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 I₂and CH₃I simultaneously. Here we demonstrate that the I₂adsorption 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 I₂and 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⁻¹at 25 °C). In the dynamic mixed-gas adsorption with 150 ppm of I₂and 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.

Membranes have the potential to substantially reduce energy consumption of industrial chemical separations, but their implementation has been limited owing to a performance upper bound—the trade-off between permeability and selectivity. Although recent developments of highly permeable polymer membranes have advanced the upper bounds for various gas pairs, these polymers typically exhibit limited selectivity. We report a class of hydrocarbon ladder polymers that can achieve both high selectivity and high permeability in membrane separations for many industrially relevant gas mixtures. Additionally, their corresponding films exhibit desirable mechanical and thermal properties. Tuning of the ladder polymer backbone configuration was found to have a profound effect on separation performance and aging behavior.