Preparation of a Novel Environmentally Friendly Hydrophobic Deep Eutectic Solvent ChCl-THY and its Application in Removal of Hexavalent Chromium from Aqueous Solution.

A liquid-liquid extraction methodology was developed for the removal of Cr(VI) from contaminated water using a novel green hydrophobic deep eutectic solvent (DES) as an efficient sole extracting agent. The hydrophobic DES was obtained by mixing choline chloride and thymol in 1:4 molar ratio at 70 ̊C for 10 min and was denoted as ChCl-THY(1:4). The ChCl-THY(1:4) works efficiently for removal of high (20 mg/L) as well as low (500 µg/L) concentration of Cr(VI) from artificially contaminated natural water with > 95% extraction efficiency (E%) at optimised reaction conditions (pH 2-6, 40 ̊C). The DES was characterized by 1 H NMR and FTIR spectroscopy and the data suggest that interaction occurs between Cl- ion of choline chloride and H atoms of thymol molecules. Physicochemical properties such as density, melting point, moisture and solubility were studied and discussed. Herein, no sharp melting point was observed for ChCl-THY(1:4) in DSC curve. DES was regenerated using 0.1 M NaOH as stripping agent and 50-60% extraction efficiency could be attained in the next cycle. A plausible mechanism of interaction between Cr(VI) species and DES was also explored with the help of FTIR spectroscopy. This article is protected by copyright. All rights reserved.