Capture and immobilization of gaseous ruthenium tetroxide RuO4 in the UiO-66-NH2 metal–organic framework

Abstract

¹⁰⁶Ru is a radioactive isotope usually generated by the nuclear industry within power plant reactors. During a nuclear accident, ¹⁰⁶Ru reacts with oxygen, leading to the production of highly volatile ruthenium tetroxide RuO₄. The combination of volatility and radioactivity makes ¹⁰⁶RuO₄, one of the most radiotoxic species and justifies the development of a specific setup for its capture and immobilization. In this study, we report for the first time the capture and immobilization of gaseous RuO₄ within a porous metal–organic framework (UiO-66-NH₂). We used specific installation for the production of gaseous RuO₄ as well as for the quantification of this gas trapped within the filtering medium. We proved that UiO-66-NH₂ has remarkable affinity for RuO₄ capture, as this MOF exhibited the worldwide highest RuO₄ decontamination factor (DF of 5745), hundreds of times higher than the DF values of sorbents daily used by the nuclear industry (zeolites or activated charcoal). The efficiency of UiO-66-NH₂ can be explained by its pore diameters well adapted to the capture and immobilization of RuO₄ as well as its conversion into stable RuO₂ within the pores. This conversion corresponds to the reactivity of RuO₄ with the MOF organic sub-network, leading to the oxidation of terephthalate ligands. As proved by powder X-ray diffraction and NMR techniques, these modifications did not decompose the MOF structure.