Thermo-responsive tributyl-4-vinylbenzylphosphonium alkanesulfonate ionic liquid-based draw solute for forward osmosis.

[Display omitted] • Ionic liquids (ILs) were synthesized as draw solutes for forward osmosis (FO) system. • Thermo-responsive behavior of draw solute in water facilitates their regeneration. • Tributyl-4-vinylbenzylphosphonium-based IL ([TVBP][CnS]) has thermo-responsiveness. • The alkyl chain length affects the drawing-ability and recovery properties. • [TVBP][CnS] shows excellent FO performance and easy recovery. The thermo-responsive ionic liquid (ILs) potentially appropriate draw solutes in the forward osmosis (FO) system were studied by varying the alkyl group chain length of the anion. This study investigated the tributyl-4-vinylbenzylphosphonium cation ([TVBP]⁺)-based ILs with alkanesulfonate anions (1-butanesulfonate ([C4S]⁻) , 1-pentanesulfoante ([C5S]⁻), and 1-hexanesulfoante ([C6S]⁻)). The [TVBP][C5S] and [TVBP][C6S] exhibited lower critical solution temperatures (LCSTs) from 6 to 34 °C at different concentrations, enabling their recovery. When using distilled water, 2000 ppm NaCl, and 20 wt% orange juice aqueous solutions as the feed solution, the water flux of the 8 wt% [TVBP][C5S] solution was approximately 11.26, 8.01, and 6.76 L m⁻²h⁻¹ (LMH), respectively, in the mode of the active layer facing the draw solution. These results suggested the applicability of the LCST-type IL as a draw solute. [ABSTRACT FROM AUTHOR]