Structural remodeling of UiO-66(Ce) into oxygen vacancy defect-rich CeO₂: Enhancing selective adsorption of As(III)

Long-term exposure to arsenic-contaminated water endangers human health. Removing arsenite (As(III)) efficiently and selectively from water is challenging due to its higher toxicity and mobility than arsenate (As(V)). This study successfully synthesizes ultrasmall, defect-rich CeO₂ (CeO₂-D) with abundant oxygen vacancy derived from metal organic framework (MOF) UiO-66(Ce) via simple acetate etching. The structurally remodeled CeO₂-D can achieve As(III) adsorption capacities of 189 mg/g at natural pH, which surpasses that of UiO-66(Ce) by 32.6-fold. At pH 11, the As(III) adsorption capacities can reach higher to 247 mg/g far beyond the literature reports. Meanwhile, in binary As(III/V) solution, CeO₂-D's adsorption selectivity for As(III)/As(V) increased from 3-fold to 8-fold from natural pH to about 11. Density functional theory (DFT) results prove CeO₂-D's adsorption energy for As(III) is significantly lower than As(V). CeO₂-D's superior adsorption for As(III) is dominated by the synergistic effect between oxygen vacancy defects and reversible Ce³⁺/Ce⁴⁺ redox. Conversely, As(V) adsorption predominantly proceeds via As(V)[sbnd]O[sbnd]Ce coordination bonds. This study presents a novel, simple and straightforward strategy to modify MOF structure, enabling precise control of selectivity and adsorption capacity for As(III). The CeO₂-D arsenic removal strategy shows advantages in alkaline arsenic wastewater, providing a scalable, cost-effective solution for groundwater and industrial treatment.