I20-Scanning-X-ray spectroscopy (XAS/XES)
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Wenjie
Li
,
Shanlin
Gao
,
Chunbo
Lai
,
Xinling
Li
,
Wanjing
Xiao
,
Xinyu
Wang
,
Huibo
Lin
,
Yang
Zhang
,
Haijun
Liu
,
Gan
Yang
,
Chenghua
Xu
,
Luke J. R.
Higgins
,
Andrew M.
Beale
,
Marc
Pera-Titus
,
Zhiyong
Deng
Diamond Proposal Number(s):
[40509]
Open Access
Abstract: Methanol oxidative carbonylation is a highly desired reaction for the industrial production of dimethyl carbonate (DMC), offering a more sustainable alternative to the conventional, environmentally unfriendly phosgene-methanol process. Although supported copper nanoparticle catalysts can facilitate this reaction, their rapid deactivation due to Cu sintering and overoxidation limits their industrial applicability. In this study, we present robust and reusable single-atoms and cluster-like Cu catalysts (catalyst loading up to 6.5 wt %) supported on N-doped carbon, synthesized via pyrolysis of Cu-doped ZIF-8 precursors. The formation and stability of highly dispersed Cu species during the reaction was confirmed using a comprehensive suite of characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared (FT-IR), high-resolution transmission electron microscopy (HR-TEM), aberration corrected high angle annular dark field-scanning transmission electron microscopy (AC-HAADF-STEM), X-ray photoelectron spectroscopy (XPS), NH3-TPD, H2-TPR, and X-ray absorption spectroscopy (XAS). This unique copper architecture achieved an exceptional DMC selectivity of 99.4% and a space-time yield of 3249 mg DMC·g–1·h–1 (TOFDMC,B = 34.4 h–1; TOFDMC,S = 294 h–1) at 120 °C for 2 h. The catalysts demonstrated excellent reusability, maintaining their performance over at least seven consecutive runs without deactivation. Postreaction analysis of the spent catalyst after seven runs revealed that Cu was largely free of leaching, sintering, and overoxidation.
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Jul 2025
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Ramesh
Rijal
,
Jack
Stephens
,
Daniel
Sier
,
Nicholas T. T.
Tran
,
Truong V. B.
Nguyen
,
Jonathan W.
Dean
,
Pierce
Bowman
,
Minh
Dao
,
Paul
Di Pasquale
,
Tony
Kirk
,
Chanh Q.
Tran
,
Shusaku
Hayama
,
Matteo
Aramini
,
Nitya
Ramanan
,
Sofia
Diaz-Moreno
,
Christopher T.
Chantler
Open Access
Abstract: This study of manganese (Mn, Z = 25) introduces a novel combination of extended-range high energy resolution fluorescence detection (XR-HERFD), multiple-crystal spectrometers and advanced binary data splicing techniques to address challenges in X-ray emission spectroscopy. XR-HERFD enhances spectral precision by utilizing high-resolution crystal analysers and optimized detector configurations. The systematic application of these methods using multiple Bragg crystal analysers at Diamond Light Source has led to substantial improvements in data quality. Simultaneously, advanced binary data splicing integrates multiple datasets to correct distortions and improve resolution, resulting in sharper spectral features. Our results show a significant increase in peak counts and a notable reduction in full width at half-maximum (FWHM), with peak amplitudes increasing by 83% and resolution improving by 46%. These developments provide greater detail for X-ray absorption or emission spectra, offering valuable insights into complex materials, and permitting advances and breakthroughs in atomic relativistic quantum mechanics, chemical sensitivity of atomic transitions and modelling of solid-state effects.
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Jul 2025
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[23496]
Open Access
Abstract: Arsenic immobilization in soils and sediments is primarily controlled by its sorption onto or incorporation into reactive soil minerals, such as iron (oxyhydr)oxides. However, coexisting ions (e.g., dissolved bicarbonate, phosphate, silica, and organic matter) can negatively impact the interaction of the toxic arsenate species with iron (oxy)hydroxides. Of special note is inorganic phosphate, which is a strong competitor for sorption sites due to its analogous chemical and structural nature to inorganic arsenate. Much of our understanding of this competing nature between phosphate and arsenate focuses on the impact on mineral sorption capacities and kinetics. However, we know very little about how coexisting phosphate will alter the stability and transformation pathways of arsenate-bearing Fe (oxyhydr)oxides. In particular, the long-term fate and behavior regarding arsenate immobilization are unknown under anoxic conditions. Here, we document, through mineral transformation reactions, the immobilization of both phosphate (P) and arsenate [As(V)] in secondary mineral products and characterize their changing compositions during the transformations. We did this while controlling the initial P/As(V) ratios. Our results document that, in the absence or at low P/As(V) ratios, the initial ferrihydrite rapidly transforms to green rust sulfate (GRSO4), which further transforms into magnetite after 180 days. Meanwhile, high P/As(V) ratios resulted in a mixture of GRSO4 and vivianite, with magnetite as a minor fraction. Invariably, the speciation and partitioning of As(V) were also affected by the P/As(V) ratio. A higher P/As(V) ratio also led to a faster partial reduction of mineral-bound As(V) to As(III). The most important finding is that the initial ferrihydrite-bound As(V) became structurally incorporated into magnetite [low P/As(V) ratio] or vivianite [high P/As(V) ratio] and was thus immobilized and not labile. Overall, our results highlight the influence of coexisting phosphate in controlling the toxicity and mobility in anoxic, Fe2+-rich subsurface settings, such as contaminated aquifers.
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Jun 2025
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B18-Core EXAFS
I14-Hard X-ray Nanoprobe
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[25930, 24074, 21441]
Open Access
Abstract: Uranium (U) is a natural radioactive metal and a persistent environmental pollutant. Characterising the influence of arbuscular mycorrhizal fungi (AMF) on U bioaccumulation and partitioning in plants is crucial to understand U soil-to-plant transfer mechanisms. High resolution elemental mapping, spectroscopy and microscopy techniques were conducted on uranyl nitrate dosed Plantago lanceolata roots colonised with Rhizophagus irregularis. U-rich particles accumulated within the root cells, with higher abundance in epidermal and outer cortex cells of mycorrhizal root samples than in non-mycorrhizal roots. Electron microscopy determined two different crystalline U phases, an acicular crystal and a novel rounded aggregate formation, the latter of which was only found within the mycorrhizal root cells. Multiple imaging and spectroscopic techniques enabled the dominant elements with these U biominerals to be determined. Co-localisation between U, phosphorus and oxygen indicated the dominance of U-phosphate biominerals, but metals including calcium and zinc were also found to co-localise. The most dominant U compound was uranyl orthophosphate, likely accompanied by autunite. This study demonstrates alteration in U localisation and U particle morphology within Plantago roots as a direct consequence of AMF colonisation. This knowledge will allow more accurate U food-chain transfer modelling and better assessment of AMF-assisted phytoremediation feasibility.
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Jun 2025
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Abstract: Development of sustainable hydrogen-based fuel systems requires both efficient ways to produce hydrogen and extract energy from it. In nature, this reaction is performed efficiently by hydrogenase enzymes. Studying the mechanism of hydrogenase enzymes is difficult due to their exceptionally high turnover frequencies. As a result, new techniques are required to probe their catalytic cycle.
X-ray Absorption Spectroscopy is a promising technique, due to the structural and electronic information obtainable, but requirements to utilize cryogenic samples to avoid photodamage hinder its applicability. To avoid this, a specially designed cell was developed to allow room-temperature X-ray spectroscopy to be performed on hydrogenase samples under electrochemical control. This cell was successfully trialed using HERFD-XAS measurements of both [NiFe] and [FeFe] hydrogenases and demonstrated promise in mitigating photodamage via novel electrochemical protective methods. Preliminary work using model nickel complexes also demonstrated the feasibility of accessing VtC transitions during X-ray Emission Spectroscopy, allowing access to new probes of the active site.
The feasibility of Time-Resolved Multiple Probe spectroscopy, an ultrafast infrared spectroscopy method, was also tested in order to investigate sub-turnover kinetics of [NiFe] hydrogenases. This demonstrated the existence of intermediates with lifetimes below that accessible by more conventional methods.
This work provides multiple avenues to investigate the mechanism of [NiFe] hydrogenases.
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May 2025
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Ajeesh Kumar
Somakumar
,
Ivo
Romet
,
Agnieszka
Grabias
,
Marcin
Kruk
,
Shusaku
Hayama
,
Damian
Wlodarczyk
,
Justyna
Barzowska
,
Yadhu Krishnan
Edathumkandy
,
Eduard
Feldbach
,
Puxian
Xiong
,
Yaroslav
Zhydachevskyy
,
Monika
Trzaskowska
,
Hanka
Przybylinska
,
Andrzej
Suchocki
Open Access
Abstract: An extensive experimental study of trivalent iron (Fe3+) ions in orthorhombic lithium gallate nanocrystals was undertaken. Various spectroscopic methods, such as Raman spectroscopy, extended X-ray absorption fine structure, the Mössbauer effect, electron paramagnetic resonance, photoluminescence, thermoluminescence, and cathodoluminescence were used to investigate the synthesized phosphor. This study revealed the existence of multiple Fe3+ sites, out of which the tetrahedral sites are preferentially occupied. Extensive optical studies showed that the Fe3+ doped lithium gallate phosphor is a promising candidate for various luminescence and thermoluminescence-related applications in the near-infrared regime.
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May 2025
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[26014]
Open Access
Abstract: We successfully synthesised ceria and Cu-doped ceria thin films on fluorine-doped tin oxide (FTO) glass using electrochemical deposition methods. Although X-ray diffraction characterisation did not confirm the presence of pure CeO2 phase, XPS and high-resolution fluorescence detection method to collect XANES data at Ce L3 edge confirmed the presence of only Ce4+ and the spectral features resembled that of CeO2 in all the as-synthesised samples. In situ reactivity studies in the H2 atmosphere of these samples employing XANES data, recorded during the heating and cooling cycle, revealed the extent of Ce4+ conversion to Ce3+. Most importantly the stability of converted Ce3+ appears to depend on the presence of reducible transition metal, where the presence of copper ions indeed decreased the reduction temperature of Ce4+ and upon cooling the formed Ce3+ appears to be stable in a reducing atmosphere. In the absence of copper, not only is the extent of reduction to Ce3+ much less compared with the copper-containing samples but also, the reduced Ce3+ ions appear to reoxidise to Ce4+ upon cooling to room temperature. These results are in line with observed results of powder CeO2 samples typically used as catalyst supports.
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May 2025
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[24399]
Open Access
Abstract: The catalytic conversion of C–H to C–F bonds is a critical synthetic transformation of relevance to the pharmaceutical, agrochemical, and medicinal chemical industries. When coupled with an oxidant and a fluorine donor, biomimetic Mn-porphyrins have been shown to be capable of achieving this reaction. However, the definition of the active forms of these fluorinating Mn-porphyrins remains an unsolved challenge, which limits mechanistic understanding of the process and makes it challenging to systematically design better catalytic materials. Herein, we present a combination of kinetic, spectroscopic, and theoretical studies focused on alkane fluorination over Mn-containing porphyrins. Specifically, by correlating kinetic studies with resonance Raman, UV–vis, and high-energy resolution fluorescence detected X-ray absorption spectroscopic analysis of the various states of the catalyst, we provide evidence that a 6-coordinated Mn(IV) complex with −F and −OI(F)Ar axial ligands is the active species responsible for selective fluorination via Hydrogen Atom Transfer. This active state is distinct from the Mn═O species previously proposed to be the active intermediates for alkane fluorination and oxidation.
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Mar 2025
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B18-Core EXAFS
I18-Microfocus Spectroscopy
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[31873, 31884, 38007]
Open Access
Abstract: Some of the largest Mexican uranium (U) deposits are located in Chihuahua. The most important is in Sierra Peña Blanca, northwest of the capital, which was explored and partially exploited in the 1980s. After the closure of activities, the mining projects were left exposed to weathering. To characterize the spread of U minerals towards the neighboring Laguna del Cuervo, sediment samples were collected in the main streams of the drainage pattern of the largest deposits. The U mineral fragments from the fine sand portion were extracted using fluorescence light at 365 nm. The morphology and elemental composition of these particles were analyzed by focused ion beam microscopy (FIB) and scanning transmission electron microscopy (STEM). The particle density in samples close to the U sources was quantified using gamma spectrometry. The highest density was 2500 part./g, and the lowest was 124 part./g. X-ray absorption spectroscopy (XAS) allowed us to establish via XANES the speciation of U in the U particles, confirming the U(VI) oxidation state, while the exploitation of the EXAFS spectrum put in evidence of the presence of uranophane. Finally, the Fe, Sr, and U distributions in the particle and its matrix were obtained via X-ray fluorescence microtomography (XRF-µCT). It was concluded that the particle is composed of uranophane, imbricated with quartz and other oxides.
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Mar 2025
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Abstract: X-ray absorption spectroscopy has proved to be valuable tool in the characterisation of materials, enabling determination of the oxidation states of metal atoms and ions via analysis of the near edge XANES region and the local coordination geometry via analysis of the XANES and EXAFS regions of the spectra. One significant limitation of these methods is that the data represent the per-atom average of the state and structure of the element under investigation. When studying mixed oxidation state materials or materials in which the element is in more than one type of site this limitation decreases the value of the data. However, if the sites differ by spin-state, it is hypothesised that selectivity may be achieved by the use of high energy resolution fluorescence detection HERFD-XANES in which the spin-state selectivity arises by collecting the spectra using X-ray emission energies that discriminate between the two spin states. This may be achieved in the case of iron by using the Kb emission lines, rather than the more typical Kb emission lines. In this thesis the hypothesis of spin-state selectivity is tested by applying the technique to study the HERFD-XANES of a series of Prussian blue analogue (PBA) materials in which the spin-state of the iron atoms is determined by the bonding to either the C or N atom of the CN ligands and then Prussian blue (PB) itself, where iron atoms are present in both spin states. The ability of the technique to resolve changes in the oxidation states of each of the iron centres is furthermore tested in in situ studies of PB acting as a sodium ion battery material in both the aqueous and non-aqueous environments.
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Mar 2025
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