In-situ grown polyaniline interlayer enables a high-pressure-tolerant nanofiltration membrane with enhanced flux for Mg2+/Li+ separation

Nanofiltration (NF) shows great promise for recovering lithium (Li + ) from brine. Conventional strategies to improve the water flux of nanofiltration membrane usually destroy the stability of nanofiltration membrane. We developed a high-pressure-tolerant NF membrane by engineering an in-situ grown polyaniline (PANI) interlayer on a hydrolyzed poly (aryl ether ketone) (PEEK) substrate. This PANI interlayer, which exhibits excellent compatibility with PEEK, provides a robust platform for the subsequent formation of a polyamide (PA) selective layer via interfacial polymerization, thereby overcoming the inherent difficulty in functionalizing PEEK. The three-layer PEEK/PANI/PA structure ensures that the PANI interlayer protects the PA selective layer from direct interaction with the finger-like pores of the PEEK substrate, thereby preventing its structural collapse under high pressure. This unique configuration ensures structural integrity and enables high water flux. The optimal membrane obtained a high water flux of 118.97 L m −2  h −1 and a Mg 2+ /Li + separation factor of 15.8 at 30 bar. Long-term testing at 50 bar demonstrated stable operation for approximately 18 h, defining the performance limit of this membrane system. This work provides a solution for Mg 2+ /Li + separation nanofiltration membranes with improved water flux and high-pressure tolerance.