Improvement of permeability and antifouling performance of PVDF membranes via dopamine-assisted deposition of zwitterionic copolymer

Hydration is critical to restricting surface fouling in membrane separation processes. In order to tightly coat hydrophobic membrane surfaces with zwitterions that afford excellent hydration ability, herein, a facile strategy combining copolymer design and dopamine-assisted co-deposition was described. Three copolymers containing dopamine methacrylamide (DMA) unit and 2-methacryloyloxyethyl phosphorylcholine (MPC) unit, with/without a third hydrophilic unit, were synthesized via free radical polymerization, and characterized by 1H nuclear magnetic resonance (1H NMR) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy and gel-permeation chromatography (GPC). Subsequently, the as-synthesized copolymers were co-deposited with dopamine hydrochloride on polyvinylidene fluoride (PVDF) membrane surfaces. X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscopy (AFM) and water contact angle (WCA) measurements were conducted to analyze the superficial chemical composition, morphologies, roughness and hydrophilicity of the membranes. Systematical filtration and antifouling experimental investigations showed that the zwitterionic-copolymer-modified membranes demonstrated high permeate fluxes, good rejection performance, and great antifouling properties, attributing to the enhanced hydrophilicity of the membrane surfaces. Especially, the p(DM)/PDA-PVDF modified membrane exhibited outstanding water flux of 192.5 L·m−2·h−1 and ideal BSA rejection of 96.1 % with excellent flux recover ratio (FRR1: 82.6 %, FRR3: 97.8 %). This work presents a feasible hydrophilic modification strategy of hydrophobic membranes, which is expected to provide a new avenue to overcome the permeability-selectivity trade-off limitations and fouling problems in membrane separation processes.