Photoinduced Reductive Decomposition of Perflurooctanoic Acid in Water: Effect of Temperature and Ionic Strength

Abstract

Aqueous photo-reductive decomposition of perflurooctanoic acid (PFOA) was investigated as a function of temperature (293, 298, and 313 K) and ionic strength (2.5, 5.0, or 20.0 mmol/L as NaCl). As an advanced reduction process, iodide was used under UV irradiation to produce highly reactive reducing reagent hydrated electrons. PFOA was reduced by hydrated electrons and short-chain perfluorinated acid intermediates including perfluoroheptanoic acid, perfluorohexanoic acid, perfluoropentanoic acid, perfluorobutyric acid, pentafluoropropionic acid, and trifluoroacetic acid were detected during the reaction. In this study, the same intermediates were observed under different temperature and ionic strength conditions. It was found that the increase of reaction temperature could positively affect the decomposition of PFOA. Defluorination of PFOA was observed to increase as the temperature increased. After 6 h, the defluorination efficiency increased from 47.71% to 80.91% when the system temperature increased from 293 to 313 K. As the temperature increased, the maximum concentration of the six short-chain perfluorinated acid intermediates decreased. Meanwhile, there was a positive correlation between the ionic strength and PFOA decomposition rate. According to the Brønsted–Bjerrum equation, Z_A Z_B was calculated to be 2.2, indicating that both single-charged and double-charged species play a role during the decomposition process.