Supramolecular host-guest complex of methylated β-cyclodextrin with polymerized ionic liquid ([vbim]TFSI)<inf>n</inf> as highly effective and energy-efficient thermo-regenerable draw solutes in forward osmosis
- Publisher:
- Elsevier BV
- Publication Type:
- Journal Article
- Citation:
- Chemical Engineering Journal, 2021, 411, pp. 128520-128520
- Issue Date:
- 2021-05-01
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© 2021 Elsevier B.V. Supramolecular inclusion complexes with lower critical solution temperature (LCST) properties were investigated for the first time as forward osmosis (FO) draw solutes. Randomly methylated-β-cyclodextrin (Rm-β-CD) host molecules accommodate polymerized ionic liquids (([vbim]TFSI)n PILs) through their hydrophobic TFSI− anions 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-β-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-β-CD/0.078 M oligo([vbim]TFSI) induced competitive FO water flux (Jv ~13.73 L m−2h−1) and negligible reverse solute flux (Js ~4.41 × 10−3 mol m−2h−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−2h−1, demonstrating its competence for FO desalination. When heated slightly above its Tc = 29 °C (TTP = 30 °C), thermal precipitation (TP) is ensued with the release of TFSI− anions in oligo([vbim]TFSI) from Rm-β-CD. Due to its hydrophobicity, oligo([vbim]TFSI) precipitates while entrapping the suspended Rm-β-CDs between its chains causing flocculation and sedimentation. Thus, with only +5 °C heating above FO temperature (25 °C), 95% of draw solutes are effectively recovered from the spent DS after settling. Residual (~5%) Rm-β-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-β-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.
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