Construction of pseudo-zwitterionic polyamide RO membranes surface by grafting positively charged small molecules

Abstract

Membrane fouling is the major obstacle to hinder the extensive application of polyamide thin-film composite reverse osmosis (PA TFC RO) membranes in the water purification and reclamation fields. In this study, a series of hydrophilic and charge-tuned antifouling RO membranes were fabricated by grafting three kinds of small molecules of multi-grade amines N,N-dimethylethylenediamine (DMEDA), (2-aminoethyl) guanidine (AEGu) and (2-aminoethyl)triethylenediamine (AEDABCO) via layer-by-layer interfacial polymerization (LbL-IP). Detailed characterizations revealed that the three tailored membranes presented obviously diminished surface negative charge and reduced PA layer thickness, the water permeability increased by 67.4 %, 34.7 % and 75.6 % compared to the pristine membrane, reached 4.05 L m−2 h−1 bar−1, 3.26 L m−2 h−1 bar−1, and 4.28 L m−2 h−1 bar−1, respectively, meanwhile kept high NaCl rejection > 98.5 %. The dynamic fouling tests indicated that the tailored membranes exhibited much improved antifouling performance towards most of the model organic foulants. Meanwhile the membranes assembled with cationic groups exhibited an enhanced antibacterial property against E. coli. These functional small charged molecules and the convenient modification method provide a valuable pattern for designing antifouling PA TFC RO membranes, which is important for sustainable water purification.