Elemental depth-profiling of chlorinated polyamide-based TFC-membranes with Elastic Recoil Detection

Chlorine resistance of nanofiltration (NF) and reverse osmosis (RO) membranes is of high importance in the water treatment industry. Elastic Recoil Detection (ERD) is now presented as a powerful tool to uniquely provide elemental depth-profiles, including hydrogen, of NaOCl-treated polyamide (PA)-based thin-film composite (TFC) membranes. The influence of pressure, pH and chlorine feed-concentration on the volume-averaged Cl-uptake, the location of Cl throughout the membrane and the z-gradient in Cl/N-ratio is demonstrated. The results suggest that (i) higher volume-averaged Cl-uptakes are achieved at higher chlorine doses and at acidic pH; (ii) chlorination is mostly restricted to the top-layer; (iii) a gradient in Cl/N-ratio exists along the membrane depth; (iv) the shape of this gradient is influenced by the chlorination pH and the applied pressure. Conclusions on the chlorination mechanisms could also be deduced. Conversely, no conclusive relationships between H-fractions and Cl-uptake could be drawn,...