Launching deep eutectic solvents (DESs) and natural deep eutectic solvents (NADESs), in combination with different harmless co-solvents, for the preparation of more sustainable membranes

Deep eutectic solvents (DESs) and natural deep eutectic solvents (NADESs, derived from natural-source molecules) were used for the first time in the preparation of porous poly(vinylidene fluoride) (PVDF) and poly(acrylonitrile) (PAN) membranes. Halogen-free Brønsted acidic DES and zwitterionic carboxy- and sulfo-betaines DESs and NADESs were selected for their potentiality to solubilize the chosen polymers. Solubility prediction was assessed through the analyses of the solvents’ thermodynamic factors and the calculation of the relative solubilities in terms of relative energy difference and Hansen and Hildebrand parameters. Porous membranes were, thus, prepared via phase separation technique adding to the dope solutions different non-toxic co-solvents (Rhodiasolv® PolarClean, triethyl phosphate and dimethysulfoxide) with the aim of reducing solution viscosity. The effect of different coagulation bath compositions, such as water and water/isopropanol, was investigated in order to control and tailor the morphology and architecture of the produced membranes. The pore dimensions and distribution, porosity, contact angle and water permeability tests were carried out in order to characterize the produced membranes. The results of the study showed the potentiality of DESs and NADESs to be employed as solvents for the preparation of more sustainable polymeric membranes for water treatment applications. • DESs and NADESs are used as new sustainable solvents for membrane preparation. • The addition of sustainable co-solvents to dope solution reduces viscosity issues. • PVDF and PAN membranes are successfully prepared. • The type of employed DES or NADES influences membrane morphology and properties.