The chlorination mechanism of integrally asymmetric cellulose triacetate (CTA)-based and thin film composite polyamide-based forward osmosis membrane

Abstract

This study investigates the change in performance and properties of various forward osmosis (FO) membranes resulting from exposure to chlorine by conducting performance test and characterization using ATR-FTIR, XPS, zeta potential, NMR and, particularly, ToF-SIMS analyses. The data obtained through the ToF-SIMS measurements suggested that chlorine first reacted with the acetyl/acetate group of the cellulose triacetate (CTA)-based membrane and then with the pyranose ring. Chlorine bound to the membrane surface weakened the H-bond of the CTA-based membrane, resulting in an increase in water flux and reverse salt flux (RSF) as the chlorine exposure time or chlorine concentration increased. A high chlorine dosage cleaved the pyranose ring, leading to loss of membrane selectivity. After chlorination with a high chlorine dosage, the structure of the CTA-based membrane eventually presented fatigue upon an increase in filtration time, and the oxidation of the CTA-based membrane due to exposure to chlorine was maximal at pH 7. The polyamide (PA)-based FO membrane was more sensitive to chlorine under acidic conditions, resulting in a greater loss of selectivity than that of the CTA-based FO membrane. However, an alkaline chlorine solution insignificantly affected both the CTA-based and TFC-based FO membranes. This study shows that the TFC PA-based FO membrane yields a high water flux, but its chlorine tolerance must be improved to be practically applicable in various fields.