Sub10 μm macroporous aramid substrates with a hierarchically structured interface for organic solvent nanofiltration

Compared with traditional methods for elaborately tailoring the active layer of thin-film composite (TFC) membranes, this study focused on building novel substrates for potential applications in developing organic solvent nanofiltration (OSN) membranes. One kind of “three-parts” hierarchically structured interface with nanospheres and macro surface pores was successfully prepared via Michael addition and Schiff's base (M&S) reactions between N-(2-aminoethyl)-3-aminopropyl triethoxysilane (NAE-A) and glycerite (a natural polyphenol) in the aramid substrate. The thickness was reduced to sub10 μm with the aid of the high-speed spin coating process coupling nonsolvent-induced phase separation (HSSC-co-NIPS) method. The composition characterization results demonstrated the introduction of glycerite, and the reactions occurred in/on the substrate. Scanning electron microscopy (SEM) images clearly showed that the sub10 μm substrate contained a “three-level” hierarchically structured interface that included: (1) a “stalk-like” structure; (2) glycerite-NAE-A silane (GNAS) nanospheres; and (3) the substrate surface. These phenomena also resulted in better surface hydrophilicity. All types of organic solvents, including harsh solvents, such as tetrahydrofuran (THF) and N,N-dimethylformamide (DMF), had stable permeability within the substrate, as did apolar n-hexane and isopar™ G. Therefore, the as-prepared TFC OSN membrane, which had an extremely short polymerization time, retained broad-spectrum solvent stability and had the highest solvent permeance in acetonitrile (24.5 ± 0.4 L m−2 h−1·bar−1). In addition, the resultant TFC membrane almost completely rejected the popular macrolide antibiotic azithromycin (AZM, 748.98 g mol−1) in ethanol, which is used to treat COVID-19.