Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants due to the high stability of their carbon–fluorine bonds. Plasma treatment has attracted attention as a potential method for PFAS degradation. Previous studies have indicated that the degradation of perfluorocarboxylic acids (PFCAs), including perfluorooctanoic acid (PFOA), is strongly related to processes occurring at the plasma–liquid interface. Therefore, modification of the interfacial environment may affect the degradation behavior. In this study, the influence of sodium dodecyl sulfate (SDS) concentration on PFOA defluorination during plasma treatment was investigated.

An aqueous PFOA solution with an initial concentration of 5 mg/L was prepared, and NaCl was added as an electrolyte to adjust the conductivity to 400 μS/cm. The SDS concentration in the reactor was varied from 0 to 8 mg/L. Plasma was generated using a high-voltage pulsed power supply, and samples were collected after 10, 20, and 30 min of treatment. The released fluoride ion concentration was measured, and the degree of defluorination was estimated based on the theoretical fluorine content of PFOA.

The degree of defluorination showed a dependence on SDS concentration. After 30 min of treatment, the average defluorination efficiencies were 22.82 ± 4.45%, 18.43%, 53.79 ± 11.41%, 42.83 ± 16.27%, and 24.89 ± 4.01% at SDS concentrations of 0, 2, 4, 6, and 8 mg/L, respectively. Relatively high defluorination was observed at moderate SDS concentrations, particularly at 4 and 6 mg/L. In contrast, increasing the concentration to 8 mg/L did not improve the degree of defluorination compared with the control experiments. These results suggest that the effect of SDS on PFOA defluorination is concentration-dependent and that moderate SDS concentrations may influence the degradation process through changes in interfacial properties. However, considerable variation was observed among replicate experiments, especially at 4 and 6 mg/L SDS.

Further experiments will be conducted to improve reproducibility and investigate additional SDS concentrations to clarify the relationship between surfactant concentration, interfacial properties, and plasma-induced PFOA degradation.
 

PFAS,PFOA,plasma,SDS,defluorination,plasma–liquid interface