Tailoring the structure of polyamide thin film composite membrane with zwitterions to achieve high water permeability and antifouling property

Abstract

A series of carefully designed polyamide thin film composite nanofiltration membranes (TFCMs) were prepared via interfacial polymerization of piperazine (PIP), N-aminoethyl piperazine (AEP) or N-aminoethyl piperazine propane sulfonate (AEPPS) with trimesoyl chloride (TMC) on top of hydrolysed polyacrylonitrile ultrafiltration supporting membranes (hPAN-UF). Chemical structures of the TFCMs were evaluated by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The cross section and surface characteristics of the TFCMs were examined by scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle measurements and zeta potential. Membrane fouling characteristics were studied by the adsorption of bovine serum albumin (BSA) and lysozyme (LYZ). Varying the diamine affected the structure of the resulting membranes, which ultimately defined separation performance and antifouling property. The results of water contact angle indicated zwitterionic membranes were more hydrophilic, which incorporated polyamide selective layer thickness to account for their high water flux (80.3 L m⁻² h⁻¹). Compared with other TFCMs, zwitterionic membranes showed an improved antifouling property due to their high hydrophilicity, low surface electrical charges and smooth surface roughness. These results provide important insights into the high water permeability and low fouling characteristics of zwitterionic nanofiltration membranes from molecular structure and interfacial polymerization process.