期刊
JOURNAL OF MEMBRANE SCIENCE
卷 429, 期 -, 页码 23-33出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.memsci.2012.11.023
关键词
Thin-film composite; Nanocomposite; Membrane; Quartz crystal microbalance; Charge density
资金
- Water Resources Research Institute (WRRI) of the University of North Carolina
- US Geological Survey (USGS) under the WRRI project [11-03-W, 2007-01991-11, 2011-1481-02]
- US Department of Energy Office of Nuclear Physics [DE-FG02-97ER41041, DE-FG02-97ER41033]
A reliable, user-friendly, bench-top method was developed and evaluated for the measurement of negative charge density in the active layers of thin-film composite and thin-film nanocomposite membranes. The method consists of isolating the active layer on a quartz crystal microbalance (QCM) sensor (i.e., AL + sensor sample), exposing the AL + sensor sample to an aqueous cesium solution at any pH of interest, and measuring with a QCM the mass of cesium ion that associates with the negative sites of the active layer. Results showed that QCM measurements of charge density in active layers were: (1) repeatable within 3% for tests performed with the same AL + sensor sample under the same experimental conditions; (2) reproducible within 3.8% for tests performed with the same AL + sensor sample when the ionic strength of cesium solutions was varied by 300%; (3) reproducible within 4% for active layers isolated from nearby locations of the same membrane sheet; and (4) consistent within 2.1% at pH=10.5 with results obtained using the previously reported Rutherford backscattering spectrometry method on non-isolated active layers. The results therefore demonstrate the robustness, repeatability, reproducibility, and accuracy of the QCM method. We also demonstrated that the ionization behaviors of the polyamide-based thin-film composite and nanocomposite membranes tested were similar: both membranes had bimodal pK(a) distributions and negative charge densities of approximate to 0.5 M at full ionization. (C) 2012 Elsevier B.V. All rights reserved.
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