Polypeptide modified polyelectrolyte-based membrane with excellent antimicrobial property and permeability via brush assisted assembly and chlorination treatment

The fabrication of a polyelectrolyte-based nanofiltration (NF) membrane with combined functions by a straightforward and scalable approach draws great attention. Herein, a polypeptide modified 1.5-bilayer polyelectrolyte NF membrane was fabricated by a novel brush assisted layer-by-layer (LBL) assembly technology using poly(allylamine hydrochloride) and poly(sodium-4-styrene sulfonate) as a polycation and a polyanion , and polylysine as a surface modifier. A denser separation layer can be formed by this approach compared to the classical static LBL assembly under the same assembled layer number. The membrane has an ultrathin separation layer (25 nm), and negatively charged surface in a neutral solution. It exhibits high rejections to potassium citrate (96.6%) and tetrasodium ethylenediamine tetraacetate (96.8%), and moderate rejection to sodium sulfate (85.3%). The molecular weight cut-off (MWCO) is 1360 Da. It also shows excellent antimicrobial property for the representative Gram-negative bacteria and fouling resistance to humic acid as foulant model. Moreover, chlorination treatment was firstly utilized to optimize the membrane structure and enhance the permeability from ca. 1.96 to 15.2 L/m 2  h bar, simultaneously keeping a high salt rejection. It was found that the chlorination process increases the negative charge density of the membrane surface and enlarges the free volumes between the polyelectrolyte chains.