Synergistic regulation of oxygen vacancies and surface hydroxyl groups in Fe-doped CeO2 for enhanced fluoride adsorption

Effective defluoridation remains a pressing challenge in water purification, particularly in complex water matrices. Cerium dioxide (CeO 2 ) is a promising fluoride adsorbent due to its tunable oxygen-deficient structure and high surface reactivity. However, the underlying mechanisms by which oxygen vacancies (V o ) and surface functionalities cooperatively influence fluoride adsorption remain unclear. Herein, a series of Fe-doped CeO 2 (Fe-CeO 2 ) materials were synthesized to systematically explore the role of Fe-induced V o in enhancing defluoridation performance. Among them, the 9 % Fe-CeO 2 sample exhibited the highest adsorption capacity (43.70 mg/g), achieving a 10.22 % increase over pristine CeO 2 and outperforming multiple benchmark adsorbents in both capacity and kinetics. Spectroscopic characterizations (XRD, XPS, FTIR, Raman) and density functional theory (DFT) calculations revealed a critical balance: moderate Vₒ concentrations not only provided direct adsorption sites but also facilitated hydroxyl group (–OH) formation, both essential for fluoride capture. However, excessive V o concentrations led to surface lattice reconstruction and suppressed –OH generation, resulting in a U-shaped relationship between V o content and adsorption performance. The material also demonstrated high stability under extreme pH conditions, strong selectivity in the presence of co-existing anions, excellent reusability over five adsorption-desorption cycles, and effective fluoride removal (< 1.0 mg/L) under environmentally relevant conditions. These findings offer mechanistic insight into defect engineering and highlight the potential of Fe-CeO 2 as a robust adsorbent for practical water defluoridation applications.