Highly efficient Cr(vi) removal from water using deep eutectic solvents: a sustainable and comprehensive approach

Addressing the persistent challenge of hexavalent chromium (Cr(vi)) pollution, this study introduces a sustainable extraction strategy using a novel hydrophobic deep eutectic solvent (HDES) composed of acetic acid and tetraoctylammonium bromide. Under optimized conditions (1 : 4 molar ratio), the HDES exhibited robust extraction capabilities, removing over 95% of Cr(vi) across a broad pH window (2-10). The extraction mechanism was best described by the pseudo-second-order kinetic model, while thermodynamic parameters confirmed a spontaneous and endothermic process (ΔH° = 38.21 kJ mol; ΔG° = -16.88 kJ mol^-1). Notably, the method achieved a high enrichment factor of 87-fold in real wastewater samples. The environmental friendliness of the protocol was validated by an AGREE score of 0.76. This work represents the first successful application of an acetic acid-based HDES for Cr(vi) removal, establishing a scalable, efficient, and green methodology for environmental remediation.