Influence on Crystallinity of Nanoporous Covalent Organic Frameworks for Efficient Sequestration of Organic Iodides and Iodine

In spent nuclear fuel (SNF) reprocessing plants, various off-gas systems (OGS) are known to contain significant amounts of radioactive 129I2, CH3129I, and CH3CH2129I. The capture and immobilization of volatile contaminants, such as iodine, methyl iodide, and ethyl iodide, is a critical challenge. Herein, we report four crystalline nanoscalar COFs with large surface areas and Lewis basic centers that enable effective capture of I2, CH3I, and CH3CH2I under various conditions. COF-OH0 exhibited one of the highest reported adsorption capacities for organic iodides, reaching 1.6 g g–1 for CH3I and 1.1 g g–1 for CH3CH2I at 75 °C. COF-OH0 exhibited impressive static and dynamic iodine capture capacities of 4.46 and 2.8 g g–1, respectively, at 75 °C. Treatment with radioactive organic iodides (ROIs) induces a postsynthetic modification that converts imine N sites to cationic centers through quaternization. The resulting cationic framework is effective for selective adsorption of toxic anionic contaminants from water. In dynamic adsorption studies, COF-OH0 demonstrated exceptional capture capacities of 1.83 and 1.95 g g–1 for triiodide anion and molecular iodine from water, respectively. Our findings suggest that an increase in the number of −OH groups within these tautomeric COFs reduces the capacity to capture iodine and organic iodide. Mechanistic insights were provided by in silico studies and analytical techniques, enhancing the understanding of I2 and iodine species uptake mechanisms while contributing to the development of the adsorbents.