The concentration of positive and negative functional groups (FGs) in nanofiltration (NF) and reverse osmosis membranes (RO) have been successfully quantified as a function of pH by ion probing using Rutherford Backscattering Spectrometry (RBS). The concentration of FGs was higher for the NF (TFC-S?) than for the RO (FT30?) membrane tested within the pH range of 3.5-10.3 studied. The isoelectric point obtained from FGs concentration measurements of TFC-S?(NF) membrane was found to be pH～5.5, consistent with values reported in the literature for polyamide NF membranes.
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