Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
J Environ Sci (China). 2016 Apr;42:126-133. doi: 10.1016/j.jes.2015.05.008. Epub 2015 Jul 2.
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.
全氟辛酸（PFOA）难以降解和矿化。本研究考察了温度对 PFOA 光解分解的影响。在 UV 光（201-600nm）下，温度从 25°C 升高到 85°C 时，PFOA 在 60 分钟内的分解率从 34%提高到 99%。在 25°C 时，由于量子产率低，仅分解了 34%，而在 85°C 时，量子产率提高了 12 倍。在设定的条件下，在 60 分钟内，脱氟率从 25°C 时的 8%增加到 85°C 时的 50%。在 85°C 下，30 至 90 分钟内，PFOA 产生的全氟羧酸（PFCAs，C7-C5）、PFCAs（C4-C3）和 TFA（三氟乙酸，C2）加速并达到最大值。然而，在 25°C 下，尽管延长了 180 分钟的辐照，这些反应也没有发生。PFOA 通过释放一个 CF2 单元逐步分解。在每个循环过程中，升高温度会提高辐照和水分子与中间自由基之间反应的量子产率。使用光解法，从 25°C 时去除每 μmol PFOA 的能耗从 82.5 kJ 降低到 85°C 时的 10.9 kJ。光解与热相结合实现了 PFOA 的高效降解和脱氟。
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