Tailoring the Polyamide Active Layer of Thin-Film Composite Forward Osmosis Membranes with Combined Cosolvents during Interfacial Polymerization

In this study, the method of using combined cosolvents to tailor the polyamide (PA) active layer during the interfacial polymerization (IP) process was explored for improving the performance of thin-film composite forward osmosis (TFC-FO) membranes. It was found that the TFC-FO membrane prepared by introducing combined cosolvents, that is, simultaneously adding N,N-dimethyl formamide (DMF) into an aqueous phase solution and triphenyl phosphate (TPP) into an organic phase solution, exhibited better performance than adding a single cosolvent, which showed a synergistic effect of combined cosolvents. Compared with the reference membrane without using a cosolvent, the water flux of the TFC-FO membrane using combined cosolvents can be increased by nearly 1.6 times under FO mode and 2.0 times under pressure-retarded osmosis (PRO) mode, whereas its reverse salt flux increased slightly and its salt rejection under reverse osmosis (RO) mode can still reach more than 97%. The PA layer morphology and microstructure of the TFC-FO membranes prepared by adding different cosolvents were thoroughly characterized. The use of combined cosolvents can generate more PA polymer during IP, which leads to the formation of multilayer-like PA morphology and the increase of PA layer thickness.