Amino-grafted MOF-based composite membranes for improving Li+/Mg2+ separation performance

Advanced ion transportation channels aided by charge and suitable aperture play a crucial role in achieving precise separation of ions. Here, we report a MOF composite membrane with electropositive surface and sub-nanometer-sized ion transport channels for efficient Li+/Mg2+ separation. The membranes were fabricated using MOF "porous monomers" and trimesoyl chloride (TMC) through interfacial polymerization, and subsequently modified with amino-functionalized polyethyleneimine (PEI). The abundant porosity of the MOFs composite membrane includes the inner and the intergranular pores of MOF provided a rapid transport channel for Li+ ions, and a superior Li+ permeation rate of 0.68 mol m−2h−1 (a 10 times enhancement compared to the currently leading MOF membranes). Moreover, the improved positively charged surface (from −78 mV to + 4 mV at pH = 7) and reduced mean pore diameter (from 1.13 nm to 0.8 nm) of the membrane caused a remarkable selectivity of 13.2 for Li+/Mg2+. The design concept of the above MOFs based membrane provides a novel approach for developing high-quality MOF composite membranes for improving Li+/Mg2+ separation performance.