Facet-dependent dual active sites of CeO 2 govern distinct adsorption mechanisms for fluorinated organics and inorganic fluoride

Abstract Understanding how crystal facets dictate the adsorption mechanisms of multifunctional oxides is crucial for designing selective materials for fluorine-containing contaminants. Here, CeO2 nanocrystals with dominant (111) facets in octahedra (Oct), (110) facets in rods (Rod), and (100) facets in cubes (Cube) were synthesized to elucidate facet-dependent interactions with fluorinated organics and inorganic fluoride. Oct exhibited the highest capacity and kinetics for perfluorooctanoic acid (PFOA) adsorption, while Rod showed superior performance toward F–. Spectroscopic analyses and site-quenching tests revealed distinct active sites: surface hydroxyl groups and oxygen vacancies governed F– uptake via ion exchange and vacancy filling, whereas unsaturated Ce(IV) Lewis acid sites drove PFOA adsorption through C–F bond polarization and lattice oxygen substitution. Pyridine-IR and phosphate inhibition experiments confirmed the key role of facet-dependent Lewis acidity, following the order Oct > Rod > Cube. DFT calculations further demonstrated that the (110) facet favors hydroxyl and F– binding, while the (111) facet exhibits the strongest Lewis acidity and charge transfer with fluorinated organics. This study establishes the structure–facet–function correlation in CeO2, unveiling dual active-site mechanisms that differentiate inorganic and organic fluorine adsorption and offering mechanistic insights for rational design of advanced fluorine-selective materials.