Designing polyurea membranes with twisted and durable skeleton for thermal/acid-stable efficient dye/salt separation

Nanofiltration membranes integrating superior separation performance with robust operational stability are imperative for some harsh scenarios such high temperature and acid environment. Nevertheless, the simultaneous attainment of these two attributes remains a formidable challenge for benchmark polyamide nanofiltration membranes due to their unstable molecular structure under these scenarios. Herein, we report a kind of polyurea nanofiltration membranes with twisted and rigid skeleton, enabling exceptional dye/salt separation performance and remarkable resistance to strong acid and elevated temperature. The key to this comprehensive performance lies in employing tetrakis(4-aminophenyl)methane as the amine monomer. Its moderate reactivity and twisted geometry jointly facilitate the formation of a suitably loose polymer network by slowing polymerization and preventing dense chain packing, while the rigid aromatic structure confers enhanced robustness through a durable polymer backbone. Our polyurea membranes demonstrate rejections exceeding 96.7 % for six dyes with molecular weights above 586 Da, while maintaining low rejections below 20.0 % for four representative inorganic salts. The optimized membranes exhibit an impressive Congo Red/Na 2 SO 4 selectivity of 121.9 with a high water permeance of 22.3 L m −2  h −1 bar −1 , outperforming the commercial nanofiltration membrane NF270. Furthermore, the membranes retain stable separation performance even under 80 °C or after exposure to 20 wt% H 2 SO 4 for 30 days, which is attributed to their rigid aromatic backbone and chemically stable urea linkages. This advancement adds a novel dimension for exploiting highly selective and durable nanofiltration membranes suited for demanding separation processes.