Metal–Organic Cage Extended Amorphous Network via Anionic Organic Linkers for Cr2O72– and Iodine Adsorption on Nanopores

Abstract

The covalent linking of metal–organic cages (MOCs) with a nanoscale cavity is an efficient strategy to construct functional materials with different properties compared with bulk MOCs, but studies based on this topic are still less explored. In addition, toxic chemical and pollutant uptake, especially iodine vapor adsorption on MOC-based materials, still lacks investigation. Herein, an MOC-extended amorphous network (denoted MOC–DASD) via the covalent linking of an aldehyde-functionalized cationic Pd12L24 MOC (with about 3.5 nm in diameter) with an anionic organic linker, 4,4′-diamino-2,2′-stilbenedisulfonic acid (DASD), was constructed and applied to absorb Cr2O72– in water and capture I2 molecules in vapor. The covalent linkage of MOC and DASD via C═N bonds was confirmed by IR, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and ζ-potential tests. In addition, the original NO3– anions can be easily removed from the MOC–DASD due to the introduction of an anionic linker, thus releasing more effective cavities for guest adsorption. Although there is a lack of exchangeable anions, MOC–DASD still exhibits the ability to capture Cr2O72– in water with moderate capacity and high selectivity. In addition, the MOC–DASD showed a significantly enhanced iodine vapor uptake capacity. The iodine uptake capacity of MOC–DASD reached 3.67 g/g, which is 1.8 times higher than that of bulk MOC. A mechanistic study shows that some of the iodine was closely adsorbed by charge transfer. The release of iodine at 120 °C reveals that approximately 74% of the absorbed iodine can be removed, and the MOC can uptake the iodine again with a capacity of 1.5 g/g, showing good reusability.