A method to quantify composition, purity, and cross-link density of the active polyamide layer in reverse osmosis composite membranes using 13C cross polarization magic angle spinning nuclear magnetic resonance spectroscopy

A method for harvesting and purifying the thin polyamide (PA) active layer from thin-film composite (TFC) reverse osmosis (RO) membranes was developed, enabling quantitative nuclear magnetic resonance (NMR) measurements of composition cross-linking in PA that can be directly related to membrane performance. Using our chemical separation process, we report on four trimesoyl chloride (TMC)/isophthaloyl (IPC)/m-phenylene diamine (MPD)-based TFC which cross-link density intentionally reduced by replacing trifunctional TMC monomers with their linear IPC difunctional analog. While NMR results show a two-fold decrease causes 30% increase salt passage, addition analog leads increased polar amine groups reduce water permeance due tighter binding membrane. Our demonstrate 13C cross polarization magic angle spinning (CPMAS) is powerful quantitatively monitoring purity, cross-linking, will an essential tool ascertaining atomistic models structure.