Low-pressure electroneutral loose nanofiltration membranes with polyphenol-inspired coatings for effective dye/divalent salt separation

Abstract

Abstract Low-pressure electroneutral loose nanofiltration (NF) membranes were facilely fabricated by co-deposition of polyphenol-inspired epigallocatechin gallate (EGCg) and polyethyleneimine (PEI) on polyethersulfone (PES) ultrafiltration substrates. The effects of PEI with different molecular weights on co-deposition behavior, morphologies, surface properties, as well as separation performance of the resultant membranes were investigated in detail. The results showed that with the increase of PEI molecular weight from 600 to 10,000, the co-deposition amount of EGCg/PEI on membrane surface decreased, while the EGCg/PEI selective layer became denser. As a result, the EGCg/PEI 600 co-deposited membrane, which possessed an electroneutral surface with the best hydrophilicity, exhibited the optimal separation performance among the co-deposited membranes in the context of textile wastewater treatment. It had the highest pure water permeability (19.0 L/(m2·h·bar)) and excellent rejections towards dyes with different charges (e.g. 99.0% for Congo Red) as well as the lowest rejections towards divalent salts (e.g. 4.1% for Na2SO4) at an operating pressure of 2\u202fbar. Moreover, the membranes exhibited good organic solvent resistance, structural stability together with favorable performance in dealing with textile effluent, demonstrating their great potential in practical applications.