Thermostable Nanofiltration Membranes via a Co-Monomer Strategy for High-Temperature Separation

The increasing demand for separation and purification at high temperature emphasizes the importance of thermostable thin-film composite (TFC) nanofiltration (NF) membranes. The performance of the selective layer is profoundly influenced by its molecular structure, and thus the optimization of interfacial polymerization monomers can substantially enhance the thermal stability of the NF membranes. Although some new amine monomers have been reported for the preparation of thermostable TFC membranes, piperazine (PIP) and m-phenylenediamine (MPD) are still the most widely used monomers. In this work, a co-monomer strategy integrating PIP with MPD as the aqueous monomers was employed to improve the rigidity of the polyamide selective layer, thereby fabricating thermostable TFC NF membranes. Precise modulation of PIP/MPD ratios enables effective control over the diffusion rate of aromatic monomers, and hence achieves tunable chemical composition and physical properties. Temperature-dependent pore size analysis and molecular dynamics simulations demonstrated that the incorporation of MPD significantly enhances the thermal stability of the polyamide selective layer. Remarkably, the TFC NF membrane maintains exceptional MgSO4 rejection (>98.5%) across a broad temperature range from 25 °C to 85 °C. This research not only provides fundamental insights into the design of co-monomer systems but also establishes a robust strategy for fabricating thermostable NF membranes.