Abstract The wide application of lithium batteries in consumer electronics and electric vehicles bring about ever-rising demand of lithium resources globally. Nanofiltration (NF) membranes with high Mg2+/Li+ selectivity could achieve highly efficient separation of lithium from natural brines, which provides a good alternative for steady lithium supply. In this work, we developed a dual-skin layer nanofiltration membrane comprised of a polyethylene-imine (PEI) layer grafted on a polyamide layer. The polyamide layer was prepared via interfacial polymerization to endow the NF membrane with sub-nm pores, while the PEI layer was grafted on the polyamide surface via amidation reaction to further equip the membrane with enhanced positive charge. With the synergistic effect of size sieving from the polyamide layer and electrostatic exclusion from the PEI layer, the dual-skin layer NF membrane exhibits a high rejection of 98.5% to MgCl2 and a low rejection of 46.2% to LiCl, suggesting a high Mg2+/Li+ selectivity. As using this dual-skin layer NF membrane for separating Li+ from a simulated brine, a high Mg2+/Li+ separation factor (SMg,Li) up to 33.4 was achieved, which is the highest value among the pressure-driven polymeric nanofiltration membranes reported so far.

中文翻译：

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用于高选择性 Li+/Mg2+ 分离的双皮层纳滤膜

摘要 锂电池在消费电子和电动汽车中的广泛应用，带动了全球对锂资源的需求不断增长。具有高 Mg2+/Li+ 选择性的纳滤 (NF) 膜可以实现从天然卤水中高效分离锂，为稳定锂供应提供了良好的替代方案。在这项工作中，我们开发了一种双皮层纳滤膜，由接枝在聚酰胺层上的聚乙烯亚胺 (PEI) 层组成。聚酰胺层通过界面聚合制备，赋予NF膜以亚纳米级孔，而PEI层通过酰胺化反应接枝在聚酰胺表面，进一步为膜配备增强的正电荷。通过聚酰胺层的尺寸筛分和 PEI 层的静电排斥的协同效应，双皮层 NF 膜对 MgCl2 表现出 98.5% 的高截留率和 46.2% 对 LiCl 的低截留率，表明高 Mg2+/ Li+ 选择性。由于使用这种双皮层 NF 膜从模拟盐水中分离 Li+，实现了高达 33.4 的高 Mg2+/Li+ 分离因子 (SMg,Li)，这是报道的压力驱动聚合物纳滤膜中的最高值远的。