Organic Iodide Capture in a Titanium Metal-Organic Framework Driven by Multiple Noncovalent Interactions

Efficient capture of airborne radioactive alkyl iodines (e.g., CH₃I and CH₃CH₂I) released from nuclear waste is vital to environmental protection and human health. The state-of-the-art framework sorbents offer the advantage of covalent immobilization of alkyl iodines via N-alkylation reaction with large capacity but typically face the essential challenge of sluggish reaction rate despite the large existence of open channels for guest diffusion. Here, we demonstrate experimentally and theoretically the critical role and superiority of noncovalent interactions in organic iodide capture. Specifically, we document the discovery of a novel topological titanium framework (BIT-61), where the infinite chains of corner-sharing Ti-centered octahedra with terminal Cl atom and dimethylformamide molecule are connected by aromatic naphthalene-based linkers. Mechanistic studies show that a network of multiple noncovalent binding sites on pore surface including −CH₃, Cl, and O atoms on Ti octahedra as well as electron-rich naphthalene allow for rapid constraint of CH₃I, CH₃CH₂I, and CH₃CH₂CH₂I while maintaining a high loading capacity. Particularly, in terms of the average adsorption rate (determined at 80% of the maximum uptake capacity), BIT-61 exhibits a K_80% value of 1.22 g g^-1 h^-1 for CH₃I, higher than that of reported metal-organic framework and covalent organic framework adsorbents with a maximum time of 61.