Thermoresponsive magnetic ionic liquids as forward osmosis draw solutes for seawater desalination

Abstract

Thermoresponsive magnetic ionic liquids (TMILs) showing lower critical solution temperature (LCST)-behavior were fabricated and utilized as forward osmosis (FO) draw solutes for seawater desalination. The MILs, 8-alkyl-1,8-diazabicyclo[5.4.0]undec‑7-ene bromotrichloroferrate (DBU-R[FeBrCl3], or d-R-FeX4) with different alkyl chain lengths (R = C4H9, C6H13, C7H15, or C8H17), exhibited tunable LCSTs from 30 to 65 °C by varying the chain length and the solution concentration. Upon heating above their LCSTs, more than 43% of the TMILs could be magnetically extracted via phase separation, demonstrating a facile magnet-assisted draw solution regeneration approach. In addition, an aqueous solution containing 25 wt% D-Bu-FeX4 was able to achieve a water flux as high as 4.5 L m−2 h−1 (LMH) in desalinating seawater. Their ionic nature, together with unique thermo- and magnetic-responsive behaviors, make them promising candidates as ideal FO draw solutes for desalination and wastewater reclamation.

Keywords

• Magnetic ionic liquids
• LCST
• Draw solution
• Forward osmosis
• Seawater desalination