A zwitterionic copolymer-interlayered ultrathin nanofilm with ridge-shaped structure for ultrapermeable nanofiltration

Abstract

Interlayered thin-film composite (TFC) membranes have a great potential for enhancing salt separation in wastewater reclamation, because of the highly permeable and selective properties. However, mechanistic insights regarding the structural features of the surface nanofilms and their corresponding interlayers, which lead to enhanced separation efficiency, remain poorly understood. Herein, we report a zwitterionic copolymer 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-amino-ethyl methacrylate hydrochloride (AEMA) (P[MPC-co-AEMA]) interlayered TFC membrane that exhibits an ultrahigh water permeance of 20.4 L m−2 h−1 bar−1 (almost three folds higher water permeance than that of the pristine PA membrane), together with a simultaneously enhanced rejection of inorganic salts (96.8% against Na2SO4). Detailed mechanistic investigations revealed that the promoted membrane separation property was mainly explained as the enriched amine monomer diffusion-driven instability induced by the P[MPC-co-AEMA] interlayer. This triggers membrane sealing and inhibits its growth, leading to the formation of an ultrathin PA nanofilm with a thickness of 12 nm, a ridge-shaped surface structure with enhanced specific surface area, and enhanced crosslinking. The fundamental mechanism revealed in this study lays a solid foundation for the engineering of the high-performance TFC membrane, which is appealing for the energy-efficient water remediation industry.