title: Depth heterogeneity of fully aromatic polyamide active layers in reverse osmosis and nanofiltration membranes.
abstract: We studied the depth heterogeneity of fully aromatic polyamide (PA) active layers in commercial reverse osmosis (RO) and nanofiltration (NF) membranes by quantifying near-surface (i.e., top 6 nm) and volume-averaged properties of the active layers using X-ray photoelectron spectrometry (XPS) and Rutherford backscattering spectrometry (RBS), respectively. Some membranes (e.g., ESPA3 RO) had active layers that were depth homogeneous with respect to the concentration and pK(a) distribution of carboxylic groups, degree of polymer cross-linking, concentration of barium ion probe that associated with ionized carboxylic groups, and steric effects experienced by barium ion. Other membranes (e.g., NF90 NF) had active layers that were depth heterogeneous with respect to the same properties. Our results therefore support the existence of both depth-homogeneous and depth-heterogeneous active layers. It remains to be assessed whether the depth heterogeneity consists of gradually changing properties throughout the active layer depth or of distinct sublayers with different properties.
authors.affiliation: Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
authors.forename: Orlando
authors.initials: O
authors.lastname: Coronell
authors.forename: Benito J
authors.initials: BJ
authors.lastname: Mariñas
authors.forename: David G
authors.initials: DG
authors.lastname: Cahill
mesh_terms: D001464:Barium / Q000032:analysis / Q000737:chemistry; D003432:Cross-Linking Reagents / Q000737:chemistry; D005374:Filtration / Q000295:instrumentation*; D008422:Materials Testing; D008567:Membranes, Artificial; D009757:Nylons / Q000737:chemistry*; D009995:Osmosis; D012834:Silver / Q000032:analysis / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis; D018508:Water Purification / Q000295:instrumentation
chemical_list: D003432:Cross-Linking Reagents; D008567:Membranes, Artificial; D009757:Nylons; D014874:Water Pollutants, Chemical; D001464:Barium; D012834:Silver