LDH-Enhanced Degradation of PFASs: Influence of Reactant Configurations within Nanoconfined Spaces on Hydrated...

Hydrated electron (e_aq^-) reduction is an efficient pathway for degrading per- and polyfluoroalkyl substances (PFASs). Nanoconfined spaces can shield e_aq^- from quenchers in bulk solution and shorten diffusion distances, thereby enhancing utilization efficiency. However, the role of e_aq^- precursors and PFASs configurations within nanoconfined domains in governing e_aq^- transport remains unclear. In this study, polyindole (Pind) was synthesized within layered double hydroxide (LDH) interlayers as an e_aq^- precursor, while perfluorooctanoic acid (PFOA) was simultaneously enriched through electrostatic interaction. Although the e_aq^- yield increased with Pind loading, the PFOA degradation rate followed a unimodal trend, reaching a maximum at 27.2% Pind loading, where complete degradation was achieved within 3 h. Molecular dynamics simulations revealed stronger hydrophobic interactions among Pind molecules than between Pind and PFOA, leading to a configuration where PFOA surrounded Pind aggregates. With increasing Pind loading, this arrangement forced more e_aq^- to travel longer distances to attack C-F bonds, reducing their utilization efficiency despite higher overall yields. This "yield-transport" self-antagonism underscores the critical role of nanoconfined configurations in e_aq^- transport and utilization efficiency and provides mechanistic insights for the rational design and optimization of nanoconfinement systems.