Tuning the selectivity of thin film composite forward osmosis membranes: Effect of co-solvent and different interfacial polymerization synthesis routes

The selectivity of thin film composite membranes supported by a sulfonated polyetheretherketone (sPEEK) hydrophilized polyethersulfone (PES) layer was enhanced by introducing a more volatile co-solvent, i.e. tetrahydrofuran (THF), and by using an alternative simplified preparation method (SIM), which combines the coagulation step of the phase inversion process and the impregnation of the amine monomer of the interfacial polymerization process. The addition of THF to the polymer casting solutions produced TFC membranes with higher retention but lower permeance. The lowest structural parameter (similar to 383 mu m) was found for the TFC membrane with a -10% sPEEK 10% THF support and led to water fluxes of 23 LMH in PRO mode and 11 LMH in FO mode using a DI water feed solution and a 0.5 M NaCl draw solution. A minimal membrane bottom surface porosity was necessary to accomplish satisfying water fluxes in FO. The SIM method resulted in TFC membranes with comparable selectivity but significantly higher permeance and smoother polyamide selective layers.