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

Published

February 12, 2022

Author(s)

Ryan Nieuwendaal, Christopher Stafford, Jeff Wilbur

Abstract

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

Citation

Journal of Membrane Science

Volume

648

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.memsci.2022.120346

Local Download

Keywords

REVERSE OSMOSIS MEMBRANES, THIN FILM COMPOSITE MEMBRANES, WATER DESALINATION, POLYAMIDE, SOLID-STATE NMR, QUANTITATIVE NMR, CROSSLINK DENSITY

Citation

Nieuwendaal, R. , Stafford, C. and Wilbur, J. (2022), A method to quantify composition, purity, and cross-link density of the polyamide active layer in reverse osmosis composite membranes using 13C cross-polarization magic angle spinning nuclear magnetic resonance spectroscopy, Journal of Membrane Science, [online], https://doi.org/10.1016/j.memsci.2022.120346, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=933252 (Accessed October 9, 2025)