Biological Samples Preparation for Speciation at Cryogenic Temperature using High-Resolution  X-Ray Absorption Spectroscopy

The study of elements with X-ray absorption spectroscopy (XAS) is of particular interest when studying the role of metals in biological systems. Sample ...

Université Grenoble Alpes

ESRF, The European Synchrotron

Current models of the formation and distribution of gold deposits on Earth are based on the long-standing paradigm that hydrogen sulfide and chloride are the ligands responsible for gold mobilization and precipitation by fluids across the lithosphere. Here we challenge this view by demonstrating, using in situ X-ray absorption spectroscopy and solubility measurements, coupled with molecular dynamics and thermodynamic simulations, that sulfur radical species, such as the trisulfur ion S3(-), form very stable and soluble complexes with Au(+) in aqueous solution at elevated temperatures (>250 °C) and pressures (>100 bar). These species enable extraction, transport, and focused precipitation of gold by sulfur-rich fluids 10-100 times more efficiently than sulfide and chloride only. As a result, S3(-) exerts an important control on the source, concentration, and distribution of gold in its major economic deposits from magmatic, hydrothermal, and metamorphic settings. The growth and decay of S3(-) during the fluid generation and evolution is one of the key factors that determine the fate of gold in the lithosphere.

Sulfur radical species form gold deposits on Earth.

Original high-pressure glass-like carbon windows developed for x-ray spectroscopy applications are presented. The scientific and technological background of this new technical development is exposed, in particular the limitations of our existing beryllium windows in the context of x-ray absorption spectroscopy (XAS) measurements of solutions with very low solute concentrations at hydrothermal conditions (0.1-200 MPa, 30-600 °C). The benefits of glass-like carbon are exposed, notably its non-crystalline character, the absence of impurities which has been verified by micro-fluorescence laboratory measurements, and its non-toxicity which makes its machining safer. Finite elements mechanical calculations and experimental pressure tests were conducted to determine the pressure limits of windows with two different geometries: cylindrical (thickness 0.5 mm) and inversed-dome shape (thickness 0.5 mm at the tip of the dome). The former break at 150 MPa and the latter show no sign of rupture at 400 MPa. Recent XAS measurements conducted with the new dome shaped windows are presented to show the advantages of the design that allow for the detection of very low concentrations in the transmission mode (down to 30 ppm) and the acquisition of fluorescence XAS spectra in diluted solutions at high pressure. Eventually the perspectives of this original development are discussed. 

Novel high-pressure windows made of glass-like carbon for x-ray analysis.

We have studied the local structure and valence electronic unoccupied states of thermoelectric CsBiTe and superconducting CsBiPbTe (T ∼ 3 K) by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) measurements. The Bi-L edge EXAFS reveals wide Bi-Te distance distribution for both compounds indicating complex atomic arrangements in the studied system. The mean square relative displacements (MSRDs) of the Bi-Te bond distances appear largely increased in Pb substituted system due to larger overall local disorder, however, one of the Bi-Te bonds shows a reduced disorder. On the other hand, the Bi-L edge XANES is hardly affected by Pb substitution while the Te-L edge XANES reveals increased density of unoccupied Te 5p states. This suggests that the carriers introduced by the Pb substitution in CsBiPbTe preferentially goes on Te sites. Similarly, the Cs-L edge XANES also shows small changes due to Pb-substitution and reduced local disorder indicated by the reduced width of the Cs-L edge white line. We have also shown that the X-ray photoemission spectroscopy (XPS) measurements on various electronic core levels are in a qualitative agreement with the XANES results. These findings are consistent with carrier doping and a reduced disorder in one direction to be likely factors to drive the thermoelectric CsBiTe into a bulk superconductor by Pb-substitution in CsBiPbTe.

Determination of the local structure of CsBiPbTe (x = 0, 0.5) by X-ray absorption spectroscopy.

The construction of a high-temperature reaction cell for operando X-ray absorption spectroscopy characterization is reported. A dedicated cell was designed to operate as a plug-flow reactor using powder samples requiring gas flow and thermal treatment at high temperatures. The cell was successfully used in the reaction of dry reforming of methane (DRM). We present X-ray absorption results in the fluorescence detection mode on a 0.4 wt. % Ni/ZrO catalyst under realistic conditions at 750 °C, reproducing the conditions used for a conventional dynamic microreactor for the DRM reaction. The setup includes a gas distribution system that can be fully remotely operated. The reaction cell offers the possibility of transmission and fluorescence detection modes. The complete setup dedicated to the study of catalysts is permanently installed on the Collaborating Research Groups French Absorption spectroscopy beamline in Material and Environmental sciences (CRG-FAME) and French Absorption spectroscopy beamline in Material and Environmental sciences at Ultra-High Dilution (FAME-UHD) beamlines (BM30B and BM16) at the European Synchrotron Radiation Facility in Grenoble, France.

A new high temperature reactor for operando XAS: Application for the dry reforming of methane over Ni/ZrO catalyst.

The production of carbon-neutral fuels from CO presents an avenue for causing an appreciable effect in terms of volume toward the mitigation of global carbon emissions. To that end, the production of isoparaffin-rich fuels is highly desirable. Here, we demonstrate the potential of a multifunctional catalyst combination, consisting of a methanol producer (InCo) and a Zn-modified zeolite beta, which produces a mostly isoparaffinic hydrocarbon mixture from CO (up to ∼85% isoparaffin selectivity among hydrocarbons) at a CO conversion of >15%. The catalyst combination was thoroughly characterized via an extensive complement of techniques. Specifically,  X-ray absorption spectroscopy (XAS) reveals that Zn (which plays a crucial role of providing a hydrogenating function, improving the stability of the overall catalyst combination and isomerization performance) is likely present in the form of ZnO clusters within the zeolite component, in contrast to previously reported estimations.

Eric Lahera

OSUG,
UMS 832 CNRS,
OSUG, UMS 832 CNRS

Université Grenoble Alpes

Biological Samples Preparation for Speciation at Cryogenic Temperature using High-Resolution X-Ray Absorption Spectroscopy

Eric Lahera

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Université Grenoble Alpes

Biological Samples Preparation for Speciation at Cryogenic Temperature using High-Resolution X-Ray Absorption Spectroscopy

OSUG,
UMS 832 CNRS,
OSUG, UMS 832 CNRS