Novel positively-charged polyamine nanofiltration membrane prepared by oligomer triggered interfacial polymerization for molecular separation

Nanofiltration (NF) has the potential to achieve the efficient effluent separation. However, conventional polyamide-based NF membranes face several challenging issues, including negatively charged surface, insufficient water permeance and low selectivity of organic micropollutants. Herein, we designed a novel polyamine membrane generated from the nucleophilic substitution reaction between 1,4,7,10-tetraazacyclododecane (Cyclen) and 1,3,5-tris(bromomethyl)benzene (TBB), and proposed its fabrication via oligomer triggered interfacial polymerization (OT-IP). As the crucial component of the polyamine membrane, the amine-linked Cyclen-TBB selective layer was assembled onto a porous substrate through interfacial polymerization between alkaline aqueous solution and organic solution consisting of Cyclen and TBB premixed in n-hexane. The resultant Cyclen-TBB composite membrane possessed an effective pore size of ∼1.6 nm and strongly positively charged surface with a zeta potential of +18.4 mV in a neutral solution. Owing to these characteristics, the Cyclen-TBB composite membrane exhibited a high water permeance of 77.0 L·m−2·h−1·bar−1, and high rejections to positively charged dyes and drugs with molecular weights above 500 Da. Moreover, the composite membrane possessed splendid chemical resistance under both acidic or alkaline conditions, and operational stability during continuous filtration. These results demonstrate that novel highly permeable and positively-charged polyamine NF membranes are potential candidates for selective separation of molecules, and provide a feasible alternative for application in the treatment of industrial and pharmaceutical effluents.