Magnetic methoxy‑modified COF: A high-performance adsorbent for magnetic solid-phase extraction of perfluoroalkyl substances in aqueous matrices

Perfluoroalkyl substances (PFASs) are persistent environmental contaminants, requiring sensitive analytical methods for trace-level detection in aqueous matrices. Herein, a high-performance magnetic methoxy‑modified covalent organic framework composite (Fe₃O₄@TAPB-OMePDA-COF) was synthesized via an in-situ growth strategy. The composite served as a magnetic solid-phase extraction (MSPE) adsorbent to extract 14 target PFASs. Comprehensive characterization confirmed the successful construction of a core-shell architecture with high crystallinity, well-developed mesoporosity, and strong magnetic responsiveness. Compared with its methoxy (OMe)-free analog (Fe₃O₄@TAPB-PDA-COF), the OMe-functionalized composite exhibited markedly enhanced extraction performance for PFASs, with chromatographic peak areas increasing by approximately 1-2 orders of magnitude. Van der Waals dispersion forces contributed predominantly to the overall adsorption energy, whereas the directional hydrogen bonds may contribute to preferential interactions with PFASs bearing polar headgroups. Density functional theory calculations revealed that OMe introduction elevated the HOMO energy level of the COF framework. The modification introduced additional H···OMe hydrogen-bonding interactions alongside the original H···N interactions, providing a molecular-level rationale for the enhanced PFAS enrichment observed experimentally. The optimized MSPE combined with liquid chromatography-tandem mass spectrometry exhibited a wide linear range (1.0-16,000 ng L⁻¹), low detection limits (0.1-3.4 ng L⁻¹), high enrichment factors (36-329), and satisfactory recoveries (71.5%-98.5%). Multiple PFASs were detected in the surface water, groundwater, and domestic sewage with total concentrations ranging from 329.6 ng L⁻¹ to 1638 ng L⁻¹. This study provided molecular-level insights into OMe-regulated adsorption of PFASs and offered a rational design strategy for developing functionalized magnetic COF adsorbents for extraction of trace PFASs in complex aqueous matrices.