Unveiling decrosslinking degree on polyamide nanofiltration membranes: Structure-performance relationship and...

Polyamide (PA) nanofiltration membranes (NFMs) possess highly crosslinked structures, leading to several technical limitations such as poor selectivity, low permeance, and severe fouling. This study devised a novel isopropanol (IPA)-induced decrosslinking strategy to systematically modulate PA crosslinking density by precisely controlling IPA concentration and temperature. IPA induces swelling effects and hydrogen bonding, selectively extracting loosely crosslinked PA chain segments and allowing for network relaxation and rearrangement to form a uniform structure with lower overall crosslinking density. The optimised NF membrane post-treated with IPA at 60 °C (NF-IPA@60) achieved 32.94 % decrosslinking with enhanced surface negative charge density and enlarged pore size. Compared to the control membrane (NF-H₂O), NF-IPA@60 exhibited higher pure water permeance (27.3 LMH/bar) while maintaining 92.7 % Na₂SO₄ rejection. Enhanced Donnan exclusion significantly improved micropollutant removal, particularly for anionic contaminants such as perfluorooctanoic acid and perfluorooctanesulfonic acid. Pearson correlation analysis established clear structure-performance relationships for the decrosslinking strategy. Natural water testing showed that NF-IPA@60 exhibit total organic carbon removal efficiencies exceeding 88.2 %, with 3.15-fold improvement in organic/mineral selectivity and excellent antifouling properties. This study provides a novel theoretical framework and technical approach for high-performance NFM design, offering significant potential for overcoming traditional membrane technology bottlenecks.