Supramolecular Host-Guest Complex Of Methylated Beta-Cyclodextrin With Polymerized Ionic Liquid ([Vbim]Tfsi)(N) As Highly Effective And Energy-Efficient Thermo-Regenerable Draw Solutes In Forward Osmosis

Supramolecular inclusion complexes with lower critical solution temperature (LCST) properties were investigated for the first time as forward osmosis (FO) draw solutes. Randomly methylated-beta-cyclodextrin (Rm-beta-CD) host molecules accommodate polymerized ionic liquids (([vbim]TFSI)n PILs) through their hydrophobic TFSIanions as guests. LCST properties were tuned by varying the chain lengths of ([vbim]TFSI)(n), from which, short chain oligo([vbim]TFSI) was found most suitable. Draw solutions (DS) of Rm-beta-CD/oligo([vbim]TFSI) complex have highly tunable cloud-point temperatures (Tc), fast LCST kinetics and sufficient osmotic properties for an efficient FO. Under PRO mode, 0.5 M Rm-beta-CD/0.078 M oligo([vbim]TFSI) induced competitive FO water flux (Jv-13.73 L m(2)h(-1)) and negligible reverse solute flux (J(s)-4.41 x 10(-3) mol m(2)h(-1)) against DI water feed. It successfully processed different saline feeds (0.034 M and 0.6 M NaCl) with reasonable FO performance and superior Js/JV-0.001 mol m(2)h(-1), demonstrating its competence for FO desalination. When heated slightly above its Tc = 29 degrees C (TTP = 30 degrees C), thermal precipitation (TP) is ensued with the release of TFSIanions in oligo ([vbim]TFSI) from Rm-beta-CD. Due to its hydrophobicity, oligo([vbim]TFSI) precipitates while entrapping the suspended Rm-beta-CDs between its chains causing flocculation and sedimentation. Thus, with only +5 degrees C heating above FO temperature (25 degrees C), 95% of draw solutes are effectively recovered from the spent DS after settling. Residual (-5%) Rm-beta-CD in the DS supernatant is subsequently removed via nanofiltration at 99.33% rejection, producing non-toxic water effluent based on in vitro cytotoxicity results. Energy consumption estimates reveal the feasibility of Rm-beta-CD/oligo([vbim]TFSI) as it requires minimal heat energy for recovery. This study offers new insights on the potential of host-guest complexes as a new class of energy-efficient draw solutes for FO desalination technology.