X-ray Near-edge Spectroscopy Research Articles

Unveiling Reaction Mechanisms of Non-Aqueous Zn-Ion Batteries – Zn/LiFePO4 System

Zinc-ion batteries (ZIBs) are among the most promising energy storage technologies because of their low cost, safety, and environmental friendliness. In this work, we focus on investigating the electrochemical reaction mechanisms of ZIBs with Lithium iron phosphate (LiFePO4) as an active material in the positive electrode, Zn(OTf)2+LiCl dissolving Tetraethylene glycol dimethyl ether (TEGDME) as the electrolyte, as well as metallic Zinc as the negative electrode. After testing the ZIB cells by galvanostatic cycling, the cells with TEGDME exhibit the best electrochemical performance in terms of long-term stability. The initial specific discharge capacity is 118.3 mAh g-1 and the capacity retention is 91.4% after 100 cycles at a current density of 10 mA g-1. We propose the reaction mechanisms during the charge-discharge processes involve extraction/insertion processes of Li+ into/out of the olivine structure of LiFePO4 as evidenced by X-ray near-edge spectroscopy (XANES). According to X-ray diffraction (XRD) analysis of the discharged and charged LiFePO4 electrodes, the crystal structure changes from LiFePO4 to FePO4 when charging and back into LiFePO4 again when discharging. Besides, XRD and scanning electron microscopy (SEM) confirm that the cycled Zn electrode is hardly present with passivation and/or corrosion. Therefore, this new combination of Zn/LiFePO4 and TEGDME has a potential for ZIB applications.

Biological Oxidation of Fe(II)-Bearing Smectite by Microaerophilic Iron Oxidizer Sideroxydans lithotrophicus Using Dual Mto and Cyc2 Iron Oxidation Pathways.

Fe(II) clays are common across many environments, making them a potentially significant microbial substrate, yet clays are not well established as an electron donor. Therefore, we explored whether Fe(II)-smectite supports the growth of Sideroxydans lithotrophicus ES-1, a microaerophilic Fe(II)-oxidizing bacterium (FeOB), using synthesized trioctahedral Fe(II)-smectite and 2% oxygen. S. lithotrophicus grew substantially and can oxidize Fe(II)-smectite to a higher extent than abiotic oxidation, based on X-ray near-edge spectroscopy (XANES). Sequential extraction showed that edge-Fe(II) is oxidized before interior-Fe(II) in both biotic and abiotic experiments. The resulting Fe(III) remains in smectite, as secondary minerals were not detected in biotic and abiotic oxidation products by XANES and Mössbauer spectroscopy. To determine the genes involved, we compared S. lithotrophicus grown on smectite versus Fe(II)-citrate using reverse-transcription quantitative PCR and found that cyc2 genes were highly expressed on both substrates, while mtoA was upregulated on smectite. Proteomics confirmed that Mto proteins were only expressed on smectite, indicating that ES-1 uses the Mto pathway to access solid Fe(II). We integrate our results into a biochemical and mineralogical model of microbial smectite oxidation. This work increases the known substrates for FeOB growth and expands the mechanisms of Fe(II)-smectite alteration in the environment.

Sparse ab initio x-ray transmission spectrotomography for nanoscopic compositional analysis of functional materials.

The performance of functional materials is either driven or limited by nanoscopic heterogeneities distributed throughout the material's volume. To better our understanding of these materials, we need characterization tools that allow us to determine the nature and distribution of these heterogeneities in their native geometry in 3D. Here, we introduce a method based on x-ray near-edge spectroscopy, ptychographic x-ray computed nanotomography, and sparsity techniques. The method allows the acquisition of quantitative multimodal tomograms of representative sample volumes at sub-30 nm half-period spatial resolution within practical acquisition times, which enables local structure refinements in complex geometries. To demonstrate the method's capabilities, we investigated the transformation of vanadium phosphorus oxide catalysts with industrial use. We observe changes from the micrometer to the atomic level and the formation of a location-specific defect so far only theorized. These results led to a reevaluation of these catalysts used in the production of plastics.

Influence of Fe doping on the Yb valence state and the magnetic structures in HoFe6Sn6-type YbMn6−yFeySn6 alloys (y ≤ 1.00)

We determine the magnetic structures of HoFe6Sn6-type (Immm) YbMn6−yFeySn6 alloys (y=0.25, 0.50, 0.75 and 1.00) from powder neutron diffraction experiments. The valence state and local magnetism of Yb are investigated using X-ray Near Edge Spectroscopy (XANES) and X-ray Magnetic Circular Dichroism (XMCD) at the Yb L3 edge. The mean Yb valence decreases upon Fe doping (from υ~2.66 down to υ~2.46) and there is no 4f Yb magnetism throughout the series. The Fe for Mn substitution leads to change in the spins arrangement of the 3d sublattice by reinforcing antiferromagnetic exchange interactions without significant change in T=Mn/Fe moment magnitude (m~2.35 µB). The ground state of the alloy with y=0.25 is ferromagnetic whilst Fe richer alloys are helimagnets with wave-vector k=0, qy, 0. The turn-angle increase upon Fe doping manifests by a mitigation of the Yb L3 dichroic effect, solely due to hybridization between its 5d states and the self-polarized 3d states of T.

Fast Heat Transport Inside Lithium-Sulfur Batteries Promotes Their Safety and Electrochemical Performance.

SummaryLithium-sulfur batteries are paid much attention owing to their high specific capacity and energy density. However, their practical applications are impeded by poor electrochemical performance due to the dissolved polysulfides. The concentration of soluble polysulfides has a linear relationship with the internal heat generation. The issue of heat transport inside lithium-sulfur batteries is often overlooked. Here, we designed a functional separator that not only had a high thermal conductivity of 0.65 W m−1 K−1 but also alleviated the diffusion of dissolved active materials to the lithium anode, improving the electrochemical performance and safety issue. Lithium-sulfur batteries with the functional separator have a specific capacity of 1,126.4 mAh g−1 at 0.2 C, and the specific capacity can be remained up to 893.5 mAh g−1 after 100 cycles. Pouch Cells with high sulfur loading also showed a good electrochemical performance under a lean electrolyte condition of electrolyte/sulfur (E/S) = 3 μL mg−1.

The formation of stoichiometric uranium brannerite (UTi2O6) glass-ceramic composites from the component oxides in a one-pot synthesis

Brannerite glass-ceramic composites have been suggested as suitable wasteform materials for high-actinide content wastes, but the formation of glass-ceramic composites containing stoichiometric uranium brannerite (UTi2O6) has not been well-studied. Uranium brannerite glass-ceramic composites were synthesised at by a one-pot cold-press and sinter route from the component oxides. As a comparison, two further samples were produced using an alkoxide-nitrate route. A range of compositions with varying molar ratios of uranium and titanium oxides (from 1:2 to 1:3.20) were synthesised, with a range of different heat treatments (1200 °C for 12–48 h, and 1250 °C for 12 h). All compositions were analysed by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray near-edge spectroscopy, and found to contain UTi2O6 as the majority crystalline phase forming within a glass matrix of nominal stoichiometry Na2AlBSi6O16. In compositions with UO2:TiO2 ratios of 1:2 and 1:2.28, particles of UO2 were observed in the glass matrix, likely due to dissolution of TiO2 in the glass phase; this was prevented by the addition of excess TiO2. This work demonstrates the suitability of this system to produce highly durable wasteforms with excellent actinide waste loading, even with a simple one-pot process. Some grains of brannerite consist of a UO2 particle encapsulated in a shell of UTi2O6, suggesting that brannerite crystallises around particles of UO2 until either the UO2 is fully depleted, or the kinetic barrier becomes too large for further diffusion to occur. We propose that the formation of brannerite within glass-ceramic composites at lower temperatures than that for pure ceramic brannerite is caused by an increase in the rate of diffusion of the reactants within the glass.

PyXAS - an open-source package for 2D X-ray near-edge spectroscopy analysis.

In the synchrotron X-ray community, X-ray absorption near-edge spectroscopy (XANES) is a widely used technique to probe the local coordination environment and the oxidation states of specific elements within a sample. Although this technique is usually applied to bulk samples, the advent of new synchrotron sources has enabled spatially resolved versions of this technique (2D XANES). This development has been extremely powerful for the study ofheterogeneous systems, which is the case for nearly all real applications. However, associated with the development of 2D XANES comes the challenge of analyzing very large volumes of data. As an example, a single 2D XANES measurement at a synchrotron can easily produce ∼106 spatially resolved XANES spectra. Conventional manual analysis of an individual XANES spectrum is no longer feasible. Here, a software package is described that has been developed for high-throughput 2D XANES analysis. A detailed description of the software as well as example applications are provided.

Microbial communities and biogenic Mn-oxides in an on-site biofiltration system for cold Fe-(II)- and Mn(II)-rich groundwater treatment

This study investigated relationships between microbial communities, groundwater chemistry, and geochemical and mineralogical characteristics in field-aged biofilter media from a two-stage, pilot-scale, flow-through biofiltration unit designed to remove Fe(II) and Mn(II) from cold groundwater (8 to 15 °C). High-throughput 16S rRNA gene amplicon sequencing of influent groundwater and biofilter samples (solids, effluents, and backwash water) revealed significant differences in the groundwater, Fe filter, and Mn filter communities. These community differences reflect conditions in each filter that select for populations that biologically oxidize Fe(II) and Mn(II) in the two filters, respectively. Genera identified in both filters included relatives of known Fe(II)-oxidizing bacteria (FeOB), Mn(II)-oxidizing bacteria (MnOB), and ammonia-oxidizing bacteria (AOB). Relatives of AOB and nitrite-oxidizing bacteria were abundant in sequencing reads from both filters. Relatives of FeOB in class Betaproteobacteria dominated the Fe filter. Taxa related to Mn-oxidizing organisms were minor members of the Mn-filter communities; intriguingly, while Alphaproteobacteria dominated (40 ± 10% of sequencing reads) the Mn filter community, these Alphaproteobacteria did not classify as known MnOB. Isolates from Fe and Mn filter backwash enrichment studies provide insight on the identity of MnOB in this system. Novel putative MnOB isolates included Azospirillum sp. CDMB, Solimonas soli CDMK, and Paenibacillus sp. CDME. The isolate Hydrogenophaga strain CDMN can oxidize Mn(II) at 8 °C; this known FeOB is likely capable of Mn(II) oxidation in this system. Synchrotron-based X-ray near-edge spectroscopy (XANES) coupled with electron paramagnetic resonance (EPR) revealed the dominant Mn-oxide that formed was biogenic birnessite. Co-existence of amorphous and crystallized Mn-oxide surface morphologies on the Mn-filter media suggest occurrence of both biological and autocatalytic Mn(II) oxidation in the biofilter. This study provides evidence that biofiltration is a viable approach to remove iron, manganese, and ammonia in cold groundwater systems, and that mineralogical and microbiological approaches can be used to monitor biofiltration system efficacy and function.

Colloidal gold in sulphur and citrate-bearing hydrothermal fluids: An experimental study

The stability of colloidal gold (gold nanoparticles) in sulphur-bearing and citrate-bearing solutions was investigated at temperatures up to 225 °C using Synchrotron X-ray Near-edge Spectroscopy (XANES), and up to 350 °C with a visual check of colour changes. The citrate-based colloidal gold solutions, with or without colloidal silica in the solution, are only stable up to 225 °C. In contrast, the gold colloids in Na2S solutions are not stable upon heating to 150 °C, but stable up to 300 °C when 0.5–1.5 wt% of colloidal silica is present in the solution. The colloidal gold particles started to aggregate and deposit from the solution with the aggregation and growth of silica particles at 350 °C. The concentrations of gold as colloids in the solutions are up to 0.5 mmol (∼95 ppm), more than three orders of magnitude higher than gold solubility as aqueous complexes under the same condition calculated based on available thermodynamic data. These results provide the first evidence that high concentrations of colloidal gold are stable in sulphur-bearing fluids at elevated temperatures (∼300 °C). This implies that the formation of gold colloids is an effective way to concentrate gold in hydrothermal sulphur-bearing fluids to form high-grade gold ores.

In situ XANES study of Cobalt in Co-Ce-Al catalyst applied to Steam Reforming of Ethanol reaction

The effect of ceria in cobalt-ceria-alumina catalyst was studied using in situ X-ray near edge spectroscopy (XANES) at Co K-edge and Ce LIII-edge. The introduction of ceria in this catalyst resulted in a significant removal of Co from CoAl2O4 spinel phase to Co and CoO phases. The Co K-edge revealed the symmetry changes in Co according to the temperature and atmosphere in reduction process. We also showed the stability of Co sites as well the oxidation state of ceria in operando steam reforming of ethanol (SRE) reaction. After reduction of Ce4+ to Ce3+, no significant changes were observed by XANES. Gas Chromatography (GC) analysis showed a high ethanol conversion at 500°C, high hydrogen yield and low formation of undesired products as methane and ethylene. The results showed a Co/Ce/Al2O3 catalyst as promising material to be applied in hydrogen production in SRE reaction.

Aluminium X-ray absorption near-edge spectroscopy analysis of discoloured ultramarine blue in 20th century oil paintings

A specific case of synthetic ultramarine degradation was observed in three oil paintings from the early 20th century. Pigment particles were found to have been discoloured, resulting in intricate patterns of white lines, approximately 10 to 30 microns wide, criss-crossing the paint surface. Colour in ultramarine pigments comes from the encapsulated sulphur radical anions, chromophores, inside the cage framework built from SiO44− and AlO45− tetrahedral units linked by the oxygen atoms. In healthy pigment, the charge is balanced by cations such as sodium and the framework stabilises the reactive radicals, preserving the colour. This discolouration mechanism was investigated using X-ray near edge spectroscopy (XANES).XANES was used at the aluminium K-edge to investigate the coordination of the Al atoms in the pigment framework. Using the focused synchrotron beam available at the PHOENIX beamline from the Swiss Light Source, scans with high spatial resolution (5μm) and with a relatively low (2μm) depth interaction could be performed, enabling analysis of the discoloured lines on samples collected from one of the paintings. The comparison of spectra from healthy (blue) and discoloured (white) areas, supported a degradation mechanism involving the removal of aluminium atoms from tetrahedral coordination in the ultramarine framework, which results in the formation of six-coordinate aluminium compounds separate from the pigment structure. This causes a permanent opening of the cage framework, enabling the reaction of the chromophore and subsequent colour loss.

Time-dependent mean-field theory for x-ray near-edge spectroscopy

We derive a time-dependent density functional theory appropriate for calculating the near-edge X-ray absorption spectrum in molecules and condensed matter. The basic assumption is to increase the space of many-body wave functions from one Slater determinant to two. The equations of motion derived from Dirac's variational principle provide an exact solution for the linear response when the interaction Hamiltonian has only a core-electron field. The equations can be solved numerically nearly as easily as the ordinary real-time time-dependent Kohn-Sham equations. We carry out the solution under conditions that permit comparison with the expected power-law behavior. Our extracted power-law exponents are similar to those derived by Nozieres and DeDominicis, but are not in quantitative agreement. We argue that our calculational method can be readily generalized to density functionals that take into account the more general electron-electron interactions that are needed for treating dynamic effects such as plasmon excitations.

Atmospheric SO2Emissions Since the Late 1800s Change Organic Sulfur Forms in Humic Substance Extracts of Soils

Atmospheric SO2 emissions in the UK and globally increased 6- and 20-fold, respectively, from the mid-1800s to the 1960s resulting in increased S deposition, acid rain, and concurrent acidification of terrestrial and aquatic ecosystems. Structural analyses using synchrotron-based X-ray near-edge spectroscopy (XANES) on humic substance extracts of archived samples from the Rothamsted Park Grass Experiment reveal a significant (R2 = -0.58; P < 0.05; N = 7) shift in soil organic sulfur (S) forms, from reduced to more oxidized organic S between 1876 and 1981, even though soil total S contents remained relatively constant. Over the last 30 years, a decrease in emissions and consequent S deposition has again corresponded with a change of organic S structures of humic extracts-reverting in the direction of their early industrial composition. However, the observed reversal lagged behind reductions in emissions by 19 years, which was computed using cross correlations between time series data (R2 = 0.66; P = 0.0024; N = 11). Presently, the ratio of oxidized-to-reduced organic S in humic substance extracts is nearly double that of early industrial times at identical SO2 emission loads. The significant and persistent structural changes of organic S in humic substances as a response to SO2 emissions and S deposition may have effects on recuperation of soils and surface waters from acidification.

Evidence for the Incorporation of Lead into Barite from Waste Rock Pile Materials

Because Pb is one of the most toxic elements and is found as a major contaminant in mining environments, this study aims to identify the distribution of this element in host phases issued from the alteration of mine wastes. The sampling location was a former mine near Oakland, California (USA). This mine was once a source of sulfide minerals from which sulfuric acid was made. The material discussed in this paper was collected in iron hardpans that were formed within the waste rock pile resulting from the excavation work. In most contaminated environments (soils, mine waste), secondary metal-bearing phases arising from alteration processes are usually fine-grained (from 10 microm to less than 1 microm) and highly heterogeneous, requiring the use of micron-scale techniques. We performed micro-Raman spectroscopy, microscanning X-ray diffraction (SXRD), and microextended X-ray near edge spectroscopy (XANES) to determine the relationships between Pb and a Ba/Fe-rich host phase. Micro-Raman spectroscopy suggests that Pb is preferentially incorporated into barite rather than goethite. Results from micro-Raman experiments show the high sensitivity of this analytical tool to the incorporation of Pb into barite by being especially sensitive to the variations of the S-O bond and showing the characteristic bands due to the contribution of Pb. This association is confirmed and is well-illustrated by micro-SXRD mineral species maps showing the correlation between Pb and barite. Microfocused XANES indicates that Pb is present as Pb2+, agreeing with the in situ physicochemical parameters.

Structural and morphological studies on SiOxNy thin films

In this work, the structure and morphology of silicon oxynitride films deposited by the PECVD technique were studied. The films were deposited under two different conditions: (a) SiOxNy with chemical compositions varying from SiO2 to Si3N4 via the control of a N2O+N2+SiH4 gas mixture, and (b) Si-rich SiOxNy films via the control of a N2O+SiH4 gas mixture. The analyses were performed using X-ray near edge spectroscopy (XANES) at the Si-K edge, transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS). For samples with chemical composition varying from SiO2 to Si3N4, the diffraction patterns obtained by TEM exhibited changes with the chemical composition, in agreement with the XANES results. For silicon-rich silicon oxynitride samples, the formation of a-Si clusters was observed and the possibility of obtaining Si nanocrystals after annealing depending on the composition and temperature was realized.

Importance of organosulfur utilization for survival of Pseudomonas putida in soil and rhizosphere.

The sulfur present in both agricultural and uncultivated soils is largely in the form of sulfonates and sulfate esters and not as free, bioavailable inorganic sulfate. Desulfurization of the former compounds in vitro has previously been studied in Pseudomonas putida, a common rhizosphere inhabitant. Survival of P. putida strains was now investigated in three sulfur-deficient Danish soils which were found to contain 60 to 70% of their sulfur in sulfonate or sulfate ester form, as determined by X-ray near-edge spectroscopy. The soil fitness of P. putida S-313 was compared with that of isogenic strains with mutations in the sftR and asfA genes (required for in vitro desulfurization of sulfate esters and arylsulfonates, respectively) and in the ssu locus (required in vitro for the desulfurization of both sulfonates and sulfate esters). asfA or sftR mutants showed significantly reduced survival compared to the parent strain in bulk soil that had been enriched with carbon and nitrogen to mimic rhizosphere conditions, but this reduced survival was not observed in the absence of these additives. In a tomato rhizosphere grown in compost, survival of sftR and ssu mutants was reduced relative to the parent strain. The results demonstrate that the ability to desulfurize sulfonates and sulfate esters is critical for survival of bacteria in the rhizosphere but less so in bulk soils outside the influence of plant roots, where carbon is the limiting nutrient for growth.

EXAFS study of noble gases implanted in highly stressed amorphous carbon films

In this work we report on the study of the local environment of Ar and Kr atoms implanted into an amorphous carbon (a-C) matrix. By intentionally changing the a-C deposition conditions we were able to trap noble gas (NG) atoms under different internal pressure (intrinsic stress) ranging from 1 up to 12 GPa. This enables us to investigate the effects of the internal pressure on the implanted NG atoms subjected to the highly strained environment of the carbon matrix. For this purpose, extended X-ray absorption fine spectroscopy (EXAFS) was performed on the K absorption edge of the implanted Ar (3.2 keV) and Kr (14.3 keV) atoms as a function of the intrinsic stress of the carbon matrix. The analysis of X-ray near edge spectroscopy (XANES) shows an evident increase of the white line for both gases as the stress increases. This result is indicative of clustering of the implanted NG atoms. The analysis of the EXAFS results for Ar atom indicates an increase of the first neighbor distance from 2.4 to about 2.8 Å with increasing compressive stress. The latter figure is comparable to the Ar–Ar (Kr–Kr) inter-atomic distance of compressed solid Ar (Kr). This finding gives further evidence for the formation of small NG clusters in a highly strained a-C matrix.