Tröger's base-regulated interfacial polymerization of polyamide nanofiltration membranes with enhanced performance

Abstract

Interfacially fabricated polyamide thin film composite (TFC) membranes have been widely used in molecular and ion nanofiltration. However, it is still a great challenge to desirably control the thickness and performance of polyamide layer due to the uncontrollable interfacial polymerization (IP) process. In this work, Tröger's base (TB), consisting of two benzene rings connected by a bicyclic aliphatic methanodiazocine unit was used to regulate the IP between trimesoyl chloride (TMC) and piperazine (PIP). The incorporation of TB molecule accelerates the diffusion rate of PIP toward the water/hexane interface and enhances the reaction activity of TMC as a catalyst, thus largely promoting the interfacial reaction rate and resulting in the formation of polyamide layer with an extremely thin thickness. The thickness of the polyamide layer was tuned from 63.1 to 17.4 nm by increasing the TB content in aqueous solution. The TFC nanofiltration membrane fabricated through TB regulated IP process showed a water permeance of 18.5 ± 1.4 L m−2 h−1 bar−1 and simultaneously a salt rejection of 98.3% for Na2SO4 with overall desalination performance exceeding most nanofiltration membranes and commercial membranes. This work proposes a strategy for regulating the reaction rate of PIP and TMC during the IP process using a TB structured additive, which provides an alternative means for fabricating highly permeable TFC nanofiltration membranes.