TFC reverse osmosis polyamide membranes—Effect of increasing sulfonic group concentration on water flux and salt rejection performance

ABSTRACT Thin film composite ( TFC ) membranes for reverse osmosis were prepared with a polyamide top layer with an increasing concentration of sulfonic groups obtained with mixtures of m ‐phenylenediamine (MPD), and the sulfonated diamine, 4‐diaminobenzensulfonic acid (DABS) crosslinked with trimesoyl chloride via interfacial polymerization. The presence of sulfonic groups in the top layer diminishes the roughness of the surface of the membrane as observed by scanning electron microscopy and atomic force microscopy. It was also found that the best curing temperature for stabilization of the top polyamide layer in the TFC membrane was 90 °C. Increased hydrophilicity with an increasing concentration of DABS in the top layer of the membrane was confirmed by contact angle measurements. The results show that concentrations above 5 wt % DABS were detrimental for the membrane flux and salt rejection, R (%). The incorporation of sulfonic groups up to 5 wt % DABS improves the flux and R (%) as compared to a TFC membrane without ionic groups. Constant salt rejection was observed in the TFC membrane with 5 wt % DABS which at least maintain a nearly constant water flux after three cycles and improve R (%) after repeated testing of the same membrane in a RO high pressure cell. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135 , 46500.