Polyamide thin film composite membranes on cross-linked polyimide supports: Improvement of RO performance via activating solvent

For thin film composite (TFC) reverse osmosis (RO) membranes, a trade-off is evident between water permeance and salt rejection; and yet to improve their RO performance it is desirable to increase flux without sacrificing selectivity. This paper describes the fabrication of polyamide TCF membranes on highly solvent stable cross-linked polyimide UF supports and the use of an activating solvent as a strategy to increase water flux; and in certain cases, water permeance and salt rejection are increased simultaneously. Performance was evaluated in terms of NaCl rejection and water permeance before and after post-treatment with dimethylformamide (DMF) as the activating solvent. Additionally, the morphology of the TFC membranes was characterized by SEM, their hydrophilicity was determined by contact angle measurements, and zeta (ζ)-potential was obtained by a streaming potential based method. NaCl rejection was found to be improved for TFC membranes with initial NaCl rejections below 90%, reaching a maximum value of 94%. Water permeance was also increased and to greater extent for membranes with low initial permeance values. The biggest improvement was obtained for a TFC membrane with initial permeance value of 0.2 L·m− 2·h− 1·bar− 1, rising to 1.6 L·m− 2·h− 1·bar− 1 with a rejection of 93.8%.