Heterogeneous Elemental Composition and Carboxy Group Distribution Across a Polyamide Active Layer of ESPA2 Thin-film Composite Reverse Osmosis Membrane

Abstract

The objective of this study was to investigate depth heterogeneity of ESPA2 thin-film composite reverse osmosis（RO）membrane in terms of elemental composition and carboxy group distribution. It was found that the O/N ratio is highest at the surface of the polyamide active layer. It was also found that the concentration of deprotonated carboxy group, which was indirectly quantified by measuring ionically associated Ag^＋, was highest at the surface of the polyamide active layer and decreased with increased distance from the surface. These results demonstrated that the polyamide active layer of ESPA2 RO membrane has a depth heterogeneous structure.