Enhanced iodine adsorption: Thiophene-based covalent organic frameworks for efficient capture of molecular iodine and iodomethane

Abstract

To enhance the secure processing of radioactive nuclear fuel, it is essential to develop capture agents that effectively adsorb both molecular and organic iodine species. Traditional iodine capture agents often face limitations in adsorption range, capacity, and reusability. In this study, we synthesized two thiophene-based covalent organic frameworks (COFs), TAPB-DTDA and TAPT-DTDA, via Schiff base reactions. These COFs possess high specific surface areas and electron-rich heteroatoms (N and S) to facilitate iodine capture. The COFs’ large surface areas, combined with electron-rich sites, significantly improve molecular iodine adsorption. Organic iodide capture is achieved through intermolecular interactions via methylation at nitrogen sites. TAPB-DTDA and TAPT-DTDA exhibited high adsorption capacities, with values of 5.95 g/g and 5.38 g/g for static iodine vapor, respectively. Additionally, their K₈₀_% values were 1.05 g g^-1 h^-1 and 2.23 g g^-1 h^-1, respectively, which outperformed the adsorption rates of most iodine adsorbents reported in the literature. For methyl iodide vapor, the adsorption capacities of TAPB-DTDA and TAPT-DTDA reached 1.02 g/g and 2.12 g/g, respectively, with TAPT-DTDA setting a new capacity record among similar materials. This study clarifies the adsorption mechanisms of iodine and methyl iodide in these COFs and provides insights for designing advanced capture agents applicable to nuclear fuel processing.