Kinetic Buffering Strategy Enables Interfacially Polymerized Loose Nanofiltration Membranes for Stable Dye/Salt Separation

Abstract

The application of loose nanofiltration (LNF) membranes for dye/salt separation is hindered by a permeance–stability trade-off arising from uncontrolled interfacial polymerization (IP), which produces heterogeneous polyamide (PA) structures with poor durability. Herein, we introduce a kinetic buffering strategy using piperazine-N,N′-bis(2-ethanesulfonic acid) (PIPES) to regulate the diffusion and reaction of piperazine-2-carboxylic acid (PIP-COOH). Molecular dynamics simulations reveal that PIPES suppresses PIP-COOH migration via electrostatic repulsion and steric hindrance, reducing its diffusion coefficient by 85.1%. This controlled kinetics prevents the formation of an excessively dense incipient PA layer, enabling sustained vertical growth. Under dead-end filtration, the optimized membrane achieves a pure water permeance of 54.3 ± 1.3 L m–2 h–1 bar–1, >97% rejection of anionic dyes, and <3% Na2SO4 rejection. This kinetic buffering strategy resolves the permeance–stability dilemma, offering a rational design principle for robust LNF membranes toward sustainable textile wastewater treatment.