Poly(piperazine-amide) nanofiltration membrane with innate positive charge for enhanced bivalent cation rejection and mono/bivalent cation selectivity

Abstract

Nanofiltration (NF) membranes with high cation rejection and cation selectivity are needed to increase the efficiency in process of water treatment and valuable ions recovery. However, the conventional NF membranes based on poly(piperazine-amide) (PPA) usually show unsatisfactory performance on it, mainly due to negatively charged membrane surface. Herein, we demonstrate the regulation of intrinsic charge property of PPA membrane from negative to positive, achieved by manipulating the trans-interface diffusion of amine during interfacial polymerization. Enriched amine monomers at organic phase facilitate the formation of PPA rich in positively-charged amine termination. The obtained PPA membranes exhibit 99.2% rejection to MgCl2 and demonstrate monovalent to divalent cation selectivity of up to 65.5. In addition, a post-assembled porous interlayer composed of dendritic mesoporous silica nanoparticles is designed not only to achieve improved water permeance, but also to show the contribution of porous interlayer to water permeation through thin-film composite membrane. This work represents an approach for the fabrication of PPA NF membrane with innate positive charge for high-efficiency cation rejection/selectivity.