Showing papers on "XANES published in 2017"
TL;DR: In this paper, a host-guest chemistry strategy was proposed to construct Fe-mIm nanocluster (NC) (guest)@zeolite imidazole framework-8 (ZIF-8) precursors that can be transformed into Fe-N/C electrocatalysts with controllable structures.
Abstract: Even though Fe-N/C electrocatalysts with abundant Fe-Nx active sites have been developed as one of the most promising alternatives to precious metal materials for oxygen reduction reaction (ORR), further improvement of their performance requires precise control over Fe-Nx sites at the molecular level and deep understanding of the catalytic mechanism associated with each particular structure. Herein, we report a host–guest chemistry strategy to construct Fe-mIm nanocluster (NC) (guest)@zeolite imidazole framework-8 (ZIF-8) (host) precursors that can be transformed into Fe-N/C electrocatalysts with controllable structures. The ZIF-8 host network exhibits a significant host–guest relationship dependent confinement effect for the Fe-mIm NCs during the pyrolysis process, resulting in different types of Fe-Nx sites with two- to five-coordinated configurations on the porous carbon matrix confirmed by X-ray absorption near edge structure (XANES) and Fourier transform (FT) extended X-ray absorption fine structure ...
436 citations
TL;DR: The use of X-ray absorption near-edge structure (XANES) spectroscopy and supervised machine learning (SML) for refining the 3D geometry of metal catalysts is reported on, allowing one to solve the structure of a metal catalyst from its experimental XANES.
Abstract: Tracking the structure of heterogeneous catalysts under operando conditions remains a challenge due to the paucity of experimental techniques that can provide atomic-level information for catalytic metal species Here we report on the use of X-ray absorption near-edge structure (XANES) spectroscopy and supervised machine learning (SML) for refining the 3D geometry of metal catalysts SML is used to unravel the hidden relationship between the XANES features and catalyst geometry To train our SML method, we rely on ab initio XANES simulations Our approach allows one to solve the structure of a metal catalyst from its experimental XANES, as demonstrated here by reconstructing the average size, shape, and morphology of well-defined platinum nanoparticles This method is applicable to the determination of the nanoparticle structure in operando studies and can be generalized to other nanoscale systems It also allows on-the-fly XANES analysis and is a promising approach for high-throughput and time-dependent
206 citations
TL;DR: In this paper, a 2D vanadium carbide MXene containing surface functional groups (V2CTx) was synthesized and studied as anode material for Na-ion batteries.
Abstract: 2D vanadium carbide MXene containing surface functional groups (denoted as V2CTx, where Tx are surface functional groups) is synthesized and studied as anode material for Na-ion batteries. V2CTx anode exhibits reversible charge storage with good cycling stability and high rate capability through electrochemical test. The charge storage mechanism of V2CTx material during Na+ intercalation/deintercalation and the redox reaction of vanadium are studied using a combination of synchrotron based X-ray diffraction, hard X-ray absorption near edge spectroscopy (XANES), and soft X-ray absorption spectroscopy (sXAS). Experimental evidence of a major contribution of redox reaction of vanadium to the charge storage and the reversible capacity of V2CTx during sodiation/desodiation process are provided through V K-edge XANES and V L2,3-edge sXAS results. A correlation between the CO32− content and the Na+ intercalation/deintercalation states in the V2CTx electrode observed from C and O K-edge in sXAS results implies that some additional charge storage reactions may take place between the Na+-intercalated V2CTx and the carbonate-based nonaqueous electrolyte. The results of this study provide valuable information for the further studies on V2CTx as anode material for Na-ion batteries and capacitors.
158 citations
TL;DR: In this article, the authors reported the preparation of hierarchical Fe-doped NiO x nanotubes assembled from ultrathin nanosheets with a thickness of 24nm X-ray photoelectron spectroscopy (XPS) spectra.
146 citations
TL;DR: In this article, the authors proposed VO1.52(OH)0.77 as a possible electrode material for aqueous zinc-ion batteries (ZIBs) based on X-ray diffraction data (XRD).
Abstract: For the first time, we suggest VO1.52(OH)0.77 and Al-doped VO1.52(OH)0.77 as possible candidate electrode materials for aqueous zinc-ion batteries (ZIBs). Structural analysis data indicate successful doping of Al into the hollandite VO1.52(OH)0.77 tunnel structure, as confirmed by Rietveld refinement of the X-ray diffraction data (XRD) and X-ray absorption near edge structure (XANES) spectroscopy data. Al is preferred to replace V3+, such that the resulting average oxidation state of V increases with increasing Al content in V1−xAlxO1.52(OH)0.77. Electrochemical test results indicate significant improvement in capacity and retention in the Al-doped V1−xAlxO1.52(OH)0.77 due to the presence of strong Al–O bonds, which stabilizes the crystal structure. This is confirmed from the post-cycled data that show less variation in the lattice parameters. Combining the XRD and XANES data, we suggest that the present V1−xAlxO1.52(OH)0.77 is activated by the V4+/3+ redox reaction, accompanied by Zn2+ insertion into the tunnel structure upon reduction and Zn2+ extraction upon oxidation.
116 citations
TL;DR: In this article, a novel study on the reaction mechanism of nonaqueous aluminum/graphite cell chemistry employing 1-ethyl-3-methylimidazolium chloride:aluminum trichloride (EMIMCl:AlCl3) as the electrolyte is presented.
Abstract: Herein we report a novel study on the reaction mechanism of non-aqueous aluminum/graphite cell chemistry employing 1-ethyl-3-methylimidazolium chloride:aluminum trichloride (EMIMCl:AlCl3) as the electrolyte. This work highlights new insights into the reversibility of the anion intercalation chemistry besides confirming its outstanding cycle life exceeding 2000 cycles, corresponding to more than 5 months of cycling test. The reaction mechanism, involving the intercalation of AlCl4− in graphite, has been fully characterized by means of ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure spectroscopy (XANES) and small-angle X-ray scattering (SAXS), evidencing the accumulation of anionic species into the cathode as the main factor responsible for the slight initial irreversibility of the electrochemical process.
104 citations
TL;DR: In this article, the structural evolution of an industrial Pd/C catalyst in the presence of hydrogen and acetylene was determined by means of in situ X-ray absorption spectroscopy and Xray powder diffraction.
98 citations
TL;DR: It is proposed that the effect of the Ni ions as well as the inherent exchange interactions arising from VO+ assist to produce BMPs, which are accountable for the RT-FM in Zn1-xNixO (0< x < 0.125) system.
Abstract: The origin of room temperature (RT) ferromagnetism (FM) in Zn1–xNixO (0< x < 0.125) samples are systematically investigated through physical, optical, and magnetic properties of nanostructure, prepared by simple low-temperature wet chemical method. Reitveld refinement of X-ray diffraction pattern displays an increase in lattice parameters with strain relaxation and contraction in Zn/O occupancy ratio by means of Ni-doping. Similarly, scanning electron microscope demonstrates modification in the morphology from nanorods to nanoflakes with Ni doping, suggests incorporation of Ni ions in ZnO. More interestingly, XANES (X-ray absorption near edge spectroscopy) measurements confirm that Ni is being incorporated in ZnO as Ni2+. EXAFS (extended X-ray absorption fine structure) analysis reveals that structural disorders near the Zn sites in the ZnO samples upsurges with increasing Ni concentration. Raman spectroscopy exhibits additional defect driven vibrational mode (at 275 cm–1), appeared only in Ni-doped sampl...
98 citations
TL;DR: In this paper, a spin-crossover (SCO) complex was investigated by magnetic susceptibility measurements and Mosbauer spectroscopy in the solid state and by temperature-dependent UV/vis spectrograms in a thin film deposited by physical vapor deposition (PVD) on quartz glass.
Abstract: To investigate the ability for spin-state switching of spin-crossover (SCO) complexes adsorbed to solid substrates, the SCO complex [Fe(H2B(pz)2)2(phenme4)] (pz = pyrazole, phenme4 = 3,4,7,8-tetramethyl-1,10-phenanthroline) is prepared. The new complex is investigated by magnetic susceptibility measurements and Mosbauer spectroscopy in the solid state and by temperature-dependent UV/vis spectroscopy in a thin film deposited by physical vapor deposition (PVD) on quartz glass. Thermal- and light-induced SCO is observed in the bulk and the film on glass. Submonolayers of this complex obtained by PVD are studied by temperature-dependent near-edge X-ray absorption fine structure (NEXAFS) on Au(111) as well as Bi(111) and by scanning tunneling microscopy (STM) on Au(111). NEXAFS shows thermal- and light-induced spin-state switching of the complex on Bi(111), however, with a large temperature-independent high-spin fraction (∼50%). On the other hand, combined evidence from NEXAFS and STM indicates that on Au(111)...
72 citations
TL;DR: In this paper, the reduction properties of CeO2-x nanoparticles prepared using different synthesis parameters when exposed to a CO reducing atmosphere were investigated, and an improved reduction tendency was observed for these synthesized nanoparticles.
69 citations
TL;DR: Results verify a novel 8R monovalent Cu site, an eventually large Cu+ presence upon heating to high temperatures in oxidative conditions, and demonstrate the unique potential in combining in-situ PXRD and XANES techniques, with which both oxidation state and structural location of the redox-active centers in the zeolite framework could be tracked.
Abstract: Using quasi-simultaneous insitu PXRD and XANES, the direct correlation between the oxidation state of Cu ions in the commercially relevant deNOx NH3-SCR zeolite catalyst Cu-CHA and the Cu ion migration in the zeolitic pores was revealed during catalytic activation experiments. A comparison with recent reports further reveals the high sensitivity of the redox-active centers concerning heating rates, temperature, and gas environment during catalytic activation. Previously, Cu+ was confirmed present only in the 6R. Results verify a novel 8R monovalent Cu site, an eventually large Cu+ presence upon heating to high temperatures in oxidative conditions, and demonstrate the unique potential in combining insitu PXRD and XANES techniques, with which both oxidation state and structural location of the redox-active centers in the zeolite framework could be tracked. (Less)
TL;DR: In this paper, the authors combine x-ray absorption near edge structure (XANES) spectroscopy with ab initio theoretical modeling to identify energetically favorable defects in hexagonal boron nitride (hBN).
Abstract: Hexagonal boron nitride (hBN) is a wide-band-gap semiconductor with applications including gate insulation layers in graphene transistors, far-ultraviolet light emitting devices and as hydrogen storage media. Due to its complex microstructure, defects in hBN are challenging to identify. Here, we combine x-ray absorption near edge structure (XANES) spectroscopy with ab initio theoretical modeling to identify energetically favorable defects. Following annealing of hBN samples in vacuum and oxygen, the B and N $K$ edges exhibited angular-dependent peak modifications consistent with in-plane defects. Theoretical calculations showed that the energetically favorable defects all produce signature features in XANES. Comparing these calculations with experiments, the principle defects were attributed to substitutional oxygen at the nitrogen site, substitutional carbon at the boron site, and hydrogen passivated boron vacancies. Hydrogen passivation of defects was found to significantly affect the formation energies, electronic states, and XANES. In the B $K$ edge, multiple peaks above the major $1s$ to ${\ensuremath{\pi}}^{*}$ peak occur as a result of these defects and the hydrogen passivated boron vacancy produces the frequently observed doublet in the $1s$ to ${\ensuremath{\sigma}}^{*}$ transition. While the N $K$ edge is less sensitive to defects, features attributable to substitutional C at the B site were observed. This defect was also calculated to have mid-gap states in its band structure that may be responsible for the 4.1-eV ultraviolet emission frequently observed from this material.
TL;DR: This work introduces polarized femtosecond XANES, combined with UV-visible spectroscopy, to reveal sequential structural evolution of CNCbl in the excited electronic state, and exposes features of the potential energy surfaces controlling cobalamin reactivity and deactivation.
Abstract: Ultrafast, polarization-selective time-resolved X-ray absorption near-edge structure (XANES) was used to characterize the photochemistry of vitamin B12, cyanocobalamin (CNCbl), in solution. Cobalamins are important biological cofactors involved in methyl transfer, radical rearrangement, and light-activated gene regulation, while also holding promise as light-activated agents for spatiotemporal controlled delivery of therapeutics. We introduce polarized femtosecond XANES, combined with UV–visible spectroscopy, to reveal sequential structural evolution of CNCbl in the excited electronic state. Femtosecond polarized XANES provides the crucial structural dynamics link between computed potential energy surfaces and optical transient absorption spectroscopy. Polarization selectivity can be used to uniquely identify electronic contributions and structural changes, even in isotropic samples when well-defined electronic transitions are excited. Our XANES measurements reveal that the structural changes upon photoex...
TL;DR: In this paper, the synthesis, structural, morphology, electronic/atomic structure and photocatalyst properties of Cu doped TiO 2, ZnO and Ni(OH) 2 nanostructures were reported.
TL;DR: In this article, a series of size-selected Ptn/SiO2 samples were analyzed using X-ray photoelectron spectroscopy (XPS), low energy ion scattering, grazing-incidence small-angle x-ray scattering, and XANES.
Abstract: X-ray absorption near-edge structure (XANES) is commonly used to probe the oxidation state of metal-containing nanomaterials; however, as the particle size in the material drops below a few nanometers, it becomes important to consider inherent size effects on the electronic structure of the materials. In this paper, we analyze a series of size-selected Ptn/SiO2 samples, using X-ray photoelectron spectroscopy (XPS), low energy ion scattering, grazing-incidence small-angle X-ray scattering, and XANES. The oxidation state and morphology are characterized both as-deposited in UHV, and after air/O2 exposure and annealing in H2. The clusters are found to be stable during deposition and upon air exposure, but sinter if heated above ∼150 °C. XANES shows shifts in the Pt L3 edge, relative to bulk Pt, that increase with decreasing cluster size, and the cluster samples show high white line intensity. Reference to bulk standards would suggest that the clusters are oxidized; however, XPS shows that they are not. Inste...
TL;DR: In this article, Nanocrystalline Ni Zn ferrites were synthesized by a novel and facile chemical method via a polymer precursor and their structural and magnetic properties were evaluated and discussed in correlation with the cationic distribution.
TL;DR: In this article, the I5+ ion of the I3− group in calcite and vaterite is bonded by three and two additional O atoms (i.e., coordination numbers ǫ = 6 and 5), respectively, and is incorporated via the charged coupled substitution I5−+Na+↔ C4+++Ca2+, with the Na+ cation at a nearest Ca2+ site being the most energetically favorable configuration.
TL;DR: In this paper, the structural changes induced by reversible formation of Bronsted acidic sites and hydronium ions with water in a zeolite with MFI structure are reported as a function of temperature using a combination of physicochemical methods and theory.
Abstract: The structural changes induced by reversible formation of Bronsted acidic sites and hydronium ions with water in a zeolite with MFI structure are reported as a function of temperature using a combination of physicochemical methods and theory. In the presence of an ample concentration of water, the protons are present as hydrated hydronium ions (H3O+(H2O)n) that are ion-paired to the zeolite. Loss of water molecules hydrating the hydronium ions leads to an unstable free hydronium ion that dissociates to form the hydroxylated T-site. The formation of this SiOHAl species leads to the elongation of one of the four Al–O bonds and causes significant distortion of the tetrahedral symmetry about the Al atom. This distortion leads to the appearance of new pre-edge features in the Al K-edge X-ray absorption near edge structure (XANES) spectra. The pre-edge peak assignment is confirmed by time-dependent density functional theory calculation of the XANES spectrum. The XANES spectra are also sensitive to solutes or so...
TL;DR: The role of Ag doping and defects in the ZnO NPs were discussed for the observed antibacterial and photoluminescence behaviour and XPS and XANES studies confirmed the deficiency of concentration of defects in ZNO after Ag doping.
TL;DR: In this article, high-energy resolution fluo-rescence detection X-ray absorption near edge structure (HERFD XANES) measurements quantify the electron dona-tion and are correlated with the catalytic activity and selectivity.
Abstract: 1,3-Dialkylimidazolium ionic liquid coatings act as electron-donors increasing the selectivity for partial hydrogenation of 1,3-butadiene catalyzed by iridium complexes supported on high-surface-area γ-Al2O3. High-energy resolution fluo-rescence detection X-ray absorption near edge structure (HERFD XANES) measurements quantify the electron dona-tion and are correlated with the catalytic activity and selectivity. The results demonstrate broad opportunities to tune electronic environments and catalytic properties of atomically dispersed supported metal catalysts.
TL;DR: In this paper, the authors demonstrate that δ-Bi2O3 can be synthesized at low temperature through a facile sol-gel route in the presence of metavanadate oxyanion (VO3−).
TL;DR: The present study has demonstrated the possibility of application of TXRF for the oxidation state determination and elemental speciation of radioactive substances in a nondestructive manner with very small amount of sample requirement.
Abstract: Total reflection X-ray fluorescence (TXRF)-based X-ray absorption near-edge spectroscopy has been used to determine the oxidation state of uranium in mixed-valent U3O8 and U3O7 uranium oxides. The TXRF spectra of the compounds were measured using variable X-ray energies in the vicinity of the U L3 edge in the TXRF excitation mode at the microfocus beamline of the Indus-2 synchrotron facility. The TXRF-based X-ray absorption near-edge spectroscopy (TXRF-XANES) spectra were deduced from the emission spectra measured using the energies below and above the U L3 edge in the XANES region. The data processing using TXRF-XANES spectra of U(IV), U(V), and U(VI) standard compounds revealed that U present in U3O8 is a mixture of U(V) and U(VI), whereas U in U3O7 is mixture of U(IV) and U(VI). The results obtained in this study are similar to that reported in literature using the U M edge. The present study has demonstrated the possibility of application of TXRF for the oxidation state determination and elemental spe...
TL;DR: It was observed that there is almost complete transfer of photon energy from Zn2P2O7 to Eu3+, whereas this transfer is inefficient and almost incomplete in case of Sm3+, which is indeed important information for the realization of pyrophosphate-based tunable phosphors.
Abstract: Considering the fact that pyrophosphate-based hosts are in high demand for making highly efficient luminescence materials, we doped two visible lanthanide ions, viz. Sm3+ and Eu3+, in Zn2P2O7. Interestingly, it was oberved that pure Zn2P2O7 displayed blue-green dual emission on irradiation with ultraviolet light. Emission and lifetime spectroscopy shows the presence of defects in pyrophosphate samples which are responsible for such emission. DFT calculations clearly pinpointed that the electronic transitions between defect states located at just below the conduction band minimum (arises due to VO1+ and VO2+ defects) and valence band maximum, as well as impurity states situated in the band gap, can lead to dual emission in the blue-green region, as is also indicated by emission and lifetime spectra. X-ray absorption near edge spectroscopy (XANES) shows the stabilization of europium as well as samarium ion in the +3 oxidation state in α-Zn2P2O7. The fact that α-Zn2P2O7 has two different coordination numbers...
TL;DR: Upon nitrogen substitution, the total density of state close to Fermi level is increased to raise the valence-band maximum, as revealed by VB-PES spectra, indicating an electron donation from nitrogen, molecular bonding C/N/O coordination or/and lattice structure reorganization in GO:Nx.
Abstract: Nitrogen-doped graphene oxides (GO:Nx) were synthesized by a partial reduction of graphene oxide (GO) using urea [CO(NH2)2]. Their electronic/bonding structures were investigated using X-ray absorption near-edge structure (XANES), valence-band photoemission spectroscopy (VB-PES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). During GO:Nx synthesis, different nitrogen-bonding species, such as pyrrolic/graphitic-nitrogen, were formed by replacing of oxygen-containing functional groups. At lower N-content (2.7 at%), pyrrolic-N, owing to surface and subsurface diffusion of C, N and NH is deduced from various X-ray spectroscopies. In contrast, at higher N-content (5.0 at%) graphitic nitrogen was formed in which each N-atom trigonally bonds to three distinct sp2-hybridized carbons with substitution of the N-atoms for C atoms in the graphite layer. Upon nitrogen substitution, the total density of state close to Fermi level is increased to raise the valence-band maximum, as revealed by VB-PES spectra, indicating an electron donation from nitrogen, molecular bonding C/N/O coordination or/and lattice structure reorganization in GO:Nx. The well-ordered chemical environments induced by nitrogen dopant are revealed by XANES and RIXS measurements.
TL;DR: In this paper, the oxygen-vacancy-rich FMMGS hybrids were used as anode materials for Li2MoO4 batteries with high capacity and rate capability.
Abstract: The search for new electrode materials is of paramount importance for the practical apply of lithium-ion batteries (LIBs). Herein, flower-like MoO2 microislands consist of MoO2 nanorods grown on both sides of graphene sheets were synthesized via a solvo-thermal method, followed by a simple thermal treatment in argon. Our EXAFS and ESR data suggest there oxygen-vacancies in MoO2 of the FMMGS hybrids. Besides, by tunning the ratio of glucose and CTAB, samples with different oxygen-vacancies content were synthesized. When used as anode materials for lithium-ion batteries, the oxygen-vacancy-rich FMMGS hybrids exhibited obviously higher capacity, rate capability than any nonvacancy samples. Importantly, synchrotron-radiation-based X-ray absorption near-edge structure (XANES), extended X-ray absorption fine-structure (EXAFS) and ex situ X-ray diffraction (ex situ XRD) were employed to elucidate the Li-ion insertion and extraction processes in the MoO2 electrode. Our data clearly revealed that Li2MoO4 was gener...
TL;DR: In this paper, the local structure about Fe(II) and Fe(III) in silicate melts was investigated in-situ using iron K-ray absorption near-edge structure (XANES) spectroscopy.
TL;DR: In this article, the authors highlight the use of the x-ray absorption spectroscopy (XAS) as a local structural tool unlike X-ray diffraction for selected atoms in advanced functional materials including energy storage materials, dielectric materials and thermoelectric material.
Abstract: This paper highlights the use of the x-ray absorption spectroscopy (XAS) as a local structural tool unlike x-ray diffraction for selected atoms in advanced functional materials including energy storage materials, dielectric materials and thermoelectric materials. The information concerning the oxidation states and local atomic structure around probing atoms will be revealed using x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS). The XAS beamline: BL5.2 at the Synchrotron Light Research Institute (SLRI) (public organization), Thailand, and its characteristic including available of measured energy ranges, examples of measured spectra of Mg, S and Ti K-edge XAS are also presented. In addition, in situ XAS set up and experiment carried out at this beamline are also outlined.
TL;DR: In this article, temperature-dependent photoluminescence (PL) of titanium oxide (TiO2) shows an evolution of blue emission when exposed to 50 keV Ar+ ions.
Abstract: Temperature-dependent photoluminescence (PL) of titanium oxide (TiO2) shows an evolution of blue emission when exposed to 50 keV Ar+ ions. The origin of observed PL has been examined by X-ray absorption near-edge spectroscopy (XANES) at Ti-K,L and O-K edges, revealing the reduction of ligand field splitting owing to the formation of oxygen vacancies (OVs) by destroying TiO6 octahedral symmetry. Detailed PL and XANES analyses suggest that the fluence (ions/cm2) dependent increase in OVs not only boosts the conduction electrons but also increases the density of holes in localized self-trapped exciton (STE) states near the valence band. Based on these observations, we propose a model in which doped conduction electrons are recombining radiatively with the holes in STE states for blue light emission.
TL;DR: In this article, the authors investigated properties involved in the enhancement in electrocatalytic carbon dioxide (CO2) reduction to carbon monoxide (CO) in electrochemically treated Ag surfaces with surface sensitive analysis methods such as Auger spectroscopy, atomic force microscopy (AFM) coupled with Kelvin probe force microscope (KPFM) techniques, and near edge X-ray absorption fine structure (NEXAFS) Spectroscopy.
TL;DR: In this paper, the authors employed X-rays as an equivalent but accelerated cause of degradation, as an excitation source of luminescence and as an element-selective probe of both dopants and host-lattice chemical species.
Abstract: The efficient blue luminescence of Eu2+ doped BaMgAl10O17 is well-known to be severely degraded by prolonged irradiation with vacuum-ultraviolet light. The degradation process at the atomic level is however not fully understood. In this work we employed X-rays as an equivalent but accelerated cause of degradation, as an excitation source of luminescence and as an element-selective probe of both dopants and host-lattice chemical species. The X-ray absorption near edge structure (XANES) recorded in high energy resolution mode reveals that the structural properties of the host lattice are preserved during irradiation, while Eu2+ is rapidly oxidized. The correlation between Eu oxidation as derived from XANES and the decrease of blue luminescence is however not linear and a significant fraction of Eu2+ survives degradation, implying additional mechanisms for the quenching of the luminescence. Defects created during the photogeneration may reduce the ability of the remaining Eu2+ to receive or to radiatively re...