In this work, the removal of phenol from aqueous solution was investigated by screening three ionic liquids (ILs) having one common cation, trioctylammonium (TOA), combined with three different anions, namely 3,4-dimethylbenzoate (IL1), 4-tert-butylbenzoate (IL2), and 4-phenylbutanoate (IL3), at room temperature. The results indicate that [TOA][4-phenylbutanoate] (IL3) gave the best efficiency and, hence, was selected for the optimization of process parameters: pH, contact time, concentration, phase ratio, and temperature. The optimum conditions were found to be pH 5, contact time of 5 min, phase ratio (VIL/Vw) of 1:5, initial concentration of phenol of 3000 ppm, and temperature of 298 K. The extraction thermodynamics were studied, and the enthalpy, entropy, and free energy of partition were evaluated. The modes of interaction of these ILs with phenol were modeled using the Conductor-Like Screening Model for Real Solvent (COSMO-RS). Additionally, the cytotoxicity of these ILs toward human cells was investigated. The results indicate that they possess less toxicity than the more commonly used 1-butyl-1-methylpyrrolidinium bis-(trifluoromethylsulfonyl)imide. It has been concluded from the experimental results that ammonium-based ILs with carboxylate anions are efficient for extraction of phenol from polluted water.
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