Direct Observation of Enhanced Iodine Binding within a Series of Functionalized Metal–Organic Frameworks with Exceptional Irradiation Stability

Abstract

Optimization of active sites and stability under irradiation are important targets for sorbent materials that might be used for iodine (I 2 ) storage. Herein, we report the direct observation of I 2 binding in a series of Cu(II)-based isostructural metal−organic frameworks, MFM-170, MFM-172, MFM-174, NJU-Bai20, and NJU-Bai21, incorporating various functional groups (−H, −CH 3 , − NH 2 , −C�C−, and −CONH−, respectively). MFM-170 shows a reversible uptake of 3.37 g g −1 and a high packing density of 4.41 g cm −3 for physiosorbed I 2 . The incorporation of −NH 2 and − C�C− moieties in MFM-174 and NJU-Bai20, respectively, enhances the binding of I 2 , affording uptakes of up to 3.91 g g −1 . In addition, an exceptional I 2 packing density of 4.83 g cm −3 is achieved in MFM-174, comparable to that of solid iodine (4.93 g cm −3 ). In situ crystallographic studies show the formation of a range of supramolecular and chemical interactions−C�C− sites, respectively, and adsorbed I 2 molecules. These observations have been confirmed via a combination of solid-state nuclear magnetic resonance, X-ray photoelectron, and Raman spectroscopies. Importantly, γ-irradiation confirmed the ultraresistance of MFM-170, MFM-174, and NJU-Bai20 suggesting their potential as efficient sorbents for cleanup of radioactive waste.