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Issue 3, 2019
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Molecular-scale structures of uranyl surface complexes on hematite facets

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Abstract

As the fate, transport and bioavailability of U(VI) in subsurface environments are strongly influenced by its adsorption structures on iron minerals such as hematite, we systematically studied the molecular-scale structures of U(VI) complexes formed at the interfaces of hematite and water with periodic density-functional theory (DFT) calculation, extended X-ray absorption fine structure (EXAFS) measurements, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) integrated with X-ray energy dispersive spectroscopy (XEDS). The combined theoretical and experimental results revealed that U(VI) was complexed on three hematite facets in an inner-sphere coordination, but edge-sharing bidentate mononuclear (2E) complexes were formed on {001} facets, and corner-sharing bidentate binuclear (2C) ones were on both {012} and {110} facets. Moreover, the U(VI) adsorption site densities on the {012} and {110} facets of hematite were both about 0.32 #U nm−2, significantly higher than the adsorption site density (0.18 #U nm−2) on the {001} counterpart, which was consistent with the results of STEM-XEDS quantification. The results suggest that the U(VI) adsorption performance with hematite was strongly dependent on the coordination environment of U(VI) on the hematite facets. This study clarifies the molecular-scale structures of the U(VI) surface coordination on different hematite facets and also provides new insights into predicting the long-term fate and transport of highly radiotoxic actinyl ions in subsurface environments.

Graphical abstract: Molecular-scale structures of uranyl surface complexes on hematite facets

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Supplementary files

Article information


Submitted
16 Aug 2018
Accepted
18 Jan 2019
First published
19 Jan 2019

Environ. Sci.: Nano, 2019,6, 892-903
Article type
Paper

Molecular-scale structures of uranyl surface complexes on hematite facets

X. Huang, X. Hou, F. Wang, B. Guo, F. Song, L. Ling, J. Zhao and L. Zhang, Environ. Sci.: Nano, 2019, 6, 892
DOI: 10.1039/C8EN00899J

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