B18-Core EXAFS
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Diamond Proposal Number(s):
[13606]
Open Access
Abstract: Among all iron oxides, hematite (α-Fe2O3), goethite (α-FeOOH), and ferrihydrite (FeOOH⋅nH2O) are the most common mineral species. While immobilization of Mo6+ by surface adsorption on ferric oxides has been studied extensively, the mechanisms of incorporation in their structure have been researched little. The objective of this study was to investigate the relation between Mo content and its structural incorporation in hematite, goethite, and six-line ferrihydrite by a combination of X-ray absorption spectroscopy (XAS), powder X-ray diffraction (pXRD), and inductively-coupled plasma optical emission spectrometry (ICP-OES). Synthesized in the presence of Mo, the hematite, goethite, and six-line ferrihydrite phases incorporated up to 8.52, 0.03, and 17.49 wt. % Mo, respectively. For hematite and goethite, pXRD analyses did not indicate the presence of separate Mo phases. Refined unit-cell parameters correlated with increasing Mo concentration in hematite and goethite. The unit-cell parameters indicated an increase in structural disorder within both phases and, therefore, supported the structural incorporation of Mo in hematite and goethite. Analysis of pXRD measurements of Mo-bearing six-line ferrihydrites revealed small amounts of coprecipitated akaganéite. X-ray absorption near edge structure (XANES) measurements at the Mo L3-edge indicated a strong distortion of the MoO6 octahedra in all three phases. Fitting of extended X-ray absorption fine structure (EXAFS) spectra of the Mo K-edge supported the presence of such distorted octahedra in a coordination environment similar to the Fe position in the investigated specimen. Incorporation of Mo6+ at the Fe3+-position for both hematite and goethite resulted in the formation of one Fe vacancy in close proximity to the newly incorporated Mo6+ and, therefore, charge balance within the hematite and goethite structures.
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May 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[12643]
Abstract: X-ray absorption fine structure analysis has been successfully used to determine the coordination environment and therefore uptake mechanism towards the uranyl cation for a selection of commercially available ion exchange resins in non-saline and saline conditions ([Cl−] = 22.7 g L−1, 0.64 M) similar to those found in sea water.
The resins tested were Purolite S985, S910 and S957, Dowex M4195, Ps-EDA, Ps-DETA and Ps-PEHA, which contain polyamine, amidoxime, mixed sulfonic/phosphonic acid, bispicolylamine, ethylenediamine, diethylenetriamine and pentaethylenehexamine functional groups, respectively. Purolite S910 and S957 were both found to extract the uranyl cation through a chelation mechanism. The uranium coordination environment on uranyl loaded Purolite S910 was found to be either tetra- or hexa-coordinate in the equatorial plane, with a 2:1 ratio of
amidoxime:uranium in the fit suggesting either monodentate or η2 coordination by two amidoxime groups. The uranium environment for uranyl loaded Purolite S957 was found to be tetra-coordinate in the equatorial plane, with both sulfonic and phosphonic acid groups being involved in sorption. The presence of chloride in the loading solution had no effect on the uranyl coordination environment observed on any of the resins. In contrast, Dowex M4195, Purolite S985, Ps-EDA, Ps-DETA and Ps-PEHA exhibited an anion exchange mechanism for uranyl uptake as the corresponding extended X-ray absorption fine structure (EXAFS) data best fit a [UO2(SO4)3]4− structure.
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Dec 2019
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B18-Core EXAFS
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Open Access
Abstract: The analysis of reference materials is a fundamental part of the data analysis process, in particular for XAS experiments. The beamline users and more generally the XAS community can greatly benefit from the availability of a reliable and wide base of reference sample spectra, acquired in standard and well-characterized experimental conditions. On B18, the Core EXAFS beamline at the Diamond Light Source, in the past years we have collected a series of XAS data on well characterized compounds. This work constitutes the base for a reference sample database, available as a data analysis tool to the general XAS community. This data repository aims to complement the bare spectroscopic information with characterisation, preparation, provenance, analysis and bibliographic references, so improving the traceability of the deposited information. This integrated approach is the base of success and wide distribution of data repositories in other fields, and we hope it will provide on one side a precious facility for the training of students and researchers new to the technique, and at the same time encourage the discussion of best practices in the data analysis process. The database will be open to the contribution of experimental data from the user community, and will provide bibliographic reference information and access control.
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Sep 2019
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B18-Core EXAFS
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Kurt F.
Smith
,
Katherine
Morris
,
Gareth
Law
,
Ellen H.
Winstanley
,
Francis R.
Livens
,
Joshua S.
Weatherill
,
Liam G.
Abrahamsen-Mills
,
Nicholas D.
Bryan
,
J. Frederick W.
Mosselmans
,
Giannantonio
Cibin
,
Stephen
Parry
,
Richard
Blackham
,
Kathleen A.
Law
,
Samuel
Shaw
Diamond Proposal Number(s):
[17243]
Open Access
Abstract: Understanding interactions between iron (oxyhydr)oxide nanoparticles and plutonium is essential to underpin technology to treat radioactive effluents, in clean-up of land contaminated with radionuclides, and to ensure the safe disposal of radioactive wastes. These interactions include a range of adsorption, precipitation and incorporation processes. Here, we explore the mechanisms of plutonium sequestration during ferrihydrite precipitation from an acidic solution. The initial 1 M HNO3 solution with Fe(III)(aq) and 242Pu(IV)(aq) underwent controlled hydrolysis via the addition of NaOH to pH 9. The majority of Fe(III)(aq) and Pu(IV)(aq) was removed from solution between pH 2 and 3 during ferrihydrite formation. Analysis of Pu-ferrihydrite by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy showed that Pu(IV) formed an inner sphere tetradentate complex on the ferrihydrite surface, with minor amounts of PuO2 present. Best fits to the EXAFS data collected from Pu-ferrihydrite samples aged for two- and six- months showed no statistically significant change in the Pu(IV)-Fe oxyhydroxide surface complex despite the ferrihydrite undergoing extensive recrystallisation to hematite. This suggests the Pu remains strongly sorbed to the iron (oxyhydr)oxide surface and could be retained over extended time periods.
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Sep 2019
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B18-Core EXAFS
I18-Microfocus Spectroscopy
I20-EDE-Energy Dispersive EXAFS (EDE)
I20-Scanning-X-ray spectroscopy (XAS/XES)
Controls
Detectors
Optics
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Sofia
Diaz-Moreno
,
Monica
Amboage
,
Mark
Basham
,
Roberto
Boada
,
Nicholas E.
Bricknell
,
Giannantonio
Cibin
,
Thomas
Cobb
,
Jacob
Filik
,
Adam
Freeman
,
Kalotina
Geraki
,
Diego
Gianolio
,
Shusaku
Hayama
,
Konstantin
Ignatyev
,
Luke
Keenan
,
Iuliia
Mikulska
,
J. Frederick W.
Mosselmans
,
James J.
Mudd
,
Stephen A.
Parry
Open Access
Abstract: This manuscript presents the current status and technical details of the Spectroscopy Village at Diamond Light Source. The Village is formed of four beamlines: I18, B18, I20-Scanning and I20-EDE. The village provides the UK community with local access to a hard X-ray microprobe, a quick-scanning multi-purpose XAS beamline, a high-intensity beamline for X-ray absorption spectroscopy of dilute samples and X-ray emission spectroscopy, and an energy-dispersive extended X-ray absorption fine-structure beamline. The optics of B18, I20-scanning and I20-EDE are detailed; moreover, recent developments on the four beamlines, including new detector hardware and changes in acquisition software, are described.
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Jul 2018
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Controls
Data acquisition
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Open Access
Abstract: Although remote access to beamline synchrotron facilities is now a common operation mode at macromolecular crystallography beamlines thanks to substantial efforts in automated processes for sample preparation and handling, experiment planning and analysis, this is still not the case for XAFS beamlines. Here the experience and developments undertaken at LNLS and Diamond in automation are described, in an attempt to tackle the specific challenges posed by the high variability in experimental conditions and configurations that XAFS measurements require.
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Jul 2018
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B18-Core EXAFS
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Diamond Proposal Number(s):
[13606]
Abstract: Among all highly-crystalline iron oxides present in the environment, akaganéite (β-FeO(OH, Cl)) possesses one of the most unconventional structural setups and is a known scavenger for large quantitates of molybdenum (Mo6+). The factors controlling the exact mechanism for Mo6+ incorporation into the akaganéite crystal structure are poorly understood and the ability of dissimilatory Fe(III)-reducing microorganisms to reduce pure akaganéite or Mo-carrying iron oxides is not well characterized. In the current study, we investigated the short-range order around Mo6+ in akaganéite and the fate of Mo6+ under microbially-mediated Fe(III)-reducing conditions. We found that akaganéite can incorporate up to 14.11 ± 0.22 wt% Mo, while the Fe content decreases from 59.70 ± 0.31 to 40.40 ± 0.24 wt%, which indicates a loss of 2–3 Fe atoms for each Mo incorporated. Simultaneously, the crystal structure unit cell parameters a, b and c decrease, while β increases with increasing Mo content. Surprisingly, dissolution of akaganéite by Shewanella loihica PV-4 showed higher dissolution rates of Mo-bearing akaganéite compared to Mo-free akaganéite. Moreover, these results suggest the reduction of Mo6+ is most likely microbially-induced (Fe3+ → Fe2+, Mo6+ + 2Fe2+ → Mo4+ + 2Fe3+). Furthermore, X-ray absorption spectra collected at the Mo L3-edge show a peak-splitting of the white line with a splitting gap of 2.7 eV and an increased amplitude for the first peak. This observation indicates Mo6+ is octahedrally coordinated by oxygen, assuming a strongly distorted MoO6-octhaedron. Fitting of the short-range order around Mo6+ in akaganéite supports the presence of a strongly distorted MoO6-octahedron in a coordination environment similar to the Fe position in akaganéite and the formation of Fe-vacancies close to the newly incorporated Mo6+.
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Oct 2017
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B18-Core EXAFS
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Diamond Proposal Number(s):
[12777]
Abstract: Ca2Mn3O8 exhibits a complex layered structure comprised of Mn3O84− layers separated by Ca2+ ions. In contrast with the more traditional triangular delafossite layered materials the Mn3O84− layers additionally exhibit an ordered vacancy, which forms a ‘bow-tie’ like arrangement of the Mn4+ ions. We report a comprehensive study of the magnetic properties of a series of Ca2Mn3O8 materials with different morphologies. EXAFS and XANES analysis confirm no differences in either manganese environment or oxidation state between materials. Apparent differences in magnetic order from SQUID magnetometry can be rationalised by uncompensated surface spins arising as a result of changes to the surface to volume ratio between morphologies. Furthermore, these data suggest these materials are potentially frustrated in nature, due to the triangular connectivity of Mn4+ spins, with a simple ‘spin-up/spin-down’ (↑↓) antiferromagnetic model unable to explain the data collected.
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Sep 2017
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B18-Core EXAFS
I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[11865]
Abstract: Endochondral ossification is the process by which bone is deposited during development, growth and repair of the skeleton. The regulation of endochondral ossification is extremely important as developmental flaws can result in severe skeletal abnormalities. However, until recently the limitations of available methodologies have restricted our understanding of this fundamental physiological process. The analysis of chemical elements that are intimately associated with discrete biochemical stages of ossification within bone could provide new insight to such processes at the atomic level. In this study we present detailed characterisation of the elemental inventory within actively ossifying bone during development in mice using synchrotron microfocus X-ray techniques. X-ray fluorescence imaging showed differential distributions of Zn, Sr and Ca, which may be correlated with the processes of cartilage replacement (Zn), active ossification (Sr) and fully ossified tissues (Ca). Quantification of these trace elements confirmed their relative distributions. These results represent the first detailed visualisation of local endochondral ossification processes using trace elemental mapping. Such studies have far reaching applications not only in the medical field, but to our understanding of the evolution of the bony skeleton given that trace element inventories have been shown to be preserved through deep time (millions of years).
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Mar 2017
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B18-Core EXAFS
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John B.
Brazier
,
Mark A.
Newton
,
Elena M.
Barreiro
,
Stephen
Parry
,
Luis A.
Adrio
,
Christopher J.
Mulligan
,
Klaus
Hellgardt
,
King Kuok (mimi)
Hii
,
Paul B. J.
Thompson
,
Rachel
Nichols
,
Bao N.
Nguyen
Diamond Proposal Number(s):
[9584]
Open Access
Abstract: The reduction of γ-Al2O3-supported PdO in flowing aqueous ethanol was investigated. Quick EXAFS (QEXAFS) performed at the Pd K-edge reveals that the presence of Cl can have a profound
effect on the reduction process. At low loadings of Pd (1 wt-%), the size dependency of the process is inverted, compared to Cl-free samples. The extent of reduction was found to be dependent
on loading/particles size. It is shown, using in situ QEXAFS at the Cl K- and Pd L3-edges, that residual Cl is not removed by the flowing solvent mixture, even at an elevated temperature of 350 K. The origins of these behaviours are discussed in terms of the differing effects that Cl may have when bonded to oxidic or reduced metal centres and the results were compared to earlier
observations made on the effects of Cl on commercial polyurea encapsulated Pd ENCAT™ NP 30 catalysts.
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Feb 2017
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