From Ionic Self-Assembly to Polyiodide Trapping: Nitrogen-Site-Rich Organic Single-Crystals for Charge-Transfer Iodine Capture

Abstract

Radioactive iodine isotopes are volatile fission products with long half-lives, creating persistent risks during nuclear-waste management. Herein, a rational molecular design strategy was employed to assemble a multicarboxylated biphenyltetracarboxylate anion with nitrogen-site-rich cationic ligands. Here, hierarchical ionic self-assembly denotes a stepwise process in which oppositely charged molecular modules first form charge-balanced ion pairs and are subsequently organized through noncovalent packing/stacking into layered single-crystalline ionic frameworks; using this strategy, nitrogen-site-rich ionic organic single-crystals (N-IOCs) were constructed. The developed N-IOCs exhibit exceptional iodine adsorption performance in both vapor and solution phases, reaching 5.16 g/g from vapor and 1079 mg/g from cyclohexane. They also show rapid adsorption kinetics, good moisture resistance, high retention efficiency, and reusability. The highest iodine-capture performance is likely associated with the ordered nitrogen-rich framework environment, in which imidazole-containing sites provide favorable electronic features for host-iodine charge-transfer interactions.