Solvent Effects on the Extraction of Azo Dyes by Hydrophobic Deep-Melting Eutectics from Waste Water

Madeline Sandvik, “Solvent Effects on the Extraction of Azo Dyes by Hydrophobic Deep-Melting Eutectics from Waste Water”
Mentors: Mark Dietz & Nathan Kaul, Chemistry & Biochemistry

The discharge of toxic dyestuffs from textile and leather processing into waterways represents a major source of environmental pollution in Third World countries. Although many methods have been proposed for the removal of dyes from water, all suffer from one or more drawbacks that limit their utility. Adsorption on activated charcoal, for example, requires that the sorbent be either regenerated or disposed of, thereby either consuming energy or chemicals or creating a secondary waste disposal problem. Solvent extraction, in which dye-laden water is contacted with an immiscible organic solvent into which the dye is readily extracted, represents a potentially less-problematic alternative. Unfortunately, conventional organic solvents are themselves often environmentally unfriendly. As a result, there has been growing interest in the use of “green solvents”, including plant-derived oils, ionic liquids (ILs), liquid polymers, and hydrophobic deep eutectics (HDESs), in this application. In this study, we examine the effectiveness of HDESs, unique liquids formed by combining an appropriate hydrogen bond donor and a hydrogen bond acceptor, as extraction solvents for the removal of representative azo dyes (e.g., Methyl Yellow, Orange IV, Bromothymol Blue), a particularly problematic dye family. Following synthesis of selected HDESs and their characterization by thermogravimetric analysis and differential scanning calorimetry, several HDESs comprising mixtures of menthol and various long-chain carboxylic acids have been evaluated as extraction solvents. Preliminary results indicate that these solvents are able to efficiently extract all of the dyes examined. Work to quantify the differences between the various HDES systems and to determine the effect of solution conditions on the extraction efficiency is now in progress.

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