Analysis of Radioactive Iodine Trapping Mechanism by Zinc-Based Metal–Organic Frameworks with Various N‑Containing Carboxylate Ligands

This study aimed to develop effective adsorbents for capturing radioactive iodine in nuclear power waste gas. Two zinc metal–organic frameworks (Zn-MOFs) were synthesized and found to have favorable properties such as a large surface area, thermal stability, surface rich in π-electron-containing nitrogen, and redox potential. Adsorption experiments revealed maximum capacities of 1.25 and 1.96 g g^–1 for the MOFs at 75 °C, with the pseudo-second-order kinetic model fitting the data well. The Langmuir equation provided a better fit in cyclohexane, with maximum adsorption amounts of 249 and 358 mg g^–1 for Zn-MOF-1 and Zn-MOF-2, respectively. The MOFs were also stable during six cycles of adsorption and desorption. Furthermore, electron transfer occurred due to the synergistic adsorption of Zn, N, and O atoms, resulting in the conversion of some iodine to polyiodide. Zn-MOF-2 exhibited better chemisorption than Zn-MOF-1 due to a smaller highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap. Notably, it was discovered that N-containing radicals had stronger interactions with iodine compared to radicals without N. These findings provide valuable insights into MOF synthesis and environmental protection.