Host–guest assembly engineered nanofiltration membrane for high‐efficiency ion–ion separation

Abstract Ultra‐high permeance and ion–ion selective polyamide (PA) membranes hold immense potential for desalination and brine valorization. To address the inherent limitations of conventional PA membranes that balance permeance and selectivity, we developed a novel host–guest strategy by co‐embedding host and guest molecules into the membrane, termed Host–Guest Modulated Interfacial Polymerization (HGMIP). This approach successfully incorporates host–guest molecules into the PA matrix, where host cavities act as artificial water channels, hence enhancing permeance. Simultaneously, the host–guest self‐assembly also fine‐tunes reaction kinetics and pore size, producing membranes with low molecular weight cut‐off (MWCO) and improved surface charge and morphology. Consequently, the optimized PA‐H1 ⊃ G and PA‐H2 ⊃ G membranes show exceptional size and charge‐dependent ion sieving (Li + /Mg 2+ = 66, Cl − /SO 4 2− = 289) with improved permeance, highlighting clear advantages over state‐of‐the‐art membranes. This work establishes host–guest chemistry as a versatile platform for engineering PA membranes with tailored nanochannels and surface properties, enabling precise ion–ion separation without compromising permeance.