Rapid and stable removal of reactive Blue-221 and Red-230 from water via DES-Based liquid–liquid extraction: application of environmental samples

The rapid, efficient, and effective separation and removal of dyes, which are among the major environmental issues in the textile industry, were systematically examined by using deep eutectic solvent (DES), which is a novel agent extracting from aqueous environments. The removal of Reactive Red 230 (RR230) and Reactive Blue 221 (RB221) from aqueous solution was thoroughly carried out for both pure and their mixtures. The extraction properties of dyes were studied with respect to DES type and molar ratio, pH, dye concentration, DES/organic phase volume ratio, type of organic phase, aqueous phase volume, and matrix environment effects. For each dye, removal studies were conducted with dye mixtures prepared at a concentration of 100 mg L⁻¹, with RR230 yielding a removal efficiency of 99.90% and RB221 yielding 99.81%. Two different organic solvents were chosen as the receiving phase, and remarkably similar results were achieved in the range of aqueous/DES volume ratios (5:1–15:1). The use of CH₂Cl₂ in the extraction studies resulted in higher extraction efficiency as this ratio increased (15:1–40:1). Furthermore, for removal of this dyes, a simple process consisting of 10-s shaking and 1-min centrifugation was found to be sufficient. While the extraction of RR230 was significantly affected by the pH of the aqueous environment, no significant change was observed for RB221 at different pH values. It is quite remarkable that the extraction stability of the RR230 and RB221 are maintained up to 20,000 mg L⁻¹ in aqueous solutions prepared from pure forms and up to 10,000 mg L⁻¹ in mixtures. Even at volumetric ratios of 400:10:1 for aqueous/DES/organic phases, the extraction efficiency for both dyes remained at the level of ≥ 95%. Eventually, the removal results obtained from the extraction experiments by adding RR230 and RB221 mixtures to environmental water samples reveal that the applied method can also be used for real samples.