Enhancement of Mg2+/Li+ selectivity and water permeability in nanofiltration membranes using dopamine-functionalized graphitic carbon nitride

Achieving a balance between high water permeability and excellent ion separation performance remains a significant challenge for traditional nanofiltration (NF) membranes due to the inherent trade-off between permeability and selectivity. This study proposes an innovative modification strategy involving dopamine (DA)-functionalized ball-milled graphitic carbon nitride (BM-g-C 3 N 4 ), leading to the successful fabrication of high-performance NF membranes. The ball-milling process significantly improves the dispersibility of g-C 3 N 4 , while DA functionalization enhances the hydrophilicity of the membrane surface and the adhesion to the substrate. The results demonstrate that the incorporation of DA functionalized BM-g-C 3 N 4 (DA@BM-g-C 3 N 4 ) effectively reduces defects in the separation layer and provides additional water transport channels. The modified membrane exhibited outstanding separation performance, with the separation factor (SF) increasing from 13.77 to 22.42 and permeation flux improving from 9.9 L/(m 2 ·h) to 17.54 L/(m 2 ·h), tested in a 2.0 g·L −1 MgCl 2 /LiCl mixed salt solution. Furthermore, the fabricated NF membranes showed excellent ion separation efficiency and long-term operational stability, with the rejection rate of Mg 2+ remaining stable between 92.74 % and 97.78 % after 200 h of continuous operation.