Cu-loaded MOF-303 for iodine adsorption: The roles of Cu species and pyrazole ligands

The capture of toxic radioiodine is an increasingly important priority for the safe development of nuclear energy. Copper is a promising alternative for expensive silver to capture iodine. To develop novel copper-based adsorbents and determine the effect of copper species on iodine adsorption, the metal–organic framework with dual-pyrazole ligands (MOF-303) is employed as the scaffold to bind Cu2+ species. Cu0 nanoparticles were formed after the reduction by NaBH4. The obtained Cu2+-MOF-303 and Cu0-MOF-303 show high iodine uptake capacities at 353 K, 747 mg·g−1 and 837 mg·g−1, respectively. They also show high iodine uptake capacities of more than 300 mg·g−1 at a high temperature (423 K), which are better than other Cu-based adsorbents. Besides, the loading of Cu can enhance the iodine selectivity under humid vapor, and iodine adsorption rate in iodine-cyclohexane solutions. The Cu0 on Cu0-MOF-303 can react with iodine directly via the redox mechanism. For Cu2+-MOF-303, the adjacent pyrazole ligands can chelate with Cu2+ ions strongly and transfer charges to trapped iodine to form polyiodide anions, and thus stable CuI species could also be generated. The strategy of anchoring Cu species using MOF-303 provides large channels for iodine diffusion, and highly-dispersed Cu and N sites for iodine capture.