e-Polylysine regulated nanofiltration membrane with high free volume for efficient separation of dye/salt

X Wang and TT Li and ZH Li and MH Su and SF Zhang and F Liu, JOURNAL OF MEMBRANE SCIENCE, 729, 124147 (2025).

DOI: 10.1016/j.memsci.2025.124147

Highly selective solute-solute separation remains a significant challenge for nanofiltration membranes, with the free-volume microstructure playing a critical role in determining perm-selectivity. This study presents a thin-film composite membrane fabricated through interfacial polymerization between bio-based e-polylysine (e-PL) and triformyl chloride (TMC) for efficient dye/salt separation. e-PL, with its unique molecular chain structure and steric hindrance, slows diffusion while maintaining adequate reactivity, promoting the formation of a selective layer with an optimal free-volume. In comparison to the small-molecule lysine used as an aqueous monomer, the polyamide membrane prepared with e-PL exhibits a larger free-volume fraction (from 15.64 % to 38.85 %), enhanced pore connectivity, and a higher molecular weight cutoff. The optimized membrane demonstrates excellent performance, including high pure water flux (99.1 L m-2 h-1), mixed solution permeate flux (58.1 L m-2 h-1), and an impressive dye/salt separation factor (up to 597.8 for NaCl/Congo Red). The design strategy outlined here offers valuable insights for developing nanofiltration membranes with tunable pore structures, particularly for dye desalination applications.

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