PFAS Adsorption on Amine-Functionalized Silica Nanoparticles: Interactions, Mechanisms, and Molecular Insights

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants that raise significant concerns, driving the need for improved remediation methods and better understanding of PFAS interactions with sorbent materials. Here, we systematically synthesized and compared a series of amine-functionalized ultraporous mesostructured silica nanoparticles (UMNs), which have previously shown great affinity for a range of PFAS, to investigate the factors governing PFAS interactions with amine-functionalized material surfaces, using both experimental and computational approaches. Similar UMN physicochemical properties allow direct comparison, with the major difference between nanoparticles being the nature of the amine group (primary, secondary, tertiary, or polyamine). Adsorption experiments showed that all UMNs exhibited great affinity across a wide range of PFAS, with particularly strong affinity for longer-chain and more hydrophobic PFAS and sulfonic acids, and only minor variations were observed in their performance among different amine functionalization schemes. pH-dependent studies demonstrated that PFAS adsorption decreased when exposure occurred at pH 11, consistent with amine deprotonation. However, PFAS already bound remain strongly retained on UMNs with less than 10% desorption even at high pHs. Molecular dynamics (MD) simulations and solvation free energy calculations further revealed that PFAS-UMN interactions are mainly driven by the important collaborative contributions of hydrophobic contacts and electrostatic interactions, and the modest contribution of desolvation penalties, giving clear molecular insight into the experimentally observed trends. Overall, this work reveals the chemistry that will drive efficient sorbent-based PFAS removal from contaminated environments.