Fabrication of a Novel Nanofiltration Membrane with Enhanced Performance via Interfacial Polymerization through the Incorporation of a New Zwitterionic Diamine Monomer

It is known that the polyamide (PA) barrier layer's inherent microstructure and surface physicochemical properties of thin film composite nanofiltration membrane are crucial for its separation performance. Herein, we designed and synthesized a new zwitterionic aromatic diamine monomer 3-(4-(2-((4-aminophenyl)amino)ethyl)morpholino-4-ium)propane-1-sulfonate (PPD-MEPS) through a three steps reaction, and this hydrophilic molecule was incorporated into the active layer to tailor the poly(piperazine-amide)-based nanofiltration membranes with significantly improved water permeability and antifouling properties. As a p-phenylenediamine (PPD) derivative, PPD-MEPS possesses two active amine units, which can react with trimesoyl chloride in the organic phase during the interfacial polymerization reaction process. Thus, the super-hydrophilic zwitterions were not only on the membrane surface but also across the whole PA layer to facilitate water molecule transportation. The successful augmentation of zwitterions into the PA layer was well illustrated by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) results and X-ray photoelectron spectroscopy analysis. With increasing loading content of PPD-MEPS in PIP aqueous solution, the as-fabricated nanofiltration membranes (NFMs) exhibited higher hydrophilicity, increased active layer thickness, and molecular weight cut off. When the zwitterionic monomer reached 60% to PIP for NFM-4, the water permeability went up to 9.82 L m-2 h-1 bar-1, increasing by 45%; meanwhile, the Na2SO4/NaCl selectivity increased from 2.54 to 4.03. In addition, the fouling experiments illustrated that the fouling resistance of the zwitterion-modified NFMs to bovine serum albumin was significantly improved.