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

Radioactive molecular iodine (I₂) and organic iodides, mainly methyl iodide (CH₃I), coexist in the off-gas stream of nuclear power plants at low concentrations, whereas few adsorbents can effectively adsorb low-concentration I₂ and CH₃I simultaneously. Here we demonstrate that the I₂ adsorption can occur on various adsorptive sites and be promoted through intermolecular interactions. The CH₃I 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 I₂ and CH₃I 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 CH₃I adsorption capacity (1.53 g·g^-1 at 25 °C). In the dynamic mixed-gas adsorption with 150 ppm of I₂ and 50 ppm of CH₃I, COF-TAPT presents an excellent total iodine capture capacity (1.51 g·g^-1), surpassing various benchmark adsorbents. This work deepens the understanding of I₂/CH₃I adsorption mechanisms, providing guidance for the development of novel adsorbents for related applications.