Amino functionalization of covalent organic frameworks for enhancing adsorption capacity of radioactive iodine

In recent years, the persistent threat of nuclear contamination on human health has highlighted the urgent need for efficient strategies to remove radioactive iodine from nuclear wastes. This work proposes an efficient method to enhance the iodine adsorption capacity of covalent organic framework (COF) adsorbents by amine functionalization using toluene-2,4-diisocyanate (TDI) and N-aminoethylpiperazine (AEP). The resulting TpPa-TDI-AEP demonstrated exceptional iodine adsorption capacities of 6.81 g/g in the gas phase and 1570.50 mg/g in the liquid phase, approxmately 2.4 and 5 times than those of the unmodified COF material, and surpassing the perforamnce of most existing adsorbents. The notable adsorption performances benefit from the abundant nucleophilic nitrogen atoms, which facilitate the formation of charge transporter complexes and enable reversible capture of iodine through strong electrostatic interactions. Density function theory (DFT) calculations confirmed that the piperazine rings in the post-grafted portion promote the generation of higher oxidation state iodides (e.g., I 5 - ) through strong coordination ability. As a result, the modified COF exhibits increased binding energy, a broader adsorption range, and significantly improved capacity for various iodine species. In addition, the reversible nature of polyiodide formation endows the composite excellent cyclic stability and recyclability. Combined with its favorable chemical and thermal stability, low cost, and mild synthesis conditions, make TpPa-TDI-AEP a promising candidate for efficient disposal of radioiodine from nuclear waste.