Molecular design of a multi-functional monomer for the fabrication of high-performance microporous polyamide membrane

Organic solvent nanofiltration (OSN) is a pivotal green technology for molecular separations in pharmaceuticals and fine chemicals, offering precision and efficiency. However, its broader application is hindered by the persistent trade-off between membrane permeability and selectivity. Herein, we address this challenge through the rational design of a novel rigid and muti-functional tetra-amine monomer, 2,2′,4,4′-tetraaminobiphenyl (BIPDA), which was employed in interfacial polymerization with trimesoyl chloride (TMC) to fabricate an ultrathin polyamide nanofilm. The unique rigid geometry and muti-functionality of BIPDA monomer yielded an ultrathin (25.5 ± 1.3 nm), microporous selective layer, which conferred the membrane with a high methanol permeance of 10.4 ± 0.4 L m −2  h −1  bar −1 and a 317 Da MWCO, outperforming most polymeric OSN benchmarks. It also demonstrated precise charge-based molecular separation, near completely rejecting Methyl Orange while permitting the passage of Methylene Blue. Furthermore, it maintained >95 % rejection for the selected four pharmaceuticals and meanwhile showed excellent operational stability. In a practical demonstration, the membrane efficiently concentrated the tetracycline solution sevenfold within 6 h. This work successfully validates a bottom-up molecular design strategy to decouple the permeability-selectivity trade-off issue, thereby providing valuable insights for developing advanced membranes for pharmaceutical concentration and molecular separations.