Post-synthetically modified crown ether-based supramolecular framework for efficient radium sequestration.

The proliferation of uranium tailings elevates environmental risks through 226Ra (t1/2 = 1600 years), a persistent uranium decay product exhibiting radiation/chemotoxicity threats and subsurface migration. Current 226Ra2+ sorbents, designed for low-activity (<100 Bq L-1) scenarios, fail in acute contamination (> 104 Bq L-1). Herein, we have engineered a Zr-MOF (ZJU-X100-SO4) with bifunctional sites featuring crown-ether motifs for alkaline earth recognition and sulfate groups for enhanced cation binding. While demonstrating great performance for the surrogate Ba2+, its key breakthrough is the efficient removal towards 226Ra2+ (83% in 10 min) in high-activity solution (40000 Bq L-1), excellent selectivity under 106-fold concentrations of competing ions, and great sorption activity under strongly acidic conditions. Additionally, its sorption performance exceeds that of synthesized ferrihydrite and far surpasses commercial sorbents. A combination of XAFS, SC-XRD, and DFT calculations elucidate a multi-site binding mechanism synergizing supramolecular trapping, size-matching confinement, and sulfate-bridged chelation. This work represents a case of utilizing MOF material to capture 226Ra2+, which provides both a practical solution for emergency radionuclide containment and fundamental insights into the molecular-level design of high-performance sorbents for nuclear waste management.