I19-Small Molecule Single Crystal Diffraction
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David P.
August
,
Robert A. W.
Dryfe
,
Sarah J.
Haigh
,
Paige R. C.
Kent
,
David A.
Leigh
,
Jean-Francois
Lemonnier
,
Zheling
Li
,
Christopher A.
Muryn
,
Leoni I.
Palmer
,
Yiwei
Song
,
George F. S.
Whitehead
,
Robert J.
Young
Diamond Proposal Number(s):
[17379]
Abstract: Fabrics—materials consisting of layers of woven fibres—are some of the most important materials in everyday life. Previous nanoscale weaves include isotropic crystalline covalent organic frameworks that feature rigid helical strands interlaced in all three dimensions, rather than the two-dimensional layers of flexible woven strands that give conventional textiles their characteristic flexibility, thinness, anisotropic strength and porosity. A supramolecular two-dimensional kagome weave and a single-layer, surface-supported, interwoven two-dimensional polymer have also been reported. The direct, bottom-up assembly of molecular building blocks into linear organic polymer chains woven in two dimensions has been proposed on a number of occasions, but has not previously been achieved. Here we demonstrate that by using an anion and metal ion template, woven molecular ‘tiles’ can be tessellated into a material consisting of alternating aliphatic and aromatic segmented polymer strands, interwoven within discrete layers. Connections between slowly precipitating pre-woven grids, followed by the removal of the ion template, result in a wholly organic molecular material that forms as stacks and clusters of thin sheets—each sheet up to hundreds of micrometres long and wide but only about four nanometres thick—in which warp and weft single-chain polymer strands remain associated through periodic mechanical entanglements within each sheet. Atomic force microscopy and scanning electron microscopy show clusters and, occasionally, isolated individual sheets that, following demetallation, have slid apart from others with which they were stacked during the tessellation and polymerization process. The layered two-dimensional molecularly woven material has long-range order, is birefringent, is twice as stiff as the constituent linear polymer, and delaminates and tears along well-defined lines in the manner of a macroscopic textile. When incorporated into a polymer-supported membrane, it acts as a net, slowing the passage of large ions while letting smaller ions through.
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Dec 2020
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B22-Multimode InfraRed imaging And Microspectroscopy
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Xinchen
Kang
,
Bin
Wang
,
Kui
Hu
,
Kai
Lyu
,
Xue
Han
,
Ben F.
Spencer
,
Mark D.
Frogley
,
Floriana
Tuna
,
Eric J. L.
Mcinnes
,
Robert A. W.
Dryfe
,
Buxing
Han
,
Sihai
Yang
,
Martin
Schroeder
Diamond Proposal Number(s):
[19171]
Open Access
Abstract: Efficient electro-reduction of CO2 over metal–organic framework (MOF) materials is hindered by the poor contact between thermally synthesized MOF particles and the electrode surface, which leads to low Faradaic efficiency for a given product and poor electrochemical stability of the catalyst. We report a MOF-based electrode prepared via electro-synthesis of MFM-300(In) on an indium foil, and its activity for the electrochemical reduction of CO2 is assessed. The resultant MFM-300(In)-e/In electrode shows a 1 order of magnitude improvement in conductivity compared with that for MFM-300(In)/carbon-paper electrodes. MFM-300(In)-e/In exhibits a current density of 46.1 mA cm–2 at an applied potential of −2.15 V vs Ag/Ag+ for the electro-reduction of CO2 in organic electrolyte, achieving an exceptional Faradaic efficiency of 99.1% for the formation of formic acid. The facile preparation of the MFM-300(In)-e/In electrode, coupled with its excellent electrochemical stability, provides a new pathway to develop efficient electro-catalysts for CO2 reduction.
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Sep 2020
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B22-Multimode InfraRed imaging And Microspectroscopy
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Xinchen
Kang
,
Kai
Lyu
,
Lili
Li
,
Jiangnan
Li
,
Louis
Kimberley
,
Bin
Wang
,
Lifei
Liu
,
Yongqiang
Cheng
,
Mark D.
Frogley
,
Svemir
Rudic
,
Anibal J.
Ramirez-Cuesta
,
Robert A. W.
Dryfe
,
Buxing
Han
,
Sihai
Yang
,
Martin
Schroder
Diamond Proposal Number(s):
[19171]
Open Access
Abstract: Incorporation of mesopores and active sites into metal-organic framework (MOF) materials to uncover new efficient catalysts is a highly desirable but challenging task. We report the first example of a mesoporous MOF obtained by templated electrosynthesis using an ionic liquid as both electrolyte and template. The mesoporous Cu(II)-MOF MFM-100 has been synthesised in 100 seconds at room temperature, and this material incorporates crystal defects with uncoupled Cu(II) centres as evidenced by confocal fluorescence microscopy and electron paramagnetic resonance spectroscopy. MFM-100 prepared in this way shows exceptional catalytic activity for the aerobic oxidation of alcohols to produce aldehydes in near quantitative yield and selectivity under mild conditions, as well as having excellent stability and reusability over repeated cycles. The catalyst-substrate binding interactions have been probed by inelastic neutron scattering. This study offers a simple strategy to create mesopores and active sites simultaneously via electrochemical formation of crystal defects to promote efficient catalysis using MOFs.
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Oct 2019
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Open Access
Abstract: The mechanism of the two-phase Brust–Schiffrin synthesis of alkane thiol protected metal nanoparticles is known to be highly sensitive to the precursor species and reactant conditions. In this work X-ray absorption spectroscopy is used in conjunction with liquid/liquid electrochemistry to highlight the significance of Br− in the reaction mechanism. The species [AuBr4]− is shown to be a preferable precursor in the Brust–Schiffrin method as it is more resistant to the formation of Au(I) thiolate species than [AuCl4]−. Previous literature has demonstrated that avoidance of the Au(I) thiolate is critical to achieving a good yield of nanoparticles, as [Au(I)X2]− species are more readily reduced by NaBH4. We propose that the observed behavior of [AuBr4]− species described herein explains the discrepancies in reported behavior present in the literature to date. This new mechanistic understanding should enable nanoparticle synthesis with a higher yield and reduce particle size polydispersity.
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Sep 2017
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B18-Core EXAFS
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Diamond Proposal Number(s):
[13953]
Abstract: We report the use of XAFS (X-ray absorption fine structure) as an in situ method to follow the electrochemically driven deposition of palladium nanoparticles at a liquid/liquid interface. A novel glass/plastic hybrid electrochemical cell was used to enable control of the potential applied to the liquid/liquid interface. In situ measurements indicate that the nucleation of metallic nanoparticles can be triggered through chronoamperometry or cyclic voltammetry. In contrast to spontaneous nucleation at the liquid/liquid interface, whereby fluctuations in Pd oxidation state and concentration are observed, under a fixed interfacial potential the growth process occurs at a steady rate leading to a build-up of palladium at the interface. Raman spectroscopy of the deposit suggests that the organic electrolyte binds directly to the surface of the deposited nanoparticles. It was found that the introduction of citric acid results in the formation of spherical nanoparticles at the interface.
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Mar 2017
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Open Access
Abstract: Energy dispersive extended X-ray absorption fine structure (EDE) has been applied to Pd nanoparticle nucleation at a liquid/liquid interface under control over the interfacial potential and thereby the driving force for nucleation. Preliminary analysis focusing on Pd K edge-step height determination shows that under supersaturated conditions the concentration of Pd near the interface fluctuate over a period of several hours, likely due to the continuous formation and dissolution of sub-critical nuclei. Open circuit potential measurements conducted ex-situ in a liquid/liquid electrochemical cell support this view, showing that the fluctuations in Pd concentration are also visible as variations in potential across the liquid/liquid interface. By decreasing the interfacial potential through inclusion of a common ion (tetraethylammonium, TEA+) the Pd nanoparticle growth rate could be slowed down, resulting in a smooth nucleation process. Eventually, when the TEA+ ions reached an equilibrium potential, Pd nucleation and particle growth were inhibited.
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May 2016
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[8861]
Open Access
Abstract: With the advent of high-throughput and imaging core level spectroscopies (including X-ray absorption spectroscopy, XAS, as well as electron energy loss spectroscopy, EELS), automated data processing, visualisation and analytics will become a necessity. As a first step towards these objectives we examined the possibilities and limitations of a simple automated XANES peak fitting procedure written in MATLAB, for the parametrisation of XANES features, including ionisation potentials as well as the energies and intensities of electronic transitions. Using a series of Au L3-edge XANES reference spectra we show that most of the relevant information can be captured through a small number of rules applied to constrain the fits. Uncertainty in this strategy arises mostly when the ionisation potential (IP) overlaps with weak electronic transitions or features in the continuum beyond the IP, which can result in ambiguity through multiple equally good fits.
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May 2016
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[8861]
Open Access
Abstract: Voltammetry for charge (ion and electron) transfer at two immiscible electrolyte solutions (VCTIES) has been used to provide insight into the ligand exchange and redox processes taking place during the interfacial reaction of aqueous hexacyanoferrate(II) with tetrachloroaurate ([AuCl4]−) in 1,2-dichloroethane (DCE). VCTIES permitted the detection of the reactants, intermediates and products at the liquid/liquid interface. A model for the sequence of interfacial processes was established with the support of speciation analysis of the key elementary reactions by X-ray absorption spectroscopy (XAS). The potential-driven transfer of [AuCl4]− from the organic into the aqueous phase is followed by reduction and ligand exchange by the aqueous hexacyanoferrate(II) to form dicyanoaurate ([Au(CN)2]−). Inferences from the reactions point to the likely formation of [AuCl2]− during the reduction sequence. The reaction is influenced by ligand exchange equilibria between [AuCl4]−, [AuCl3(OH)]– and [AuCl2(OH)2]–which are shown to be dependent on the chloride ion concentration and pH of the solution. The difference between the Gibbs energy of transfer at the water | DCE interface View the MathML source(ΔGDCEW°)of AuCl4– and [AuCl3(OH)]–, and the difference between [AuCl3(OH)]– and [AuCl2(OH)2]–were found to change by a value close to the difference between View the MathML sourceΔGDCEW° of Cl– and that of OH–. The intermediate Au(I) species, [AuCl2]−, was seen to decompose at neutral pH and in the absence of Cl– in water to form metallic Au, although it was stable in >10 mM HCl for an hour. Time-dependent VCTIES and X-ray absorption fine structure (XAFS) speciation analysis of the homogeneous aqueous phase indicate that reaction between [AuCl4]− and hexacyanoferrate(II) is accompanied by the formation of an intermediate ionic species, formed when the concentration of [AuCl4]− is close to that of hexacyanoferrate(II). This species, whose identity was not precisely determined, was also generated by reaction between [AuCl2]− and hexacyanoferrate(III). The species is shown by VCTIES to be more hydrophilic than [Au(CN)2]−, [AuCl2]− and [AuCl4]−.
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Feb 2016
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B18-Core EXAFS
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S.-y
Chang
,
Y.
Grunder
,
S. G.
Booth
,
L. B.
Molleta
,
A.
Uehara
,
J. F. W.
Mosselmans
,
G.
Cibin
,
V.-t.
Pham
,
L.
Nataf
,
R. A.
Dryfe
,
S. L. M
Schroeder
Diamond Proposal Number(s):
[8405]
Open Access
Abstract: The interfacial reduction of aqueous [PdCl4]2− at the interface with an organic solution of ferrocene has been characterised by X-ray absorption fine structure (XAFS) spectroscopy. Use of a liquid–liquid interface as a model for homogeneous nucleation permits control of the thermodynamic driving force for nucleation, through variation of the [PdCl4]2− and ferrocene concentrations in the bulk of the adjacent phases. We demonstrate that this approach permits characterisation of the system under conditions of (i) no particle nucleation, (ii) fast spontaneous nucleation of stable nanoparticles and (iii) an intermediate state, in which formation of metastable Pd sub-critical nuclei takes place. Analysis of the XAFS spectra in the metastable state revealed a stochastically fluctuating equilibrium in which Pd nuclei are constantly formed and re-dissolved, as evident from oxidation state fluctuations detected by the Pd XAFS. Supersaturation was evidently sufficient to induce nanoparticle formation but insufficient for nuclei to grow beyond the critical cluster size. We were able to maintain a system in this metastable state for several hours. Such sub-critical clusters are predicted by classical nucleation theory, but have not been detected except in liquid-cell TEM imaging and scanning electrochemical microscopy studies.
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Dec 2015
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B18-Core EXAFS
I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[11293, 8861]
Open Access
Abstract: The mechanism of the Brust-Schiffrin gold nanoparticle synthesis has been investigated through the use
of ion transfer voltammetry at the water|1,2-dichloroethane
(DCE) solution interface, combined with X-ray absorption fine structure
(XAFS) of the reaction between [AuCl4]-
and thiol (RSH) in homogeneous toluene (TL) solution. Ion transfer calculations indi-
cate the formation of [AuCl2]- at RSH:Au ratios from 0.2 – 2 with a time-dependent variation observed over several days. At RSH:Au ratios above 2 and after time periods greater than 24 hours, the formation of Au(I)SR is also observed. The relative concentrations of reaction products observed at the liquid/liquid interface are in excellent agreement with those observed by XAFS for the corresponding reaction in a single homogeneous phase. BH4- ion transfer reactions between water and DCE indicate that the reduction of [AuCl4]-
and/or [AuCl2]- to Au nanoparticles by BH4- proceeds in the bulk organic phase. On the other hand, BH4- was unable to reduce the insoluble [Au(I)SR]n species to Au nanoparticles. The number and size of the nanoparticles formed was dependent on the concentration ratio of
RSH:Au, as well as the experimental duration because of the competing
formation of the [Au(I)SR]n
precipitate. Higher concentrations of nanoparticles, with diameters of 1.0 – 1.5 nm, were formed at RSH:Au ratios from 1 to 2.
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Nov 2015
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