Anion-exchange strategy boosts iodine adsorption in amorphous metal-organic cage-based extended networks

The covalent linking of metal organic cages (MOCs) is an efficient strategy for constructing MOC-based extended networks, but relatively few studies have focused on this topic. In addition, the application of MOC-based extended networks for iodine adsorption is limited. Herein, a cationic MOC-extended amorphous network, namely, aMOC-BTH-NO 3 - , was constructed by hydrazone-linked an aldehyde-functionalized cationic Pd 12 L 24 (L = 3,5-di-pyridin-4-yl-benzaldehyde) MOC with benzene-1,3,5-tricarbohydrazide (BTH). The anions in this cationic network are easy to exchange. By exchanging with other anions with different shapes and charges, including Br - 、SCN - 、SO 4 2- , and PO 4 3- , four other MOC-based extended networks with different anions, namely, aMOC-BTH-Br - , aMOC-BTH-SCN - , aMOC-BTH-SO 4 2- and aMOC-BTH-PO 4 3- , were obtained. Furthermore, they were applied to capture iodine vapor. The results revealed that the SCN - exchanged network, aMOC-BTH-SCN - , presented the highest iodine capacity, reaching 5.7 g/g, which was 2.6 times greater than that of the original aMOC-BTH-NO 3 - . Mechanistic studies revealed that in addition to the charge transfer interactions between iodine and the network, anions also contribute to the iodine adsorption capacity by regulating the cavities and forming additional interactions with iodine molecules. Approximately only 66 % of the absorbed iodine in I 2 @aMOC-BTH-CN - can be desorbed when heated at 120 °C, but it can still capture iodine again with a capacity of 3.8 g/g after four cycles, which is still higher than that of aMOC-BTH-NO 3 - , thus indicating its good reusability.