381436 Design of Zwitterionic Reverse Osmosis Membranes with Excellent Anti-Fouling Performance By Michael Addition
Membrane fouling is one of the most severe challenges to the application of reverse osmosis (RO) membrane. Zwitterion is a neutral molecule with a positive and a negative electrical charge, and proved to be a kind of non-fouling material. However, strict preparation conditions and high cost limit the application of zwitterionic materials.
In this work, an efficient and simple method to prepare zwitterionic polyamide (PA) RO membranes with excellent anti-fouling performance by Michael addition was proposed. The zwitterionic structure was designed by using common amino compounds as the positively charged section, using carboxylic and sulfonic compounds as the negatively charged section, respectively. Six different kinds of zwitterionic RO membranes were prepared based on positively charged materials, including hyperbranched polyethylenimine (PEI), tetraethylenepentamine, 1,3-diaminoguanidine monohydrochloride, and negatively charged materials, including acrylic acid (AA), 2-methyl-2-butenoic acid, 3-sulfopropyl methacrylate, 6-maleimidohexanoic acid.
Enzyme-linked immunosorbent assay (ELISA) and fluorescent protein adsorption test at different pH values were adopted to evaluate the static anti-fouling property of optimized zwitterionic membranes. Dynamic membrane fouling experiment was conducted to investigate the anti-fouling property of resultant membranes during long-term operation with lysozyme aqueous solution. Separation performance for NaCl solution was also studied.
ELISA result demonstrated that the protein adsorption quantity of resultant six zwitterionic membranes were only about 3%~11% of that of conventional PA membrane. In particular, the protein adsorption quantity of PEI-AA zwitterionic membrane was only 3%~5% in the pH range from 5.0 to 9.0, showing excellent anti-fouling property in acid, neutral, and alkaline conditions. Almost no fluorescent protein was observed on the surface of zwitterionic membranes after immersed in Cy3-BSA solution and shaking for 3 hours. On the contrary, many fluorescent points could obviously be observed on conventional PA membrane surface. In dynamic membrane fouling experiment, the permeation flux of conventional PA membrane declined rapidly to about 36% of initial flux after operation for 10 hours. However, the permeation flux of PEI-AA zwitterionic membrane declined slightly and still reached up to 90% of initial flux. Zwitterionic membranes also owned good separation performance for NaCl solution at operation pressure of 1.6 MPa. The water flux of zwitterionic membranes were even slightly higher than conventional PA membrane.
Therefore, an efficient and feasible strategy was proposed to tremendously improve the anti-fouling property of PA RO membrane, showing significant effect on the research and application of anti-fouling membranes.