Extraction of PFOA from dilute wastewater using ionic liquids that are dissolved in N-octanol

KH Zhang and D Kujawski and C Spurrell and D Wang and JC Yan and JC Crittenden, JOURNAL OF HAZARDOUS MATERIALS, 404, 124091 (2021).

DOI: 10.1016/j.jhazmat.2020.124091

Polyfluoroalkyl Substances (PFAS) such as perfluorooctanoic acid (PFOA) are resistant to biodegradation leading to adverse health outcomes. Therefore, PFAS removal from drinking water is paramount. Liquid-liquid extraction processes can remove them from water; however, the hydrophobic and oleophobic properties of PFOA lead to the low extraction efficiency and severe emulsification, especially for the ppm-levels concentration of PFOA. Therefore, we introduced ionic liquid (IL) methyltrioctylammonium bis(trifluoromethylsulfonyl)imide (A336 NTf2) as extractant into octanol. We found that using hexadecyl trimethyl ammonium bromide (CTAB) as an extractant caused severe and stable emulsion. In comparison, A336NTf2 could suppress the emulsification with high extraction efficiency. The extraction performance of PFOA was examined as a function of various parameters. The results showed that the extraction efficiency was strongly dependent on the concentration of IL and aqueous pH. Further research revealed the extraction mechanisms at the molecular-level, and density functional theory (DFT) and molecular dynamic (MD) simulation agreed with the trends in the experiment. We determined that the extraction efficiency of PFOA from water could be up to 88.21 wt% for the optimized condition, indicating that the extraction system of A336NTf2 + octanol was efficient for separating PFOA from the diluted aqueous solution.

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