Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 51, Issue 6, Pages 3471-3479Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.7b00339
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Funding
- National Natural Science Foundation of China [21422704, U1532259, 11605118]
- Science Foundation of Jiangsu Province [BK20150313, BK20140007]
- State Key Laboratory of Pollution Control and Resource Reuse Foundation [PCRRF16003]
- Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
- Jiangsu Provincial Key Laboratory of Radiation Medicine and Protection, Young Thousand Talented Program in China
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Heavy Elements Chemistry Program [DE-FG02-13ER16414, DE-SC0016568]
- Center for Actinide Science and Technology (CAST), an Energy Frontier Research Center
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Tc-99 is one of the most problematic radioisotopes in used nuclear fuel owing to its combined features of high fission yield, long half-life, and high environmental mobility. There are only a handful of functional materials that can remove TcO4-anion from aqueous solution and identifying for new, stable materials with high anion-exchange capacities, fast kinetics, and good selectivity remains a challenge. We report here an 8-fold interpenetrated three-dimensional cationic metal organic framework material, SCU-100, which is assembled from a tetradentate neutral nitrogen-donor ligand and two-coordinate Ag+ cations as potential open metal sites. The structure also contains a series of 1D channels filled with unbound nitrate anions. SCU-100 maintains its crystallinity in, aqueous solution over a wide pH range from 1 to 13 and exhibits excellent beta and gamma radiation-resistance. Initial anion exchange studies show that SCU-100 is able to both quantitatively and rapidly remove TcO4- from water within 30 min. The exchange capacity for-the surrogate ReO4-reaches up to 541 mg/g and the distribution coefficient K-d is up to 1.9 X 10(5) mL/g,which are significantly higher than all previously tested inorganic anion sorbent materials. More importantly, SCU-100 can selectively capture TcO4-in the presence of large excess of competitive anions (NO3-, SO4(2)-, CO32-, and PO43-)-and remove as much as 87% of TcO4-from the Hanford low-level waste melter off-gas scrubber simulant stream within 2 h. The sorption mechanism is well elucidated by single crystal X-ray diffraction, showing that the sorbed ReO4- anion is able to selectively coordinate to the open Ag+ sites forming Ag-O-Re bonds and a series of hydrogen bonds. This further leads to a single-crystal-to-single-crystal transformation from an 8-fold interpenetrated framework with disordered nitrate anions to a 4-fold interpenetrated framework with fully ordered ReO4-anions. This work represents a practical case of TcO4- removal by a MOF material and demonstrates the promise of using this type of material as a scavenger for treating anionic radioactive contaminants during the nuclear waste partitioning and remediation processes.
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