Tunable crosslinking PPTA nanofiltration membranes with tailored pore architectures for high-efficiency dye/salt separation

The development of high-performance nanofiltration membranes for efficient dye/salt separation remains a critical challenge in sustainable wastewater treatment. Herein, we report a tunable strategy to fabricate poly(p-phenylene terephthalamide) (PPTA)-based membranes with tailored pore architectures and surface functionalities. By employing low-temperature polycondensation of terephthaloyl chloride (TPC) and p-phenylenediamine (PPD) in an N-methyl-2-pyrrolidone (NMP) system, followed by selective end-capping, carboxyl- or amine-terminated membranes (PPTA tpc and PPTA ppd ) were synthesized. These membranes exhibited ultrafiltration-level permeance (643.1 and 697.3 L m −2  h −1  bar −1 ) but limited Congo Red (CR) rejection (∼90 %). To refine pore size, trimesoyl chloride (TMC) was utilized to crosslink surface amine groups, generating gradient-pore membranes (PPTA tpc -TMC m and PPTA ppd -TMC m ) with tunable crosslinking degrees. Systematic studies revealed that controlled crosslinking time enabled precise modulation of pore size, facilitating gradient dye rejection while balancing salt permeability. The optimized PPTA tpc -TMC 300s , PPTA ppd -TMC 20s , PPTA ppd -TMC 30s membranes achieved excellent separation factor of 710, 367, and 277 for NaCl/CR, NaCl/Acid Fuchsin (AF), and NaCl/Sunset Yellow (SY) solutions with a pure water permeance of 452.5, 42.5, 28.1 L m −2  h −1  bar −1 , respectively. Long-term stability tests confirmed sustained performance (>99 % dye rejection) due to crosslinking-enhanced structural rigidity. This study establishes a strategic paradigm for fabricating PPTA membranes with programmable pore architectures, elucidating the critical interplay between surface chemistry, tunable pore dimensions, and separation performance.