Showing papers on "XANES published in 2018"
TL;DR: In this article, the structural information about short range ordering of the oxygen (O) atoms around silicon (Si) atoms were compared with the results as obtained by Near Edge X-ray Absorption Fine Structure (NEXAFS) and RAMAN experiments, suggesting this technique may be used as a screening tool for routine PDF studies of amorphous materials.
Abstract: At present synchrotron and neutron sources are the preferred choices for the Pair Distribution Function (PDF) analysis, but there is a need to explore PDF in a laboratory XRD system for quick feedback about the short range structure of the amorphous materials. Present work considered both crystalline (quartz) and amorphous silica to study the structural differences in silica by PDF analysis using Ag radiations in laboratory XRD. The structural information about short range ordering of the oxygen (O) atoms around silicon (Si) atoms as obtained by the PDF were compared with the results as obtained by Near Edge X-ray Absorption Fine Structure (NEXAFS) and RAMAN experiments. The PDF studies showed that the amorphous silica possessed short range periodicity within the basic unit of (SiO4)4− tetrahedra with a Si O & O O distance are of about 1.622 A and 2.713 A while the short range as well as long range ordered structure present in quartz with Si O & O O distance are 1.562 A and 2.661 A respectively. Raman spectra showed some asymmetry in amorphous silica which corresponds to the defects present in the lattice and thus forming the n-fold ring structure with Si and O resulting in the wide variation of bridging bond angle Si O Si in amorphous silica. NEXAFS studies revealed the structure of amorphous silica and quartz in the intermediate range (3–5 A) at the Si L and O K edges. The structural information about short range ordering of the O around Si atoms as obtained by these methods were found to be in good match with the results as obtained by PDF, suggesting this technique may be used as a screening tool for routine PDF studies of amorphous materials.
118 citations
TL;DR: The present study serves as an important structural benchmark for the rapidly expanding field of spinel ferrite nanoparticle research.
Abstract: Magnetic spinel ferrite MFe2O4 (M = Mn, Co, Ni, Zn) nanoparticles have been prepared via simple, green and scalable hydrothermal synthesis pathways utilizing sub- and supercritical conditions to attain specific product characteristics. The crystal-, magnetic- and micro-structures of the prepared crystallites have been elucidated through meticulous characterization employing several complementary techniques. Analysis of energy dispersive X-ray spectroscopy (EDS) and X-ray absorption near edge structure (XANES) data verifies the desired stoichiometries with divalent M and trivalent Fe ions. Robust structural characterization is carried out by simultaneous Rietveld refinement of a constrained structural model to powder X-ray diffraction (PXRD) and high-resolution neutron powder diffraction (NPD) data. The structural modeling reveals different affinities of the 3d transition metal ions for the specific crystallographic sites in the nanocrystallites, characterized by the spinel inversion degree, x, [M2+1−xFe3+x]tet[M2+xFe3+2−x]octO4, compared to the well-established bulk structures. The MnFe2O4 and CoFe2O4 nanocrystallites exhibit random disordered spinel structures (x = 0.643(3) and 0.660(6)), while NiFe2O4 is a completely inverse spinel (x = 1.00) and ZnFe2O4 is close to a normal spinel (x = 0.166(10)). Furthermore, the size, size distribution and morphology of the nanoparticles have been assessed by peak profile analysis of the diffraction data, transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The differences in nanostructure, spinel inversion and distinct magnetic nature of the M2+ ions directly alter the magnetic structures of the crystallites at the atomic-scale and consequently the macroscopic magnetic properties of the materials. The present study serves as an important structural benchmark for the rapidly expanding field of spinel ferrite nanoparticle research.
97 citations
TL;DR: This work presents a database of computed XAS spectra, using the Green's formulation of the multiple scattering theory implemented in the FEFF code, which constitutes the largest existing collection of computed x-ray absorption spectra to date.
Abstract: X-ray absorption spectroscopy (XAS) is a widely-used materials characterization technique. In this work we present a database of computed XAS spectra, using the Green's formulation of the multiple scattering theory implemented in the FEFF code. With more than 500,000 K-edge X-ray absorption near edge (XANES) spectra for more than 40,000 unique materials, this database constitutes the largest existing collection of computed XAS spectra to date. The data is openly distributed via the Materials Project, enabling researchers across the world to access it for free and use it for comparisons with experiments and further analysis.
97 citations
TL;DR: The application and quantification of in situ copper K-edge X-ray absorption near-edge structure (XANES) result in a majority relation between the production of CuI and methanol from methane that complies with the expectations of a two-electron mechanism founded upon CuII/CuI redox couples.
Abstract: The application and quantification of in situ copper K-edge X-ray absorption near-edge structure (XANES), when linked to independently made reactor-based studies of methanol production, result in a majority relation between the production of CuI and methanol from methane that complies with the expectations of a two-electron mechanism founded upon CuII/CuI redox couples.
77 citations
TL;DR: In this article, a carbon and nitrogen self-doped TiO 2 hollow spheres (CNTH) with oxygen vacancies and Ti3+ were synthesized by a one-pot hydrothermal strategy in H2O C2H5OH HF H 2O2 mixed solution with TiCN as a precursor of anatase TiO2 and selfdoping source of N and C. The resulting CNTH photocatalyst showed enhanced visible-light photocatalytic activity for H2 production.
67 citations
TL;DR: In this paper, the authors characterized different rare earth element (REE) binding environments and associated mineral phases in coal and coal combustion byproducts (CCBs) are not well understood.
64 citations
TL;DR: In this paper, the authors combined small-angle X-ray scattering (SAXS) and Xray absorption near-edge structure (XANES) spectroscopy, ab initio simulations, and machine learning (artificial neural network) techniques to detect significant differences between the sizes of particle agglomerates.
Abstract: Size-selected clusters, soft-landed on an oxide substrate, is a promising and highly tunable material for heterogeneous catalysis. Agglomeration of the deposited clusters, however, leads to changes in the particle properties and structure. The latter for such cluster assemblies can also be different from that in self-standing nanoparticles of similar sizes. To monitor the formation of such complex materials, in situ studies at different length scales are required. Toward that goal, we combined small-angle X-ray scattering (SAXS), X-ray absorption near-edge structure (XANES) spectroscopy, ab initio simulations, and machine learning (artificial neural network) techniques. We detected significant differences between the sizes of particle agglomerates, as probed by SAXS, and the sizes of locally ordered regions, as seen by XANES. We interpret these differences as an evidence for the fractal, grape-cluster-like structure of the agglomerates; thus, XANES and SAXS provide highly complementary structural informat...
64 citations
TL;DR: In this article, a MgFexAl2-xO4 synthetic spinel, where x varies from 0 to 0.26, is presented as support for Ni-based catalysts, offering stability and carbon control under various conditions of methane reforming.
Abstract: We report a MgFexAl2–xO4 synthetic spinel, where x varies from 0 to 0.26, as support for Ni-based catalysts, offering stability and carbon control under various conditions of methane reforming. By incorporation of Fe into a magnesium aluminate spinel, a support is created with redox functionality and high thermal stability, as concluded from temporal analysis of products (TAP) experiments and redox cycling, respectively. A diffusion coefficient of 3 × 10–17 m2 s–1 was estimated for lattice oxygen at 993 K from TAP experiments. X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) modeling identified that the incorporation of iron occurs as Fe3+ in the octahedral sites of the spinel lattice, replacing aluminum. Simulation of the X-ray absorption near edge structure (XANES) spectrum of the reduced support showed that 60 ± 10% of iron was reduced from 3+ to 2+ at 1073 K, while there was no formation of metallic iron. A series of Ni/MgFexAl2–xO4 catalysts, where x varies from 0 to 0.26,...
57 citations
TL;DR: In this paper, the authors show that synchrotron radiation causes progressive changes to the XANES spectra of hydrous glasses as a function of radiation dose (here defined as total photons delivered per square micrometer), water concentration and initial Fe3+/ΣFe ratio.
Abstract: Abstract Oxygen fugacity (fo2) exerts first-order control on the geochemical evolution of planetary interiors, and the Fe3+/ΣFe ratios of silicate glasses provide a useful proxy for fO2. Fe K-edge micro-X-ray absorption near-edge structure (XANES) spectroscopy allows researchers to micro-analytically determine the Fe3+/ΣFe ratios of silicate glasses with high precision. In this study we characterize hydrous and anhydrous basalt glass standards with Mössbauer and XANES spectroscopy and show that synchrotron radiation causes progressive changes to the XANES spectra of hydrous glasses as a function of radiation dose (here defined as total photons delivered per square micrometer), water concentration, and initial Fe3+/ΣFe ratio. We report experiments from eight different radiation dose conditions and show that Fe in hydrous silicate glasses can undergo rapid oxidation upon exposure to radiation. The rate and degree of oxidation correlates with radiation dose and the product of water concentration and ferrous/ferric iron oxide ratio on a molar basis (Φ = XHO0.5·XFeO/XFeO1.5). For example, a basalt glass with 4.9 wt% dissolved H2O and Fe3+/ΣFe = 0.19 from its Mössbauer spectrum may appear to have Fe3+/ΣFe ≥ 0.35 when analyzed over several minutes at a nominal flux density of ~2 × 109 photons/s/μm2. This radiation-induced increase in Fe3+/ΣFe ratio would lead to overestimation of fO2 by about two orders of magnitude, with dramatic consequences for the interpretation of geological processes. The sample area exposed to radiation shows measureable hydrogen loss, consistent with radiation-induced breaking of O–H bonds, associated H migration and loss, and oxidation of Fe2+. This mechanism is consistent with the observation that anhydrous glasses show no damage under any beam conditions. Cryogenic cooling does not mitigate, but rather accelerates, iron oxidation. The effects of beam damage appear to persist indefinitely. We detect beam damage at the lowest photon flux densities tested (3 × 106 photons/s/ μm2); however, at flux densities ≤6 × 107 photons/s/µm2, the hydrous glass calibration curve defined by the centroid (derived from XANES spectra) and Fe3+/SFe ratios (derived from Mössbauer spectra) is indistinguishable from the anhydrous calibration curve within the accuracy achievable with Mössbauer spectroscopy. Thus, published Fe3+/ΣFe ratios from hydrous glasses measured at low photon flux densities are likely to be accurate within measurement uncertainty with respect to what would have been measured by Mössbauer spectroscopy. These new results demonstrate that to obtain accurate Fe3+/ΣFe ratios from hydrous, mafic, silicate glasses, it is first necessary to carefully monitor changes in the XANES spectra as a function of incident dose (e.g., fixed-energy scan). Defocusing and attenuating the beam may prevent significant oxidation of Fe in mafic water-bearing glasses.
53 citations
TL;DR: In this paper, an in situ X-ray absorption spectroscopy study of carbide formation and decomposition in 2.6 nm palladium nanoparticles supported on carbon during exposure to acetylene, hydrogen, and their mixtures at 100 °C was taken as a representative temperature for hydrogenation reactions.
Abstract: The presence of a core/shell behavior in Pd nanoparticles (NPs) during the formation of the metal-hydride phase has recently been highlighted combining X-ray absorption and scattering experiments [J. Phys. Chem. C 2017, 121, 18202]. In this work, we focus on the formation of the carbide phase in the bulk region and on the surface of supported palladium NPs because it affects the catalytic activity and selectivity in hydrogenation reactions. We present in situ X-ray absorption spectroscopy study of carbide formation and decomposition in 2.6 nm palladium nanoparticles supported on carbon during exposure to acetylene, hydrogen, and their mixtures at 100 °C, taken as a representative temperature for hydrogenation reactions. Fourier analysis of extended X-ray absorption fine structure (EXAFS) spectra was used to determine the average Pd–Pd bond distance in the NPs, reflecting the formation of bulk palladium carbide, while theoretical calculation of X-ray absorption near-edge structure (XANES) using the finite ...
53 citations
15 Aug 2018
TL;DR: The CuO/gC3N4/Bi2O3 composite exhibits highly enhanced photocatalytic activity in the 2,4-dichlorophenol decomposition under visible light due to the increased population of electrons and the successful consumption of the photoproduced electrons by the dissolved oxygen through the one-electron transfer reaction.
Abstract: In the present study, CuO/gC3N4/Bi2O3 composite is constructed as a ternary visible light active photocatalyst. Since CuO plays a critical role in enhancing the photocatalytic activity of the formed composite, its structural properties are particularly studied using synchrotron X-ray absorption spectroscopy (XAS), including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). XANES confirms the presence of Cu species with +2 oxidation state in the form of CuO. EXAFS furthermore confirms that each Cu cation is coordinated to four O anions in an approximately square planar configuration. The length of the Cu-O coordination is estimated to be 1.92 A, slightly shorter than that of bulk CuO (1.95 A). The CuO/gC3N4/Bi2O3 composite exhibits highly enhanced photocatalytic activity in the 2,4-dichlorophenol decomposition under visible light. The enhanced photocatalytic activity is due to the increased population of electrons and the successful consumption of the photoproduced electrons by the dissolved oxygen through the one-electron transfer reaction.
TL;DR: In this paper, the steam reforming of ethanol has been studied by near ambient pressure XPS (NAP-XPS), extended X-ray absorption fine structure (EXAFS), and Xray absorption near edge structure (XANES).
Abstract: The steam reforming of ethanol (ESR) has been studied by near ambient pressure XPS (NAP-XPS), extended X-ray absorption fine structure (EXAFS), and X-ray absorption near edge structure (XANES) unde
TL;DR: X-ray absorption spectroscopy data analysis in the near edge region (XANES) confirmed that selenium in the Se-polysaccharides structure is present at the -II oxidation state and that Se is organically bound and simulation analysis suggested that seenium is most likely bound by a glycosidic-link in a β-1,3 or α- 1,4-glycosidics bond or substituted for oxygen in a pyranosidic ring
TL;DR: In this paper, an ultrasonic-assisted sol-gel technique was used to synthesize cerium-doped hydroxyapatite (Ce/HAp-US) using a varying concentration of Ce from 0.5% to 2.0%.
Abstract: This present work focuses on the synthesis of cerium-doped hydroxyapatite (Ce/HAp-US) using an ultrasonic-assisted sol-gel technique under varying concentration of Ce from 0.5% to 2.0%. The preparative method utilized the stoichiometric molar ratio of Ca to P of 1.67 where the Ce/HAp samples were calcined at 600 °C for 2 h. The structural properties of Ce/HAp samples were characterized by various techniques including X-ray absorption near edge spectroscopy (XANES), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). Results from the XANES spectra of xCe/HAp samples at the Ce L3-edge reveal that the dominant species of cerium was Ce4+ along with some Ce3+, which have been incorporated into the HAp lattice. Results of the EDX analysis show that the Ca/P molar ratio of xCe/HAp decreased with an increase in Ce content. XRD analysis confirms that Ce3+ and Ce4+ were partially incorporated into the hexagonal framework of HAp and rhombohedral structure of β-tricalcium phosphate (β-TCP). FT-IR measurements identified the main functional groups of Ce/HAp to be hydroxyl (OH−), phosphate ( PO 4 3 - ) and carbonate ( CO 3 2 - ). The morphology obtained from TEM analysis illustrates that pure HAp-US is composed of very fine spherical particles. By incorporating Ce ions into the HAp lattice, the presence of dense dark spots, possibly the loaded Ce species, were observed.
TL;DR: The XANES M4,5-edge spectra are representative of the actinide orbital covalency in the probed core-excited states, which may be different from the ground-state covalencies.
Abstract: Relativistic multireference ab initio wave function calculations within the restricted active space (RAS) framework were performed to calculate metal and ligand X-ray absorption (XAS) near-edge spectroscopy (XANES) intensities for the metal M4,5 edges of [PuO2(H2O)5]2+, [AnVIO2]2+ (An = U, Np, Pu), and [AmCl6]3– and the Cl K edge of the Am complex. The extent of An(5f)–ligand bonding was determined via natural localized molecular orbital analyses of the relevant spin–orbit coupled multireference states. The calculated spectra are in good agreement with experiments and allow a detailed assignment of the observed spectral features. The XANES M4,5-edge spectra are representative of the actinide orbital covalency in the probed core-excited states, which may be different from the ground-state covalency. An assignment of ground-state An orbital covalency based on XAS spectra should therefore be made with caution.
TL;DR: In this article, the structural, electronic and luminescence behavior of ZnO nanorods and rGO-reduced graphene oxide (ZnO:rGO) hybrid nanostructures have been studied using X-diffraction (XRD), Raman scattering, X-ray absorption near edge structure (XANES) spectroscopy and photoluminescence (PL) studies.
TL;DR: The presented studies show how a careful combination of X-ray absorption and diffraction can differentiate the structure of the core, shell and surface of the palladium NPs under working conditions and prove their relevant roles in catalysis.
Abstract: The formation of palladium hydride and carbide phases in palladium-based catalysts is a critical process that changes the catalytic performance and selectivity of the catalysts in important industrial reactions, such as the selective hydrogenation of alkynes or alkadienes. We present a comprehensive study of a 5 wt% carbon supported Pd nanoparticle (NP) catalyst in various environments by using in situ and operando X-ray absorption spectroscopy and diffraction, to determine the structure and evolution of palladium hydride and carbide phases, and their distribution throughout the NPs. We demonstrate how the simultaneous analysis of extended X-ray absorption fine structure (EXAFS) spectra and X-ray powder diffraction (XRPD) patterns allows discrimination between the inner “core” and outer “shell” regions of the NP during hydride phase formation at different temperatures and under different hydrogen pressures, indicating that the amount of hydrogen in the shell region of the NP is lower than that in the core. For palladium carbide, advanced analysis of X-ray absorption near-edge structure (XANES) spectra allows the detection of Pd–C bonds with carbon-containing molecules adsorbed at the surface of the NPs. In addition, H/Pd and C/Pd stoichiometries of PdHx and PdCy phases were obtained by using theoretical modelling and fitting of XANES spectra. Finally, the collection of operando time-resolved XRPD patterns (with a time resolution of 5 s) allowed the detection, during the ethylene hydrogenation reaction, of periodic oscillations in the NPs core lattice parameter, which were in phase with the MS signal of ethane (product) and in antiphase with the MS signal of H2 (reactant), highlighting an interesting direct structure–reactivity relationship. The presented studies show how a careful combination of X-ray absorption and diffraction can differentiate the structure of the core, shell and surface of the palladium NPs under working conditions and prove their relevant roles in catalysis.
TL;DR: A correlation between measured optical densities and functional groups concentration is established using X-ray absorption near edge structure (XANES) spectra of reference materials and an easy-to-use python program automating XANES-based quantification of carbon functional group concentrations is provided.
Abstract: X-ray absorption spectroscopy in the soft X-ray range is used in many research fields to identify the nature of functional groups in organic compounds and carbon materials. However, the concentrations of these functional groups have so far remained difficult to quantify. Using X-ray absorption near edge structure (XANES) spectra of reference materials (polymers and compounds of known molecular composition), we established a correlation between measured optical densities and functional groups concentration. This methodology relies on an alternative method for normalization to the total amount of carbon and for deconvolution of the spectra. It allows precisely quantifying the N/C atomic ratio (σ1 = 0.02 atom %) as well as the concentration of [aromatic + olefinic] groups (σ1 = 3.7 atom %), [ketone + phenol + nitrile] groups (σ1 = 2.2 atom %), [aliphatic] groups (σ1 = 11.2 atom %) and [carboxylic] groups (σ1 = 7.4 atom %). We validated this quantification by comparing with nuclear magnetic resonance data obtained on pyrolized lignin samples. We also provide an easy-to-use python program automating XANES-based quantification of carbon functional group concentrations.
TL;DR: Formation of highly plant-available compounds such as ammonium phosphates could make secondary P-fertilizers more competitive to commercial phosphate rock-based fertilizers with positive effects on resources conservation.
Abstract: A pot experiment was carried out with maize to determine the phosphorus (P) plant-availability of different secondary P-fertilizers derived from wastewater. We analyzed the respective soils by P K-edge X-ray absorption near-edge structure (XANES) spectroscopy to determine the P chemical forms that were present and determine the transformation processes. Macro- and micro-XANES spectroscopy were used to determine the chemical state of the overall soil P and identify P compounds in P-rich spots. Mainly organic P and/or P adsorbed on organic matter or other substrates were detected in unfertilized and fertilized soils. In addition, there were indications for the formation of ammonium phosphates in some fertilized soils. However, this effect was not seen in the maize yield of all P-fertilizers. The observed reactions between phosphate from secondary P-fertilizers and co-fertilized nitrogen compounds should be further investigated. Formation of highly plant-available compounds such as ammonium phosphates could make secondary P-fertilizers more competitive to commercial phosphate rock-based fertilizers with positive effects on resources conservation.
TL;DR: In this article, Mo-and W-doped BiVO4 fine particles with a diameter of 50-200nm were prepared from Bi2O3 and, Mo- and W-drained V2O5 by an aqueous route using an acetic acid solution.
Abstract: Mo- and W-doped BiVO4 fine particles with a diameter of 50–200 nm were prepared from Bi2O3 and, Mo- and W-doped V2O5 by an aqueous route using an aqueous acetic acid solution. The Mo- and W-doped BiVO4 calcined at 673 K was elongate polyhedral particles grown along with the b-axis, while the non-doped BiVO4 prepared by the same method was featureless particles. X-ray absorption near edge structure (XANES) and electron spin resonance (ESR) measurements revealed that the Mo6+ and W6+ ions were doped at V sites, resulting in the formation of V4+ in BiVO4. The Mo- and W-doped BiVO4 powders showed lower activity for photocatalytic O2 evolution than the non-doped BiVO4. In contrast, the Mo- and W-doped BiVO4 photoelectrodes fabricated by an electrophoresis method using these fine particles gave higher photoelectrochemical performance due to a positive effect of the increase in the n-type character by Mo- and W-doping.
TL;DR: In this article, the relationship among structural symmetry, Mn oxidation state, and interlayer composition was examined through a combination of Fourier transform infrared spectroscopy (FTIR), extended X-ray absorption fine structure (EXAFS), and Xray photoelectron spectroscopic (XPS).
TL;DR: In this paper, the triclinic structure (space group; P(2)) of pyro-vanadates has been confirmed by XRD, UV-visible absorption, FTIR, Raman, FE-SEM, XANES, and photoluminescence spectroscopy.
Abstract: Ca2V2O7, Sr2V2O7, and Ba2V2O7 pyro-vanadates were synthesized using a modified chemical precipitation method and annealing. Detailed crystal structure, morphology, electronic structure and optical properties were investigated by XRD, UV-visible absorption, FTIR, Raman, FE-SEM, XANES, and photoluminescence spectroscopy. Rietveld refinement on the XRD patterns of Ca2V2O7, Sr2V2O7, and Ba2V2O7 has confirmed the triclinic structure (space group; P(2)) of the pyro-vanadates. The band gap energy of Ca2V2O7, Sr2V2O7, and Ba2V2O7 is estimated to be ∼2.67 eV, ∼2.97 eV and ∼3.09 eV, respectively. XANES spectra at the Ca L-edge, Sr K-edge and Ba L-edge have confirmed the Ca2+, Sr2+ and Ba2+ ions in the Ca2V2O7, Sr2V2O7 and Ba2V2O7 compounds, respectively. V K-edge XANES spectra have strengthened the presence of sub-pentavalent V ions in all of the pyro-vanadates. O K-edge XANES spectra of Ca2V2O7, Sr2V2O7 and Ba2V2O7 have shown dominating tetrahedral symmetry of the V ions which is also corroborated with the V K-edge XANES. Broad-band emission spectra, ranging from 400 nm to 700 nm, have been observed from the charge-transfer transitions of VO4 tetrahedra. 3T1 → 1A1 and 3T2 → 1A1 transitions, from the VO4 tetrahedra, have provided two distinct emission peaks from the compounds which exhibit a red-shift with the decreasing ionic-radii of alkali-earth metal ions. The mixed compounds, with equal weight proportions, have shown remarkable emission characteristics towards the realization of rare-earth element free white-light-emitting devices.
TL;DR: It is shown that the feature peaks also change when the coordination number of the Cu cation is varied, while these feature peaks are independent of the zeolite topology, which helps elucidate the experimental XANES features at an atomic and an electronic level.
Abstract: Cu K-edge X-ray absorption near edge spectra (XANES) has been widely used to study the properties of Cu-SSZ-13. In this contribution, the sensitivity of the XANES features to the local environment for a Cu+ cation with linear configuration and a Cu2+ cation with square planar configuration in Cu-SSZ-13 is reported. When a Cu+ cation is bonded to H2O or NH3 in a linear configuration, the XANES has a large peak around 8983 eV. The intensity of this peak decreases as the linear configuration is broken. As for the Cu2+ cations in a square planar configuration with a coordination number of 4, two peaks around 8986 and 8993 eV are found. An intensity decrease for both peaks around 8986 and 8993 eV is found in a NH3_4_Z2Cu model as the N-Cu-N angle changes from 180° to 100°. We correlate these features to the variation of 4p state by PDOS analysis. In addition, the feature peaks for both the Cu+ cation and Cu2+ cation do not show a dependence on the Cu-N bond length. We further show that the feature peaks also c...
TL;DR: In this paper, the authors provided the synthesis, characterization, and catalytic performance of a variety of period 4 and 5 solid solutions of molybdenum-based bimetallic phosphides (MMoP, M = Fe, Co, Ni, Ru).
Abstract: Bimetallic phosphides are promising materials for biomass valorization, yet many metal combinations are understudied as catalysts and require further analysis to realize their superior properties. Herein, we provide the synthesis, characterization, and catalytic performance of a variety of period 4 and 5 solid solutions of molybdenum-based bimetallic phosphides (MMoP, M = Fe, Co, Ni, Ru). From the results, the charge sharing between the metals and phosphorus control the relative oxidation of Mo and reduction of P in the lattice, which were both indirectly observed in binding energy shifts in X-ray photoelectron spectroscopy (XPS) and absorption energy shifts in X-ray absorption near-edge spectroscopy (XANES). For MMoP (M = Fe, Co, Ni), the more oxidized the Mo in the bimetallic phosphide, the higher the selectivity to benzene from phenol via direct deoxygenation at 400 °C and 750 psig. This phenomenon was observed in the bimetallic materials synthesized across period 4, where aromatic selectivity and degr...
TL;DR: In this article, a comparative study has been made for the defect induced room temperature ferromagnetism of single crystal, poly-crystal, and nanorod zinc oxide (ZnO) based on the magnetic properties and electronic properties by means of X-ray absorption near edge structure spectroscopy (XANES), X -ray photoelectron spectroglobalization, ultraviolet photo electrophoresis (UPS), valence band photoemission spectromission (VB-PES), and SQUID-type magnetometry.
Abstract: A comparative study has been made for the defect induced room temperature ferromagnetism of single crystal, poly-crystal, and nanorod zinc oxide (ZnO), based on the magnetic properties and electronic properties by means of X-ray absorption near edge structure spectroscopy (XANES), X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), valence band photoemission spectroscopy (VB-PES), and SQUID-type magnetometry. Magnetic measurement demonstrates the defect-induced ferromagnetic nature at room temperature in different ZnO films and a strong correlation between their electronic properties and magnetic responses. The higher ferromagnetic behaviour in polycrystalline ZnO is attributed to the increasing number of surface defects and native defect sites (oxygen vacancies and zinc interstitials) present in ZnO. XANES studies reveal that the number of unoccupied p states in polycrystalline ZnO is higher than single crystal ZnO as well as nanorod ZnO. The more amount of oxygen vacancy caus...
TL;DR: In this paper, the structural, chemical bonding, morphological, optical, and fluorescence properties including the local atomic structure of each calcined sample were systematically investigated by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), UV-visible diffuse reflectance spectra (UV-DRS), photoluminescence (PL) and synchrotron Xray absorption spectrum (XAS), respectively.
TL;DR: This study provides mechanistic time-resolved understanding for the development of improved heteroleptic CuI photosensitizers, which can be used for the light-driven production of hydrogen from water.
Abstract: We report the light-induced electronic and geometric changes taking place within a heteroleptic CuI photosensitizer, namely [(xant)Cu(Me2 phenPh2 )]PF6 (xant=xantphos, Me2 phenPh2 =bathocuproine), by time-resolved X-ray absorption spectroscopy in the ps-μs time regime. Time-resolved X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis enabled the elucidation of the electronic and structural configuration of the copper center in the excited state as well as its decay dynamics in different solvent conditions with and without triethylamine acting as a sacrificial electron donor. A three-fold decrease in the decay lifetime of the excited state is observed in the presence of triethylamine, showing the feasibility of the reductive quenching pathway in the latter case. A prominent pre-edge feature is observed in the XANES spectrum of the excited state upon metal to charge ligand transfer transition, showing an increased hybridization of the 3d states with the ligand p orbitals in the tetrahedron around the Cu center. EXAFS and density functional theory illustrate a significant shortening of the Cu-N and an elongation of the Cu-P bonds together with a decrease in the torsional angle between the xantphos and bathocuproine ligand. This study provides mechanistic time-resolved understanding for the development of improved heteroleptic CuI photosensitizers, which can be used for the light-driven production of hydrogen from water.
TL;DR: Polarized ultrafast time-resolved X-ray absorption near edge structure (XANES) allows characterization of excited state dynamics following excitation and results in the relaxed S1 excited state structure within 500 fs of excitation.
Abstract: Polarized ultrafast time-resolved X-ray absorption near edge structure (XANES) allows characterization of excited state dynamics following excitation. Excitation of vitamin B12, cyanocobalamin (CNCbl), in the αβ-band at 550 nm and the γ-band at 365 nm was used to uniquely resolve axial and equatorial contributions to the excited state dynamics. The structural evolution of the excited molecule is best described by a coherent ballistic trajectory on the excited state potential energy surface. Prompt expansion of the Co cavity by ca. 0.03 A is followed by significant elongation of the axial bonds (>0.25 A) over the first 190 fs. Subsequent contraction of the Co cavity in both axial and equatorial directions results in the relaxed S1 excited state structure within 500 fs of excitation.
TL;DR: In this article, the synthesis of a series of zinc(II) complexes with Schiff bases products of condensation of 2-tosylamonobenzaldehide with various amino alcohols containing aliphatic spacers of a variable length (CH2)n (n = 2.2-6) was performed.
TL;DR: In this article, the role of Li concentrations (0.25-1.0%) on structural properties of Tb (1%) doped zinc oxide nanoparticles was investigated, where a small concentration of terbium was used to get minimum lattice distortion in the original structure.