Enhanced Iodine Capture Using a Postsynthetically Modified Thione-Silver Zeolitic Imidazole Framework

Efficient management of radionuclides that are released from various processes in the nuclear fuel cycle is of significant importance. Among these nuclides, radioactive iodine (mainly ¹²⁹I and ¹³¹I) is a major concern due to the risk it poses to the environment and to human health; thus, the development of materials that can capture and safely store radioactive iodine is crucial. Herein, a novel silver-thione-functionalized zeolitic imidazole framework (ZIF) was synthesized via postsynthetic modification and assessed for its iodine uptake capabilities alongside the parent ZIF-8 and intermediate materials. A solvent-assisted ligand exchange procedure was used to replace the 2-methylimidazole linkers in ZIF-8 with 2-mercaptoimidazole, forming intermediate compound ZIF-8 = S, which was reacted with AgNO₃ to yield the ZIF-8 = S-Ag⁺ composite for iodine uptake. Despite possessing the lowest BET surface area of the derivatives, the Ag-functionalized material demonstrated superior I₂ adsorption in terms of both maximum capacity (550 g I₂/mol) and rapid kinetics (50% loading achieved in 5 h, saturation in 50 h) compared to that of our pristine ZIF-8, which reached 450 g I₂/mol after 150 h and 50% loading in 25 h. This improvement is attributed to the presence of the Ag⁺ ions, which provide a strong chemical driving force to form a stable Ag-I species. The results of this study contribute to a broader understanding of the strategies that can be employed to engineer adsorbents with robust iodine uptake behavior.