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XANES

About: XANES is a research topic. Over the lifetime, 7737 publications have been published within this topic receiving 188032 citations.


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TL;DR: In this paper, an extended X-ray absorption spectroscopic (XAS) analysis of LiMnO2 has been performed to probe the evolution of electronic and crystal structures upon chemical and electrochemical delithiation/relithiation.
Abstract: Mn K-edge X-ray absorption spectroscopic (XAS) analyses have been performed to probe the evolution of electronic and crystal structures of layered LiMnO2 upon chemical and electrochemical delithiation/relithiation. According to the X-ray absorption near-edge structure studies, it becomes clear that the trivalent manganese ion in LiMnO2 is significantly oxidized by acid treatment and is not fully recovered by subsequent lithiation reaction with n-BuLi. The extended X-ray absorption fine structure results presented here demonstrate that the local structure around manganese in LiMnO2 is changed from a layered α-NaFeO2-type structure to a spinel-like one upon chemical delithiation reaction. It is also found from the XAS analyses for the cycled LiMnO2 that the electrochemical charge−discharge process gives rise not only to the partial oxidation of manganese ion but also to the migration of Mn into the interlayer lithium site, resulting in the coexistence of the layered structure and the spinel one. Such result...

79 citations

Journal ArticleDOI
TL;DR: The excited state structural dynamics of NiTMP prior to thermal relaxation are examined and a short-lived transient signal is assigned to the spectroscopic signature of the Ni(I) species, resulting from intramolecular charge transfer on a time scale that has eluded previous synchrotron studies.
Abstract: Photoexcited Nickel(II) tetramesitylporphyrin (NiTMP), like many open-shell metalloporphyrins, relaxes rapidly through multiple electronic states following an initial porphyrin-based excitation, some involving metal centered electronic configuration changes that could be harnessed catalytically before excited state relaxation. While a NiTMP excited state present at 100 ps was previously identified by X-ray transient absorption (XTA) spectroscopy at a synchrotron source as a relaxed (d,d) state, the lowest energy excited state (J. Am. Chem. Soc., 2007, 129, 9616 and Chem. Sci., 2010, 1, 642), structural dynamics before thermalization were not resolved due to the ∼100 ps duration of the available X-ray probe pulse. Using the femtosecond (fs) X-ray pulses of the Linac Coherent Light Source (LCLS), the Ni center electronic configuration from the initial excited state to the relaxed (d,d) state has been obtained via ultrafast Ni K-edge XANES (X-ray absorption near edge structure) on a time scale from hundreds of femtoseconds to 100 ps. This enabled the identification of a short-lived Ni(I) species aided by time-dependent density functional theory (TDDFT) methods. Computed electronic and nuclear structure for critical excited electronic states in the relaxation pathway characterize the dependence of the complex's geometry on the electron occupation of the 3d orbitals. Calculated XANES transitions for these excited states assign a short-lived transient signal to the spectroscopic signature of the Ni(I) species, resulting from intramolecular charge transfer on a time scale that has eluded previous synchrotron studies. These combined results enable us to examine the excited state structural dynamics of NiTMP prior to thermal relaxation and to capture intermediates of potential photocatalytic significance.

79 citations

Journal ArticleDOI
TL;DR: In this paper, the structural properties of the nano particles with the heat treatment temperature was studied by X-ray diffraction and Fe K-shell Xray absorption spectroscopy, showing that at lower annealing temperatures the nano particle comprise both maghemite and hematite phases.

79 citations

Journal ArticleDOI
TL;DR: In this article, the structure of spinel ferrite nanoparticles is studied as a function of their size and experimental conditions of their synthesis using X-ray absorption spectroscopy.
Abstract: The structure of Mn05Zn05Fe2O4 spinel ferrite nanoparticles is studied as a function of their size and the experimental conditions of their synthesis using X-ray absorption spectroscopy The nanoparticles of different sizes down to approximately 2 nm and with a narrow size distribution were synthesized using co-precipitation in reverse microemulsions Simultaneous refinement of the X-ray absorption fine structure (EXAFS) of three constituting metals shows a migration of Mn and Zn ions to the octahedral site of the spinel lattice compensated by the corresponding migration of the Fe ions To a smaller extent, Mn ions switch the occupation site already in bulk and in larger nanoparticles, while a sporadic migration of Zn is detected only in the nanoparticles with sizes below approximately 5 nm X-ray absorption near edge structure (XANES) reveals considerable variations in the position of the Mn K edge, suggesting the average Mn valence in the nanoparticles to be higher than 3+ Annealing at 500 °C relaxes the structure of as-synthesized nanoparticles toward the structure of the ceramic bulk standard

79 citations

Journal ArticleDOI
TL;DR: In this article, the properties of supported Ni particles on HZMS-5 and Al2O3-HZSM-5 were comparably investigated by diverse characteristic techniques, which are consistently evidenced by TEM and XRD as well as H-2 chemisorption and IR spectra of adsorbed CO.
Abstract: The properties of supported Ni particles on HZMS-5 and Al2O3-HZSM-5 were comparably investigated by diverse characteristic techniques. Ni/Al2O3-HZSM-5 had at least three times higher concentrations of accessible Ni atoms (average diameter Ni-0: 8.8 nm) compared to Ni/HZSM-5 (average diameter Ni-0 : 35 run), which are consistently evidenced by TEM and XRD as well as H-2 chemisorption and IR spectra of adsorbed CO. The Ni nanoparticles interacted strongly with the binder through the interaction between NiO and Al2O3, explored by the combined extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), and H-2 temperature-programmed reduction (TPR) techniques. The Bronsted acid sites on two supports probed by IR of adsorbed pyridine were similar, but Lewis acid sites contributed by the gamma-Al2O3 were more abundant on Al2O3-HZSM-5. The acid sites of the two catalysts responded differently to metal incorporation and subsequent treatments, reflecting changes in Al environments illuminated by Al-27 MAS NMR. In situ IR spectra of adsorbed species demonstrates that Al2O3-HZSM-5 has higher adsorption capacity for phenol, cyclohexanone, and cyclohexanol due to stronger adsorption of these compounds on the gamma-Al2O3 binder. (c) 2012 Elsevier B.V. All rights reserved.

79 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023186
2022403
2021212
2020232
2019242
2018256