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Dehydration of the Uranyl Peroxide Studtite, [UO2(η2-O2)(H2O)2]·2H2O, Affords a Drastic Change in the Electronic Structure: A Combined X-ray Spectroscopic and Theoretical Analysis

Journal Article · · Inorganic Chemistry
 [1];  [1];  [2];  [3];  [2];  [1];  [4];  [3];  [2]
  1. Institute for Nuclear Waste Disposal (INE), Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany
  2. School of Chemistry, University of Dublin, Trinity College, College Green, Dublin 2, Ireland
  3. Institute of Energy and Climate Research, IEK-6, Nuclear Waste Management and Reactor Safety, Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Strasse, 52428 Jülich, Germany; JARA High-Performance Computing, Schinkelstrasse 2, 52062 Aachen, Germany
  4. Pacific Northwest National Laboratory, MSIN K8-96, P.O. Box 999, Richland, Washington 99352, United States
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The dehydration of studtite, [UO2(2-O2)(H2O)2]·2H2O, to metastudtite, [UO2(2-O2)(H2O)2], uranyl peroxide minerals that are major oxidative alteration phases of UO2 under conditions of geological storage, has been studied using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy. XPS of the U 4f region shows small but significant differences between studtite and metastudtite, with the 4f binding energy of studtite the highest reported for a uranyl mineral studied by this technique. Further information on the changes in the electronic structure was elucidated using U M4-edge High Energy Resolution XANES (HR-XANES) spectroscopy, which directly probes f-orbital states. The transition from the 3d to the 5f* orbital is sensitive to variations of the U=Oaxial bond length and to changes in the bond covalency. We report evidences that the covalence in the uranyl fragment decreases upon dehydration. Photoluminescence spectroscopy at near liquid helium temperatures reveals significant spectral differences between the two materials, correlating with the X-ray spectroscopy results. A theoretical investigation has been conducted on the structures of both studtite and metastudtite and benchmarked to the HR-XANES spectra. These illustrate the sensitivity of the 3d to the 5f * transition towards U=Oaxial bond variation.
Research Organization:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Organization:
USDOE
DOE Contract Number:
AC05-76RL01830
OSTI ID:
1423413
Report Number(s):
PNNL-SA-130840; 49695; KP1704020
Journal Information:
Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 4 Vol. 57; ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English

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