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Instruments / Technical Area	Publication Details	Published
I20-EDE-Energy Dispersive EXAFS (EDE)	Electrochemical Redox Couples: A Combined XAS and Modulation excitation study Armando Ibraliu , Xiaolei Fan , Luke Keenan , Daniel Bowron , Sofia Diaz-Moreno , Chris Hardacre XAFS2021 Show Abstract ▼ Abstract: The use of X-ray absorption spectroscopy (XAS) to follow liquid phase catalysed reactions is widely used. However, in catalysis, small quantities of active species are usually present, complicating the differentiation of spectator and active species. In these cases, the use of Modulation Excitation (ME) techniques can be used to achieve a better signal-to-noise ratio by cycle averaging. ME coupled with phase-sensitive detection can significantly improve the sensitivity of the spectroscopic technique by filtering out contributions of spectator species that are unaltered by the external stimulation. This has been used in combined XAS/DRIFTS studies of gas phase reactions, successfully identifying surface intermediates present in small concentration. [1] In this study, ME assisted by phase-sensitive detection analysis has been applied to the study of liquid-phase reactions using XAS. This methodology has been successfully applied to the study of the electrochemical oxidation of Na4FeII(CN)6. The experiment was undertaken in a newly three-electrode designed electrochemical cell at the I20-EDE beamline at Diamond Light Source. 30, 50, and 75 mM aqueous solutions of the iron complex in 1 M NaF/NaCl electrolytes were investigated. Cyclic voltammograms were measured during potential cycling with potential limits ± 1.5 V, at 200 and 300 mV/s scan rates, for 100 cycles. This perturbed the system reversibly allowing the cycle averaging of the XAS data. This study shows that ME assisted by phase-sensitive detection analysis can be successfully applied to XAS for the study of liquid-phase reactions. Signal-to-noise ratios were improved significantly through cycle averaging, and additional information were extracted from the phase-resolved FT-EXAFS spectra demonstrating the enhanced sensitivity.	Jul 2021
I20-EDE-Energy Dispersive EXAFS (EDE) I20-Scanning-X-ray spectroscopy (XAS/XES)	Structural evolution of iron forming iron oxide in a deep eutectic-solvothermal reaction Oliver S. Hammond , Ria S. Atri , Daniel Bowron , Liliana De Campo , Sofia Diaz-Moreno , Luke L. Keenan , James Doutch , Salvador Eslava , Karen J. Edler Nanoscale 13 DOI: 10.1039/D0NR08372K Diamond Proposal Number(s): [17574] Open Access Show Abstract ▼ Abstract: Deep eutectic solvents (DES) and their hydrated mixtures are used for solvothermal routes towards greener functional nanomaterials. Here we present the first static structural and in situ studies of the formation of iron oxide (hematite) nanoparticles in a DES of choline chloride[thin space (1/6-em)]:[thin space (1/6-em)]urea where xurea = 0.67 (aka. reline) as an exemplar solvothermal reaction, and observe the effects of water on the reaction. The initial speciation of Fe3+ in DES solutions was measured using extended X-ray absorption fine structure (EXAFS), while the atomistic structure of the mixture was resolved from neutron and X-ray diffraction and empirical potential structure refinement (EPSR) modelling. The reaction was monitored using in situ small-angle neutron scattering (SANS), to determine mesoscale changes, and EXAFS, to determine local rearrangements of order around iron ions. It is shown that iron salts form an octahedral [Fe(L)3(Cl)3] complex where (L) represents various O-containing ligands. Solubilised Fe3+ induced subtle structural rearrangements in the DES due to abstraction of chloride into complexes and distortion of H-bonding around complexes. EXAFS suggests the complex forms [–O–Fe–O–] oligomers by reaction with the products of thermal hydrolysis of urea, and is thus pseudo-zero-order in iron. In the hydrated DES, the reaction, nucleation and growth proceeds rapidly, whereas in the pure DES, the reaction initially proceeds quickly, but suddenly slows after 5000 s. In situ SANS and static small-angle X-ray scattering (SAXS) experiments reveal that nanoparticles spontaneously nucleate after 5000 s of reaction time in the pure DES before slow growth. Contrast effects observed in SANS measurements suggest that hydrated DES preferentially form 1D particle morphologies because of choline selectively capping surface crystal facets to direct growth along certain axes, whereas capping is restricted by the solvent structure in the pure DES.	Jan 2021
	Resilience of malic acid natural deep eutectic solvent nanostructure to solidification and hydration Oliver S. Hammond , Daniel Timothy Bowron , Andrew J. Jackson , Thomas Arnold , Adrian Sanchez Fernandez , Nikolaos Tsapatsaris , Victoria Garcia Sakai , Karen J. Edler The Journal Of Physical Chemistry B DOI: 10.1021/acs.jpcb.7b05454 Open Access Show Abstract ▼ Abstract: Little is presently known about the unique nanostructure of Deep Eutectic Solvents (DES). The order of the liquid-solid phase transition is contended and whether DES-water mixtures are merely aqueous solutions, or have properties dominated by the eutectic pair, is unclear. Here, we unambiguously show the structure of choline chloride-malic acid (malicine) as a liquid, and also in solid and hydrated forms, using neutron total scattering on D/H isotope-substituted samples, and quasi-elastic neutron scattering (QENS). Data were refined using Empirical Potential Structure Refinement. We show evidence for a stoichiometric complex ion cluster in the disordered liquid, with strong choline-chloride bonding and a hydrogen bond donor (HBD) contribution. The 1:1 eutectic stoichiometry makes these ionic domains more well-defined, with less HBD clustering than seen previously for reline. There is minimal structural difference for the solidified material, demonstrating that this DES solidification is a glass transition rather than a first order phase change. QENS data support this by showing a gradual change in solvent dynamics rather than a step change. The DES structure is mostly retained upon hydration, with water acting both as a secondary smaller HBD at closer range to choline than malic acid, and forming transient wormlike aggregates. This new understanding of DES structure will aid understanding of the properties of these novel green solvents on the molecular length scale in chemical processes, as well as giving an insight into the apparent role of natural DESs in plant physiology.	Jul 2017
I20-Scanning-X-ray spectroscopy (XAS/XES) Optics	Rotation of X-ray polarization in the glitches of a silicon crystal monochromator John Sutter , Roberto Boada Romero , Daniel Bowron , Sergey Stepanov , Sofia Diaz-Moreno Journal Of Applied Crystallography 49, 1209-1222 DOI: 10.1107/S1600576716009183 Open Access Show Abstract ▼ Abstract: EXAFS studies on dilute samples are usually carried out by collecting the fluorescence yield using a large-area multi-element detector. This method is susceptible to the ``glitches'' produced by all single-crystal monochromators. Glitches are sharp dips or spikes in the diffracted intensity at specific crystal orientations. If incorrectly compensated, they degrade the spectroscopic data. Normalization of the fluorescence signal by the incident flux alone is sometimes insufficient to compensate for the glitches. Measurements performed at the state-of-the-art wiggler beamline I20-scanning at the Diamond Light Source have shown that the glitches alter the spatial distribution of the sample’s quasi-elastic X-ray scattering. Because glitches result from additional Bragg reflections, multiple-beam dynamical diffraction theory is necessary to understand their effects. Here, the glitches of the Si (111) four-bounce monochromator of I20-scanning just above the Ni $K$ edge are associated with their Bragg reflections. A fitting procedure that treats coherent and Compton scattering is developed and applied to a sample of extremely dilute (100~micromolal) aqueous solution of Ni(NO$_3$)$_2$. The depolarization of the wiggler X-ray beam out of the electron orbit is modeled. The fits achieve good agreement with the sample's quasi-elastic scattering with just a few parameters. The X-ray polarization is rotated up to $\pm 4.3^\circ$ within the glitches, as predicted by dynamical diffraction. These results will help users normalize EXAFS data at glitches.	Aug 2016

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