Interfacial polymerization of thin-film composite forward osmosis membranes using ionic liquids as organic reagent phase

Ionic liquids (ILs) were used as the organic reagent phase in interfacial polymerization (IFP) to prepare thin film composite (TFC) membranes with a crosslinked polyimide (PI) as support for use in forward osmosis (FO). In a very straightforward and environmentally benign method, phase inversion, PI cross-linking, and amine monomer impregnation steps were all performed simultaneously. To prepare suitable supports, PI concentration and solvent/co-solvent (NMP/THF) ratios in the casting solution were optimized. The crosslinking of the support allows contact with a broad range of organic reagent phases during IFP. The effect of triethylamine and sodium dodecyl sulphate as additives in the coagulation bath on the performance of the final membranes was studied. The best hexane-based TFC-FO membrane was obtained on supports prepared from 14 wt% PI solutions containing a 3:1 ratio of NMP:THF and in the presence of 0.1 wt % SDS. The IL, 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide ([C(4)mim] [Tf2N]) was selected as IL organic phase to replace hexane. The resultant TFC membrane had a performance similar to that of a TFC synthesized using hexane as organic phase but did not require any additives. To reduce IL costs, a mixture of ([C(4)mim] [Tf2N]/hexyl acetate was applied in which the optimal monomer concentrations were 0.5 wt% MPD and 0.3 w/v.% TMC. This TFC membrane outperformed all other membranes in this work with a selectivity (J(s)/J(w)) of 0.25 g/L and a normalized water flux (J(w)/Delta pi) of 0.41 LMH/bar for a 0.5 M NaCl draw solution in FO mode.