title: Physico-chemical characterization of nanofiltration membranes.
abstract: This study presents a methodology for an in-depth characterization of six representative commercial nanofiltration membranes. Laboratory-made polyethersulfone membranes are included for reference. Besides the physical characterization [molecular weight cut-off (MWCO), surface charge, roughness and hydrophobicity], the membranes are also studied for their chemical composition [attenuated total reflectance Fourier spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS)] and porosity [positron annihilation spectroscopy (PAS)]. The chemical characterization indicates that all membranes are composed of at least two different layers. The presence of an additional third layer is proved and studied for membranes with a polyamide top layer. PAS experiments, in combination with FIB (focused ion beam) images, show that these membranes also have a thinner and a less porous skin layer (upper part of the top layer). In the skin layer, two different pore sizes are observed for all commercial membranes: a pore size of 1.25-1.55 angstroms as well as a pore size of 3.20-3.95 angstroms (both depending on the membrane type). Thus, the pore size distribution in nanofiltration membranes is bimodal, in contrast to the generally accepted log-normal distribution. Although the pore sizes are rather similar for all commercial membranes, their pore volume fraction and hence their porosity differ significantly.
authors.affiliation: Laboratory for Applied Physical Chemistry and Environmental Technology, Department of Chemical Engineering, K. U. Leuven W. de Croylaan 46, 3001 Leuven, Belgium. katleen.boussu@cit.kuleuven.be
authors.forename: Katleen
authors.initials: K
authors.lastname: Boussu
authors.forename: Jérémie
authors.initials: J
authors.lastname: De Baerdemaeker
authors.forename: Charles
authors.initials: C
authors.lastname: Dauwe
authors.forename: Marc
authors.initials: M
authors.lastname: Weber
authors.forename: Kelvin G
authors.initials: KG
authors.lastname: Lynn
authors.forename: Diederik
authors.initials: D
authors.lastname: Depla
authors.forename: Steliana
authors.initials: S
authors.lastname: Aldea
authors.forename: Ivo F J
authors.initials: IF
authors.lastname: Vankelecom
authors.forename: Carlo
authors.initials: C
authors.lastname: Vandecasteele
authors.forename: Bart
authors.initials: B
authors.lastname: Van der Bruggen