Ionic liquid‐based surfactants-mediated turing patterning in nanofiltration membranes via bidirectional diffusion control of piperazine and trimesoyl chloride for synergistic permselectivity enhancement

Thin-film composite (TFC) nanofiltration (NF) membranes fabricated via conventional interfacial polymerization (IP) inherently suffer from the permeability-selectivity trade-off due to diffusion-limited monomer transport. Here, we unveil an ionic liquid (IL)-based surfactants ([C₁₂mim][Cl]) as a dynamic bidirectional regulator of piperazine (PIP) and trimesoyl chloride (TMC) that uniquely reengineers IP kinetics to fabricate high-performance NF membranes with simultaneous enhancement in both water permeability and ion selectivity. Unlike existing additives that often passively decelerate amine diffusion, [C₁₂mim][Cl] establishes a critical diffusion asymmetry (D_TMC > D_PIP) by simultaneously accelerating TMC mobility while spatially confining PIP through intermolecular binding and viscosity modulation. This diffusion-driven instability triggers spontaneous Turing patterning, yielding an ultrathin (≈24 nm) polyamide (PA) layer with a loosely packed hierarchical network and enhanced carboxyl density (59.8 mM m⁻²). The synergistic interplay of Turing structure and intensified Donnan exclusion achieves unprecedented performance of NF membrane: water permeance (19.3 LMH bar⁻¹, +210 %) and mono-/divalent ion selectivity (83), surpassing over current leading benchmarks. This work establishes a universal strategy to fabricate high-performance NF membranes with large permeable surface and enhanced carboxyl density through an ionic liquid‐based surfactants-mediated IP, breaking the permeability-selectivity trade-off and offering transformative potential for precision separations.