Uranyl Peroxide Nanocluster (U₆₀) Persistence and Sorption in the Presence of Hematite

The presence of uranium-based nanomaterials in environmental systems may significantly impact our current understanding of the fate and transport of U(VI). Sorption of the uranyl peroxide nanocluster [(UO₂)(O₂)(OH)]₆₀^60- (U₆₀) to hematite (α-Fe₂O₃) was studied using batch sorption experiments with varying U₆₀, hematite, and alkali electrolyte (i.e., NaCl, KCl, and CsCl) concentrations. Data from electrospray ionization mass spectrometry and centrifugal microfiltration revealed that U₆₀ persisted in the presence of hematite and the background electrolyte for at least 120 days. K⁺ ions were removed from solution with uranium whereas Li⁺ ions remained in solution, indicating that the U₆₀ cluster behaved like an anion and that the Li⁺ ions did not play a significant role in the sorption mechanism. Analysis of the reacted mineral surface using X-ray photoelectron and Raman spectroscopies confirmed the presence of U(VI) and uranyl species with bridged peroxo groups associated with the mineral surface. These results indicate that uranyl peroxide nanoclusters may persist in the aqueous phase under environmentally relevant conditions for reasonably long periods of time, as compared to that of the uranyl cation.