well–intercalated PDDA between MXene nanosheets, the interlayer spacing between neighboring nanosheets was greater than 2 nm, which was conductive to enhance water permeance. Simultaneously, the introduction of PDDA endowed the membrane with positive charge, which exhibited sharply improved Li + /Mg 2+ selectivity by an order of magnitude due to enhanced Donnan effect. The prepared MXene/PDDA membrane with a modification mass ratio of 1:10 exhibited high Li + /Mg 2+ selectivity of 29.3 with MgCl 2 saline solution permeance of 9.8 L m −2  h −1 ·bar −1 and pure water permeance of 32.3 L m −2  h −1 ·bar −1 , which was promising for lithium extraction. Such membrane constructing concept could be expanded to other kinds of membranes based on 2D nanosheets for effective ion sieving.