Chemically Stable Guanidinium Covalent Organic Framework for the Efficient Capture of Low-Concentration Iodine at High Temperatures

Abstract

The capture of radioactive I₂ vapor from nuclear waste under industrial operating conditions remains a challenging task, as the practical industrial conditions of high temperature (≥150 °C) and low I₂ concentration (∼150 ppmv) are unfavorable for I₂ adsorption. We report a novel guanidinium-based covalent organic framework (COF), termed TGDM, which can efficiently capture I₂ under industrial operating conditions. At 150 °C and 150 ppmv I₂, TGDM exhibits an I₂ uptake of ∼30 wt %, which is significantly higher than that of the industrial silver-based adsorbents such as Ag@MOR (17 wt %) currently used in the nuclear fuel reprocessing industry. Characterization and theoretical calculations indicate that among the multiple types of adsorption sites in TGDM, only ionic sites can bond to I₂ through strong Coulomb interactions under harsh conditions. The abundant ionic groups of TGDM account for its superior I₂ capture performance compared to various benchmark adsorbents. In addition, TGDM exhibits exceptionally high chemical and thermal stabilities that fully meet the requirements of practical radioactive I₂ capture (high-temperature, humid, and acidic environment) and differentiate it from other ionic COFs. Furthermore, TGDM has excellent recyclability and low cost, which are unavailable for the current industrial silver-based adsorbents. These advantages make TGDM a promising candidate for capturing I₂ vapor during nuclear fuel reprocessing. This strategy of incorporating chemically stable ionic guanidine moieties in COF would stimulate the development of new adsorbents for I₂ capture and related applications.