Stereochemical tuning, post-synthesis crosslinking and quaternizing to tune the membrane performance of ultra-stable polyamine nanofiltration membranes

Solvent resistant and pH-stable nanofiltration membranes play a crucial role in solvent or water reuse across various industries, including pharma, chemical, dairy and mining, where stringent pH conditions and chemical stability are imperative. Previous research introduced a chlorine-resistant top-layer for nanofiltration membranes, using 1,2,4,5-tetra(bromomethyl)benzene and 1,2-diaminocyclohexane, with also exceptional stability at extreme pH values and a broad solvent resistance thanks to its crosslinked nature. To further optimize this remarkably stable and versatile membrane material, the unique property of 1,2-diaminocyclohexane, i.e. its stereochemistry, is employed here to manipulate membrane properties through diastereomerism and enantiomeric excess. Filtration experiments employing different 1,2-diaminocyclohexane isomers revealed significant variations in membrane performance, emphasizing the impact of stereochemistry on separation performance. Adjusting the enantiomeric excess of 1,2-diaminocyclohexane resulted in notable changes in membrane permeability and rejection, highlighting the general power of stereochemical control in membrane synthesis. Additionally, post-synthesis modifications, including further crosslinking and quaternization, allowed to tune the membrane structure and performance in both aqueous and solvent media, offering opportunities for optimization towards specific applications. SEM and XPS providing insights into membrane morphology and composition, confirmed the influence of stereochemistry and post-synthesis modifications on membrane properties. These findings demonstrate the efficacy of stereochemistry manipulation and post-synthesis techniques in tailoring pH-stable and solvent resistant nanofiltration membranes for specific applications, paving the way for advanced membrane design.