Break the net of Fe-based MOFs: Enhanced uranium adsorptive-photocatalytic capture and reduction by phosphate-functionalized defect engineering

Uranium(VI) capture from nuclear wastewater and its reduction to uranium(IV) holds significant environmental and economic value, yet its efficiency remains major challenges. In the current study, 2-hydroxyphosphonoacetic acid (HPAA) was used as a mixed linker to break the net of NH₂-MIL-53(Fe) (NMILD) crystals to introduce synthesize phosphate-functionalized defects, for boosting adsorptive-photocatalytic reductive uranium capture. The results shows that the U(VI) capture and reduction by NMILD exceeds most of the reported MOF-based materials. Under simulated solar irradiation, the uranium capture capacity and efficiency reach to 1710.16 mg/g, with a 99.8 % maximum uranium capture rate, in air condition and without sacrificial agents. NMILD also shows good selectivity, stability, and reusability. Combining savaging tests, EPR analysis and various characterizations, it is found that the main active reducing species are e⁻ and ^•O₂⁻, and the reduction product is UO₂. Considering DFT calculation and experimental results, it is concluded that the exposed Fe-O active centers and phosphate groups in NMILD synergistically enhance both the U(VI) adsorption and photocatalytic reduction. This work provides a new method for uranium capture from nuclear wastewater and a new preparation route for the modification of Fe-based MOFs.