Fine-tuning polyamide nanofiltration membrane for ultrahigh separation selectivity of Mg2+ and Li+

The extraction of lithium resources from salt-lake brine has garnered increasing attention, and a critical challenge is to achieve an effective separation of Mg2+ and Li+. This study focuses on addressing this challenge using isophthaloyl chloride (IPC) in combination with trimesoyl chloride for completing interfacial polymerization (IP) with polyallylamine. The product is an unexpectedly highly permeable and permselective polyamide nanofiltration (NF) membrane that is effective for Mg2+/Li+ separation. Adjusting the acyl chloride density with IPC influenced the IP reaction progress, thereby yielding a polyamide layer with fine-tuned properties. Various characterization results demonstrated a significant difference in the positive chargeability between the NF membranes doped with IPC and the blank NF membrane without IPC, whereas other properties remained comparable. The optimal NF membrane prepared with a low IPC molar ratio of 33% exhibited highly positively charged and high permeability characteristics. Considering the remarkable advancements in separation performance and simplified fabrication process, a fine-tuned strategy for designing highly positively charged NF membranes holds great practical potential for the industrial development of lithium extraction from salt-lake brines.