Physico-chemical characterization of nanofiltration membranes. |
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Authors: | Katleen Boussu Jérémie De Baerdemaeker Charles Dauwe Marc Weber Kelvin G Lynn Diederik Depla Steliana Aldea Ivo F J Vankelecom Carlo Vandecasteele Bart Van der Bruggen |
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Institution: | 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 |
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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. |
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Keywords: | membranes nanofiltration polymers pore size surface analysis |
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