Linear diacyl chloride enables polyamide nanofiltration membranes with balanced permeability and selectivity for efficient dye desalination

Nanofiltration (NF) membranes are crucial for dye desalination, yet their performance is often constrained by the inherent trade-off between water permeance and dye/salt selectivity. Achieving high permeance without sacrificing effective dye–salt separation remains a critical challenge. Herein, we present fumaryl chloride (FC), a linear and flexible aliphatic acyl chloride, as an alternative to trimesoyl chloride (TMC) for interfacial polymerization with piperazine (PIP) to address this challenge. Owing to its lower reactivity yet higher diffusion coefficient, FC enables the formation of a thinner, smoother, and less densely packed polyamide selective layer. Structural analyses indicate that the linear configuration of FC facilitates the assembly of loosely packed polymer chains. This architecture accelerates water transport while preserving effective dye/salt selectivity. The resulting FC-PIP membrane achieves a high water permeance of 104.6 L m −2  h −2  bar −1 and a DR80/Na 2 SO 4 selectivity of 118.3, which is 22.9 times higher than that of the conventional TMC-PIP membrane. This work provides a molecular-level strategy for designing NF membranes for dye desalination with balanced permeability and selectivity.