Integrating Sulfate with Crown Ether To Construct Supramolecular Radium Traps in an Anionic Zirconium Metal–Organic Framework

Sequestration of radiotoxic 226Ra2+ is challenged by its complex coordination chemistry, which requires a precise molecular recognition strategy. Here, we report a supramolecular trap engineered within a stable zirconium metal–organic framework (ZJU-X102-SO4) by integrating a size-selective 24-crown-8 ether with a proximal sulfate anchor. The formation of this preorganized trap and its cooperative binding mechanism were elucidated by single-crystal X-ray diffraction, solid-state NMR, XAFS, and DFT calculations. This dual-recognition design was first validated with the Ba2+ surrogate, affording rapid kinetics (equilibrium in 30 s) and a high capacity (455 mg g–1). For the target 226Ra2+, ZJU-X102-SO4 could remove 70% of 226Ra2+ within 10 min (C0 = 10 Bq mL–1) and demonstrate a capacity of 3.3 × 104 Bq g–1. In high-salinity media, a salting-out effect was observed and ZJU-X102-SO4 showed a high distribution coefficient of 5.3 × 104 mL g–1. The sequestration of 226Ra2+ was also effective in 3 M HNO3. This work presents a molecular engineering strategy for designing sorbents for the targeted sequestration of specific cations from aqueous media.