Pore-size control mechanism of support membranes on interfacial polymerization process: Achieving charge enhancement and optimizing NFMs performance

The support membrane, as the core substrate of the nanofiltration membranes (NFMs), directly affects the interfacial polymerization (IP) process and the separation performance of the resulting NFMs. However, the pore-size control mechanism of support membranes in the IP process remains incompletely elucidated. This study systematically investigated how pore size in support membranes modulates IP by governing aqueous-phase monomer transport kinetics, with emphasis on its impact on the microstructure evolution and surface charge characteristics of NFMs. Our findings revealed that the pore size of the support membrane directly affects the storage and diffusion of amine monomers, thereby impacting their supply to the organic phase.  As the pore size of the support membrane decreased, more aqueous-phase monomers were supplied for organic phase reactions due to the enhancement of monomer diffusion ability. Further pore-size reduction reduced monomer accommodation capacity, thereby limiting monomer availability during IP and inhibiting the reaction. When the pore size was 60   nm, the dual influence mechanism of the support membrane led to increased diffusion of aqueous-phase monomers into the organic phase. The resulting PA layer, enriched with unreacted amino groups, strengthened the rejection of divalent cations and achieved synchronous enhancement of repulsion effects on both divalent cations and anions (>96%).   The pore-size control mechanism of support membranes studied in this work provides new theoretical guidance for regulating the performance of NFMs.