(3fu) Boron Extraction from Aqueous Solution Via Novel Hydrophobic Deep Eutectic Solvents

Research Interests Modern chemistry and chemical engineering practices reached considerable milestones in replacing conventional organic solvents by more stable and less hazardous ones. One of the major steps taken in this direction was the development made in the field of Ionic Liquids (IL) . Although ILs are chemically and thermally stable, highly involatile, and tunable, they suffer from high production costs and potential toxic manifestations, consequently stunting their application as feasible alternatives. Another attractive and more recent milestone was achieved in 2003 when Deep Eutectic Solvents (DES) emerged as potential analogues for ILs , minus the costly and toxic part. DESs have been portrayed as the new generation “designer’s solvents”, offering several unique features such as simplicity of synthesis, biodegradability and low production cost. These unique solvents intriguingly thought to have a role in cellular processes of plants and animals which help them endure extreme environmental conditions.

Herein, new hydrophobic DES were developed as extractants of boron from aqueous medium.Boron removal is incentivized in two ways: either as a preventive measure, such as meeting drinking water regulations in desalination plants and protecting boron-sensitive agricultural crops, or as a productive measure such as recovering and reusing boron form industrial wastewater and nuclear waste streams. The DES for boron extraction were prepared from the combination of natural materials such as (menthol or thymol) as hydrogen bond acceptors (HBA) with alcohols or 1,3-diols as hydrogen bond doners (HBD). The HBDs used were in accordance with the Environemtal Protection Agency's (EPA) Safer Chemical Ingredient list. The DESs were characterized thoroughly in terms of their physical, thermal and critical properties. It was found that DESs prepared with the monohydric alcohol (1-decanol) had negligible extraction efficiency for boric acid. Conversely, DES prepared with the 1,3 diols showed extraction efficiencies of up to 97%. An extraction mechanism was proposed in which 1,3-diols reacted with the free boric acid to form stable complexes in the organic DES phase. The DES depicted high extraction efficiencies over a wide pH range from 2 to 7, and the extraction efficiency of the respective DES for boric acid was further enhanced in the presences of other interfering ions in the solution.

The new solvents offer advantages over conventional organic solvents or ionic liquids. These include: high extraction and stripping efficiencies, stabilizing water–soluble components like 2-methyl-2,4-pentanediol (MPD), enabling its use in water treatment applications, and the incorporation of green and renewable extractant components, such as menthol and thymol. Further studies on this topic include varying the molar ratio of the DES components in order to enhance the solvents’ characteristic properties.