Extraction of Phenols from Water with Functionalized Ionic Liquids

A series of hydroxyl-, benzyl-, and dialkyl-functionalized ionic liquids (ILs) were synthesized, and their extraction abilities for phenol, resorcinol, <i>p</i>-nitrophenol, guaiacol, and <i>o</i>-cresol were investigated. Results showed that the extraction efficiencies of the five phenols were significantly influenced by the pH values, salt added, phase ratio, and chemical structure of the IL. Phenols present in nonionized forms were preferable to transfer into IL phases. The anion/cation hydrogen-bonding characters of ILs were the main structural factors affecting the extraction efficiency, which also increased with increased hydrophobicity of phenols. These results are promising for the liquid–liquid extraction and enrichment of phenols in separation science and related industrial processes