Congo red recovery from water using green extraction solvents

Dyes are pollutants widely used in several industries that end up dumped as wastewater, contributing to water pollution. In the scope of improving water quality, liquid-liquid extraction is a separation technique widely used to remove pollutants from water, due to the possibility of recovering all the involved agents. In this work, deep eutectic solvents (DESs) based on mixtures of thymol with menthol, coumarin, octanoic acid and decanoic acid were applied as extraction agents to remove congo red from water. Among all the studied solvents, those formed by thymol with organic acids showed extraction efficiencies higher than 90% for low initial concentrations of congo red, using 1/5 (v/v) DES/water proportion and 1 h of stirring time as extraction parameters. The best results were achieved using Thymol:Octanoic acid (1:1) solvent. Furthermore, at the end of the process each reagent can be reused. DES reusability was checked for three extraction cycles, keeping stable.