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 99 TcO 4 – 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 4 – . More importantly, this material can selectively remove TcO 4 – in the presence of large excesses of NO 3 – and SO 4 2–, as even 6000 times of SO 4 2– in excess does not significantly affect the sorption of TcO 4 – . These superior features endow that SCU-101 is capable of effectively separating TcO 4 – from Hanford low-level waste melter off-gas scrubber simulant stream. The sorption mechanism is directly unraveled by the single crystal structure of TcO 4 – -incorporated SCU-101, as the first reported crystal structure to display TcO 4 – trapped in a sorbent material. A recognition site for the accommodation of TcO 4 – is visualized and is consistent with the DFT analysis results, while no such site can be resolved for other anions.