X-ray Absorption Near-edge Spectroscopy Spectra Research Articles

Unveiling the Redox Noninnocence of Metallocorroles: Exploring K-Edge X-ray Absorption Near-Edge Spectroscopy with a Multiconfigurational Wave Function Approach.

X-ray absorption near-edge spectroscopy (XANES) is an advanced technique for probing the local electronic structure of catalysts, effectively identifying the noninnocent nature of ligands in transition-metal complexes. Metallocorroles with noninnocent corrole rings exhibit unusual electronic structures that challenge traditional density functional theory (DFT) methods, necessitating more rigorous approaches to describe electron correlation accurately. We explored K-edge XANES spectra of Fe, Mn, and Co metallocorroles using TDDFT and wave function-based methods. This is the first investigation employing multireference methods, specifically RASSCF, RASPT2, and MC-PDFT, to analyze the redox noninnocent nature of metallocorroles reflected in their XANES spectra. We quantified the noninnocent character of the corrole and the oxidation states of the metals, capturing more than singly excited excitations responsible for the pre-edge peak. Our findings demonstrate the importance of these advanced computational techniques for accurately predicting XANES spectra, providing a reliable understanding of the electronic properties of such complexes. This study offers a new strategy for investigating ligand redox noninnocence via integrated experimental and computational XANES.

Trace Element Distribution and Arsenic Speciation in Toenails as Affected by External Contamination and Evaluation of a Cleaning Protocol.

Trace element concentrations in toenail clippings have increasingly been used to measure trace element exposure in epidemeological research. Conventional methods such as inductively coupled plasma mass spectrometry (ICP-MS) and high-performance liquid chromatography ICP-MS (HPLC-ICP-MS) are commonly used to measure trace elements and their speciation in toenails. However, the impact of the removal of external contamination on trace element quantification has not been thoroughly studied. In this work, the microdistribution of trace elements (As, Ca, Co, Cu, Fe, K, Mn, Ni, Rb, S, Sr, Ti, and Zn) in dirty and washed toenails and the speciation of As in situ in toenails were investigated using synchrotron X-ray fluorescence microscopy (XFM) and laterally resolved X-ray absorption near edge spectroscopy (XANES). XFM showed different distribution patterns for each trace element, consistent with their binding properties and nail structure. External (terrestrial) contamination was identified and distinguished from the endogenous accumulation of trace elements in toenails─contaminated areas were characterized by the co-occurrence of Co, Fe, and Mn with elements such as Ti and Rb (i.e., indicators of terrestrial contamination). The XANES spectra showed the presence of one As species in washed toenails, corresponding to As bound to sulfhydryl groups. In dirty specimens, a mixed speciation was found in localized areas, containing AsIII-S species and AsV species. ArsenicV is thought to be associated with surface contamination and exogenous As. These findings provide new insights into the speciation of arsenic in toenails, the microdistribution of trace elements, and the effectiveness of a cleaning protocol in removing external contamination.

(Invited) Understanding the Role of Dopants (Al, Zn, Zr) in Altering Charge-Storage Capacity and Cycling Profiles of VFe2Ox

Vanadium ferrite (VFe2Ox) is a defective spinel system that can incorporate substantial Li+ and exhibits a high charge–discharge rate, particularly when structured as a nanoscale aerogel.1 Cations such as Zr, Zn and Al,2 can readily enter the structure substitutionally and have strong, but differing effects on the charge-storage capacity of the material. These earth abundant, cost- effective constituent elements give this class of materials strong potential as future Li-ion battery cathodes but optimizing the stoichiometry for maximum capacity and stability will require understanding the redox sequence of the host cations (Fe, V) and role of intentional dopants.We use density functional theory calculations in concert with in situ and operando X-ray absorption near-edge spectroscopy (XANES) spectra obtained using an in-lab X-ray absorption spectrometer to uncover the quantum mechanical-level effects that underpin relevant energy- storage behaviors of doped and undoped VFe2Ox. Our experimental V K-edge and Fe K-edge spectra indicate reduction of both species during discharge but cannot distinguish between tetrahedral and octahedral Fe redox sites or fully resolve the valency of each element as a function of state of charge. Using a hybrid form of density functional theory that accounts for the strong correlation present in 3d elements, we show that both V and Fe are indeed reduced, but that only tetrahedral Fe is redox active until fully converted to Fe2+. Furthermore, both octahedral and tetrahedral Fe3+ are high spin configuration, but the 5μB moments in the fully filled majority spin channel at each symmetry site are anti-aligned. This arrangement allows for easy exchange of electrons and facilitates conduction. We also calculate XANES spectra based on first principles calculations to be compared directly to those measured in the lab. This cross- check allows us to understand the effect of Al, Zr, and Zn dopants on the redox sequence and relate these results to site preference and capacity. Our combined experimental and calculational investigation sheds light on how these complex materials store Li ions and points toward future alterations that may further improve their properties.

Negative magnetization, shielding current effect and divalent manganese in CaMn1-xTaxO3 manganites

Crystal and electronic structures, and magnetic properties of polycrystalline tantalum substituted manganites CaMn1-xTaxO3 (x = 0.00, 0.03, 0.06, 0.09 and 0.12) were studied by x-ray diffraction, x-ray absorption near edge spectroscopy (XANES) at Mn K-edge, and by magnetization measurements. Large changes of cell volume and magnetic transition temperature, in addition to shift of Mn K-edge spectra and change of shape of XANES spectra, indicate the existence of Mn3+ as well as Mn2+ species induced by the substitution of Mn4+ by Ta5+. Cell parameters and cell volume increase with increasing x because the Mn3+, Mn2+ and Ta5+ ions are larger that substituted Mn4+ ion. According to XANES results, at least the x = 0.00 sample is oxygen deficient. The negative magnetization was observed in the CaMnO3-δ sample, and a possible explanation of the phenomenon is given considering two canted (almost antiferro)magnetic sublattices and a shielding current, associated with the itinerant eg electrons, induced by the oxygen vacancies.

Comparison of sedimentary iron speciation obtained by sequential extraction and X-ray absorption spectroscopy

Iron (Fe) speciation in marine sediments and suspended particulate matter (SPM) are widely used to investigate the role of Fe minerals in marine biogeochemical cycling and to reconstruct paleo-redox conditions. A traditional method for the determination of Fe speciation are sequential extractions, in which operationally defined Fe pools are dissolved by specific extraction solutions. More recently, many studies make use of synchrotron radiation-based X-ray absorption near edge spectroscopy (XANES), especially if little sample material is available or a high spatial resolution is required. However, few studies have systematically compared Fe speciation obtained by the two methods. Here, we report Fe speciation for marine sediments (both wet and freeze-dried) and SPM from contrasting marine environments (western Baltic Sea and Amazon shelf) obtained by sequential extraction and XANES. The two methods yield comparable results regarding the approximate proportion of reactive Fe ((oxyhydr)oxide, carbonate and sulfide minerals) in the total Fe pool and the extent to which reactive Fe minerals have been converted to pyrite. However, methodological issues associated with both approaches complicate a direct comparison of specific mineral groups. Pyrite concentrations obtained by XANES are lower than those obtained by extraction, which is attributed to an underestimation by XANES due to self-absorption effects and an overestimation by the chromium reduction method due to dissolution of reduced sulfur phases that are not associated with Fe. As substantial amounts of pyrite are oxidized during freeze-drying and sample storage, we recommend to analyze wet sediments in modern marine environments. The XANES spectra of Fe (oxyhydr)oxide and Fe(III)-containing (ferric) clay minerals are similar, which is why these components cannot be differentiated by XANES. Similarly, sequential extraction schemes are known to dissolve a variable proportion of ferric clay minerals along with Fe carbonates and Fe (oxyhydr)oxides. Further investigating the role of ferric clay minerals in the low-temperature marine Fe cycle may therefore require the use of additional methods. Our findings may help to assess the transferability of XANES-based Fe speciation for small sediment and SPM samples to those reported in more traditional studies on Fe biogeochemical cycling and paleo-redox conditions.

Luminescence characteristics of Ce3+ doped multicomponent lithium fluorophosphate glasses

We have used the melt quenching technique to fabricate glass samples with the composition 20Li2O–10AlF3-2.5R-(57-x)P2O5-10Gd2O3-0.5CeF3 (R = 0, NaF, KF). These glasses were synthesized and their density, molar volume, refractive index, FTIR (Fourier-transform infrared spectroscopy) spectra, transmittance spectra, decay time analysis, and photo and radioluminescence properties were reported. Surface-sensitive techniques such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES) were investigated. As a result, the FTIR spectra of these glasses break the Q2 tetrahedral sites of the phosphate structure when adding alkali fluoride. UV emission at ∼337 nm was observed at ∼302 nm excitation. In XPS spectra, phosphorus oxidation states (P2p) were detected. The investigation of X-ray Absorption Near-Edge Structure (XANES) of Ce LIII-edge was shown at ∼5.726 keV and confirmed the presence of Ce3+ and Ce4+ was shown at ∼5.731 keV and ∼5.738 keV. The comparison of the Ce3+ and Ce4+ ratios by fitting the energy range in the XANES spectrum may confirm the luminescence characteristic of the glass. A full energy peak was observed in the pulse height spectra of a 241Am α-ray irradiation in the PLGdAfKfCe0.5 glass, and the calculated light yields of PLGdAfKfCe0.5 was 49 Ph/MeV under α-ray. From the results can be concluded that the PLGdAfKfCe0.5 glass showed promising properties as a scintillator material.

Analysis of Cimetidine Crystal Polymorphs by X-ray Absorption Near-Edge Spectroscopy.

Sulfur K-edge X-ray absorption near-edge spectroscopy (XANES) measurements were performed to characterize the crystal polymorphs of the active pharmaceutical ingredients (APIs) containing sulfur atoms. Cimetidine (CIM) was used as a model API. Each crystal form of CIM has its own XANES spectrum, so we can discriminate the crystal form by its spectrum. The analysis of the crystal structure of CIM revealed that the difference in the shape of XANES spectra was ascribable to the difference in the C-S-C bond angle of CIM molecules and the intermolecular hydrogen bonds, such as C-H···S and N-H···S, and S-S interaction. It was found that the peak shape of the XANES spectrum is gentle when the C-S-C bond angle is large, while the peak shape can be steep when the C-S-C bond angle is small. Furthermore, it was found that the peak energy values varied depending on the hydrogen bonds and S-S interaction. By linear combination fitting using XANES spectra, it was possible to quantify the ratio of CIM form A crystal in mixed powders of form A and monohydrate crystals. These results indicate that XANES measurements can be a useful technique to evaluate the crystal polymorphism of APIs containing S atom in pharmaceutical formulation.

XANES characterizations of amorphous mixed metal oxides derived from Zn/Al layered double hydroxides through thermal treatment

The amorphous phase obtained by thermal treatment of Zn/Al-layered double hydroxide (Zn/Al-LDH) was characterized by X-ray absorption near-edge Spectroscopy (XANES) and Ultraviolet–Visible Diffuse Reflection (UV–vis DR). The highly crystalline Zn/Al-LDH was synthesized through homogeneous precipitation with urea as precursor, and then calcined up to 900 ​°C. X-ray Diffraction (XRD) and Thermogravimetry-Differential Thermal Analysis (TG-DTA) results showed that the crystalline Zn/Al-LDH was changed to amorphous phase through dehydroxylation by 300 ​°C. The amorphous phase decomposed to wurtzite-ZnO and spinel (Zn/Al2O4) above 600 ​°C. The amorphous phase was characterized with Zn L-edge, O K-edge and Al K-edge spectra. Those spectra determined the formation of amorphous Zinc/Aluminium mixed metal oxide (ZAO) with characteristic electron. The ZAO showed absorption of UV light which is higher energy band gap than pure zinc oxide. The analysis indicated changes in coordination due to the formation of a metal oxide phase by dehydration of the hydroxide layer of Zn/Al-LDH, and the formation of ZAO. This research is believed to be the first to apply Zn L-edge, along with O K-edge XANES spectra to analyses and clarify the thermal behavior of Zn/Al-LDH and is demonstrated to be a powerful tool for probing the structure of a variety of mixed metal oxides and catalysts based on Zn based LDH materials.

Improved precision in As speciation analysis with HERFD-XANES at the As K-edge: the case of As speciation in mine waste.

High-energy-resolution fluorescence-detected (HERFD) X-ray absorption near-edge spectroscopy (XANES) is a spectroscopic method that allows for increased spectral feature resolution, and greater selectivity to decrease complex matrix effects compared with conventional XANES. XANES is an ideal tool for speciation of elements in solid-phase environmental samples. Accurate speciation of As in mine waste materials is important for understanding the mobility and toxicity of As in near-surface environments. In this study, linear combination fitting (LCF) was performed on synthetic spectra generated from mixtures of eight measured reference compounds for both HERFD-XANES and transmission-detected XANES to evaluate the improvement in quantitative speciation with HERFD-XANES spectra. The reference compounds arsenolite (As2O3), orpiment (As2S3), getchellite (AsSbS3), arsenopyrite (FeAsS), kaňkite (FeAsO4·3.5H2O), scorodite (FeAsO4·2H2O), sodium arsenate (Na3AsO4), and realgar (As4S4) were selected for their importance in mine waste systems. Statistical methods of principal component analysis and target transformation were employed to determine whether HERFD improves identification of the components in a dataset of mixtures of reference compounds. LCF was performed on HERFD- and total fluorescence yield (TFY)-XANES spectra collected from mine waste samples. Arsenopyrite, arsenolite, orpiment, and sodium arsenate were more accurately identified in the synthetic HERFD-XANES spectra compared with the transmission-XANES spectra. In mine waste samples containing arsenopyrite and either scorodite or kaňkite, LCF with HERFD-XANES measurements resulted in fits with smaller R-factors than concurrently collected TFY measurements. The improved accuracy of HERFD-XANES analysis may provide enhanced delineation of As phases controlling biogeochemical reactions in mine wastes, contaminated soils, and remediation systems.

Incorporating Sulfur Atoms into Palladium Catalysts by Reactive Metal–Support Interaction for Selective Hydrogenation

Incorporating Sulfur Atoms into Palladium Catalysts by Reactive Metal–Support Interaction for Selective Hydrogenation

Chemical state mapping of simulant Chernobyl lava-like fuel containing material using micro-focused synchrotron X-ray spectroscopy.

Uranium speciation and redox behaviour is of critical importance in the nuclear fuel cycle. X-ray absorption near-edge spectroscopy (XANES) is commonly used to probe the oxidation state and speciation of uranium, and other elements, at the macroscopic and microscopic scale, within nuclear materials. Two-dimensional (2D) speciation maps, derived from microfocus X-ray fluorescence and XANES data, provide essential information on the spatial variation and gradients of the oxidation state of redox active elements such as uranium. In the present work, we elaborate and evaluate approaches to the construction of 2D speciation maps, in an effort to maximize sensitivity to the U oxidation state at the U L3-edge, applied to a suite of synthetic Chernobyl lava specimens. Our analysis shows that calibration of speciation maps can be improved by determination of the normalized X-ray absorption at excitation energies selected to maximize oxidation state contrast. The maps are calibrated to the normalized absorption of U L3 XANES spectra of relevant reference compounds, modelled using a combination of arctangent and pseudo-Voigt functions (to represent the photoelectric absorption and multiple-scattering contributions). We validate this approach by microfocus X-ray diffraction and XANES analysis of points of interest, which afford average U oxidation states in excellent agreement with those estimated from the chemical state maps. This simple and easy-to-implement approach is general and transferrable, and will assist in the future analysis of real lava-like fuel-containing materials to understand their environmental degradation, which is a source of radioactive dust production within the Chernobyl shelter.

Hydration of Heavy Alkaline-Earth Cations Studied by Molecular Dynamics Simulations and X-ray Absorption Spectroscopy.

The physicochemical properties of the three heaviest alkaline-earth cations, Sr2+, Ba2+, and Ra2+ in water have been studied by means of classical molecular dynamics (MD) simulations. A specific set of cation–water intermolecular potentials based on ab initio potential energy surfaces has been built on the basis of the hydrated ion concept. The polarizable and flexible model of water MCDHO2 was adopted. The theoretical–experimental comparison of structural, dynamical, energetic, and spectroscopical properties of Sr2+ and Ba2+ aqueous solutions is satisfactory, which supports the methodology developed. This good behavior allows a reasonable reliability for the predicted Ra2+ physicochemical data not experimentally determined yet. Simulated extended X-ray absorption fine-structure (EXAFS) and X-ray absorption near-edge spectroscopy spectra have been computed from the snapshots of the MD simulations and compared with the experimental information available for Sr2+ and Ba2+. For the Ra2+ case, the Ra L3-edge EXAFS spectrum is proposed. Structural and dynamical properties of the aqua ions for the three cations have been obtained and analyzed. Along the [M(H2O)n]m+ series, the M–O distance for the first-hydration shell is 2.57, 2.81, and 2.93 Å for Sr2+, Ba2+, and Ra2+, respectively. The hydration number also increases when one is going down along the group: 8.1, 9.4, and 9.8 for Sr2+, Ba2+, and Ra2+, respectively. Whereas [Sr(H2O)8]2+ is a typical aqua ion with a well-defined structure, the Ba2+ and Ra2+ hydration provides a picture exhibiting an average between the ennea- and the deca-hydration. These results show a similar chemical behavior of Ba2+ and Ra2+ aqueous solutions and support experimental studies on the removal of Ra-226 of aquifers by different techniques, where Ra2+ is replaced by Ba2+. A comparison of the heavy alkaline ions, Rb+ and Cs+, with the heavy alkaline-earth ions is made.

X-ray Absorption Near-Edge Spectroscopy Analysis of Indomethacin in Crystalline Forms and in Amorphous Solid Dispersions.

Chlorine K-edge X-ray absorption near-edge spectroscopy (XANES) measurements were performed to characterize the crystal polymorphs of identical active pharmaceutical ingredients (APIs) containing chloride atoms and their amorphous solid dispersions (ASDs). Indomethacin (IMC), of which three crystal forms (α, β, and γ) have been reported, was used as a model API. The shape of XANES spectra was unique to each IMC crystal. The analysis of the crystal structures of IMC revealed that chlorine atoms of the IMCα form had unique intermolecular interactions and halogen bonds with oxygen atoms, while those of the IMCγ form do not have any notable interactions. This result showed that XANES measurements can detect weak interatomic interactions. The shapes of the ASD spectra were clearly different from those of the crystals, suggesting that the environment around the Cl atom of IMC was different from that of the crystals. A thermal stress test was then performed to study the transformation from the amorphous form to the crystalline form of IMC in the ASD. The powder X-ray diffraction (PXRD) patterns indicated that amorphous IMC transformed into crystals during the thermal stress test. In accordance with the PXRD results, the XANES spectra also transformed from ASD to crystalline form. These results indicate that the IMC transformation could be monitored by XANES measurement. Our findings led us to conclude that XANES measurement is a novel approach for the evaluation of crystal polymorphs of APIs and the crystalline state of APIs in ASDs.

Structural Properties of Cu-Doped ZnO Prepared by Coprecipitation Method

An experimental study to determine the effect of Cu doping on structural properties of ZnO nanoparticle has been conducted. Zn1-xCuxO (CZO) were prepared by co-precipitation method by varying Cu concentration with x = 0.00, 0.10, 0.11 and 0.12. The structural properties of the CZO sample were characterized by X-Ray diffraction (XRD) and X-ray Absorption Spectroscopy (XAS), which consist of XANES (X-ray Absorption Near-Edge Spectroscopy) and EXAFS (Extended X-ray Absorption Fine Structure). XAS measurements were performed in the energy of Cu K-edge and Zn K-edge using synchrotron radiation at SLRI (Synchrotron Light Research Institute) in Thailand. Both Cu K-edge and Zn K-edge XANES spectra indicate that the oxidation states of Cu and Zn ions are 2+. Analysis of XRD data with refinement method using Rietica software confirms the presence of Cu as doping in ZnO host lattice with the crystallite size ranging between 26 and 44 nm. Moreover, it shows that the obtained CZO samples are polycrystalline with (002) predominant reflection and exhibit a hexagonal wurtzite structure.

Atomic-level insights into the activation of nitrogen via hydrogen-bond interaction toward nitrogen photofixation

Summary As the activation of N2 molecules is generally regarded as the bottleneck in N2 reduction, it is of significant importance to develop promising strategies to efficiently activate N2 molecules. Herein, we discovered an innovative approach to activate N2 molecules via hydrogen-bond interaction in N2 photofixation. Porous Cu with surface modification of S atoms (3%-S/Cu) exhibited remarkable catalytic activity and stability in N2 photofixation. Further mechanistic studies revealed that surface S atoms directly participated in the catalytic process by accepting and donating H atoms. In addition, the forming S–H bond significantly promoted the activation of N2 molecules via hydrogen-bond interaction, contributing to the enhanced catalytic activity.

Geochemical changes of Mn in contaminated agricultural soils nearby historical mine tailings: Insights from XAS, XRD and, SEP

Manganese is ubiquitous in nature and essential for some metabolic reactions, but also it is present in the environment as a product of anthropogenic activities. Despite evidence linking high concentrations of Mn to several diseases, it is not commonly considered during environmental risk assessment of soils. Changes in chemical forms, oxidation state, and speciation of Mn in impacted agricultural soils by historical mine tailings in central Sonora in northwestern Mexico were studied using X-ray Absorption Near Edge Spectroscopy (XANES), X-ray Diffraction (XRD), and Sequential Extraction Procedures (SEP) techniques. Mn concentrations ranged from 1093 to 2919 mg·kg−1 in these soils, which exceeded the local geochemical background by up to six-fold. According to SEP, the tendency found in agricultural soils was reducible (42–66%) > soluble and exchangeable (16–42%) > residual (5–22%) > oxidizable (4–24%). In contrast, the tendency in sulfide-rich tailings samples was soluble and exchangeable (47–49%) > residual (35–41%) > oxidizable (5–11%) > reducible (5–7%), and in oxide-rich materials was residual (21–79%) > soluble and exchangeable (1–30%) > reducible (1–45%) > oxidizable (2–15%). The considerable percentage of the soluble forms indicated the potential of mobilization and availability to exposed organisms. No Mn-bearing mineral phases were identified with XRD, which suggested that manganese was mostly found in low-crystalline forms. XANES measurements indicated that the oxidation state of Mn in agricultural soil samples varied from Mn2+ through Mn4+. Conversely, the main oxidation state in mine tailings samples was Mn2+. Substantial changes were detected in Mn XANES spectra in the whole sample and residues left from SEP in agricultural soils, which confirmed the presence of all chemical forms (e.g., soluble and exchangeable, reducible, oxidizable, residual). A well-defined structure spectrum was obtained in soils once low crystallinity species and/or organic compounds were removed, which was similar to that acquired for mine tailings, suggesting mobility from tailings deposit to agricultural soils. Substantial contribution of compounds with mineral structures like birnessite (((Na, Ca, K)0.6(Mn4+, Mn3+)2O4·1.5H2O) and minor contributions of hausmannite (Mn3O4), spessartine (Mn3Al2(SiO4)3) and szmikite (MnSO4) were identified by Linear Combination Fitting (LCF) in soils, whereas the significant contribution of structures like hausmannite and spessartine, and minor contributions of rhodochrosite were found in tailings material. An LCF analysis in residues from SEP also suggests that the chemical species involved in the Mn mobilization were scachite and szmikite. In general, the results obtained indicate that leaching processes favored the presence of chemical species of Mn with a considerable potential of mobility and toxicity in agricultural soils interacting with historical mine tailings in central Sonora.

In situ X-ray absorption study of Cu species in Cu-CHA catalysts for NH3-SCR during temperature-programmed reduction in NO/NH3

Ammonia-mediated selective catalytic reduction (NH3-SCR) using Cu-exchanged chabazite zeolites as catalysts is one of the leading technologies for NOx removal from exhaust gases, with CuII/CuI redox cycles being the basis of the catalytic reaction. The amount of CuII ions reduced by NO/NH3 can be quantified by the consumption of NO during temperature-programmed reduction experiments (NO-TPR). In this article, we show the capabilities of in situ X-ray absorption near-edge spectroscopy (XANES), coupled with multivariate curve resolution (MCR) and principal component analysis (PCA) methods, in following CuII/CuI speciation during reduction in NO/NH3 after oxidation in NO/O2 at 50 °C on samples with different copper loading and pretreatment conditions. Our XANES results show that during the NO/NH3 ramp CuII ions are fully reduced to CuI in the 50–290 °C range. The number of species involved in the process, their XANES spectra and their concentration profiles as a function of the temperature were obtained by MCR and PCA. Mixed ligand ammonia solvated complexes [CuII(NH3)3(X)]+ (X = OH−/O− or NO3−) are present at the beginning of the experiment, and are transformed into mobile [CuI(NH3)2]+ complexes: these complexes lose an NH3 ligand and become framework-coordinated above 200 °C. In the process, multiple CuII/CuI reduction events are observed: the first one around 130 °C is identified with the reduction of [CuII(NH3)3(OH/O)]+ moieties, while the second one occurs around 220–240 °C and is associated with the reduction of the ammonia-solvated Cu-NO3− species. The nitrate concentration in the catalysts is found to be dependent on the zeolite Cu loading and on the applied pretreatment conditions. Ammonia solvation increases the number of CuII sites available for the formation of nitrates, as confirmed by infrared spectroscopy.

Local and electronic structure of Sr1-xGdxTiO3 probed by X-ray absorption spectroscopy

Gadolinium-doped strontium titanate (Sr1-xGdxTiO3) is a typical perovskite structure material which has been studied due their thermomechanical, termoelectrical and electrochemical properties. In this study, local and electronic structure of Sr1-xGdxTiO3 samples were analyzed through X-ray absorption spectroscopy measurements. The results obtained with the adjustment of extended X-ray absorption fine structure (EXAFS) spectra at Sr K-edge show that crystallographic model of Pm-3m space group is consistent with local structure around Sr atoms, as expected. This same analysis also reveals an increasing of the Debye-Waller as a function of the Gd content in some shells, which is associated with disorder induced by Sr vacancies due to the heterovalent Gd incorporation. EXAFS spectra at Gd LIII-edge for Sr1-xGdxTiO3 samples indicates regular GdO12 dodecahedra without displacement of Gd atoms from centrosymmetric position. A disorder was also identified in the shells beyond the first 12 O neighbors in which neither the crystallographic cubic structure of the SrTiO3 nor the orthorhombic structure of the GdTiO3 fits well. X-ray absorption near edge spectroscopy (XANES) spectrum at Ti LIII,II-edges shows an asymmetric peak because of the splitting between the eg orbitals of 3d band for SrTiO3 sample. The addition of Gd atoms to SrTiO3 structure cause an enlargement of this peak and this split is associated with a small displacement of Ti atoms from their centrosymmetric position. Several features of the XANES spectra at O K-edge for Sr1-xGdxTiO3 samples are affected by the increase of Gd concentration. According to our calculated projected density of states, these transitions are related to a reduction in the number of unoccupied O 2p - Ti 3d states caused by the split of Ti 3d band. Moreover, these XANES spectra also show a dependence of the increasing of the hybridization between O 2p and Gd 5d4f6s states.

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.

Mechanism of segmentation of lead halide perovskite at interfaces with GaN and ZnO

Structural degradation is a main problem for the commercialization of the organic lead halide perovskite solar cells. A role of the interfaces with the transparent electrodes, in this process, could be made clear by the combined ab initio calculations and the X-ray absorption measurements. The junctions of MAPbI3(MA = CH3NH3) with pure GaN and ZnO crystals, oriented with the polar [0 0 0 1] and [0 0 0 −1] surfaces, are theoretically investigated by means of the density functional theory (DFT) and simulations of the X-ray absorption near-edge spectroscopy (XANES). Unwanted decomposition of the perovskite, into the layers which are parallel to the interface, coexists with a strong binding of the halide atom at GaN [0 0 0 1] and ZnO [0 0 0 1]. In contrast, at the interfaces with the [0 0 0 −1]-oriented GaN and ZnO, aforementioned segmentation of the perovskite does not occur, because binding of the halide atom is much weaker. Thus, the adsorption properties of the halide atom at semiconductor surface might be a precondition for a choice of the substrate to grow the stable perovskite film. The I-core K-edge XANES spectra at the interface atoms contain a fingerprint of the iodide adsorption strength.