Optimizing iodine adsorption in functionalized metal-organic frameworks via an unprecedented positional isomerism strategy
Zi‐Jian Li, Juejing Liu, Guangtao Zhang, Chris J. Benmore, Linjuan Zhang, Xiao‐Feng Guo, Jian Lin
Abstract
Porous metal–organic frameworks (MOFs) have emerged as highly promising adsorbents for capturing radioiodine, a predominant fission product released during nuclear fuel reprocessing. However, systematic investigations into the correlation between MOF structure and iodine uptake capacity remain scarce. Here, we present a novel approach to enhance the iodine adsorption capacity of MOFs by optimizing linker functionalization. Using ligand-functionalized thorium-based MOFs as a structural platform, we demonstrate that ortho -amino-substitution near the node of the dicarboxylate linker significantly increases iodine adsorption capacity compared to meta -amino-substitution, where the amino groups are directed away from the node. Specifically, ortho -substituted Th-UiO-68-3,3”-(NH 2 ) 2 exhibits higher iodine uptake capacities than the meta -substituted Th-UiO-68-2,2”-(NH 2 ) 2 via both vapor diffusion-based (2.042 vs. 1.087 g/g) and solution-based (0.841 vs. 0.784 g/g) processes. Notably, the I 2 vapor adsorption capacity (2.042 g/g) of Th-UiO-68-3,3”-(NH 2 ) 2 represents the second highest among all reported Th-MOFs. Pair distribution function (PDF) studies reveal that the superior iodine uptake performance of ortho -functionalized MOFs can be attributed to the reduced steric hindrance of the amino groups compared with the meta -substituted variants. This research highlights how positional isomerism and its subtle alterations can significantly influence host–guest interactions, extending beyond simple structural considerations.