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Title: Oxygen K-Edge Emission and Absorption Spectroscopy of Iron Oxyhydroxide Nanoparticles

Abstract

Transition metal oxide and oxyhydroxide nanoparticles are the focus of considerable current interest in geochemistry. Much progress has been made in understanding the structure and phase relationships in mineral nanoparticles, but the effects of small size and modified surface structure on reactivity remains an outstanding problem. Common environmental nanoparticles have been shown to exhibit enhanced chemical reactivity relative to bulk mineral surfaces, but the origin of this behavior is not well established. We studied the electronic structure component of mineral reactivity by comparing soft x-ray absorption and emission spectra of bulk goethite ({alpha}-FeOOH) with spectra obtained from {approx} 6 nm FeOOH nanoparticles and larger FeOOH nanoparticles obtained by hydrothermal coarsening. The semiconductor band gap is reduced in the FeOOH nanoparticles, mainly due to the presence of additional states in the upper valence band. We performed ab initio simulation of the electronic structure of oxygen sites at the 010 surface of goethite, and observe that oxygen sites with reduced metal coordination contribute to the O 2p DOS at higher binding energy. Hence we conclude that FeOOH nanoparticle surfaces are more disordered than the surfaces of goethite, and that this structural component is likely the dominant cause of enhanced rates of reductivemore » dissolution.« less

Authors:
;  [1];  [2]; ;  [3];  [4]
  1. Earth Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States)
  2. Department of Physical Sciences, Chapman University, Orange, CA 92866 (United States)
  3. Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States)
  4. Chemical Sciences, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States)
Publication Date:
OSTI Identifier:
21054729
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 882; Journal Issue: 1; Conference: XAFS13: 13. international conference on X-ray absorption fine structure, Stanford, CA (United States), 9-14 Jul 2006; Other Information: DOI: 10.1063/1.2644643; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; BINDING ENERGY; ELECTRONIC STRUCTURE; EMISSION SPECTRA; GOETHITE; IRON; IRON HYDROXIDES; NANOSTRUCTURES; OXYGEN; PARTICLE SIZE; PARTICLES; REACTIVITY; SEMICONDUCTOR MATERIALS; SOFT X RADIATION; SURFACES; VALENCE; X-RAY SPECTRA

Citation Formats

Gilbert, Benjamin, Nico, Peter S., Kim, Christopher S., Dong, Chung-Li, Guo, Jinghua, and Shuh, David K. Oxygen K-Edge Emission and Absorption Spectroscopy of Iron Oxyhydroxide Nanoparticles. United States: N. p., 2007. Web. doi:10.1063/1.2644643.
Gilbert, Benjamin, Nico, Peter S., Kim, Christopher S., Dong, Chung-Li, Guo, Jinghua, & Shuh, David K. Oxygen K-Edge Emission and Absorption Spectroscopy of Iron Oxyhydroxide Nanoparticles. United States. doi:10.1063/1.2644643.
Gilbert, Benjamin, Nico, Peter S., Kim, Christopher S., Dong, Chung-Li, Guo, Jinghua, and Shuh, David K. Fri . "Oxygen K-Edge Emission and Absorption Spectroscopy of Iron Oxyhydroxide Nanoparticles". United States. doi:10.1063/1.2644643.
@article{osti_21054729,
title = {Oxygen K-Edge Emission and Absorption Spectroscopy of Iron Oxyhydroxide Nanoparticles},
author = {Gilbert, Benjamin and Nico, Peter S. and Kim, Christopher S. and Dong, Chung-Li and Guo, Jinghua and Shuh, David K.},
abstractNote = {Transition metal oxide and oxyhydroxide nanoparticles are the focus of considerable current interest in geochemistry. Much progress has been made in understanding the structure and phase relationships in mineral nanoparticles, but the effects of small size and modified surface structure on reactivity remains an outstanding problem. Common environmental nanoparticles have been shown to exhibit enhanced chemical reactivity relative to bulk mineral surfaces, but the origin of this behavior is not well established. We studied the electronic structure component of mineral reactivity by comparing soft x-ray absorption and emission spectra of bulk goethite ({alpha}-FeOOH) with spectra obtained from {approx} 6 nm FeOOH nanoparticles and larger FeOOH nanoparticles obtained by hydrothermal coarsening. The semiconductor band gap is reduced in the FeOOH nanoparticles, mainly due to the presence of additional states in the upper valence band. We performed ab initio simulation of the electronic structure of oxygen sites at the 010 surface of goethite, and observe that oxygen sites with reduced metal coordination contribute to the O 2p DOS at higher binding energy. Hence we conclude that FeOOH nanoparticle surfaces are more disordered than the surfaces of goethite, and that this structural component is likely the dominant cause of enhanced rates of reductive dissolution.},
doi = {10.1063/1.2644643},
journal = {AIP Conference Proceedings},
number = 1,
volume = 882,
place = {United States},
year = {Fri Feb 02 00:00:00 EST 2007},
month = {Fri Feb 02 00:00:00 EST 2007}
}
  • Transition metal oxide and oxyhydroxide nanoparticles are the focus of considerable current interest in geochemistry. Much progress has been made in understanding the structure and phase relationships in mineral nanoparticles, but the effects of small size and modified surface structure on reactivity remains an outstanding problem. Common environmental nanoparticles have been shown to exhibit enhanced chemical reactivity relative to bulk mineral surfaces, but the origin of this behavior is not well established. We studied the electronic structure component of mineral reactivity by comparing soft x-ray absorption and emission spectra of bulk goethite ({alpha}-FeOOH) with spectra obtained from {approx}6 nm FeOOHmore » nanoparticles and larger FeOOH nanoparticles obtained by hydrothermal coarsening. The semiconductor band gap is reduced in the FeOOH nanoparticles, mainly due to the presence of additional states in the upper valence band. We performed ab initio simulation of the electronic structure of oxygen sites at the 010 surface of goethite, and observe that oxygen sites with reduced metal coordination contribute to the O 2p DOS at higher binding energy. Hence we conclude that FeOOH nanoparticle surfaces are more disordered than the surfaces of goethite, and that this structural component is likely the dominant cause of enhanced rates of reductive dissolution.« less
  • Surface functional groups on carbon materials are critical to their surface properties and related applications. Many characterization techniques have been used to identify and quantify the surface functional groups, but none is completely satisfactory especially for quantification. In this work, we used oxygen K-edge X-ray absorption near edge structure (XANES) spectroscopy to identify and quantify the oxygen containing surface functional groups on carbon materials. XANES spectra were collected in fluorescence yield mode to minimize charging effect due to poor sample conductivity which can potentially distort XANES spectra. The surface functional groups are grouped into three types, namely carboxyl-type, carbonyl-type, andmore » hydroxyl-type. XANES spectra of the same type are very similar while spectra of different types are significantly different. Two activated carbon samples were analyzed by XANES. The total oxygen contents of the samples were estimated from the edge step of their XANES spectra, and the identity and abundance of different functional groups were determined by fitting of the sample XANES spectrum to a linear combination of spectra of the reference compounds. It is concluded that oxygen K-edge XANES spectroscopy is a reliable characterization technique for the identification and quantification of surface functional groups on carbon materials.« less
  • Here, the local structure about Fe(II) and Fe(III) in silicate melts was investigated in-situ using iron K-edge X-ray absorption near-edge structure (XANES) spectroscopy. An aerodynamic levitation and laser heating system was used to allow access to high temperatures without contamination, and was combined with a chamber and gas mixing system to allow the iron oxidation state, Fe 3+/ΣFe, to be varied by systematic control of the atmospheric oxygen fugacity. Eleven alkali-free, mostly iron-rich and depolymerized base compositions were chosen for the experiments, including pure oxide FeO, olivines (Fe,Mg) 2SiO 4, pyroxenes (Fe,Mg)SiO 3, calcic FeO-CaSiO 3, and a calcium aluminosilicatemore » composition, where total iron content is denoted by FeO for convenience. Melt temperatures varied between 1410 and 2160 K and oxygen fugacities between FMQ – 2.3(3) to FMQ + 9.1(3) log units (uncertainties in parentheses) relative to the fayalite-magnetite-β-quartz (FMQ) buffer.« less