Chlorophenols (CPs) are synthetic chemicals which are generated and used widely by different industries such as textile, pharmaceutical, metallurgic, oil, pulp and paper manufacturing. CPs are considered as hazardous pollutants due to their negative impacts on ecosystem, resistance to biodegradation and persistence in the environment. Their toxic effects are severe including DNA damage, endocrine disruption, cytotoxicity, mutagenicity, and carcinogenicity. Thus, some members of them are considered as priority pollutants by United States Environmental Protection Agency (EPA) and potential carcinogenic chemicals by the International Agency for Research on Cancer (IARC). The water contaminated by phenols must be treated before releasing to the environment. Ionic liquids (ILs) are molten salts that are liquid below 100 ºC, which have been used as solvents for many processes and as electrolytes in electrochemical devices. ILs are characterized by negligible vapor pressure and non-flammability. These compounds are liquid over a wide range of temperatures (down to -81 ºC), possess high thermal and chemical stability as well as high density and electrical conductivity in comparison to other solvents. ILs as green solvents in water treatment have become research hotspot and solubility data of water pollutants in ILs is important for assessing the potential of the use of ILs in water treatment, but relevant data for ILs are scarce. No solubility data of chlorophenols in ILs were not reported in the literature. In addition, a limited number of publications on the extraction of CPs using ILs is available. Therefore, in this work, the solubility of 3-chlorophenol (3-CP), 2,5-Dichlorophenol (DCP), 2,4, 6-Trichlorophenol (TCP), and Pentachlorophenol (PCP) in six hydrophobic ILs were measured at different temperatures. Moreover, the extraction of these CPs from water using the same ILs was conducted at different conditions of temperature, IL/water mass ratio, and extraction time. In order to investigate the cross contamination, mutual solubility of water and ILs were measured at 25 °C.
The solubility experimental results showed that 3-CP is miscible with all tested ILs. As for DCP, TCP and PCP, the solubility in all ILs decreased as the number of chlorine atoms in chlorophenols increased. Additionally, the solubility increased with increasing temperature, but the degree of increase depended on the structure of both IL and chlorinated phenol. Through extraction experiment, when1-Ethyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide ([1,3emPY][Tf2N]) was used, 98.7% extraction efficiency for 3-CP, 99.4% extraction efficiency for DCP and 99.1% extraction efficiency for TCP were achieved. When 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) was used, 98.3% extraction efficiency for 3-CP and 99.8% extraction efficiency for DCP were achieved. When 1-butyl-1-methylpiperidimium bis(trifluoromethylsulfonyl)imide ([C4mPip][Tf2N]) was used, 99.9% extraction efficiency for TCP were achieved. From mutual solubility results, it was found that the solubility of ILs in water is very small and is much smaller than the solubility of water in ILs.