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

Abstract

In spent nuclear fuel (SNF) reprocessing plants, various off-gas systems (OGS) are known to contain significant amounts of radioactive 129 I 2, CH 3 129 I, and CH 3 CH 2 129 I. 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 I 2, CH 3 I, and CH 3 CH 2 I under various conditions. COF-OH 0 exhibited one of the highest reported adsorption capacities for organic iodides, reaching 1.6 g g –1 for CH 3 I and 1.1 g g –1 for CH 3 CH 2 I at 75 °C. COF-OH 0 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-OH 0 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 I 2 and iodine species uptake mechanisms while contributing to the development of the adsorbents.