Nanomaterials often exhibit novel and uniquely useful physical and chemical properties not observed in their larger, bulk counterparts. The sheet-structured uranyl peroxide mineral studtite comprises one of the common ‘bulk’ (sensu lato) alteration phases of used nuclear fuel, due to the radiolysis of water it is in contact with.1 Under such intense fields of ionizing radiation, studtite is comparatively more susceptible to alteration with respect to other uranyl minerals; full amorphization is rapid after absorbing 7.3 x 106 Gy from the TEM electron beam.2 However, when a similar uranyl peroxide sheet topology is instead assembled into the spherical nanocapsule U60 (Figure 1), its rigidity, capsule-like form, and crystallinity are preserved in the solid state and as discrete macroanions in solution after receiving comparable doses of γ-radiation (in excess of 5.3 x 106 Gy). A combination of ESI-MS, Raman spectroscopy, ammonia-gas sensing electrode measurements, 7Li NMR, and pinhole SAXS suggest that fragmentation of the nanocapsules subsequent to exposure may be dominated by cation exchange processes. Substitution of radiolytically produced ammonium with lithium leads to minor size and spectroscopic variations that give insight into the mechanism of fragmentation. Coordinating-cation dynamicity heavily influences nanocapsule stability in an induced irradiation environment. The high surface to volume ratio of the hollow nanocapsule and open ring topology, in relation to bulk studtite, allows the rapid and facile transfer of radiolytic species and some encapsulated cations—significantly enhancing its radiation stability. Basic correlations between the size and topology of a nanocapsule and its stability in gamma radiation are compared using the smaller U24-Li and U24-K. References: [1] Armstrong, C. R., et al. PNAS, 2012,109, 1874-1877. [2] Rey, A., et al. Am. Mineral. 2009, 94, 229-235.

Stability and cation exchange dynamics of γ-irradiated actinyl peroxide nanocapsules

249th National Meeting (2015)

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