Exceptional Perrhenate/Pertechnetate Uptake and Subsequent Immobilization by a Low-Dimensional Cationic Coordination Polymer: Overcoming the Hofmeister Bias Selectivity

Abstract

We report one of the most efficient scavenger materials, a cationic crystalline coordination polymer SBN for trapping ReO4–, a surrogate for 99TcO4–, as an anionic radioactive contaminant of great concern. The uptake capacity for ReO4– reaches 786 mg/g, a value noticeably higher than the state of art anion-exchange resins and other inorganic or hybrid anion sorbents. Once being captured, ReO4– is greatly immobilized, as almost no ReO4– can be eluted using large excess of nitrate, carbonate, and phosphate anions. The processes are featured by a complete and irreversible single-crystal to single-crystal structural transformation from SBN to the ReO4–-incorporated phase (SBR). The coordination environments of NO3– and ReO4– probed by single-crystal structures clearly unravel the underlying mechanism, where each ReO4– in SBR binds to multiple Ag+ sites forming strong Ag–O–Re bonds, and to 4,4′-bipyridine through a dense hydrogen bond network. These structural insights lead to a significant difference in solubility product constants between SBN and SBR, which is further confirmed by first principle calculations showing a large binding energy difference of 35.61 kcal/mol. To the best of our knowledge, SBR is the least soluble perrhenate/pertechnetate salt reported, which may be considered as a potential waste form for direct immobilization of TcO4–.