I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[19081]
Open Access
Abstract: The protective carapace of Skogsbergia lerneri, a marine ostracod, is scratch-resistant and transparent. The compositional and structural organisation of the carapace that underlies these properties is unknown. In this study, we aimed to quantify and determine the distribution of chemical elements and chitin within the carapace of adult ostracods, as well as at different stages of ostracod development, to gain insight into its composition. Elemental analyses included X-ray absorption near-edge structure, X-ray fluorescence and X-ray diffraction. Nonlinear microscopy and spectral imaging were performed to determine chitin distribution within the carapace. High levels of calcium (20.3%) and substantial levels of magnesium (1.89%) were identified throughout development. Amorphous calcium carbonate (ACC) was detected in carapaces of all developmental stages, with the polymorph, aragonite, identified in A-1 and adult carapaces. Novel chitin-derived second harmonic generation signals (430/5 nm) were detected. Quantification of relative chitin content within the developing and adult carapaces identified negligible differences in chitin content between developmental stages and adult carapaces, except for the lower chitin contribution in A-2 (66.8 ± 7.6%) compared to A-5 (85.5 ± 10%) (p = 0.03). Skogsbergia lerneri carapace calcium carbonate composition was distinct to other myodocopid ostracods. These calcium polymorphs and ACC are described in other biological transparent materials, and with the consistent chitin distribution throughout S. lerneri development, may imply a biological adaptation to preserve carapace physical properties. Realisation of S. lerneri carapace synthesis and structural organisation will enable exploitation to manufacture biomaterials and biomimetics with huge potential in industrial and military applications.
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Jun 2022
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Andree
Iemhoff
,
Maurice
Vennewald
,
Jens
Artz
,
Chalachew
Mebrahtu
,
Alexander
Meledin
,
Thomas E.
Weirich
,
Heinrich
Hartmann
,
Astrid
Besmehn
,
Matteo
Aramini
,
Federica
Venturini
,
Fred
Mosselmans
,
Georg
Held
,
Rosa
Arrigo
,
Regina
Palkovits
Diamond Proposal Number(s):
[26053, 26030]
Abstract: Stabilization of single metal atoms is a persistent challenge in heterogeneous catalysis. Especially supported late transitions metals are prone to undergo agglomeration to nanoparticles under reducing conditions. In this study, nitrogen-rich covalent triazine frameworks (CTFs) are used to immobilize iridium complexes. Upon reduction at 400°C, immobilized Ir(acac)(COD) on CTF does not form nanoparticles but transforms into a highly active Ir single atom catalyst. The resulting catalyst systems outperforms both the immobilized complex and supported nanoparticles in the dehydrogenation of formic acid as probe reaction. This superior performance could be traced back to decisive changes of the coordination geometry positively influencing activity, selectivity and stability. Spectroscopic analysis reveals an increase of electron density on the cationic iridium site by donation from the CTF macroligand after removal of the organic ligand sphere from the Ir(acac)(COD) precursor complex upon reductive treatment. This work demonstrates the ability of nitrogen moieties to stabilize molecular metal species against agglomeration and opens avenues for catalysts design using isolated sites in high-temperature applications under reducing atmosphere.
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Mar 2022
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B18-Core EXAFS
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Diamond Proposal Number(s):
[21441, 18594]
Abstract: Molybdenum (Mo) is a key trace element and a contaminant in many environments including mine tailings and acid mine drainage systems. Under oxic conditions Mo exists in a number of forms, including mono-molybdate (Mo(VI)O42-) and various poly-molybdate species (e.g. Mo(VI)7O246-) depending on the geochemical conditions (e.g. pH). The mobility and bioavailability of Mo is often controlled by sorption to mineral surfaces, including iron (oxyhydr)oxides e.g. hematite (Fe2O3). This study uses adsorption isotherms, PHREEQC geochemical modelling, Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR), and X-ray Absorption Spectroscopy (XAS) to holistically characterise the molecular scale adsorption of molybdate to hematite as a function of pH (3-12) and Mo(VI) concentration (0.01 ×10-4 - 2 ×10-3 M). PHREEQC and ATR-FTIR indicated both pH and Mo concentration are important variables when forming mono- vs. poly- molybdate and suggest low pH (≤ 4) and high Mo(VI) concentration (≥ 5 ×10-4 M) contribute to the formation of poly-molybdate (heptamolybdate Mo7O246-). XAS found Mo adsorbed to hematite via an inner-sphere corner-sharing bidentate binuclear complex with an octahedral mono-molybdate structure at a Mo concentration of 0.6 ×10-4 M across the pH range, and at a Mo(VI) concentration of 5 ×10-4 M and pH over 5. This is the first direct observation of octahedrally coordinated Mo(VI) adsorption species on hematite, and this information has broad implications for the mobility and transport of Mo as a contaminant in the environment.
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Feb 2022
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I13-2-Diamond Manchester Imaging
I18-Microfocus Spectroscopy
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Sam
Keyes
,
Arjen
Van Veelen
,
Dan
Mckay Fletcher
,
Callum
Scotson
,
Nico
Koebernick
,
Chiara
Petroselli
,
Katherine
Williams
,
Siul
Ruiz
,
Laura
Cooper
,
Robbie
Mayon
,
Simon
Duncan
,
Marc
Dumont
,
Iver
Jakobsen
,
Giles
Oldroyd
,
Andrzej
Tkacz
,
Philip
Poole
,
Fred
Mosselmans
,
Camelia
Borca
,
Thomas
Huthwelker
,
David L.
Jones
,
Tiina
Roose
Open Access
Abstract: Phosphorus (P) is essential for plant growth. Arbuscular mycorrhizal fungi (AMF) aid its uptake by acquiring sources distant from roots in return for carbon. Little is known about how AMF colonise soil pore-space, and models of AMF-enhanced P-uptake are poorly validated. We used synchrotron X-ray computed tomography (SXRCT) to visualize mycorrhizas in soil, and synchrotron X-ray fluorescence (XRF/XANES) elemental mapping for phosphorus (P), sulphur (S) and aluminium (Al), in combination with modelling. We found that AMF inoculation had a suppressive effect on colonisation by other soil fungi and identified differences in structure and growth rate between hyphae of AMF and nonmycorrhizal fungi. Results showed that AMF co-locate with areas of high P and low Al, andpreferentially associate with organic-type P species in preference to Al-rich inorganic P. We discovered that AMF avoid Al-rich areas as a source of P. S-rich regions correlated with higher hyphal density and an increased organic-associated P-pool, whilst oxidized S-species were found close to AMF hyphae. Increased S oxidation close to AMF suggested the observed changes were microbiome-related. Our experimentally-validated model led to an estimate of P-uptake by AMF hyphae that is an order of magnitude lower than rates previously estimated; a result with significant implications for modelling of plant-soil-AMF interactions.
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Jan 2022
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B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[24074, 21441, 13559]
Open Access
Abstract: Neptunium (237Np) is an important radionuclide in the nuclear fuel cycle in areas such as effluent treatment and the geodisposal of radioactive waste. Due to neptunium’s redox sensitivity and its tendency to adsorb strongly to mineral phases, such as iron oxides/sulfides, the environmental mobility of Np can be altered significantly by a wide variety of chemical processes. Here, Np interactions with key iron minerals, ferrihydrite (Fe5O8H·4H2O), goethite (α-FeOOH), and mackinawite (FeS), are investigated using X-ray Absorption Spectroscopy (XAS) in order to explore the mobility of neptunyl(V) (Np(V)O2+) moiety in environmental (radioactive waste disposal) and industrial (effluent treatment plant) scenarios. Analysis of the Np LIII-edge X-ray Absorption Near-Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) showed that upon exposure to goethite and ferrihydrite, Np(V) adsorbed to the surface, likely as an inner-sphere complex. Interestingly, analysis showed that only the first two shells (Oax and Oeq) of the EXAFS could be modelled with a high degree of confidence, and there was no clear indication of Fe or carbonate in the fits. When Np(V)O2+ was added to a mackinawite-containing system, Np(V) was reduced to Np(IV) and formed a nanocrystalline Np(IV)O2 solid. An analogous experiment was also performed with U(VI)O22+, and a similar reduction was observed, with U(VI) being reduced to nanocrystalline uraninite (U(IV)O2). These results highlight that Np(V) may undergo a variety of speciation changes in environmental and engineered systems whilst also highlighting the need for multi-technique approaches to speciation determination for actinyl (for example, Np(V)O2+) species.
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Jan 2022
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[4940]
Open Access
Abstract: In order to provide important details concerning the adsorption reactions of Sr, batch reactions and a set of both ex situ and in situ Grazing Incidence X-ray Absorption Fine Structure (GIXAFS) adsorption experiments were completed on powdered TiO2 and on rutile(110), both reacted with either SrCl2 or SrCO3 solutions. TiO2 sorption capacity for strontium (Sr) ranges from 550 ppm (SrCl2 solutions, second order kinetics) to 1400 ppm (SrCO3 solutions, first order kinetics), respectively, and is rapid. Sr adsorption decreased as a function of chloride concentration but significantly increased as carbonate concentrations increased. In the presence of carbonate, the ability of TiO2 to remove Sr from the solution increases by a factor of ~4 due to rapid epitaxial surface precipitation of an SrCO3 thin film, which registers itself on the rutile(110) surface as a strontianite-like phase (d-spacing 2.8 Å). Extended X-ray Absorption Fine Structure (EXAFS) results suggest the initial attachment is via tetradental inner-sphere Sr adsorption. Moreover, adsorbates from concentrated SrCl2 solutions contain carbonate and hydroxyl species, which results in both inner- and outer-sphere adsorbates and explains the reduced Sr adsorption in these systems. These results not only provide new insights into Sr kinetics and adsorption on TiO2 but also provide valuable information concerning potential improvements in effluent water treatment models and are pertinent in developing treatment methods for rutile-coated structural materials within nuclear power plants.
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Dec 2021
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I18-Microfocus Spectroscopy
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Open Access
Abstract: Portlandite [Ca(OH)2] is a potentially dominant solid phase in the high pH fluids expected within the cementitious engineered barriers of Geological Disposal Facilities (GDF). This study combined X-ray Absorption Spectroscopy with computational modelling in order to provide atomic-scale data which improves our understanding of how a critically important radionuclide (U) will be adsorbed onto this phase under conditions relevant to a GDF environment. Such data are fundamental for predicting radionuclide mass transfer. Surface coordination chemistry and speciation of uranium with portlandite [Ca(OH)2] under alkaline groundwater conditions (ca. pH 12) were determined by both in situ and ex situ grazing incidence extended X-ray absorption fine structure analysis (EXAFS) and by computational modelling at the atomic level. Free energies of sorption of aqueous uranyl hydroxides, [UO2(OH)n]2–n (n = 0–5) with the (001), (100) and (203) or (101) surfaces of portlandite are predicted from the potential of mean force using classical molecular umbrella sampling simulation methods and the structural interactions are further explored using fully periodic density functional theory computations. Although uranyl is predicted to only weakly adsorb to the (001) and (100) clean surfaces, there should be significantly stronger interactions with the (203/101) surface or at hydroxyl vacancies, both prevalent under groundwater conditions. The uranyl surface complex is typically found to include four equatorially coordinated hydroxyl ligands, forming an inner-sphere sorbate by direct interaction of a uranyl oxygen with surface calcium ions in both the (001) and (203/101) cases. In contrast, on the (100) surface, uranyl is sorbed with its axis more parallel to the surface plane. The EXAFS data are largely consistent with a surface structural layer or film similar to calcium uranate, but also show distinct uranyl characteristics, with the uranyl ion exhibiting the classic dioxygenyl oxygens at 1.8 Å and between four and five equatorial oxygen atoms at distances between 2.28 and 2.35 Å from the central U absorber. These experimental data are wholly consistent with the adsorbate configuration predicted by the computational models. These findings suggest that, under the strongly alkaline conditions of a cementitious backfill engineered barrier, there would be significant uptake of uranyl by portlandite to inhibit the mobility of U(VI) from the near field of a geological disposal facility.
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Nov 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[17243]
Open Access
Abstract: Globally, the need for radioactive waste disposal and contaminated land management is clear. Here, gaining an improved understanding of how biogeochemical processes, such as Fe(III) and sulfate reduction, may control the environmental mobility of radionuclides is important. Uranium (U), typically the most abundant radionuclide by mass in radioactive wastes and contaminated land scenarios, may have its environmental mobility impacted by biogeochemical processes within the subsurface. This study investigated the fate of U(VI) in an alkaline (pH ∼9.6) sulfate-reducing enrichment culture obtained from a high-pH environment. To explore the mobility of U(VI) under alkaline conditions where iron minerals are ubiquitous, a range of conditions were tested, including high (30 mM) and low (1 mM) carbonate concentrations and the presence and absence of Fe(III). At high carbonate concentrations, the pH was buffered to approximately pH 9.6, which delayed the onset of sulfate reduction and meant that the reduction of U(VI)(aq) to poorly soluble U(IV)(s) was slowed. Low carbonate conditions allowed microbial sulfate reduction to proceed and caused the pH to fall to ∼7.5. This drop in pH was likely due to the presence of volatile fatty acids from the microbial respiration of gluconate. Here, aqueous sulfide accumulated and U was removed from solution as a mixture of U(IV) and U(VI) phosphate species. In addition, sulfate-reducing bacteria, such as Desulfosporosinus species, were enriched during development of sulfate-reducing conditions. Results highlight the impact of carbonate concentrations on U speciation and solubility in alkaline conditions, informing intermediate-level radioactive waste disposal and radioactively contaminated land management.
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Oct 2021
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[18814]
Abstract: Ashless dialkyldithiophosphate (DDP) antiwear additives are good candidates to replace the widely used metallic DDPs such as zinc dialkyldithiophosphate (ZDDP), which are less environmentally friendly. A newly designed in-situ tribological rig was utilised to perform in-situ synchrotron X-ray absorption spectroscopy (XAS) in order to examine the decomposition reactions of two types of DDPs; acidic and neutral. The tribological experiments showed that the two DDP additives decomposed to form protective tribofilms on the steel surface, which provided better antiwear protection than ZDDP regardless of the tribofilm thickness. The neutral DDP formed a thinner tribofilm (about 33 nm) than ZDDP (about 41 nm), whereas the tribofilm of the acidic DDP had a much lower thickness (<7 nm) but more superior antiwear protection. The two DDPs also provided lower friction coefficient (<0.1) than the 0.12 provided by ZDDP. The XAS experiments suggest that the DDPs decompose to form initially iron sulphate, which is quickly reduced to sulphide before forming the phosphate layers of the protective tribofilm. These layers consisted initially of iron phosphate of short chains but as rubbing continued organic phosphate with long chains started to form.
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Aug 2021
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I14-Hard X-ray Nanoprobe
I18-Microfocus Spectroscopy
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Abstract: Radioactive ‘hot’ particles can be deposited in the environment as a result of illicit activities, nuclear accidents (e.g., Chernobyl, Fukushima), weapons use, mining, and/or nuclear waste disposal. Understanding the long-term behaviour of such materials in the environment is important for understanding risk and environmental impact, and for designing remediation strategies. However, mechanistic knowledge of hot particle alteration processes, reaction products, and radionuclide speciation are limited, especially at finely resolved spatial scales. In this talk, we provide two case-studies that detail how micro- to nano-focus synchrotron X-ray techniques can be used as part of an analytical “tool kit” to fully characterise nuclear industry born hot particles. In turn, this data can inform safety assessments and clean-up / decommissioning efforts at radioactively contaminated sites.
In both case-studies, we examine highly radioactive micro-particles that were found in soil samples taken from nuclear exclusion zone that surrounds the Fukushima Daiichi Nuclear Power Plant (FDNPP). These particles were emitted from the damaged FDNPP reactors during the 2011 accident. Recent work by our group [1, 2] has shown that these particles are common forms of contamination in the nuclear exclusion zone, but the possible environmental and human-health impacts of the particles are not yet known. Recent work [3, 4] on Diamond Light Source Beamlines I18 (micro-focus X-ray spectroscopy) and I14 (Hard X-ray nanoprobe), and the Swiss Light Source micro-XAS Beamline, has permitted detailed chemical characterisation of these challenging materials. In case study 1, we will present micro-focus data that describes the speciation of actinide elements in whole FDNPP hot particles [3]. The data includes the first speciation information for plutonium released from the damaged FDNPP reactors. In case study 2, we present nano-probe characterisation of recently discovered hot particles derived from FDNPP reactor Unit 1 [4]. These particles have the highest ever recorded 134+137Cs radioactivities for particles released from the FDNPP. In our work, FIB sectioning of the particles permitted detailed SIMS, electron microscopy, and hard X-ray nano-probe analysis of the particles. In particular, combined electron-microscopy and synchrotron-based nano-focus XRF and XRD analyses were used to characterise the particles (e.g., Figure 1).
For both case studies we will provide an overview of sample preparation, analysis considerations, and discuss how the results inform management of the FDNPP legacy.
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Jul 2021
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