Investigating Aqueous Two-Phase Systems Constituted by Benzyltributylammonium Chloride-Based Deep Eutectic Solvents for Efficient Extraction of Textile Dyes

Aqueous two-phase systems (ATPS) have been considered as an eco-friendly separation system for the extraction of value-added compounds from an aqueous matrix. Deep eutectic solvents (DESs) have been used as the latest phase - forming component in ATPS. The novel DES-based ATPS composed of DESs and with K₃PO₄, K₂HPO₄, and K₂CO₃ were investigated at 298.15 K and atmospheric pressure. DESs were synthesized using benzyltributylammonium chloride (BTBAC) with methanol, ethanol, propanol, and polyethylene glycol (PEG) of average molar mass: 200, 400, and 600 in a 1:3 molar ratio. The ability of the studied salt to induce phase separation follows the order: K₃PO₄ > K₂HPO₄ ≈ K₂CO₃. The investigated ATPS were evaluated as an extraction platform for malachite green (MG), indigo blue (IB), and Sudan III (SIII) from aqueous solutions. The highest partition coefficients (K_dyes) 211.01, 716.91, and 1350.35 were observed for MG, IB, and SIII, respectively, using BTBAC:PEG 600 and K₃PO₄ ATPS. The highest extraction efficiencies (EE_dye %) around 100% were reported for all studied dyes by the same ATPS. The extraction capacity of studied ATPS depends upon log K_ow values and functional groups present in the dye structure. The obtained results highlight the potential use of DES-ATPS in the purification of dye containing wastewater.