An Electrostatic‐Interaction Engineering on Phytate‐Coordinated Polyamide Membranes for High‐Efficiency Lithium Extraction

Abstract

Phytate (PhA) holds considerable promise for constructing molecular sieve membranes due to its high density of long‐range electrostatic attractions, customizable charge density, and excellent polymer affinity. Herein, PhA‐Fe3+ complexes constructed by controllable coordination assembly are presented, based on metal‐organophosphorus biphasic interfacial coordination reactions, and use the PhA‐Fe3+ complexes to regulate the interfacial polymerization (IP) process to generate polyamide (PA) nanofiltration membranes. The PhA‐Fe3+ complexes impart a high density of long‐range electrostatic and short‐range hydrogen bonding forces to the amine monomers and provide tunable charge densities through flexible metal‐organophosphate coordination. Hydrogen bonding and strong electrostatic interactions spatially enrich the amine monomers and temporally slow down their diffusion into the hexane phase, as demonstrated by molecular simulations, resulting in a PA/PhA‐Fe3+ membrane with increased surface area, enhanced microporosity, lower thickness, higher water density near pores, and nanoscale spotted structures. Those structures are recognized as the key factor in achieving a water permeance of 19.2 L m−2 h−1 bar−1, alongside a MgCl2 rejection of 96.7% and a Li+/Mg2+ selectivity of 24.1 (Mg2+/Li+ mass ratio = 20), surpassing those of reported nanofiltration membranes. This PhA‐Fe3+ complexes‐modulated IP strategy offers fresh perspectives for constructing a highly permeable membrane for lithium extraction from salt lake brines.