Designing Ultraporous Mesostructured Silica Nanoparticles for the Remediation of Per- and Polyfluoroalkyl Substances

Concerns about per- and polyfluoroalkyl substances (PFAS) have been raised globally as they are bioaccumulative, highly persistent, and invoke a range of health risks. Although phytoremediation is a sustainable PFAS remediation strategy, its efficiency is highly dependent on the PFAS analyte chain length, with limited uptake and removal of longer-chain contaminants. This study aims to develop surface-modified ultraporous mesostructured silica nanoparticles (UMNs) to facilitate PFAS phytoremediation. UMNs were synthesized and functionalized to tune their hydrophobicity and surface charge to enhance UMN affinity for PFAS. Dynamic light scattering, ς-potential, and nitrogen physisorption show that the modified UMNs had similar physical characteristics. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis shows that positively charged UMNs have a higher affinity for PFAS than negatively charged UMNs (with 20% of perfluorooctanoic acid, or PFOA, remaining in solution vs 100% of PFOA remaining in solution, respectively). When incubated with multiple PFAS, UMNs show greater removal efficiency for longer-chain and more hydrophobic PFAS. Preliminary plant studies in soil show an increased PFOA bioconcentration when positively charged UMNs are present. Molecular dynamics simulations, which focused on interactions between the different functional groups on the silica surface and PFAS molecules, were completed and show the importance of the combination of hydrophobic and electrostatic interactions to drive PFAS uptake. Overall, this study highlights the potential of surface-modified UMNs to enhance the uptake of PFAS from the environmental matrix and promote phytoremediation.