Maximizing the Degree of Sulfonation of Polysulfone Supports in TFC Membranes for Osmotically Driven Processes

In this work, thin-film composite (TFC) polyamide membranes are prepared by introducing the highest amount of sulfonated polysulfone into the polysulfone-based support layer with the goal to improve membrane performance in osmotically driven processes. Sulfonated polymers are synthesized via a one-step reaction and used in suitable blends with pristine polysulfone to cast porous layers by phase inversion process. The sulfonated support substrates exhibit enhanced wettability over the traditional polysulfone layers as confirmed by a two-fold decrease in water contact angle. Using a 0.35 mm NaCl draw solution, the best sulfonated TFC membranes achieve up to 16 and 21 L m⁻² h⁻¹ under forward osmosis (FO) and pressure-retarded osmosis (PRO) configurations, respectively. However, no significant alterations in the support layer morphology can be detected. It is speculated, therefore, that wettability is the key factor for the observed improved osmotic flux, with a trade-off between water and reverse salt fluxes.