Enhanced extraction of antioxidants from aqueous solutions by ionic liquids

•Extraction of three antioxidants by ionic liquids (ILs) was studied.•ILs containing hydroxyl group had better extraction ability for gallic acid.•The role of hydrophobic interaction between ILs and solutes should be considered.•Hydrogen bonding was the main driving force for the extraction of the three acids. In this work, the extraction behavior of the three antioxidants, gallic acid (GA), vanillic acid (VA) and syringic acid (SA) by a series of hydrophobic ionic liquids (ILs) was investigated. The experimental results indicated that the extraction ability of the ILs highly depended on their chemical structures and the hydrophobicity of the three acids. For the ILs with perchlorate (ClO4−) as anion, the introduction of hydroxyl group on the cation improved significantly the extraction ability of ILs for GA. For the extraction of VA and SA, the hydrophobic interaction between ILs and VA or SA should also be considered. Thermodynamic analysis confirmed that hydrogen bonding was the main driving force underlying the transfer of the three acids from water to the IL phase. The three acids and ILs could be recovered and recycled, respectively by taking the advantage of pH dependence of the extraction efficiencies. These results suggested the ILs containing perchlorate anion exhibited potential applications in extraction of the three antioxidants from aqueous phase.