How external forces affect the degradation properties of perfluorooctanoic acid in mechanochemical degradation: a DFT study†

Perfluorooctanoic acid (PFOA), recognized as a persistent organic pollutant, poses a serious threat to the environment and human health. Currently, mechanochemical degradation is considered a highly promising technology for the degradation of PFOA. This study systematically employs density functional theory (DFT) and the COGEF (COnstrained GEometry to simulate Forces) model to deeply investigate the impact of external forces on the degradation properties of PFOA molecules. Through quantum chemical calculations, we analyzed in detail the changes in the electronic structure, chemical reactivity, and decarboxylation reaction process of PFOA molecules under the influence of external forces. The results show that the application of external forces significantly alters the electronic density distribution of PFOA molecules, thereby enhancing their reactive activity, especially in terms of nucleophilicity and radical reactivity at the carboxylate end. Moreover, the application of external mechanical force reduces the Gibbs free energy change of the decarboxylation reaction, thereby making the reaction energetically favorable. This study not only theoretically elucidates the mechanism of mechanochemical degradation of PFOA, but also provides a basis for optimizing its mechanochemical degradation technology. In addition, this study also provides a systematic theoretical perspective for exploring the mechanisms of mechanochemical degradation.