Amine-Functionalized Zeolitic Imidazolate Framework-8 (ZIF-8) Nanocrystals for Adsorption of Radioactive Iodine

The efficient removal of radioactive iodine (I2) has drawn worldwide attention because of the severe effects of radiotoxicity on the environment and human health. As a result, efficient porous materials for the capture and safe storage of radioactive iodine are required. In this work, nanoscale zeolitic imidazolate framework-8 (ZIF-8) and its amino-functionalized ZIF-8 derivatives with 3-amino-1,2,4-triazole (Atz), denoted as ZIF8-A, were prepared via postsynthetic modification, and their performance for I2 removal from n-hexane was investigated. The abundant amine functionalities in the ZIF8-A structure including the primary and secondary amine groups (−NH2 and −NH) and triazole-ring (−C═N–NH−) not only serve as effective adsorption sites but also form strong interactions with I2 via electron transfer from the nitrogen atom of the ligand to I2. The adsorption isotherms and the kinetics were well fitted by the Langmuir model and the pseudo-second-order kinetic model, respectively, suggesting a monolayer chemisorption process. ZIF8-A61 achieved an adsorption capacity of more than 870% compared to the pristine ZIF-8. Based on the experimental and computational results, a plausible mechanism for the adsorption of I2 on ZIF8-A nanocrystals is proposed by considering the host–guest interactions, specifically, those between the amine functional groups and I2. In addition, the reusability and structural stability of the adsorbents were investigated.