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

Abstract

Abstract Radioactive molecular iodine (I 2 ) and organic iodides, mainly methyl iodide (CH 3 I), coexist in the off-gas stream of nuclear power plants at low concentrations, whereas few adsorbents can effectively adsorb low-concentration I 2 and CH 3 I simultaneously. Here we demonstrate that the I 2 adsorption can occur on various adsorptive sites and be promoted through intermolecular interactions. The CH 3 I 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 2 and CH 3 I 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 CH 3 I adsorption capacity (1.53 g·g −1 at 25 °C). In the dynamic mixed-gas adsorption with 150 ppm of I 2 and 50 ppm of CH 3 I, COF-TAPT presents an excellent total iodine capture capacity (1.51 g·g −1 ), surpassing various benchmark adsorbents. This work deepens the understanding of I 2 /CH 3 I adsorption mechanisms, providing guidance for the development of novel adsorbents for related applications.