Secondary interfacial polymerization enables thermostable polyamide nanofiltration membranes for high-temperature separation

Thin-film composite (TFC) nanofiltration (NF) membranes have been widely used for ionic/molecular separation. However, traditional NF membranes are limited by the unstable structure under high temperature, which leads to deteriorated separation performance. Herein, we report a secondary interfacial polymerization strategy to fabricate NF membranes with superior thermal stability from the conventional monomers. NF membranes after secondary polymerization possessed thicker and negatively charged polyamide layers. The secondary polymerization consumed partial residual acyl chloride groups and improved the compactness and structural stability of the polyamide layer. Molecular dynamics simulations further proved less polymer chain mobility of the polyamide segments after the secondary polymerization. The dense and thermostable NF membranes showed high rejections to MgSO 4 and Na 2 SO 4 at 85 °C. The membranes also maintained excellent stability during temperature cycling and long-term high-temperature operations. The proposed method is promising for the fabrication of thermostable NF membranes by simultaneously adjusting the chemical and physical structure via secondary interfacial polymerization.