A nanofiltration membrane with outstanding antifouling ability: Exploring the structure-property-performance relationship

Membrane fouling is inevitable during nanofiltration of industrial liquids. Understanding the influence of membrane physicochemical properties and structures on its antifouling performance can guide the membrane selection and preparation. In this study, the antifouling ability of three commercial nanofiltration membranes (NF270, NFA4 and DK) was assessed using organic foulants with different charge patterns. Besides, the pristine and fouled membranes were systematically characterized. The results showed that although the negatively charged polyamide membrane had a strong antifouling ability to negatively charged substances, the fouling extent was still affected by the membrane pore size distribution. For the small foulants with positive charge, driven by electrostatic adsorption effect, they were easier to be anchored on the membrane surface with higher roughness. Due to the synergistic effect of membrane charge and roughness, the flux decay ratio increased from 5.1% for the NFA4 to 63.1% for the DK with more negative charge and highest roughness. Moreover, according to FTIR, XPS deep profiling and SEM cross-section analysis, it was found that the structure of the separation layer (e.g., single/double layer or cross-linking density in horizontal/longitudinal) closely related to its antifouling performance. Therefore, a nanofiltration membrane with narrow pore size distribution, moderate charge, smooth and hydrophilic surface is more prone to resist organic fouling formation. The outcomes of the work also offer several strategies to prepare antifouling nanofiltration membranes.