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, ZA ZB was calculated to be 2.2, indicating that both single‐charged and double‐charged species play a role during the decomposition process.

UV/FeⅡNTA as a novel photoreductive system for the degradation of perfluorooctane sulfonate (PFOS) via a photoinduced intramolecular electron transfer mechanism

“…Raising the temperature from of the measured rate constants, the overall apparent activation energy (Ea) was calculated to be 4.74 kJ/mol. The Ea value is much lower than those obtained in the photoreductive decomposition of PFOA in UV/KI system (59.54 kJ/mol) [73] and in the PFOA pyrolysis (154±11 kJ/mol) [74]. The observed Ea is lower than the activatio n energies of the eaqreactions, which lie in the range of 6-30 kJ/mol [20].…”

Vitamin B12 (CoII) initiates the reductive defluorination of branched perfluorooctane sulfonate (br-PFOS) in the presence of sulfide

“…Based on the temperature dependence of the measured rate constants, the overall apparent activation energy (E a ) was calculated to be 62.86 kJ/mol. This value is slightly higher than that obtained in the photoreductive decomposition of PFOA with hydrated electrons (59.54 kJ/ mol) [61], but much lower than that of PFOA pyrolysis (154 ± 11 kJ/ mol) [62]. Kim and Carraway indicated that the activation energy could be lowered by ~ 40-60 kJ/mol in the presence of VB12 for the dichlorination of PCE [63].…”

Photo enhanced degradation of polyfluoroalkyl and perfluoroalkyl substances

“… PFOA UV/KI Low-pressure Hg UV light (15 W; Wavelength = 254 nm; Photon flux = 9.9 × 10 −6 mol L −1 min −1 ) |PFOA| = 0.008 mg/L; |KI| = 0.60 mmol/L; Temperature = 293–313 K; Ionic strength = 2.5–20 mmol/L; pH = 9; Time = 6 h 100 47.7–80.9% 3.2 × 10 −1 – 1.5 h −1 Effect of temperature and ionic strength on the degradation of PFOA was studied. The efficiency showed positive correlation with both temperature and ionic strength [ 133 ] PFOS VUV VUV:Low pressure Hg lamp (10 W; wavelength = 254 nm and 185 nm) |PFOS| = 0.2 mg/L; | | = 0.60 mmol/L; pH = 10; Time = 4 h 46.2% 30% 1.2 × 10 −1 h −1 The effect of light source in UV/sulphite and VUV/sulphite process showed the VUV/sulphite showed higher degradation efficiency due to the increased amount of generated reactive species [ 134 ] UV/ 85.8% 64.6% 4.8 × 10 −1 h −1 VUV/ UV: low pressure Hg lamp (11W; wavelength: 254 nm) 97.3% 68.5% 8.7 × 10 −1 h −1 PFOS UV/NTA Low-pressure Hg UV light (14 W; Wavelength = 254 nm; Photon flux = 9.9 × 10 −6 mol L −1 min −1 ) |PFOS| = 0.005 mg/L; |NTA| = 2 mM; pH = 10; Time = 10 h 85.4% 46.8 2.7 × 10 −1 h −1 The UV/NTA process showed high efficiency as NTA not only act as photosensitizer to induce water photodissociation and photoionization but act as • OH scavenger, thus reducing its recombination with hydrated electron [ 135 ] PFOA Vis/IAA/HDTMA-Montmorillonite Low-pressure Hg UV light (36 W; Wavelength = 254 nm; Photon flux = 4.5 mW cm −2 ) |PFOA| = 10 mg/L; |IAA| = 1 mM; |clay mineral| = 2.2 g/L pH = 3; Time = 5 h 100% 90% (within 10 h of reaction) …”