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.