Morphology and Electronic Structure of the Oxide Shell on the Surface of Iron Nanoparticles

Journal Article · Thu Jun 04 04:00:00 EDT 2009 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja900353f· OSTI ID:958479

Wang, Chong M. ^[1]; Baer, Donald R. ^[1]; Amonette, James E. ^[1]; Engelhard, Mark H. ^[1]; Antony, Jiji ^[2]; Qiang, You ^[2]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Univ. of Idaho, Moscow, ID (United States)

A iron nanoparticle exposed to air at room temperature will be instantly covered by an oxide shell of typical thickness of ~ 3 nm. This native oxide shell in combination with an underlying iron core determines the physical and chemical behavior of this type of core-shell nanoparticles. One of the great challenges for characterizing this type of nanoparticles is determination of the structure of the oxide shell, as it is FeO, Fe₃O₄, γ-Fe₂O₃, α-Fe₂O₃, or anything else. Significant research effort, mostly based on x-ray diffraction and spectroscopy and electron diffraction and transmission electron microscopy imaging, has been made to determine the structure of this thin layer of iron oxide. Most of the experimental results have been framed with one of the known iron oxide structures, although it is not necessarily true that this thin layer of iron oxide consists of a standard iron oxide. In this paper, the structure of the oxide shell on iron nanoparticle is probed using electron energy loss spectroscopy (EELS) at O K-edge with a spatial resolution of several nanometers (individual particle). Two types of representative particles were studied: particles that are fully oxidized and core-shell particle which possesses a Fe core. We found that the O K-edge spectra collected on the oxide shell in the nanoparticles shows distinctive differences as compared with that of the known iron oxide. Based on finger printing and quantum mechanical calculations results, we conclude that the distances between the absorbing oxygen and the next-nearest neighbor oxygens are more widely distributed than that in bulk Fe₃O₄ for both of these two types of particles. For smaller and fully oxidized particles, there is also a broadened distribution between the absorbing oxygen and the nearest neighbor oxygens. These results clearly demonstrate that the coordination configuration in the oxide shell on Fe nanoparticle is defective as compared with that of their bulk counterpart. Of the two types particles examined in this work, the degree of disorder is larger for the smaller fully oxidized particles.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 958479
• Report Number(s): PNNL-SA--63967; 2573b; 2573; KP1704020
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 25 Vol. 131; ISSN JACSAT; ISSN 0002-7863
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
77 NANOSCIENCE AND NANOTECHNOLOGY
EELS
ELECTRONIC STRUCTURE
Environmental Molecular Sciences Laboratory
Fe nanoparticles
IRON
IRON OXIDES
MORPHOLOGY
NANOSTRUCTURES
core-shell structure
initial oxidation