Previous research on free chlorination and chloramination of nanofiltration (NF) and reverse osmosis (RO) polyamide membranes has conclusively shown that these water disinfectants damage the structural integrity of membranes and adversely affect their performance. Secondary oxidants formed from reactions of chlorine disinfectants with bromide and iodide ions have also been found to transform the active layers and affect the performance of fully aromatic polyamide membranes, but the effects on semi-aromatic polyamide membranes are still unreported. This work investigates how exposure to a secondary oxidant, hypoiodous acid (HOI), changes the active layer and rejection performance of the semi-aromatic polyamide membrane NF270. Small coupons of membrane were contacted with HOI solutions at various exposure levels. Exposed coupons were analyzed by X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and attenuated total reflectance - Fourier transform infrared spectroscopy to monitor the chemical structure of the membrane active layer. Changes in membrane performance were assessed by performing permeation experiments with Rhodamine-WT (R-WT) and sodium chloride (NaCl) solutions. Structural analysis revealed iodination of the active layer, but at levels that did not result in changes in water permeability or the rejection of R-WT and NaCl.
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Effect of iodination on NF270 nanofiltration membrane structure and performance
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