Rapid fabrication of poly(quaternary ammonium) membranes with enhanced permeance and acid stability for cation separation

Acid-resistant nanofiltration membranes are crucial for recovering valuable metal ions from acidic wastewaters, yet conventional nanofiltration membranes predominantly consist of polyamide networks that degrade in concentrated acids. Poly(quaternary ammonium) (PQA) membranes exhibit high acid stability, but are compromised by slow formation kinetics and low permeance. In this work, we designed an oligomer (PVI, M n  = 2342 Da, Đ = 1.18) bearing imidazole-based tertiary amines to undergo rapid interfacial polymerization with 1, 3, 5-tris(bromomethyl)benzene. PVI possesses high density of reactive groups with low steric hindrance, enabling the fabrication of a dense PQA membrane within sub-minute time. The resulting membrane exhibits a larger pore size and a more positively charged surface compared to conventional analogues, achieving a combination of ultrafast preparation (∼1 min), high water permeance (∼8.6 L m −2  h −1 bar −1 ) and rejection (∼96%). Meanwhile, the membrane shows high selectivity (>20) for Li  +  over Co 2+ , Ni 2+ , Mn 2+ , along with high acid stability in 1 M H 2 SO 4 for over one month, holding promise for lithium recovery from spent batteries leachates.