Development of an Environmentally Friendly nanofiltration membrane for efficient Lithium-Magnesium separation using ZIF-8-NH2 grafted polyamide

Abstract

Lithium metal, a pivotal element in modern electric vehicles and electronics, necessitates secure and sustainable supply chains. Extracting lithium from brines presents significant challenges, particularly when dealing with high magnesium-to-lithium ratios, due to the nearly identical ionic radii of lithium and magnesium ions. Herein, we propose an innovative strategy for the selective separation of Li⁺/Mg²⁺ by integrating ZIF-8-NH₂ into polyamide membranes through the interfacial polymerization (IP) of polyethyleneimine (PEI) and trimesoyl chloride (TMC). The synthesized PEI@ZIF-8-NH₂ + TMC membranes exhibit an impressive permeation rate for Li⁺ of 0.863 mol m^-2h^-1, alongside a Li⁺/Mg²⁺ selectivity ratio of 33.06. The unique pore structure of ZIF-8-NH₂ and surface chemistry facilitate efficient Li⁺/Mg²⁺ separation, driven by synergistic interactions such as elevated positive surface charges, subnanometer channels, and strong π-π stacking with polyamide layers. These developments are anticipated to augment both the selectivity and durability of MOF-based membranes, providing new directions for research and practical implementations in ion separation technology.