Mechanism of sonolytic PFAS degradation into inorganic products: A combined reactive molecular dynamics and density functional theory approaches

Per-and polyfluoroalkyl substances (PFAS) are a group of synthetic chemicals extensively utilized in various industrial and consumer applications, owing to their distinctive characteristics such as heat resistance, oil and water repellency, and chemical stability. PFAS are commonly called "forever chemicals" as they exhibit extraordinary persistence in the environment, leading to their accumulation in soil, water, air, wildlife, and human tissues. As a result, there has been a recent surge of interest in the development of effective degradation methods to address this environmental challenge. PFAS can be classified based on their terminal functional groups (Head-groups) with carboxylic and sulfonic head groups being the most common. In this study we employ a theoretical approach to study the PFAS degradation mechanism due to the application of ultrasound and the rate law governing the degradation of various PFAS compounds, including Perfluorooctane sulfonate (PFOS), Perfluorooctanoic acid (PFOA) using Reactive Molecular Dynamics (ReaxFF) simulation. The initial steps of quantum level understanding of the reaction mechanism of PFAS molecules were performed using Perflurobutanoic acid (PFBA) as a model molecule using Density Functional Theory (DFT). We studied two mechanisms of PFAS molecular destruction via ultrasound (1) head-tail bond breaking and (2) tail-tail bond breaking mechanism, thereby addressing gaps in the current understanding of reaction pathways and degradation rates associated with PFAS compounds.