Macrocyclic Schiff-base covalent organic polymers with synergistic multi-sites for high-temperature iodine/methyl...

Radioactive iodine species (iodine and methyl iodide) released from nuclear fuel reprocessing pose a persistent threat to environmental integrity and human health. Conventional adsorbents suffer from loss of dynamic adsorption performance for iodine (I₂) and methyl iodide (CH₃I) under high-temperature conditions, rendering them ineffective in practical reprocessing scenarios. In this study, covalent organic polymers (COPs) with affinity for both iodine and methyl iodide were rationally designed, and their adsorption properties were modulated by adjusting the nucleophilic N-sites and π-electron density around functionalized monomers. Through Schiff-base reaction, three COPs，TCFD-TAPT，TCFD-TAPB and TCFD-ETTA were obtained for I elemental adsorption. Except for the outstanding static uptake, the dynamic capacities of CH₃I and I₂ were also determined. The results showed that TCFD-TAPT exhibited specific adsorption of CH₃I at 150 °C with a dynamic capacity of 0.069 g/g (0.35 mg/min), whereas TCFD-TAPB dynamically captured I₂ with an uptake of 0.41 g/g (3.91 mg/h) at the same temperature, surpassing most of reported COPs. This work illustrates cooperative site recognition for efficient iodine species capture and offers new insights into the design of advanced polymeric adsorbents. The developed COPs show great potential for practical applications in nuclear off-gas treatment and radioactive iodine management.