Abstract
Removal of 99TcO4− from legacy defense nuclear tank waste at Savannah River Site is highly desirable for the purpose of nuclear safety and environmental protection, but currently not achievable given the extreme conditions including high alkalinity, high ionic strength, and strong radiation field. Herein, we present a potential solution to this long-term issue by developing a two-dimensional cationic metal organic framework SCU-103, showing ultrahigh stability in alkaline aqueous media and great resistance to both β and γ radiation. More importantly, it is very effective for 99TcO4− separation from aqueous media as demonstrated by fast exchange kinetics, high sorption capacity, and superior selectivity, leading to the successful removal of 99TcO4− from actual Savannah River Site high level tank waste for the first time, to the best of our knowledge. In addition, the uptake mechanism is comprehensively elucidated by molecular dynamics simulation and density functional theory calculation, showing a unique chemical recognition of anions with low charge density.
Highlights
Removal of 99TcO4− from legacy defense nuclear tank waste at Savannah River Site is highly desirable for the purpose of nuclear safety and environmental protection, but currently not achievable given the extreme conditions including high alkalinity, high ionic strength, and strong radiation field
If a plane across all Ni2+ atoms in the same cationic layer is defined, the tipa ligands are coordinated to the metal center in two orientations: half of them are located above the plane, whereas the others are below it
The face to face adjacent bowls are coupled into a capsule (Fig. 1c) with the size estimated by Ni···Ni separation (~16.1 × 16.1 × 16.1 Å) and the distance between two adjacent N3 atoms (~12.9 Å) (Supplementary Figure 2b)
Summary
Removal of 99TcO4− from legacy defense nuclear tank waste at Savannah River Site is highly desirable for the purpose of nuclear safety and environmental protection, but currently not achievable given the extreme conditions including high alkalinity, high ionic strength, and strong radiation field. Anion-exchange experiments performed after β and γ irradiation suggest no decrease in adsorption capacity of ReO4− as compared with the original samples, further confirming excellent radiation resistance of SCU-103 (Fig. 4d, Supplementary Table 16). Considering the high total activity of 99Tc sample needed for the anion-exchange isotherm experiment, ReO4− was used as a nonradioactive surrogate for 99TcO4− owing to its similar charge density.
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