Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE Moderate HCl post-treatment produced an optimized polyamide nanofiltration membrane.

The optimized NF-pH 2 achieved a permeance of 26.02 LMH/bar with a Na2SO4 rejection of 92.06%.

NF-pH 2 exhibited superior dissolved organic matter removal while retaining a moderate level of mineral ions.

NF-pH 2 demonstrated excellent antifouling performance and long-term operational stability.


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 Na2SO4 and 90.15% for MgSO4). During natural surface water treatment, NF-pH-2 achieved effective dissolved organic matter removal, with TOC and UV254 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.