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

Radioactive molecular iodine (I-2) and methyl iodide (CH3I) coexist in the off-gas stream of nuclear power plants at low concentrations and only few adsorbents can effectively adsorb low-concentration I-2 and CH3I simultaneously. Here, the authors demonstrate simultaneous capture of I-2 and CH3I at low concentrations by exploiting different adsorptive sites in a covalent organic framework. Radioactive molecular iodine (I-2) 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 I-2 and CH3I simultaneously. Here we demonstrate that the I-2 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 I-2 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 center dot g(-1) at 25 degrees C). In the dynamic mixed-gas adsorption with 150 ppm of I-2 and 50 ppm of CH3I, COF-TAPT presents an excellent total iodine capture capacity (1.51 g center dot g(-1)), surpassing various benchmark adsorbents. This work deepens the understanding of I-2/CH3I adsorption mechanisms, providing guidance for the development of novel adsorbents for related applications.

Automated summary

The authors demonstrate the simultaneous capture of low-concentration radioactive molecular iodine and organic iodides using a covalent organic framework. The developed material, COF-TAPT, exhibits high crystallinity, a large surface area, and abundant nucleophilic groups, resulting in excellent adsorption capacity for both iodine species.