Second interfacial polymerization on polyamide surface using aliphatic diamine with improved performance of TFC FO membranes

High performance thin film composite forward osmosis (TFC-FO) membranes were prepared by in situ modification of nascent polyamide (PA) active layer with ethane diamine (EDA) and 2-[(2-aminoethyl)amino]- ethane sulfonic acid monosodium salt (SEA) via second interfacial polymerization (SIP). The membranes were characterized with respect to membrane chemistry (by ATR-FTIR and XPS spectroscopy), surface properties comprising wettability (by static contact angle), roughness (by AFM), zeta potential, surface free energy, osmosis performance, and antifouling ability in FO process. The results indicates that SIP with aliphatic diamine is an effective strategy towards improving the FO membrane performance, such as high permeability, selectivity and antifouling tendency. EDA would shadow the valleys of pristine PA layer, and gain the highest fouling resistance; while additional hydrophilic group (−SO3Na) in SEA can enhance the wettability of membrane, consequently resulting in higher water flux without scarifying the selectivity. Meanwhile, we found that the initial osmotic water flux plays a more important role in the cake layer formation than the surface properties of membrane. When the initial flux was set as 19 LMH, the final normalized flux of SEA-M declined to about 0.45 at the end of fouling test with BSA as the foulant model, while that of three membranes can keep more than 0.8 at the initial flux 9 LMH.