Advanced design of a x-ray absorption spectroscopy setup for measuring transition metals speciation in molten carbonates, hydroxides and hydrogenosulfates.

Battery recycling is currently becoming a crucial issue. One possible treatment path involves the use of molten salts. A mechanistic understanding of the underlying processes requires being able to analyze in situ speciation in molten salts at various temperatures. This can be advantageously achieved using x-ray absorption spectroscopy, the use of Quick-EXAFS facilities being particularly appropriate. Consequently, this paper presents the design and development of a new setup allowing carrying out Quick-EXAFS experiments in oxidizing molten salts at high temperatures. We describe the different components of a cell and the performance of the heating device. We illustrate the capabilities of the setup by analyzing the temperature evolution of Co speciation upon dissolution of LiCoO2, a typical battery electrode material, in molten carbonates, hydroxides, and hydrogenosulphates.

Effectiveness of Ligand Denticity-Dependent Oxidation Protection in Copper MOD Inks.

The recent cost-driven transition from silver- to copper-based inks for printing on flexible substrates is connected with new key challenges. Given the high oxidation sensitivity of copper inks before, during, and after the curing process, the conductivity and thereby the device performance can be affected. Strategies to limit or even avoid this drawback include the development of metal organic decomposition (MOD) inks with selected "protective" ligands. In this study, the influence of the ligand on the oxide formation during the ink decomposition process is described using a wide variety of in situ characterization techniques. It is demonstrated that bidentate ligands provide an improved oxidation barrier, although the copper preservation mechanism has its limits: oxygen can interfere in every reduction pathway depending on the curing duration and atmospheric conditions. The generated insights can be applied in the further evolution toward ambient-curable copper MOD inks.

Aggregating ability of ferric chloride in the presence of phosphate ligand.

Complexing anions such as phosphate or silicate play an ambivalent role in the performance of hydrolyzing metal coagulants: On one hand, they significantly interfere with the hydrolytic pathway of conventional iron or aluminum coagulants, the associated destabilization mechanism remaining rather elusive; on the other hand, they have been shown to be key ingredients in the formulation of innovative coagulant solutions exhibiting improved removal efficiency, their action mechanism at the molecular scale being presently poorly understood. In this paper, we explore the effect of small additions of phosphate ligand on the chemical coagulation of silica nanoparticles with ferric chloride. Transmission Electron Microscopy-Energy Dispersed X-ray Spectroscopy (TEM-EDXS) combined with Extended X-ray absorption Fine Structure Spectroscopy (EXAFS) at the Fe K-edge are used to provide an insight into the nature of coagulant species, whereas jar-tests, laser diffraction, Small Angle X-ray Scattering (SAXS), and electrophoretic mobility, are used to investigate the aggregation dynamics of silica particles in the presence of phosphate ligand. We show that, in spite of a slight increase in the consumption of iron coagulant, the addition of phosphate significantly improves the formation of silica aggregates provided that the elemental Fe/P ratio remains above 7. Such effects originate from both a large increase in the overall number of coagulant species, the binding of a phosphate ligand terminating the growth of polymeric chains of edge-sharing Fe octahedra, and a change in the nature of the coagulant species that evolves with the Fe/P ratio, small polycations built-up from Fe-oligomers linked by phosphate tetrahedra being eventually formed. Those non-equilibrium nanosize Fe-P coagulant species assemble the silica nanoparticles to form hetero-aggregates whose structure is consistent with a Diffusion-Limited Cluster Aggregation mechanism.

Thermal stability of PMMA-LDH nanocomposites: decoupling the physical barrier, radical trapping, and charring contributions using XAS/WAXS/Raman time-resolved experiments.

In-depth understanding of the thermal stability of polymer-clay nanocomposites requires the use of advanced time-resolved techniques combined with multivariate data analysis, as well as the preparation of layered nanofillers with well-defined composition. The layered double hydroxide (LDH) compounds Zn2Al(OH)6·nH2O, Zn2Al0.75Fe0.25(OH)6·nH2O, ZnCuAl(OH)6·nH2O, and ZnCuAl0.5Fe0.5(OH)6·nH2O were prepared, each designed to specifically identify the physical barrier, radical trapping, and char formation contributions to the thermal stability of the PMMA-LDH nanocomposites. The unique combination of conventional methods (TG, DSC, and Raman spectroscopy) and synchrotron radiation techniques (XAS and WAXS), applied during PMMA-LDH heating, revealed the synergetic (of iron) and antagonist (of copper) effects of the LDH layers transformations on the three main endothermic steps of mass loss of the polymer. The diffusion barrier effect was proved by the downshift of the PMMA thermal decomposition temperature caused by the decrease of the LDH edifice thermostability when divalent cations were substituted in the LDH (passing from PMMA-Zn2Al(OH)6·nH2O to PMMA-ZnCuAl(OH)6·nH2O). For PMMA-Zn2Al0.75Fe0.25(OH)6·nH2O, a cooperative contribution of iron reduction, stabilisation of layered edifice, and radical trapping effects was observed for the thermal stability of the nanocomposite. LDH also acted as a diffusion barrier to the efflux and evaporation of depolymerized species, favouring the charring which exerts an additional contribution to thermal stability of the PMMA-LDH nanocomposites.

Controlling the atomic distribution in PtPd nanoparticles: thermal stability and reactivity during NO abatement.

In situ X-ray absorption spectroscopy and mass spectrometry measurements were employed to simultaneously probe the atom specific short range order and reactivity of Pd and PtPd nanoparticles towards NO decomposition at 300 °C. The nanoparticles were synthesized by a well controlled, eco-friendly wet chemical reduction of metal salts and later supported on activated carbon. Particularly for the bimetallic PtPd samples, distinct atomic arrangements were achieved using a seeding growth method, which allowed producing a random nanoalloy, or nanoparticles with Pt- or Pd-rich core. X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray diffraction provided additional insights on their electronic, morphological and long range order structural properties. The results revealed that the higher the thermal induced atomic migration observed within the nanoparticles during thermal treatments, the least were their reactivity for NO abatement.

The SAMBA quick-EXAFS monochromator: XAS with edge jumping.

Results and performances of the QEXAFS double monochromator of the SAMBA beamline (Synchrotron SOLEIL) are presented. The device is capable of speeds of up to 40 Hz, while giving the user the possibility to choose the amplitude of the scan from 0.1° to 4° in a few seconds. The device is composed of two independent units and it is possible to perform scans alternating between two different crystals, literally jumping from low (4 keV) to high (37 keV) energies.

Novel angular encoder for a quick-extended x-ray absorption fine structure monochromator.

New concepts for time-resolved x-ray absorption spectroscopy using the quick-extended x-ray absorption fine structure (QEXAFS) method are presented. QEXAFS is a powerful tool to gain structural information about, e.g., fast chemical reactions or phase transitions on a subsecond scale. This can be achieved with a monochromator design that employs a channel-cut crystal on a cam driven tilt table for rapid angular oscillations of the Bragg angle. A new angular encoder system and a new data acquisition were described and characterized that were applied to a QEXAFS monochromator to get spectra with a directly measured accurate energy scale. New electronics were designed to allow a fast acquisition of the Bragg angle values and the absorption data during the measurements simultaneously.

Stimuli-responsive controlled growth of mono- and bidimensional particles from basic zirconium sulfate hydrosols.

A thermostimulated sol-gel transition in a system prepared by mixing a ZrOCl(2) acidified solution to a hot H(2)SO(4) aqueous solution was studied by dynamic rheological measurements and quasi-elastic light scattering. The effect of temperature and of molar ratio R(S) = [Zr]/[SO(4)] on the gelation kinetics was analyzed using the mass fractal aggregate growth model. This study shows that the linear growth of aggregates occurs at the early period of transformation, while bidimensional growth occurs at the advanced stage. The bidimensional growth can be shifted toward monodimensional growth by decreasing the aggregation rate by controlling the temperature and/or molar ratio R(S). EXAFS and Raman results gave evidence that the linear chain growth is supported by covalent sulfate bonding between primary building blocks. At the advanced stage of aggregation, the assembly of linear chains through hydrogen bonding gave rise to the growth of bidimensional particles.

Combining two structural techniques on the micrometer scale: micro-XAS and micro-Raman spectroscopy.

X-ray absorption and Raman spectroscopies are complementary in the sense that both give very precise information about the local structure of a sample, both are not restricted to crystalline materials, and in both cases the volumes of the material probed are similar. The X-ray technique has the advantage of being element- and orbital-selective, and sensitive to orientational effects owing to polarization selection rules. In many cases, however, its analysis can present some ambiguity. Combining the two techniques on a micrometer scale could therefore be a very powerful method structurally. In this paper the experimental set-up developed at the LUCIA beamline and its application to a natural mineral are described.

Evolution of iron speciation during hydration of C4AF.

It is now well accepted and demonstrated that calcium silicate, calcium aluminate and calcium sulfo aluminate (ettringite, AFm) phases exhibit a good capability to fix metals and metalloids. Unfortunately the role of minor phases and especially calcium-ferric aluminate phase, shorthand C4AF is not well defined. In other systems like in soils or sediments iron phases play a key role in the fixation of pollutant. In cement sorption isotherms, indicated that various metals can be retained by the C4AF hydrated products. Therefore the capabilities of those phase to retain heavy metal should not be neglected. Previous investigations have shown that the minerals formed during the hydration of C4AF are similar to those formed from C3A (pure tri-calcium aluminate) under comparable conditions. Nevertheless no investigation was conducted at the molecular level and there is still a controversy whether Fe substitutes for Al in the hydrated minerals in whole or in part, or if it forms FeOOH clusters scattered throughout the matrix. In this context we have conducted XAS experiments using synchrotron radiation. It was found that the hydration of C4AF forms C3AH6 (hydrogarnet) in which Fe randomly substitutes for Al as well as an amorphous FeOOH phase. Intermediate products like AFm (i.e., an ill organized lamellar phase) are also formed but rapidly evolve to C3AH6; iron does not seem to be incorporated in the AFm structure.

Time-resolved study of the oxidation of ethanol by cerium(IV) using combined quick-XANES, UV-vis, and Raman spectroscopies.

Time-resolved X-ray absorption spectroscopy (Quick-XANES) has been combined with UV-vis and Raman spectroscopies to study the in situ reduction of Ce4+ to Ce3+ in ethanolic solution with a time resolution of ca. 4-5 s. For this purpose, a cam-driven oscillating double-crystal monochromator with a channel-cut crystal was combined with two spectrometers for UV-vis and Raman spectroscopies in a specialized cell which allows one to fit the optical pathways for all three spectroscopies individually. The results show that high-quality results can be obtained simultaneously, thus giving a detailed insight into the mechanisms of the investigated chemical reaction. The continuous release of nitrate and ethanol ligands from the initial Ce4+ into the solution finally leads to a trivalent cerium species which is only coordinated with water molecules after about 1800 s of reaction time.

Structural modification on silica glass surface induced by thermal poling for second harmonic generation.

O-K edge XANES spectroscopy evidences structural modification induced by thermal poling treatment in surfaces of bulk Herasil silica glass presenting second harmonic generation. Considering model silicon dioxide clusters, calculations based on full multiple scattering approach have been performed in order to explain accurately the differences observed on XANES spectra at different stage of the poling treatment. These structural modifications on extreme surface affect both network and defects by breaking Si-O-Si bridging bonds. Despite of the formation of bridging bond occurring during the thermal depoling -which erases the SHG inside the glass-, the initial structure of the unpoled sample is not reproduced.

A synthetic, structural, magnetic, and spectral study of several [Fe[tris(pyrazolyl)methane]2](BF4)2 complexes: observation of an unusual spin-state crossover.

The complexes [Fe[HC(3,5-Me2pz)3]2](BF4)2 (1), [Fe[HC(pz)3]2](BF4)2 (2), and [Fe[PhC(pz)2(py)]2](BF4)2 (3) (pz = 1-pyrazolyl ring, py = pyridyl ring) have been synthesized by the reaction of the appropriate ligand with Fe(BF4)2.6H2O. Complex 1 is high-spin in the solid state and in solution at 298 K. In the solid phase, it undergoes a decrease in magnetic moment at lower temperatures, changing at ca. 206 K to a mixture of high-spin and low-spin forms, a spin-state mixture that does not change upon subsequent cooling to 5 K. Crystallographically, there is only one iron(II) site in the ambient-temperature solid-state structure, a structure that clearly shows the complex is high-spin. Mössbauer spectral studies show conclusively that the magnetic moment change observed at lower temperatures arises from the complex changing from a high-spin state at higher temperatures to a 50:50 mixture of high-spin and low-spin states at lower temperatures. Complexes 2 and 3 are low-spin in the solid phase at room temperature. Complex 2 in the solid phase gradually changes over to the high-spin state upon heating above 295 K and is completely high-spin at ca. 470 K. In solution, variable-temperature 1H NMR spectra of 2 show both high-spin and low-spin forms are present, with the percentage of the paramagnetic form increasing as the temperature increases. Complex 3 is low-spin at all temperatures studied in both the solid phase and solution. An X-ray absorption spectral study has been undertaken to investigate the electronic spin states of [Fe[HC(3,5-Me2pz)3]2](BF4)2 and [Fe[HC(pz)3]2](BF4)2. Crystallographic information: 2 is monoclinic, P2(1)/n, a = 10.1891(2) A, b = 7.6223(2) A, c = 17.2411(4) A, beta = 100.7733(12) degrees, Z = 2; 3 is triclinic, P1, a = 12.4769(2) A, b = 12.7449(2) A, c = 13.0215(2) A, alpha = 83.0105(8) degrees, beta = 84.5554(7) degrees, gamma = 62.5797(2) degrees, Z = 2.