Adsorption and Dynamic Characteristics of PFAS Mixtures with Kaolinite: Molecular Insights into the Impact of Chain Length and Functional Group

The widespread distribution of Per-fluoroalkyl and polyfluoroalkyl substances (PFAS) in soil and sediments is a major concern for environmental and human health. Though significant progress has been made to understand the behavior of PFAS in near- and subsurface regions, much of the current insight is limited to homogeneous solutions of PFAS. However, PFAS often exists within PFAS mixtures in soil environments, and there is far less knowledge about these mixtures. In this work, the impact of binary mixture compositions of PFAS on the interfacial adsorption, structure, and diffusion characteristics with the soil mineral kaolinite has been investigated. For the first time, the effects of terminal functionalities and PFAS concentrations in a binary mixture on surface complexation have been examined on the molecular level. Importantly, the diffusion behavior of carboxylate PFAS molecules in a surface adsorbed cluster is dependent on the number of sulfonated PFAS molecules within the cluster.