Abstract：
UV/Fe3+ and persulfate are two promising advanced oxidative degradation systems for in situ remediation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), yet a lack of comprehensive understanding of the degradation mechanisms. For the first time, we used density functional theory (DFT) to calculate the entire reaction pathways of the degradation of PFOA/PFOS in water by UV/Fe3+ and persulfate. In addition, we have deeply explored the different attack pathways driven by •OH and SO4-•, and found that SO4-• determines PFOA/PFOS to obtain PFOA/PFOS free radicals through single electron transfer to initiate the degradation reaction, while •OH determines the speed of PFOA/PFOS degradation reaction. Both degradation reactions were thermodynamically advantageous and kinetically feasible under calculated conditions. Based on the thermodynamic data, persulfate was found to be more favorable for the advanced oxidative degradation of Perfluorinated compounds (PFCs). Moreover, for SO4-• and •OH co-existing in the persulfate system, pH will affect the presence and concentration of these two types of free radicals, and low pH is not necessary for the degradation of PFOA/PFOS in the persulfate system. These results can considerably advance our understanding of the PFOA/PFOS degradation process in advanced oxidation processes (AOPs), which is driven by •OH and SO4-•. This study provides a DFT calculation process for the mechanism calculation of advanced oxidation degradation of other types of PFCs pollutants, hoping to elucidate the future development of PFCs removal. Further research should focus on determining the advanced oxidation degradation pathways of other types of PFCs, to support the development of computational studies on the advanced oxidation degradation of PFCs.
摘要：
UV/Fe3和过硫酸盐是两种有前途的高级氧化降解系统，用于原位修复全氟辛酸（PFOA）和全氟辛烷磺酸（PFOS），但缺乏对退化机制的全面了解。第一次,我们使用密度泛函理论（DFT）计算了UV/Fe3和过硫酸盐降解水中PFOA/PFOS的整个反应途径。此外,我们深入探索了由·OH和SO4-·驱动的不同攻击途径，并发现SO4-•决定PFOA/PFOS通过单电子转移获得PFOA/PFOS自由基引发降解反应,而·OH决定了PFOA/PFOS降解反应的速度。在计算条件下，两种降解反应在热力学上都是有利的，并且在动力学上是可行的。根据热力学数据,发现过硫酸盐更有利于全氟化合物（PFC）的高级氧化降解。此外，对于过硫酸盐系统中共存的SO4-·和·OH，pH会影响这两种自由基的存在和浓度，过硫酸盐体系中PFOA/PFOS的降解不需要低pH。这些结果可以大大提高我们对高级氧化过程（AOPs）中PFOA/PFOS降解过程的理解，由·OH和SO4-·驱动。本研究为高级氧化降解其他类型PFCs污染物的机理计算提供了DFT计算流程,希望能阐明PFCs去除的未来发展。进一步的研究应该集中在确定其他类型的PFCs的高级氧化降解途径，以支持PFCs高级氧化降解的计算研究的发展。
