Effect of [EMIM][BF4] ionic liquid on the properties of ultrafiltration membranes

Abstract We employ a miscible mixture of an imidazolium based ionic liquid (IL) and dimethylformamide (DMF) as a good solvent of polyethersulfone (PES) for fabrication of membranes by nonsolvent induced phase separation (NIPS) method. The addition of IL to the cast solution changes solvent quality, which leads to variation of rheological behavior of polymer solution as well as developed membranes performance. We characterize the prepared membranes in terms of water flux, bovine serum albumin (BSA) rejection, pore size, porosity, and water contact angle. Results show that IL influences the kinetics and thermodynamic of phase separation of PES solution. Viscosity values as well as thermodynamic instability of PES solution increase with IL concentration, which lead to higher porosity and pore size of final membranes. Consequently, 17 wt% IL in formulation leads to an increase of mean pore size from 2.0 to 12.7 nm which improves water flux of final membranes from 0.5 to 77 kg/m2h. The results of fouling measurements show that by increasing IL content, the reversible fouling increases. Additionally, the irreversible fouling ratio reduces from 0.42 to 0.28 for 0 and 17 wt% IL containing formulations, respectively. The newly developed membranes provide 97% rejection of BSA solution and can be used as ultrafiltration membranes for the separation and concentration of macromolecules and proteins.