Efficient and simultaneous capture of iodine and methyl iodide achieved by a covalent organic framework.

Radioactive molecular iodine (I) and organic iodides, mainly methyl iodide (CHI), coexist in the off-gas stream of nuclear power plants at low concentrations, whereas few adsorbents can effectively adsorb low-concentration I and CHI simultaneously. Here we demonstrate that the I adsorption can occur on various adsorptive sites and be promoted through intermolecular interactions. The CHI adsorption capacity is positively correlated with the content of strong binding sites but is unrelated to the textural properties of the adsorbent. These insights allow us to design a covalent organic framework to simultaneously capture I and CHI at low concentrations. The developed material, COF-TAPT, combines high crystallinity, a large surface area, and abundant nucleophilic groups and exhibits a record-high static CHI adsorption capacity (1.53 g·g at 25 °C). In the dynamic mixed-gas adsorption with 150 ppm of I and 50 ppm of CHI, COF-TAPT presents an excellent total iodine capture capacity (1.51 g·g), surpassing various benchmark adsorbents. This work deepens the understanding of I/CHI adsorption mechanisms, providing guidance for the development of novel adsorbents for related applications.