Chlorine-resistant TFN RO membranes containing modified poly(amidoamine) dendrimer-functionalized halloysite nanotubes

Abstract

Abstract Incorporation of additional amines into polyamide-based reverse osmosis (RO) membranes has been suggested as a strategy to increase the chlorine resistance of such membranes. In this work, we investigate the effects of the poly(amidoamine) PAMAM dendrimers of different generations on the separation performance and chlorine resistance of thin-film nanocomposite (TFN) membranes. Three generations of PAMAM dendrimers were grafted on halloysite nanotubes (HNTs) and incorporated into the reverse osmosis (RO) membranes synthesized by interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC). ATR-FTIR, SEM, XPS, TGA, and surface contact angle analyses were used to characterize the physicochemical properties of the nanoparticles and membranes. Membranes separation performance was tested in a cross-flow RO system with synthetic brackish water. Compared to thin-film composite (TFC) membranes, TFN membranes showed a two-fold increase in water flux with a slight decrease in NaCl rejection. In addition, passive chlorination tests showed that the overall effects of chlorination on membrane performance varied based on the generation of the PAMAM dendrimers. After 12,000\xa0ppm.h chlorine exposure, a decrease in salt rejection with an increase in the water flux of the control TFC membrane was observed. In contrast, membranes with the second and third generations of PAMAM dendrimers (TFN-HNT-G2 & G3) displayed enhanced membrane stability with no statistically significant alteration in their salt rejection after chlorination. TFN-HNT-G2 had the optimum overall desalination performance after chlorination with ~85.6% water flux improvement while maintaining its average salt rejection of 96.6%. The enhanced chlorination resistance of these membranes was attributed to the scavenger role of the extra amine and amide groups from the PAMAM functionalized HNTs.