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21 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3 [Next/Last]

Instruments / Technical Area	Publication Details	Published
Insertion Devices Magnets Mechanical Engineering	Beam drift, control and polarization Sofia Diaz-Moreno , Roberto Boada DOI: 10.1107/S1574870722003172 Show Abstract ▼ Abstract: The main factors that cause the X-ray beam to drift are discussed in this chapter. Issues such as movement of the source or mechanical and thermal instabilities of the main optical elements of the beamline are translated into movement of the X-ray beam at the sample, intensity drifts and nonlinearities on the energy scale, affecting the quality of the data collected. The main steps that need to be taken to prevent and/or minimize the effects of these drifts are described, and approaches such as feedback systems are presented. The polarization of the beam delivered by the different types of X-ray sources used for synchrotron-based spectroscopy experiments is also presented. The on-axis and off-axis polarizations of the bending magnet and insertion devices such as wigglers and undulators are discussed.	May 2023
I20-Scanning-X-ray spectroscopy (XAS/XES)	Unraveling the molecular details of the “gate opening” phenomenon in ZIF-8 with X-ray absorption spectroscopy Roberto Boada , Jesus Chaboy , Shusaku Hayama , Luke Keenan , Adam A. Freeman , Monica Amboage , Sofia Diaz-Moreno The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.2c00373 Diamond Proposal Number(s): [9970] Open Access Show Abstract ▼ Abstract: The local structural changes associated with the ZIF-8 framework flexibility upon nitrogen gas adsorption have been studied by in situ X-ray absorption spectroscopy (XAS) and high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopy. Different thermodynamic conditions (isobar and isotherm) have been used to explore the so-called “gate opening” transition in which the hexagonal pore windows of the sodalite cage open, increasing the accessible volume for gas adsorption. To elucidate the source of the spectral changes in the XANES region of the absorption spectra observed along the gas adsorption and through the transition from the closed to the open pore configuration, ab initio calculations have been performed. Our results demonstrate that the transition from the closed to the open pore configurations involves not only the rotation of the MeIM ligand but also a further bend of the Me group away from the plane defined by the IM ring. Additionally, the contribution of the N2 molecules adsorbed in the center of the 4-ring window has been included in the scattering model to fully reproduce the main features of the X-ray absorption spectra in the open pore configuration.	Mar 2022
I20-Scanning-X-ray spectroscopy (XAS/XES)	Dimensionality-driven metal–insulator transition in spin–orbit-coupled IrO2 E. Arias-Egido , M. A. Laguna-Marco , C. Piquer , P. Jimenez-Cavero , I. Lucas , L. Morellon , F. Gallego , A. Rivera-Calzada , M. Cabero , J. Santamaría , G. Fabbris , D. Haskel , R. Boada , S. Diaz-Moreno Nanoscale DOI: 10.1039/D1NR04207F Diamond Proposal Number(s): [17266] Open Access Show Abstract ▼ Abstract: A metal–insulator transition is observed in spin–orbit-coupled IrO2 thin films upon reduction of the film thickness. In the epitaxially grown samples, the critical thickness (t ∼ 1.5–2.2 nm) is found to depend on growth orientation (001), (100) or (110). Interestingly from the applied point of view, the insulating behavior is found even in polycrystalline ultrathin films. By analyzing the experimental electrical response with various theoretical models, we find good fits to the Efros–Shklovskii-VRH and the Arrhenius-type behaviors, which suggests an important role of electron correlations in determining the electrical properties of IrO2. Our magnetic measurements also point to a significant role of magnetic order. Altogether, our results would point to a mixed Slater- and Mott-type of insulator.	Oct 2021
I20-EDE-Energy Dispersive EXAFS (EDE)	Important role of open copper sites on adsorption of various molecules in Cu-BTC metal organic framework Iuliia Mikulska , Roberto Boada , Shusaku Hayama , Matteo Aramini , Luke Keenan , Monica Amboage , Sofia Diaz-Moreno XAFS2021 Show Abstract ▼ Abstract: Cu-BTC metal-organic framework (MOF) has been found to be a promising candidate for removing hazardous substances from air via adsorption1. To understand the role that the copper sites in Cu-BTC play in the adsorption process, we have performed a detailed X-ray absorption spectroscopy (XAS) study. Conventional XAS and high energy resolution fluorescence detection XAS (HERFD-XAS) were collected on degassed Cu-BTC, and after being exposed to CO2, water and benzene. The EXAFS analysis reveals that, although the local environment around the copper centers in all samples is similar, differences can be found in the first and second coordination shells. We have found that the Cu-O distance in the first coordination shell is slightly larger when the sample is immersed in water and benzene than in the degassed sample, while it does not change for the sample exposed to CO2. Small differences are also observed in the Cu-Cu distance, gradually increasing from 2.49 Å in the degassed sample, to 2.52 Å, 2.58 Å and 2.63 Å upon adsorption of CO2, benzene and water, respectively. HERFD-XAS has been used to obtain information about the electronic and geometric structure around the copper metal centers, as the use of high energy resolution enhances the features in the XANES spectrum enabling the detection of subtle changes2. We have observed differences in the intensity and the energy position of some of the XANES spectral features upon adsorption of different adsorbates that can be attributed to changes in the local environment around the copper centers, as detected in the EXAFS analysis. In this study we show that XAS is a powerful and very sensitive tool for studying host-guest interactions in MOFs, providing atomic-level insights into adsorption mechanisms.	Jul 2021
I20-Scanning-X-ray spectroscopy (XAS/XES)	Mixed‐valence Ce/Zr metal‐organic frameworks: Controlling the oxidation state of cerium in one‐pot synthesis approach Maria Ronda‐lloret , Isaac Pellicer-Carreño , Aida Grau-Atienza , Roberto Boada , Sofia Diaz-Moreno , Javier Narciso-Romero , Juan Carlos Serrano-Ruiz , Antonio Sepulveda-Escribano , Enrique V. Ramos-Fernandez Advanced Functional Materials 4 DOI: 10.1002/adfm.202102582 Diamond Proposal Number(s): [19114] Open Access Show Abstract ▼ Abstract: The preparation of MOFs including a metal with an easily exchangeable oxidation state, while maintaining the same crystal structure and stability, is of paramount importance for myriad applications. In this work, a new synthesis method is reported that can be used to prepare Ce/Zr‐MOFs (UiO‐66 structure) having only Ce(III), a mixed‐valence Ce(IV)/Ce(III), or only Ce(IV) cations, as desired. The materials are characterized using a large number of techniques, including X‐ray absorption and X‐ray photoelectron spectroscopies.	May 2021
I20-Scanning-X-ray spectroscopy (XAS/XES)	Photon-in/photon-out spectroscopy at the I20-scanning beamline at Diamond Light Source Shusaku Hayama , Roberto Boada , Jesus Chaboy , Adrian Birt , Graham Duller , Leo Cahill , Adam Freeman , Monica Amboage , Luke Keenan , Sofia Diaz-Moreno Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/abfe93 Open Access Show Abstract ▼ Abstract: A scanning multi-crystal x-ray emission spectrometer to perform photon-in/photon-out spectroscopy at the I20-Scanning beamline at Diamond Light Source is described. The instrument, equipped with three analyzer crystals, is based on a 1m Rowland circle spectrometer operating in the vertical plane. The energy resolution of the spectrometer is of the order of 1 eV, having sufficient resolving power to overcome the core-hole lifetime broadening of most of the transition metals K-edges. Examples showing the capabilily of the beamline for performing high energy resolution fluorescence detection x-ray absorption spectroscopy (HERFD-XAS), non-resonant x-ray emission spectroscopy (XES) and resonant x-ray emission spectroscopy (RXES) are presented. The comparison of the Zn and Mn K-edge HERFD-XANES of ZnO and MnO with ab-initio calculations shows that the technique provides enhanced validation of the models by making subtle spectral features more visible.	May 2021
I18-Microfocus Spectroscopy	Co-application of Se and a biostimulant at different wheat growth stages: Influence on grain development Tingting Xiao , Roberto Boada , Mercè Llugany , Manuel Valiente Plant Physiology And Biochemistry 160, 184 - 192 DOI: 10.1016/j.plaphy.2021.01.025 Diamond Proposal Number(s): [18671] Show Abstract ▼ Abstract: An appropriate selenium intake can be beneficial for human health. Se-biofortified food in Se-deficient regions is becoming an increasingly common practice but there are still issues to be addressed regarding the observed Se-induced toxicity to the plant. In this respect, plant biostimulants are used to enhance nutrition efficiency, abiotic stress tolerance and crop quality. In this work, the efficacy of a plant biostimulant to counteract the Se-induced stress in wheat plants is experimentally assessed. The co-application of different Se-biofortification treatments and the biostimulant at different growth stages (tillering or heading stage) was investigated. The use of micro focused X-ray spectroscopy allows us to confirm organic Se species to be the main Se species found in wheat grain and that the proportion of organic Se species is only slightly affected by the Se application stage. Our study proves that the biostimulant had a key role in the enhancement of both the amount of grains produced per spike and their dry biomass without hindering Se enrichment process, neither diminishing the Se concentration nor massively disrupting the Se species present. This information will be useful to minimize both plant toxicity and economic cost towards a more effective and plant healthy selenium supplementation.	Mar 2021
B18-Core EXAFS	Enhancement of selective adsorption of Cr species via modification of pine biomass Jingjing Zhao , Roberto Boada , Giannantonio Cibin , Cristina Palet Science Of The Total Environment DOI: 10.1016/j.scitotenv.2020.143816 Diamond Proposal Number(s): [18561] Show Abstract ▼ Abstract: Pine biomass (Pine), pine gasification biochar (PG) and pine biomass loaded with TiO2 (Pine/TiO2) were used as sorbent materials to remove Cr(III) or Cr(VI) ions from aqueous solutions. Our results showed that Pine/TiO2 had an improved adsorption capacity respect to Pine being the adsorption capacity for Cr(VI), 12.8 mg/g, much larger than for Cr(III), 1.23 mg/g. On the other hand, PG showed much higher adsorption for Cr(III), 12.4 mg/g, than Pine/TiO2, and negligible adsorption for Cr(VI). To understand this species-dependent adsorption behavior, the adsorption mechanisms, sorbents morphology and functional sites were characterized using a multi-technique approach. The chemical state and local coordination structure of the adsorbed Cr species was studied by X-ray absorption spectroscopy (XAS). Our results show that the adsorption of Cr(III) occurred mainly through cation exchange with mineral elements in PG biochar, whereas the Cr(III) adsorption by functional groups (carboxyl and hydroxyl groups) dominate in the biomass sorbent. The enhancement of Cr(VI) adsorption in Pine/TiO2 can be explained by the presence of TiOH2+ groups present in the surface of theTiO2 microparticles. X-ray absorption spectroscopy (XAS) results reveal that Cr(VI) reduces to Cr(III) after being adsorbed by the sorbent materials.	Nov 2020
I20-Scanning-X-ray spectroscopy (XAS/XES)	Relation among oxygen stoichiometry, structure, and Co valence and spin state in single-layer La2–xAxCoO4±δ (a = Ca, Sr) perovskites Gloria Subias , Javier Blasco , Sara Lafuerza , Vera Cuartero , M. Concepción Sánchez , Roberto Boada , Sofia Diaz-Moreno , François Fauth , Joaquin Garcia Inorganic Chemistry DOI: 10.1021/acs.inorgchem.0c02174 Diamond Proposal Number(s): [11356] Show Abstract ▼ Abstract: We have investigated the role of oxygen stoichiometry and structural properties in the modulation of Co valence and spin state in single-layer La2–xAxCoO4±δ (A = Sr, Ca; 0 ≤ x ≤ 1) perovskites as well as the interplay between their local structural properties and the magnetic and charge-ordering phenomena. We show the results of high angular resolution powder X-ray diffraction and Co K-edge X-ray absorption and emission spectroscopy experiments on polycrystalline and single-crystal samples. The different doping-induced changes in the Co valence and spin state by Ca (or Sr) substitution can be understood in terms of the evolving oxygen stoichiometry. For Ca doping, the interstitial oxygen excess around the La/Ca atoms in underdoped samples is rapidly lost upon increasing the Ca content. The creation of oxygen vacancies leads to the stabilization of a mixed-valence Co2.5+ independently of the Ca content. In contrast, Sr substitution leads to almost stoichiometric samples and a lower oxygen vacancy concentration, which allows higher mixed-valence states for Co up to Co2.9+. The Co mixed-valence state along the two series is fluctuating between two valence states, Co2.4+ as in La2CoO4.2 and Co2.9+ as in LaSrCoO3.91, that become periodically ordered for the charge-ordered phases around the half-doping. The X-ray emission derived spin states agree well with the Co fluctuating mixed-valence state derived from X-ray absorption spectroscopy on consideration of a distribution of high-spin Co2+ and low-spin Co3+. Furthermore, there is no quenching of the orbital contribution for the high-spin Co2+, as concluded from a comparison with macroscopic magnetization measurements. Doping holes are mainly located in the ab plane and have a strong oxygen 2p character. The major lattice distortions, which are different for Sr and Ca doping, occur along the c axis, where changes in the oxygen stoichiometry take place. Moreover, charge-order transitions are clearly shown from the anomalous increase of the c lattice parameter with an increase in the temperature above 500 K but there is no signature for a temperature-dependent spin-state transition.	Oct 2020
B18-Core EXAFS B22-Multimode InfraRed imaging And Microspectroscopy	OX-1 metal-organic framework nanosheets as robust hosts for highly active catalytic palladium species Kirill Titov , Dmitry Eremin , Alexey S. Kashin , Roberto Boada Romero , Barbara Souza , Chris S. Kelley , Mark D. Frogley , Gianfelice Cinque , Diego Gianolio , Giannantonio Cibin , Svemir Rudic , Valentine P Ananikov , Jin-Chong Tan Acs Sustainable Chemistry & Engineering DOI: 10.1021/acssuschemeng.8b05843 Diamond Proposal Number(s): [14902, 17146] Show Abstract ▼ Abstract: A catalytic system based on OX-1 metal-organic framework nanosheets is reported, incorporating catalytically active palladium (Pd) species. The Pd@OX-1 guest@host system is rapidly synthesised via a facile single-pot supramolecular assembly method, with the possibility of controlling the Pd loading. The structures of the re-sulting framework and of the active Pd species before and after catalytic reactions are studied in detail using a wide variety of techniques including synchrotron radiation infrared spectroscopy, inelastic neutron scattering and X-ray absorption spectroscopy. Crystals of the resulting Pd@OX-1 composite material contain predomi-nantly atomic and small cluster Pd species, which selectively reside on benzene rings of the benzenedicarbox-ylate (BDC) linkers. The composites are shown to efficiently catalyse the Suzuki coupling and Heck arylation reactions under a variety of conditions. Pd@OX-1 further shows potential to be recycled for at least five cycles of each reaction as well as an ability to recapture active Pd species during both catalytic reactions.	Feb 2019

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