A stable, non-emulsifying, regenerable ionic liquid-based extraction system for safe removal of perfluorooctanoic acid from water

The main sources of polyfluoroalkyl substances (PFAS) in the environment are industrial plants at which PFAS are manufactured or used. PFAS are released from such plants in wastewater, which must be effectively decontaminated to prevent PFAS contaminating the environment. In this study, perfluorooctanoic acid (PFOA) was extracted from model aqueous solutions using a novel ionic liquid (IL) [trihexyltetradecylphosphonium] [perfluotooctanoic acid] ([P6,6,6,14][PFOA]) without an emulsification problem. Liquid-liquid extraction using the IL removed 99.7% of the PFOA from a 2000 mg/L PFOA solution after 3-6 h of mixing. The IL was easily regenerated and reused, but some of the IL was lost after multiple extraction and regeneration cycles. Immobilization of the [P6,6,6,14][PFOA] IL in a poly(vinylidene fluoride-co-hexafluoropropylene) membrane system prevented the loss of the IL. The [P6,6,6,14][PFOA]/membrane system removed 79%-85% of the PFOA from a solution containing 100 mg/L PFOA solution after 24 h of mixing. The IL immobilized in the membrane system could be regenerated by washing the system with 0.25 mol/L NaOH and could be reused multiple times giving extraction efficiencies of 72%-77%.