Temperature effect on photolysis decomposing of perfluorooctanoic acid

Perfluorooctanoic acid (PFOA) is recalcitrant to degrade and mineralize. Here, the effect of temperature on the photolytic decomposition of PFOA was investigated. The decomposition of PFOA was enhanced from 34% to 99% in 60 min of exposure when the temperature was increased from 25 to 85°C under UV light (201–600 nm). The limited degree of decomposition at 25°C was due to low quantum yield, which was increased by a factor of 12 at 85°C. Under the imposed conditions, the defluorination ratio increased from 8% at 25°C to 50% at 85°C in 60 min. Production of perfluorinated carboxylic acids (PFCAs, C7–C5), PFCAs (C4–C3) and TFA (trifluoroacetic acid, C2) accelerated and attained a maximum within 30 to 90 min at 85°C. However, these reactions did not occur at 25°C despite extended irradiation to 180 min. PFOA was decomposed in a step-wise process by surrendering one CF2 unit. In each cyclical process, increased temperature enhanced the quantum yields of irradiation and reactions between water molecules and intermediates radicals. The energy consumption for removing each μmol of PFOA was reduced from 82.5 kJ at 25°C to 10.9 kJ at 85°C using photolysis. Photolysis coupled with heat achieved high rates of PFOA degradation and defluorination.

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