Gamma-Ray-Induced Formation of Uranyl Peroxide Cage Clusters

Abstract

Aqueous solutions of lithium uranyl triperoxide, Li4[UO2(O2)3] (LiUT), were irradiated with gamma rays at room temperature and found to form the uranyl peroxide cage cluster, Li24[(UO2)­(O2)­(OH)]24 (Li–U24). Raman spectroscopy and 18O labeling were used to identify the Raman-active vibrations of LiUT. With these assignments, the concentration of LiUT was tracked as a function of radiation dose. A discrepancy between monomer removal and cluster formation suggests that the reaction proceeds by the assembly of an intermediate. Non-negative matrix factorization was used to separate Raman spectra into components and resulted in the identification of a unique intermediate species. Much of the conversion appears to be driven by water radiolysis products, particularly the hydroxyl radical. This differs from the 18O-labeled copper-catalyzed formation of U24, which progresses at a steady rate with no observation of intermediates. Li–U24 in solution decomposes at high radiation doses resulting in a solid insoluble product similar to Na-compreignacite, Na2(UO2)6O4(OH)6·7H2O, which contains uranyl oxyhydroxy sheets.

Recent advances in uranium-containing polyoxometalates

“…Very recently, Burns also used γ-ray radiation to promote the conversion of Li 4 [UO 2 (O 2 ) 3 ] into Li 24 [(UO 2 )(O 2 )(OH)] 24 in aqueous solutions. 111 They used ex situ Raman spectroscopy and 18 O labeling to track this transformation and found the dependence relationship between Li 4 [UO 2 (O 2 ) 3 ], intermediates of uranyl peroxide clusters, and the radiation dose. These two works show us direct cases to understand the formation mechanism of POMs from monomer to derived species.…”

Are U–U Bonds Inside Fullerenes Really Unwilling Bonds?

“…Understanding how atoms stay together to form stable structures is at the core of chemistry. − In nature, uranium is generally found as an oxide, showing several oxidation states . Huge advances have been made in the chemistry of the f-elements over the last decades, , including the synthesis of complexes containing actinide–ligand multiple bonds, or uranyl peroxide capsules with high oxidation states. − Nevertheless, much less experimental information is available about the formation of diactinides. Since the initial studies, it became clear that the propensity to form U-ligand bonds was greater than that for forming U–U bonds .…”

Solid-State Transformation of Uranyl Peroxide Materials through High-Level Irradiation

“…Irradiation of studtite in different aqueous systems relevant to the open environment has also been explored . Isolated uranyl triperoxide polyhedral with Li and Ca counter cations (LiUT and CaUT salts) have been studied with gamma irradiation revealing the ionization of the terminal peroxide group(s), while in solution, LiUT forms a uranyl peroxide cage cluster (U 24 ) at lower doses and at higher doses forms a uranyl oxyhydroxide sheet structure …”

“…18 Isolated uranyl triperoxide polyhedral with Li and Ca counter cations (LiUT and CaUT salts) have been studied with gamma irradiation revealing the ionization of the terminal peroxide group(s), 19 while in solution, LiUT forms a uranyl peroxide cage cluster (U 24 ) at lower doses and at higher doses forms a uranyl oxyhydroxide sheet structure. 20 In this study, we examine the NaUT salt up to 3MGy with γirradiation and up to 225 MGy of He-ion irradiation in the presence and absence of H 2 O. We follow the solid-state ■ RESULTS AND DISCUSSION Gamma-Irradiation.…”