Tailoring Polyamide Nanofiltration Membranes Through <scp>HCl</scp> ‐Assisted Heat Curing for Efficient and Stable Water Purification

ABSTRACT Polyamide (PA) nanofiltration (NF) membranes are widely used for drinking water purification, yet achieving a balance among permeance, selectivity, and fouling resistance remains challenging. In this study, a heat‐assisted HCl post‐treatment strategy was applied to tailor the structure of PA NF membranes, yielding an optimized membrane (NF‐pH‐2) with superior overall performance. The post‐treatment preserved the PA chemical backbone while increasing the surface O/N ratio to 1.35 and reducing the cross‐linking degree to 55.58%, indicating carboxyl enrichment and moderate network relaxation. As a result, NF‐pH‐2 exhibited a high‐water permeance of 26.02 LMH/bar, approximately 2.1 times higher than that of the control membrane, while maintaining high sulfate rejection (92.06% for Na 2 SO 4 and 90.15% for MgSO 4 ). During natural surface water treatment, NF‐pH‐2 achieved effective dissolved organic matter removal, with TOC and UV 254 removals of 81.67% and 83.16%, respectively, and preferential rejection of humic‐like components. Moreover, NF‐pH‐2 demonstrated excellent operational stability and antifouling performance, with flux recovery ratios of up to 98% and suppressed irreversible fouling during cyclic filtration. These results highlight NF‐pH‐2 as a promising candidate for efficient and reliable water purification applications.