Efficient and Selective Uptake of TcO₄^– by a Cationic Metal–Organic Framework Material with Open Ag⁺ Sites

Abstract

Tc 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 TcO 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 β and γ radiation-resistance. Initial anion exchange studies show that SCU-100 is able to both quantitatively and rapidly remove TcO from water within 30 min. The exchange capacity for the surrogate ReO reaches up to 541 mg/g and the distribution coefficient K is up to 1.9 × 10 mL/g, which are significantly higher than all previously tested inorganic anion sorbent materials. More importantly, SCU-100 can selectively capture TcO in the presence of large excess of competitive anions (NO, SO, CO, and PO) and remove as much as 87% of TcO 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 ReO 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 ReO anions. This work represents a practical case of TcO 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.

An Ultrafast Molecular‐Rotor‐Based Fluorescent Turn‐On Sensor for the Perrhenate Anion in Aqueous Solution

“…6 %) as a byproduct in nuclear reactors during the nuclear fission of uranium . It has been estimated that about 400 metric tonnes of 99 Tc have been produced by the fission of 235 U or 239 Pu during the past 70 years, and most of it is awaiting final disposition . In addition, a significant amount of 99 Tc is released into the environment through nuclear accidents, weapons testing, and spent nuclear fuel reprocessing .…”

“…It has been estimated that about 400 metric tonnes of 99 Tc have been produced by the fission of 235 U or 239 Pu during the past 70 years, and most of it is awaiting final disposition . In addition, a significant amount of 99 Tc is released into the environment through nuclear accidents, weapons testing, and spent nuclear fuel reprocessing . The presence of technetium is of particular importance in the management of nuclear waste, because this weak β‐emitter ( E max =293 keV) has a very long half‐life of 213 000 years .…”

“…Technetium is present in its most stable oxidation state as TcO 4 − , which is a kinetically stable anion, but it has a very high hazard potential due to its high solubility (11.3 mol L −1 ) and nearly noncomplexing nature, which makes its transportation velocity almost identical to that of ground water in the upper layer of the earth's crust . The handling of 99 Tc during the nuclear waste vitrification process presents significant challenges due to the formation of volatile compounds such as Tc 2 O 7 , which escapes into the atmosphere . Another major problem that 99 Tc poses during the nuclear waste reprocessing process is its ability to interfere with the catalytic redox reactions that are used to control the valence state of uranium, neptunium, and plutonium during solvent extraction and the back‐extraction process in PUREX (plutonium uranium redox extraction) .…”

Synthesis and Characterization of Two Cationic Silver Quinoxaline Coordination Polymers

“…A breakthrough came in 2001 when Oliver lab introduced cationic BING‐5 structure where nitrate and lead fluoride was mixed in the correct ratio and conditions . Since then, numerous cationic extended materials have been reported for anion exchange properties …”

[Ln6O8] Cluster‐Encapsulating Polyplumbites as New Polyoxometalate Members and Record Inorganic Anion‐Exchange Materials for ReO4− Sequestration

“…The exchange process was further confirmed by the Fourier-transform infrared spectroscopy spectra of ReO 4 − soaked crystals, showing the emerging Re−O ν 3 asymmetric stretching bands (≈890 cm −1 ) and concomitantly reduced intensity of Cl−O ν 1 stretching bands (≈1050 cm −1 ) ( Figure S3, Supporting Information). [16] The effect of pH on ReO 4 − sorption was investigated, showing that YPbOClO 4 -1 and ErPbOClO 4 -2 exhibit highest sorption of ReO 4 − under pH 6 (267 mg g −1 ) and pH 8 (294 mg g −1 ), respectively (Figure 3d). [16] The effect of pH on ReO 4 − sorption was investigated, showing that YPbOClO 4 -1 and ErPbOClO 4 -2 exhibit highest sorption of ReO 4 − under pH 6 (267 mg g −1 ) and pH 8 (294 mg g −1 ), respectively (Figure 3d).…”