Nanofiltration membrane via EGCG-PEI co-deposition followed by cross-linking on microporous PTFE substrates for desalination

Abstract It is imperative to fabricate nanofiltration membrane with promising separation performance and stability for desalination and wastewater treatment. In this work, inspired by polyphenol chemistry, composite nanofiltration membrane is facilely manufactured by a combined strategy of epigallocatechin-3-gallate (EGCG)-polyetheylenimine (PEI) co-deposition and trimesoyl chloride (TMC) cross-linking on porous polytetrafluoroethylene (PTFE) substrate. Separation performance of membrane was optimized by controlling EGCG-PEI coating time, EGCG-PEI mass ratio and TMC concentration. Chemical structures and surface properties of the optimal membrane were characterized systematically. It was found that a dense and defect-free selective layer was formed with negatively charged surface and molecular weight cut off of 380 Da (stokes radius of 0.46 nm). Experimental results showed that the optimal membrane yielded a pure water permeability of 9.15 L/(m2·h·bar), high rejections of salts in a sequence of Na2SO4 (95.5%) > MgSO4 (86.3%) > MgCl2 (79.1%) > NaCl (61.4%) and excellent rejections of dyes (99.9% for neutral red, methyl orange and crystal violet) at 0.2 MPa. Moreover, the membrane exhibited favorable structural stability and long-term operation stability due to the strong EGCG-PEI adhesion property and robust interfacial interactions.