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54 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6 [Next/Last]

Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS	The influence of defects on the luminescence of trivalent terbium in nanocrystalline yttrium orthovanadate Rafael Vieira Perrella , Marc Walker , Thomas Chamberlain , Richard Walton , Paulo Cesar De Sousa Filho Nano Letters 22 DOI: 10.1021/acs.nanolett.1c04937 Diamond Proposal Number(s): [14239] Show Abstract ▼ Abstract: Terbium-doped YVO4 has been considered a nonluminescent solid since the first classic studies on rare-earth-doped phosphors in the 1960s. However, we demonstrate that defect engineering of YVO4:Tb3+ nanoparticles overcomes the metal–metal charge transfer (MMCT) process which is responsible for the quenching of the Tb3+ luminescence. Tetragonal (Y1–xTbx)VO4 nanoparticles obtained by colloidal precipitation showed expanded unit cells, high defect densities, and intimately mixed carbonates and hydroxides, which contribute to a shift of the MMCT states to higher energies. Consequently, we demonstrate unambiguously for the first time that Tb3+ luminescence can be excited by VO43– → Tb3+ energy transfer and by direct population of the 5D4 state in YVO4. We also discuss how thermal treatment removes these effects and shifts the quenching MMCT state to lower energies, thus highlighting the major consequences of defect density and microstructure in nanosized phosphors. Therefore, our findings ultimately show nanostructured YVO4:Tb3+ can be reclassified as a UV-excitable luminescent material.	Apr 2022
B18-Core EXAFS	Exploiting the flexibility of the pyrochlore composition for acid-resilient iridium oxide electrocatalysts in proton exchange membranes David Burnett , Enrico Petrucco , Reza J. Kashtiban , Stewart F. Parker , Jonathan D. B. Sharman , Richard I. Walton Journal Of Materials Chemistry A DOI: 10.1039/D1TA05457K Diamond Proposal Number(s): [11646, 8986] Show Abstract ▼ Abstract: Iridate pyrochlore oxides (Na,Ca)2-x(Ir2-yMy)O6·nH2O (M = Sb, Zr, Ru, Rh) are studied as resilient electrocatalysts for the oxygen evolution reaction under acid conditions. The materials crystallise from aqueous solution under alkali hydrothermal conditions with 10-40 nm crystallite size. Refinement of their crystal structures using both powder neutron and X-ray diffraction determined the composition of the materials, and Ir LIII-edge XANES spectroscopy shows the average Ir oxidation state to be close to 4.5 in all materials, consistent with bond valence sums. All materials show high electrocatalytic activity for the oxygen evolution reaction and the electrocatalyst which best maintains activity on cycling is the sodium-free Ca2-xIr2O6·nH2O, while the (Na,Ca)2-xIr2O6·nH2O material shows highest activity when normalised for surface area. In membrane electrode assemblies, carbon corrosion is minimised, making the materials suitable for use in catalyst layers in proton exchange membrane devices, such as electrolysers and fuel cells. Under strongly acidic conditions it is proved that while A-site Ca and Na are readily leached, the average pyrochlore structure is maintained, as is electrocatalytic activity, with charge balance achieved by inclusion of protons in the pyrochlore structure in the form of bridging hydroxyls, as seen using inelastic neutron scattering spectroscopy.	Nov 2021
B18-Core EXAFS	Hydrothermal synthesis of iridium-substituted NaTaO3 perovskites David L. Burnett , Christopher D. Vincent , Jasmine A. Clayton , Reza J. Kashtiban , Richard I. Walton Nanomaterials 11 DOI: 10.3390/nano11061537 Diamond Proposal Number(s): [8708] Open Access Show Abstract ▼ Abstract: Iridium-containing NaTaO3 is produced using a one-step hydrothermal crystallisation from Ta2O5 and IrCl3 in an aqueous solution of 10 M NaOH in 40 vol% H2O2 heated at 240 °C. Although a nominal replacement of 50% of Ta by Ir was attempted, the amount of Ir included in the perovskite oxide was only up to 15 mol%. The materials are formed as crystalline powders comprising cube-shaped crystallites around 100 nm in edge length, as seen by scanning transmission electron microscopy. Energy dispersive X-ray mapping shows an even dispersion of Ir through the crystallites. Profile fitting of powder X-ray diffraction (XRD) shows expanded unit cell volumes (orthorhombic space group Pbnm) compared to the parent NaTaO3, while XANES spectroscopy at the Ir LIII-edge reveals that the highest Ir-content materials contain Ir4+. The inclusion of Ir4+ into the perovskite by replacement of Ta5+ implies the presence of charge-balancing defects and upon heat treatment the iridium is extruded from the perovskite at around 600 °C in air, with the presence of metallic iridium seen by in situ powder XRD. The highest Ir-content material was loaded with Pt and examined for photocatalytic evolution of H2 from aqueous methanol. Compared to the parent NaTaO3, the Ir-substituted material shows a more than ten-fold enhancement of hydrogen yield with a significant proportion ascribed to visible light absorption.	Jun 2021
B18-Core EXAFS I11-High Resolution Powder Diffraction	Ce(OH)2Cl and lanthanide-substituted variants as precursors to redox-active CeO2 materials Alexander J. A. Dunn , James W. Annis , Janet M. Fisher , David Thompsett , Richard Walton Dalton Transactions 38 DOI: 10.1039/D0DT03435E Diamond Proposal Number(s): [14239, 18786] Open Access Show Abstract ▼ Abstract: The cerium(III) hydroxide chloride Ce(OH)2Cl crystallises directly as a polycrystalline powder from a solution of CeCl3·7H2O in poly(ethylene) glycol (Mn = 400) heated at 240 °C and is found to be isostructural with La(OH)2Cl, as determined from high-resolution synchrotron powder X-ray diffraction (P21/m, a = 6.2868(2) Å, b = 3.94950(3) Å, c = 6.8740(3) Å, β = 113.5120(5)°). Replacement of a proportion of the cerium chloride in synthesis by a second lanthanide chloride yields a set of materials Ce1−xLnx(OH)2Cl for Ln = La, Pr, Gd, Tb. For La the maximum value of x is 0.2, with an isotropic expansion of the unit cell, but for the other lanthanides a wider composition range is possible, and the lattice parameters show an isotropic contraction with increasing x. Thermal decomposition of the hydroxide chlorides at 700 °C yields mixed-oxides Ce1−xLnxO2−δ that all have cubic fluorite structures with either expanded (Ln = La, Gd) or contracted (Ln = Pr, Tb) unit cells compared to CeO2. Scanning electron microscopy shows a shape memory effect in crystal morphology upon decomposition, with clusters of anisotropic sub-micron crystallites being seen in the precursor and oxide products. The Pr- and Tb-substituted oxides contain the substituent in a mixture of +3 and +4 oxidation states, as seen by X-ray absorption near edge structure spectroscopy at the lanthanide LIII edges. The mixed oxide materials are examined using temperature programmed reduction in 10%H2 in N2, which reveals redox properties suitable for heterogeneous catalysis, with the Pr-substituted materials showing the greatest reducibility at lower temperature.	Oct 2020
B18-Core EXAFS I11-High Resolution Powder Diffraction	Isolated zirconium centres captured from aqueous solution: the structure of zirconium mandelate revealed from NMR crystallography James M. Crosland , Emily K. Corlett , Dave Scapens , Nathalie Guillou , Steven P. Brown , Richard Walton Chemical Communications 19 DOI: 10.1039/D0CC03647A Diamond Proposal Number(s): [18786] Open Access Show Abstract ▼ Abstract: Zirconium tetramandelate (2-hydroxy-2-phenylacetate) has been used for selective gravimetric analysis of zirconium for over 70 years. Herein its crystal structure is reported from synchrotron powder X-ray diffraction and 13C solid-state NMR. The complex is a rare example of isolated zirconium cations, rather than the clusters prevalent in aqueous solutions.	Aug 2020
B18-Core EXAFS	(M,Ru)O2(M = Mg, Zn, Cu, Ni, Co) rutiles and their use as oxygen evolution electrocatalysts in membrane electrode assemblies under acidic conditions David Burnett , Enrico Petrucco , Katie M. Rigg , Christopher M. Zalitis , Jamie G. Lok , Reza J. Kashtiban , Martin R. Lees , Jonathan D. B. Sharman , Richard I. Walton Chemistry Of Materials DOI: 10.1021/acs.chemmater.0c01884 Diamond Proposal Number(s): [14239] Show Abstract ▼ Abstract: The rutiles (M,Ru)O2 (M = Mg, Zn, Co, Ni, Cu) are formed directly under hydrothermal conditions at 240 °C from potassium perruthenate and either peroxides of zinc or magnesium, or poorly crystalline oxides of cobalt, nickel or copper. The polycrystalline powders consist of lath-shaped crystallites, tens of nanometres in maximum dimension. Powder neutron diffraction shows that the materials have expanded a axis and contracted c axis compared to the parent RuO2, but there is no evidence of lowering of symmetry to other AO2-type structures, supported by Raman spectroscopy. Rietveld refinement shows no evidence for oxide non-stoichiometry and provides a formula (MxRu1-x)O2 with 0.14 < x < 0.2, depending on the substituent metal. This is supported by energy-dispersive X-ray analysis on the transmission electron microscope, while Ru K-edge XANES spectroscopy shows that upon inclusion of the substituent the average Ru oxidation state is increased to balance charge. Variable temperature magnetic measurements provide evidence for atomic homogeneity of the mixed metal materials, with suppression of the high temperature antiferromagnetism of RuO2 and increased magnetic moment. The new rutiles all show enhanced electrocatalysis compared to reference RuO2 materials for oxygen evolution in 1 M H2SO4 electrolyte at 60 °C, with higher specific and mass activity (per Ru) than a low surface area crystalline RuO2, and with less Ru dissolution over 1000 cycles compared to an RuO2 with a similar surface area. Magnesium substitution provides the optimum balance between stability and activity, despite leaching of the Mg2+ into solution, and this was proved in membrane electrode assemblies.	Jun 2020
B18-Core EXAFS	In situ XAFS of acid-resilient iridate pyrochlore oxygen evolution electrocatalysts under operating conditions David Burnett , Enrico Petrucco , Andrea E. Russell , Reza J. Kashtiban , Jonathan D. B. Sharman , Richard I. Walton Physical Chemistry Chemical Physics 38 DOI: 10.1039/D0CP01378A Diamond Proposal Number(s): [11646] Open Access Show Abstract ▼ Abstract: Pyrochlore iridates (Na,Ca)2−xIr2O6·H2O are acid-stable electrocatalysts that are candidates for use in electrolysers and fuel cells. Ir LIII-edge X-ray absorption fine structure spectroscopy in 1 M H2SO4 at oxygen evolution conditions suggests the involvement of the electrons from the conduction band of the metallic particles, rather than just surface iridium reacting.	May 2020
B18-Core EXAFS	Ga2.52V2.48O7.33(OH)0.67, a synthetic member of the nolanite/akdalaite-type family of oxyhydroxides containing trivalent vanadium Daniel S. Cook , Martin R. Lees , Janet M. Fisher , David Thompsett , Richard I. Walton Journal Of Solid State Chemistry DOI: 10.1016/j.jssc.2020.121396 Diamond Proposal Number(s): [13841] Show Abstract ▼ Abstract: The oxyhydroxide Ga2.52V2.48O7.33(OH)0.67 is prepared by reaction between Ga metal and Na3VO4 in a 1:1 monoethanolamine:water mixture at 240 °C. Powder neutron diffraction shows the material to be isostructural with the minerals nolanite and akdalaite, with cations occupying tetrahedral and octahedral interstitial sites in a hexagonal close-packed array of oxide/hydroxide (P63mc, a = 5.7906(2) Å, c = 9.2550(5) Å). Rietveld refinement against the data shows that Ga preferentially occupies tetrahedral sites, as well as some octahedral sites, and hence all V is octahedrally coordinated. The oxidation state of vanadium is confirmed as close to V3+ using V K-edge X-ray absorption near-edge structure spectroscopy, consistent with the refined chemical composition. The material is metastable, dehydrating around 300 °C and then decomposing above 500 °C, as shown by thermogravimetric analysis and thermodiffraction. The oxide Ga2.52V2.48O8 produced after dehydration at 300 °C is shown to contain a larger proportion of V4+ than the parent oxyhydroxide, to ensure charge balance, but the essential hexagonal structure is maintained. Variable temperature magnetisation measurements show that although both materials appear to obey the Curie-Weiss Law at high temperatures, at low temperatures the inverse susceptibility curves are non-linear. There is, however, no evidence for strong magnetic exchange and the extracted effective moments are consistent with the presence of more V3+ in the oxyhydroxide compared to the oxide.	Apr 2020
B18-Core EXAFS	Structures of mixed manganese ruthenium oxides (Mn 1−x Ru x )O 2 crystallised under acidic hydrothermal conditions Lucy K. Mcleod , Geoffrey H. Spikes , Reza J. Kashtiban , Marc Walker , Alan Chadwick , Jonathan Sharman , Richard I. Walton Dalton Transactions 135 DOI: 10.1039/C9DT04156G Diamond Proposal Number(s): [14239] Open Access Show Abstract ▼ Abstract: A synthesis method for the preparation of mixed manganese–ruthenium oxides is presented along with a detailed characterisation of the solids produced. The use of 1 M aqueous sulfuric acid mediates the redox reaction between KRuO4, KMnO4 and Mn2+ to form ternary oxides. At reaction temperature of 100 °C the products are mixtures of α-MnO2 (hollandite-type) and β-MnO2 (rutile-type), with some evidence of Ru incorporation in each from their expanded unit cell volumes. At reaction temperature of 200 °C solid-solutions β-Mn1−xRuxO2 are formed and materials with x ≤ 0.6 have been studied. The amount of Ru included in the oxide is greater than expected from the ratio of metals used in the synthesis, as determined by elemental analysis, implying that some Mn remains unreacted in solution. Powder X-ray diffraction (XRD) shows that while the unit cell volume expands in a linear manner, following Vegard's law, the tetragonal lattice parameters, and the a/c ratio, do not follow the extrapolated trends: this anisotropic behaviour is consistent with the different local coordination of the metals in the end members. Powder XRD patterns show increased peak broadening with increasing ruthenium content, which is corroborated by electron microscopy that shows nanocrystalline material. X-ray absorption near-edge spectra show that the average oxidation state of Mn in the solid solutions is reduced below +4 while that of Ru is increased above +4, suggesting some redistribution of charge. Analysis of the extended X-ray absorption fine structure provides complementary local structural information, confirming the formation of a solid solution, while X-ray photoelectron spectroscopy shows that the surface oxidation states of both Ru and Mn are on average lower than +4, suggesting a disordered surface layer may be present in the materials.	Feb 2020
I11-High Resolution Powder Diffraction	A hydrothermally stable ytterbium metal–organic framework as a bifunctional solid-acid catalyst for glucose conversion David Burnett , Ryan Oozeerally , Ralentri Pertiwi , Thomas W. Chamberlain , Nikolay Cherkasov , Guy J. Clarkson , Yuni K. Krisnandi , Volkan Degirmenci , Richard I. Walton Chemical Communications 316 DOI: 10.1039/C9CC05364F Diamond Proposal Number(s): [13284] Open Access Show Abstract ▼ Abstract: Yb6(BDC)7(OH)4(H2O)4 contains both bridging hydroxyls and metal-coordinated waters, possessing Brønsted and Lewis acid sites. The material crystallises from water at 200 °C. Using the solid as a heterogenous catalyst, glucose is converted into 5-hydroxymethylfurfural, via fructose, with a total selectivity of ∼70% after 24 hours at 140 °C in water alone: the material is recyclable with no loss of crystallinity.	Sep 2019

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