Task-Driven Tailored\nCovalent Organic Framework for\nDynamic Capture of Trace Radioactive CH<sub>3</sub><sup>131</sup>I\nunder High-Flow Rate Conditions

The removal of radioactive gaseous iodine is crucial\nfor sustainable\nnuclear energy development, safe spent fuel management, and secure\ndisposal of radioactive waste and radioactive medical waste. However,\nthe efficient capture of gaseous iodine, particularly methyl iodide,\nunder conditions of low concentration and high-flow rate that are\nrepresentative of real-world scenarios remains underexplored. Herein,\nwe adopted a “theory-first” strategy to design adsorbents\nwith a superior affinity for methyl iodide. The rigorous theoretical\ncalculations for both physisorption and chemisorption have guided\nus to rationally design a piperazine-based covalent organic framework\nmaterial (Pip-COF, Pip = piperazine). The pioneering hot-testing under\ndynamic conditions, featuring low concentrations of 5 ppm radioactive\nCH<sub>3</sub><sup>131</sup>I and a high-flow rate of 600 mL/min,\ndemonstrated Pip-COF’s exceptional capture performance. Pip-COF\nexhibits saturated capacities of 39 mg/g at 75 °C and 78 mg/g\nat 25 °C, significantly outperforming the previously reported\nbest COF (COF-TAPT, 6 mg/g at 25 °C) in this scenario. The gradual\nprocess of methylation and the identification of specific high-affinity\nsites were elucidated by time-resolved FT-IR spectroscopy and density\nfunctional theory (DFT) analysis, consistent with the design philosophy.\nThis study exemplifies rational material design in facilitating the\nseparation of trace pollutants in challenging environments.