Bottom-up synthesis of Fe doped Ce-based bimetal adsorbent with outstanding defluorination capability: Regulation of Ce valence and oxygen vacancies by iron

Fluoride (F − ) pollution in surface water seriously endangers ecological safety. Cerium-based adsorbents have original advantages in adsorbing F − such as abundant oxygen vacancies and variable valence states. However, high cost and separation difficulty limit their application in fluoridated surface water treatment. This work synthesized bimetallic oxide adsorbents (FeCe@C) to enhance the efficacy of cerium-based adsorbents for F − removal and systematically examined how Fe(II) doping influenced fluoride removal efficiency. Results indicated that FeCe@C adsorbed F − better than the pure Ce-based adsorbent (Ce@C), with q max  = 243.31 mg/g at 25℃, and reached adsorption equilibrium in merely five minutes, with significantly better adsorption performance than fluoride adsorbents reported in previous literature. F − adsorption process aligned with the Temkin (R 2  > 0.963), pseudo-second-order kinetic (R 2  > 0.999) and Elovich model (R 2  > 0.993), suggesting that the F − adsorption mechanism was governed by chemisorption-dominated heterogeneous surface reactions. Further results proved that the doping of iron exhibited a significant effect on the generation of Ce(III) active sites and oxygen vacancies in FeCe@C, which showed a positive correlation (R 2  = 0.87 and 0.98). And unlike other metal doping mechanisms, the doped Fe species promoted the formation of Ce(III) through redox reactions during the adsorption process, achieving the reverse conversion of Ce(IV) to Ce(Ⅲ), rather than directly participating in adsorption. Density functional theory (DFT) calculations demonstrated that iron doping effectively enhanced electron transfer and the interaction between F − and the adsorbent, resulting in a higher F − adsorption capacity. This study provides fundamental theory for enhanced fluoride removal and offers new ideas for elevating the efficacy of cerium-based adsorbents.