Effect of sulphonated polyethersulfone substrate for thin film composite forward osmosis membrane

Sulphonated polyethersulfone (SPES) has been synthesized for developing high performance thin film composite (TFC) forward osmosis (FO) membranes with enhanced hydrophilic support layer. Sulphonated substrate not only affects the membrane performance but also changes the membrane morphology from finger-like structure to a sponge-like morphology at higher degree of sulphonation thereby affecting the mechanical strength of the FO membrane. Non-sulphonated TFC-FO membrane with 12 wt.% polymer concentration shows a faint finger-like structure while sulphonated samples at a similar polymer concentration show a fully sponge-like structure with a much higher performance. For example, a water flux of 35 Lm^-2 h^-1 and 0.28 g L^-1 specific reverse solute flux was achieved with sulphonated TFC-FO membrane sample (50 wt.% SPES) under the FO mode using 2 M NaCl as the draw solution and deionized water as feed. Substrate sulphonation also considerably decreased the membrane structural parameter from 1096 μm without sulphonation to 245 μm at 50 wt.% sulphonation. This study therefore shows that, besides surface morphology, the water flux of the FO membrane can also be enhanced by improving its substrate hydrophilic property.