High permeance of polyamide nanofiltration membranes with adjustable pore structure based azo-porous polymer interlayer

As an advanced water harvesting technology, nanofiltration can help solve the problem of global water scarcity. Nonetheless, a common “trade-off” effect exists between permeability and selectivity in nanofiltration (NF) membranes, and addressing this trade-off is crucial for advancing NF membrane technology. The introduction of an interlayer to improve the surface properties of the substrate is considered to be a more direct, practical, and effective way to improve membrane performance. A polyamide composite nanofiltration (NF) membrane with superior permeability and selectivity was developed by incorporating a porous organic polymer (POP) interlayer into the substrate via an in situ azo coupling reaction, which enhances the substrate's pore structure. The influence of aromatic diamine monomers with varying chain lengths on the surface properties of interlayers-specifically pore structure, hydrophilicity, and roughness-was examined, along with their impact on the separation capabilities of the NF membranes. Molecular simulation was used to analyze the pore size variation trend of azo-porous polymers (Azo-POPs) with monomer chain length. The optimized TFC-0C-S membrane exhibited a pure water permeance of 44.7 ± 0.5 L m −2  h −1  bar −1 , while demonstrating a Na 2 SO 4 rejection of 97.2 ± 0.2 %. This research offers insights for the meticulous design of the interlayer to enhance the pore structure of NF membranes.