Identifying the Recognition Site for Selective Trapping of ⁹⁹TcO₄^– in a Hydrolytically Stable and Radiation Resistant Cationic Metal–Organic Framework

Abstract

Effective and selective removal of TcO from aqueous solution is highly desirable for both waste partitioning and contamination remediation purposes in the modern nuclear fuel cycle, but is of significant challenge. We report here a hydrolytically stable and radiation-resistant cationic metal-organic framework (MOF), SCU-101, exhibiting extremely fast removal kinetics, exceptional distribution coefficient, and high sorption capacity toward TcO. More importantly, this material can selectively remove TcO in the presence of large excesses of NO and SO, as even 6000 times of SO in excess does not significantly affect the sorption of TcO. These superior features endow that SCU-101 is capable of effectively separating TcO from Hanford low-level waste melter off-gas scrubber simulant stream. The sorption mechanism is directly unraveled by the single crystal structure of TcO-incorporated SCU-101, as the first reported crystal structure to display TcO trapped in a sorbent material. A recognition site for the accommodation of TcO is visualized and is consistent with the DFT analysis results, while no such site can be resolved for other anions.

Successful Decontamination of 99TcO4− in Groundwater at Legacy Nuclear Sites by a Cationic Metal‐Organic Framework with Hydrophobic Pockets

“…Unfortunately, the cationic framework of SCU‐101 is unexpectedly incorporated by negatively charged and hydrophilic oxalate anions, leading to a decreased positive charge density of the framework and, more importantly, a lower uptake selectivity towards TcO 4 − . In this work, we report a stable cationic metal‐organic framework, SCU‐102, that can overcome both of these issues and exhibits a record‐high TcO 4 − uptake selectivity among all anion‐exchange materials reported up to now ,. The use of this material can lead to the successful decontamination of groundwater at the U.S. Hanford site.…”

“…The other strategy is to build a hydrophobic cationic cavity that can efficiently recognize the low‐charge anion through hydrophobic hydrogen bond interactions,– where crystal degradation does not necessarily occur during the anion exchange. This strategy was partially implemented by our recently reported cationic MOF SCU‐101 containing the hydrophobic ligand tetrakis[4‐(1‐imidazolyl)phenyl]methane (tipm, Figure a)) and Ni 2+ . Unfortunately, the cationic framework of SCU‐101 is unexpectedly incorporated by negatively charged and hydrophilic oxalate anions, leading to a decreased positive charge density of the framework and, more importantly, a lower uptake selectivity towards TcO 4 − .…”

Mechanically fabricated Metal–organic framework/resin composite nanoparticles for efficient basic catalysis

“…Metal–organic frameworks (MOFs) are promising porous materials for diverse applications due to their adjustable of apertures and versatile framework functionalities, which lead to potential applications in gas separation and storage, sensing, and catalysis . Among them, zeolitic imidazole frameworks (ZIFs) represent a series of MOFs composed by the coordination interaction of metal ions with the nitrogen atoms from imidazole or its derivatives .…”

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 …”