Capturing radioactive strontium by a metal-organic cage: Developing functional recognition sites through acyl-type metal node engineering

Recently, Science Bulletin published the research findings of Professors Shi Weiqun and Mei Lei from the Institute of High Energy Physics, Chinese Academy of Sciences. The study presents a viable approach for engineering acyl-type metal nodes to create oxygen-rich interior sites within MOCs, enabling the specific recognition of metal ions, including radioactive contaminants, while preserving the structural integrity of the MOCs. A novel MOC, referred to as UOC, featuring a uranyl-sealed calix[4]resorcinarene (C[4]R)-based multisite cavity, was synthesized as a prototype. In UOC, peroxide-bridged dimeric uranyl units at both ends of the coordination cage provide abundant oxygen sites for coordination, forming a cryptand-like cavity that facilitates the efficient recognition and encapsulation of Sr²⁺ through a size-matching effect. Additionally, hydrophobic binding cavities at both ends of UOC facilitate the co-encapsulation of two distinct guest species. Inspired by the strong binding affinity of UOC for Sr²⁺, it was employed as a solid adsorbent to capture low concentrations of Sr²⁺ from strontium-contaminated simulated groundwater. A removal efficiency of 99.7% for Sr²⁺ at an initial concentration as low as 0.013 mmol L^-1 was achieved, demonstrating its significant potential for the selective removal of trace amounts of radioactive ⁹⁰Sr²⁺. In summary, this work demonstrates the feasibility of incorporating acyl-type metal nodes into MOCs for the recognition and encapsulation of metal ions, provides new insights into the design of precise recognition sites within MOC cavities, and proposes a novel strategy for developing materials to purify radioactive metals.

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