Ultrafast Capture of Aqueous Triiodide by a K ⁺ ‐Coordinated Crown‐Ether Covalent Organic Framework

Comprehensive Summary Radioiodine poses severe long‐term risks owing to its persistence and bioaccumulation in aquatic ecosystems, yet the rapid removal of triiodide (I 3 – ), the most stable iodine species in water, remains a fundamental challenge. Here, we report JUC‐725@K + , a two‐dimensional K + ‐coordinated crown‐ether covalent organic framework (COF), in which the ordered confinement of K + within the crown‐ether domains markedly enhances the framework's affinity for ultrafast I 3 – capture. Driven by the synergistic effects of ion fixation, solvation suppression, and enhanced binding energy, JUC‐725@K + achieves 99% I 3 – removal within 6 min, with an exceptional apparent adsorption rate constant of 16.5 g·g –1 ·min –1 , outperforming all previously reported porous iodine adsorbents. High removal efficiency above 97% is maintained under continuous‐flow conditions, highlighting the robustness of the material. Meanwhile, K + incorporation greatly improves interfacial hydrophilicity, accelerating aqueous mass transport. Density functional theory further confirms that K + confinement strengthens I 3 – binding in the parent COF, establishing an ion‐cooperative host‐guest chemistry for scalable radioiodine capture.