Hydrophobic deep eutectic solvents used for highly efficient extraction of Cr(VI) from acidity aqueous phase

The hydrogen bond interactions between TOPO and different HBDs were studied. • The maximum extraction capacity of HDES based on TOPO to Cr(VI) reached 187 mg/g. • The extraction mechanism of Cr(VI) can be inferred as ion association mechanism. • The mass transfer rate of extraction is controlled by the diffusion action. • Chromium(VI) loaded DES phase can be separated by using 0.12 mol/L Na 2 SO 3 . Efficient and environmentally friendly treatment of Cr(VI) in water is essential for enhancing aquatic ecosystems. In this work, hydrophobic deep eutectic solvents based on trioctylphosphorus oxide were used for efficient extraction and recovery of Cr(VI) from the acidic aqueous phase. By using binary phase diagram analysis and molecular dynamics simulation, the hydrogen bond interactions between hydrogen bond donors (decanoic acid, decanol and thymol) and TOPO were studied. The experimental results demonstrated that 0.1 g HDES achieved over 95% extraction efficiency from a 3.0 mL 500 mg/L Cr(VI) solution at pH = 0.5. And the maximum extraction capacity reached 187 mg/g. Furthermore, the extraction process was largely unaffected by variations in anions. Combined with the characterization of FT-IR and UV–vis, the extraction mechanism of Cr(VI) by HDES can be inferred as the ion association mechanism. Thermodynamic revealed that the extraction process is spontaneous and characterized by a decrease in endothermic entropy. Mass transfer at the interface appears to control the diffusion rate. Notably, when 0.12 mol/L Na 2 SO 3 was used as the stripping agent, the HDES maintained stable extraction performance over eight extraction-regeneration cycles. This study offers a promising strategy for the efficient, sustainable extraction of Cr(VI) using a novel green solvent. Download: Download high-res image (177KB) Download: Download full-size image