Nanocapsules induce in situ grafting of polyelectrolytes and structural rearrangement of polyamide layers

Highly permselective and antifouling nanofiltration (NF) membranes are desirable materials for ion sieving. Integrating favorable properties through interfacial polymerization (IP) is challenging. Herein, nano-encapsulation of polyethyleneimine (PEI) is performed using a functional group pre-protection approach. By precisely controlling the release process of the nanocapsules during IP reaction to achieve in situ deep cross-linking of PEI. Nanocapsule-modulated IP (NMIP) strategy affects the morphology of polyamide network in several ways, with the Turing structure endowing the membrane with higher water permeance (15.1 L m^-2h⁻¹ bar⁻¹) and a narrowed pore size that enhances the ion-sieving properties (Cl^-/SO₄^2- selectivity of 68.5). The nearly electroneutral separation layer shows low fouling rates and flux recoveries of up to 97.1 % in the treatment of charged organics and high stability under long-term high-loaded contamination conditions. This study unlocks new avenues for the precise, low-cost fabrication of high-performance ion-sieving materials.