I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[6042, 7087]
Abstract: The cellular and subcellular distributions of trace elements can provide important clues to understanding how the elements are transported and stored in plant cells, but mapping their distributions is a challenging task. The distributions of arsenic, iron, zinc, manganese and copper, as well as physiologically related macro-elements, were mapped in the node, internode and leaf sheath of rice (Oryza sativa) using synchrotron X-ray fluorescence (S-XRF) and high-resolution secondary ion mass spectrometry (NanoSIMS). Although copper and silicon generally showed cell wall localization, arsenic, iron and zinc were strongly localized in the vacuoles of specific cell types. Arsenic was highly localized in the companion cell vacuoles of the phloem in all vascular bundles, showing a strong co-localization with sulfur, consistent with As(III)–thiol complexation. Within the node, zinc was localized in the vacuoles of the parenchyma cell bridge bordering the enlarged and diffuse vascular bundles, whereas iron and manganese were localized in the fundamental parenchyma cells, with iron being strongly co-localized with phosphorus in the vacuoles. The highly heterogeneous and contrasting distribution patterns of these elements imply different transport activities and/or storage capacities among different cell types. Sequestration of arsenic in companion cell vacuoles may explain the limited phloem mobility of arsenite.
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Sep 2013
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[17819]
Abstract: The use of solar energy to activate chemical pathways in a sustainable manner drives the development in photocatalysis. While catalyst optimisation is a major theme in this pursuit, the development of novel photocatalytic reactors to enhance productivity is also imperative. In this work we combine, for the first time, microstructured optical fibre technology with photocatalysis, creating a photocatalytic microreactor coated with titania decorated with palladium nanoparticles. By doing so, we can create a system capable of effectively combining photons, liquids and gases within a monolithic, highly confined, transparent silica geometry. We utilise a range of characterisation techniques to selectively focus on the photocatalyst that resides exclusively within the internal capillaries of this system. In doing so we validate our design approach, and demonstrate the ability to simultaneously control both nanoparticle size and metal content. Further, we justify our unique design, showing its activity in photocatalytic hydrogen generation from water. In doing so highlighting the importance in developing light propagation properties from optical fibres, and the significant potential of this technology in the expansive photocatalysis landscape.
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Feb 2020
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[6174]
Abstract: Since deposited dredged sediments are rich in metallic contaminants, they present a risk for environment. This work aims to study dredged sediments chemical composition, identify metal-carrier minerals and understand their mobility. Combining chemical and spectroscopic techniques at multi-scale for an integrative approach of trace elements (zinc, lead, iron) behaviour is therefore necessary. The global mineralogy and the chemistry of the sediment were determined by X-ray diffraction and fluorescence (XRF), respectively. Zn and Pb enriched fractions were separated using a sequential chemical extraction procedure and measured by inductively coupled plasma atomic emission and mass spectroscopy. Microanalyses using scanning electron microscopy (SEM), electron microprobe microanalysis (EPMA), combined with synchrotron radiation X-ray fluorescence (?-XRF) were carried out to characterize mineralogical phases and identify Zn and Pb carrier minerals. Iron oxyhydroxides and iron sulphides were consistently identify as Zn and Pb carriers. The assumption that carbonate fraction was the major Zn carried phase, as demonstrated by chemical extraction results, was not verified by EPMA or ?-XRF.
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Mar 2012
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[7755, 3895]
Open Access
Abstract: The use of fluorescence full spectral micro-X-ray absorption near-edge structure (µXANES) mapping is becoming more widespread in the hard energy regime. This experimental method using the Ca K-edge combined with micro-X-ray diffraction (µXRD) mapping of the same sample has been enabled on beamline I18 at Diamond Light Source. This combined approach has been used to probe both long- and short-range order in calcium carbonate granules produced by the earthworm Lumbricus terrestris. In granules produced by earthworms cultured in a control artificial soil, calcite and vaterite are observed in the granules. However, granules produced by earthworms cultivated in the same artificial soil amended with 500 p.p.m. Mg also contain an aragonite. The two techniques, µXRD and µXANES, probe different sample volumes but there is good agreement in the phase maps produced.
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Jan 2014
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I18-Microfocus Spectroscopy
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Feb 2013
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I18-Microfocus Spectroscopy
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Open Access
Abstract: We have determined the chemical speciation of dissolved sulfur and the sulfur concentration at fixed oxygen and sulfur fugacities for a wide range of silicate melt compositions (from Fe-rich basalt to dacite). Each melt was equilibrated at 1300 °C and 1-atmosphere pressure at oxygen fugacities (fO2) between −1.67 and +1.6 log units relative to the Fayalite–Magnetite–Quartz (FMQ) buffer and absolute sulfur fugacities between −5.1 and −1.2 log units. The fO2 and fS2 of the experiments were controlled by using gas mixtures of CO–CO2–SO2. The speciation of sulfur in the quenched glasses was determined using both X-ray Absorption Near-Edge Spectroscopy (XANES), and from the dependence of equilibrium sulfur concentration on the fS2/fO2 ratio measured by secondary-ion mass spectrometry (SIMS) and electron microprobe.
The speciation of dissolved sulfur in each melt undergoes an abrupt transformation from S2− to S6+ with increasing fO2, and this transition is shifted ∼0.5 log units higher in fO2 as melt FeO concentration increases from ∼5 wt% to ∼18 wt%. Since sulfide concentrations at constant fO2 and fS2 are consistently greater for more FeO-rich melts, the compositional effect on speciation may be explained by the well-known sensitivity of the sulfide capacity (
CS2−
) of the melt to FeO concentration.
S6+/S2− ratios for the glasses exhibit a linear relationship with Fe3+/Fe2+, indicating that the redox couples for iron and sulfur can be directly related to one another. We used thermodynamic data to model the interrelationship between Fe and S oxidation states in terms of the equilibrium
FeS+8FeO1.5=8FeO+FeSO4
Fitting the data to our experiments at 1300 °C we obtained the following expression for the temperature-dependence of speciation:
log(S6+S2−)=8log(Fe3+Fe2+)+8.7436×106T2−27703T+20.273
This equation fits the data for all our compositions and is also consistent with earlier results at 1050 °C and 950 °C. We used the interdependence of S and Fe oxidation states to infer electron transfer between Fe2+ and S6+ during quenching of glasses from Mauna Kea, Hawaii. The effect is sufficient to cause significant overestimation of equilibrium Fe3+/ΣFe in natural glasses and corresponding overestimate of fO2 by about 0.8 log units.
Glasses equilibrated under the most oxidizing conditions (containing S6+ only) have equilibrium S concentrations that are negatively correlated with their mole fractions of tetrahedral (Si + Ti) cations.
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Feb 2019
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I18-Microfocus Spectroscopy
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Marta
Ugarte
,
Geoffrey W
Grime
,
Gillian
Lord
,
Tina
Geraki
,
Joanna
Collingwood
,
Mary
Finnegan
,
Hannah
Farnfield
,
Michael
Merchant
,
Melanie
Bailey
,
N. I.
Ward
,
Peter
Foster
,
Paul N
Bishop
,
Neville N
Osborne
Diamond Proposal Number(s):
[7454]
Abstract: Inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify the total amount of trace elements in retina from adult male Sprague-Dawley rats (n = 6). Concentration of trace elements within individual retinal areas in frozen sections of the fellow eye was established with the use of two methodologies: (1) particle-induced X-ray emission (PIXE) in combination with 3D depth profiling with Rutherford backscattering spectrometry (RBS) and (2) synchrotron X-ray fluorescence (SXRF) microscopy. The most abundant metal in the retina was zinc, followed by iron and copper. Nickel, manganese, chromium, cobalt, selenium and cadmium were present in very small amounts. The PIXE and SXRF analysis yielded a non-homogenous pattern distribution of metals in the retina. Relatively high levels of zinc were found in the inner part of the photoreceptor inner segments (RIS)/outer limiting membrane (OLM), inner nuclear layer and plexiform layers. Iron was found to accumulate in the retinal pigment epithelium/choroid layer and RIS/OLM. Copper in turn, was localised primarily in the RIS/OLM and plexiform layers. The trace elements iron, copper, and zinc exist in different amounts and locations in the rat retina.
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Oct 2012
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[8203, 9597]
Abstract: We present a newly developed capsule design that resolves some common problems associated with the moni- toring and control of oxygen fugacity (fO2) in high-pressure piston cylinder experiments. The new fO2 control assem- bly consists of an AuPd outer capsule enclosing two inner capsules: one of AuPd capsule containing the experimental charge (including some water), and the other of Pt containing a solid oxygen buffer plus water. The inner capsules are sepa- rated by crushable alumina. The outer capsule is surrounded by a Pyrex sleeve to simultaneously minimise hydrogen loss from the cell and carbon infiltration from the graphite fur- nace. Controlled fO2 experiments using this cell design were carried out at 1.0 GPa and 1,000 °C. We used NiPd, CoPd and (Ni, Mg)O fO2 sensors, whose pressure sensitivity is well cal- ibrated, to monitor the redox states achieved in experiments buffered by ReReO2, NiNiO and CoCoO, respectively. Results for the fO2 sensors are in good agreement with the intended fO2 established by the buffer, demonstrating excel- lent control for durations of 2448 h, with uncertainties less than ± 0.3 log bar units of fO2.
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Jan 2015
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[11314]
Abstract: Osmium nanocrystals can be fabricated by electron (3–50 nm, formed by atom migration), 785–815 nm laser (20–50 nm, in micelle islands), and microwave (ca. 1 nm in arrays, >100 mg scale) irradiation of a polymer-encapsulated OsII carborane; microfocus X-ray absorption studies at the Os LIII-edge show differences between the three preparation methods, suggesting that the electron-beam irradiated materials have a significant support interaction and/or surface oxidation, while the laser and microwave samples are more like metallic osmium.
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Oct 2017
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[6601, 7744]
Abstract: Arsenic (As) is one of four metals/metalloids in tobacco being considered for regulation. In vitro toxicological response to As varies substantially, determined primarily by valence and compound speciation, and inorganic arsenite (As(III)) compounds are the most toxic to humans. This study uses X-ray absorption near edge structure (XANES) to determine valence states of As from the tobacco plant to the crucial combustion stage that creates respirable smoke. Samples studied include cultivated plants (some burdened with additional As), reference standards, and commercial products, along with smoke condensate and ash from these samples. The relative contributions of As(III) and As(V) to the XANES spectra are analyzed, and a consistent pattern of redox changes emerges. Tobacco leaf and manufactured products tend to be dominated by As(V) whereas combustion produces respirable smoke invariably in As(III) form and ash invariably as As(V). The valence state of precursor tobacco is not a controlling factor because all the As mobilized in smoke is reduced during combustion. This study concludes that tobacco combustion exposes smokers to potentially the most toxic forms of arsenic, and this exposure is magnified in regions where arsenic is present in tobacco crops at relatively high concentrations.
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Feb 2014
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