Edge Structure Spectra Research Articles

Redox reactions between chromium(VI) and hydroquinone: Alternative pathways for polymerization of organic molecules

Chromium (VI) reduction by organic compounds is one of the major pathways to alleviate the toxicity and mobility of Cr(VI) in the environment. However, oxidative products of organic molecules receive less scientific concerns. In this study, hydroquinone (H2Q) was used as a representative organic compound to determine the redox reactions with Cr(VI) and the concomitant oxidative products. Spectroscopic analyses showed that Cr(III) hydroxides dominated the precipitates produced during redox reactions of Cr(VI) and H2Q. For the separated filtrates, the acidification induced the oxidative polymerization of organic molecules, accompanied with the complexation with Cr(III). The aromatic domains dominated the chemical structures of the black and fluffy organic polymers, which was different to the natural humic acids due to the shortage of aliphatic chains. Results of linear combination fitting (LCF) for Cr K-edge X-ray absorption near edge structure (XANES) spectra demonstrated that up to 90.4% of Cr inventory in precipitates derived after the acidification of filtrates was Cr(III) complexed with humic-like polymers, suggesting that Cr(III) possibly acted as a linkage among organic molecules during the polymerization processes of H2Q. This study demonstrated that Cr(VI) may lead to the polymerization of organic molecules in an acidic solution, and thus, it could raise scientific awareness that the oxidative decomposition of organic molecules may not be the only pathway while interacting with the strong oxidant of Cr(VI).

Calcium X-ray absorption near edge structure (XANES) spectra: A thermometer for the firing temperature of ceramics?

Test samples have been fabricated similar to Poverty Point Objects (PPOs) using silty loam from the UNESCO World Heritage Site Poverty Point. In an oxidative atmosphere these objects were fired in a defined way to 3000C, 5000C, and 8000C respectively. For all samples, including a non-heated one, X-ray absorption near edge structure (XANES) spectra were measured at the Ca-K-edge. Two of the characteristic features of these spectra were used for obtaining for the first time a calibration curve for determining the firing temperature of ceramic objects. Using this calibration curve, the “firing temperature”, i.e. the highest temperature these objects have been used at of two Poverty Point Objects found at smaller sites (Terral Lewis, Caney Mounds) could be estimated at ~5000C - a typical temperature for a wood fire. This result supports in a direct way the hypothesis that at least some of the Poverty Point Objects have been used as cooking stones.

The stability of divalent Ge in silicate melts and its geochemical properties

The oxidation state of Ge in silicate glasses, quenched from melts, was determined by X-ray absorption spectroscopy. The melts were equilibrated over the range of relative oxygen fugacities (fO2) from IW -3 to IW +10, where IW is the iron-wüstite oxygen buffer in logarithmic units. X-ray absorption near edge structure (XANES) spectra of the samples show that over the range in fO2 from IW -2.8 to IW+2.4, the Ge4+/(Ge2+ + Ge4+) ratio increases from 0.05 to 0.95. Modelling of extended X-ray absorption fine structure (EXAFS) gives the Ge2+–O bond length as 1.89±0.03Å. Olivine–melt partitioning experiments were also conducted, which show that Ge2+ is highly incompatible, with DGe2+ol/melt < 0.005, whereas DGe4+ol/melt is ∼ 1, where D is the partition coefficient. The geochemical properties of Ge during the magmatic differentiation of the Moon and other reduced rocky planets and achondrite parent bodies will therefore be entirely different to that familiar from terrestrial examples. In particular, the incompatible nature of Ge2+ may explain the anomalous enrichment of Ge in KREEP basalts.

Zr(IV) surface sites determine CH3OH formation rate on Cu/ZrO2/SiO2 - CO2 hydrogenation catalysts

Cu/ZrO 2 /SiO 2 are efficient catalysts for the selective hydrogenation of CO 2 to CH 3 OH. In order to understand the role of ZrO 2 in these mixed-oxides based catalysts, in situ X-ray absorption spectroscopy has been carried out on the Cu and Zr K-edge. Under reaction conditions, Cu remains metallic, while Zr is present in three types of coordination environment associated with 1) bulk ZrO 2 , 2) coordinatively saturated and 3) unsaturated Zr(IV) surface sites. The amount of coordinatively unsaturated Zr surface sites can be quantified by linear combination fit of reference X-Ray absorption near edge structure (XANES) spectra and its amount correlates with CH 3 OH formation rates, thus indicating the importance of Zr(IV) Lewis acid surface sites in driving the selectivity toward CH 3 OH. This finding is consistent with the proposed mechanism, where CO 2 is hydrogenated at the interface between the Cu nanoparticles that split H 2 and Zr(IV) surface sites that stabilizes reaction intermediates. Density and role of Lewis acidic Zr(IV) surface sites in Cu/SiO 2 /ZrO 2 based catalyst to promote CO 2 -to-CH 3 OH synthesis is elucidated by in-situ X-ray absorption spectroscopy.

Extraction behavior comparison of hydrophilic ionic liquids for chromium on humic acid–microporous system

In soil, humic acids (HAs) are found on the external surface of micropores. HAs supply a sorption site for metals. In the present work, the fate of hexavalent Cr (Cr(VI)) without effect of other metals in microporous system was observed. By component-fitted X-ray absorption near the edge structure (XANES) spectra, approximately 84% of hexavalent Cr (Cr(VI)) was adsorbed on HA–zeolite Y (simulated HA on external surface of microporous system in soil). The reduction of Cr(VI)–HA (Cr(VI) adsorbed on HA) occurred to form Cr(III)–HA (Cr(III) adsorbed on HA) in HA–zeolite Y. The hydrophilic ionic liquids (ILs) (1-butyl-3-methylimidazolium chloride ([C4mim][Cl]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4])) were used to extract the chromium compounds in HA–zeolite Y. By XANES, Cr(VI)–HA desorbed from the external surface of zeolite Y and was substantially reduced to Cr(III)–HA in [C4mim][Cl] and [C4mim][BF4]. The extraction and reduction efficiencies of chromium species were less in [C4mim][BF4] than in [C4mim][Cl] due to high hydrogen bond basicity of [C4mim][Cl]. The 1H NMR and FTIR spectra also show that the interaction between extracted chromium species and cations of [C4mim][Cl] is associated with the feasibilities of extraction and reduction. The extracted and non-extractable Cr(VI)/Cr(III) mole ratios in ILs and HA–zeolite Y were decreased, respectively, which diminished the toxicity of the chromium compounds in HA–zeolite Y. Appropriate ILs, e.g., [C4mim][Cl], used as extracting solutions, can enhance extraction and reduce toxicity for Cr(VI) compounds.

Luminescence of Fluorochlorozirconate Glasses Doped with Manganese Ions

A series of fluorochlorozirconate glasses doped with manganese ions is synthesized and investigated as possible red‐emitting phosphors in comparison with conventional green‐emitting fluorozirconate glasses doped with Mn2+. It is found that the replacement of fluorine by chlorine ions results in broadening and a long‐wavelength shift of the manganese luminescence band into the red region (peaked at 615 nm) although the emission spectrum still has some contribution of the green sub‐band. It turns out also that decay kinetics of luminescence from fluorochlorozirconate glasses becomes nonexponential in contrast to single‐exponential decay observed for green luminescence from Mn2+‐doped fluorozirconate glasses. The observation of two emission components in the luminescence spectrum of fluorochlorozirconate glasses is interpreted as being due to the presence of two Mn2+ emission centers in different local environments. The presence of 2+ valence states of manganese ions in both types of glasses is confirmed by recording X‐ray absorption near edge structure (XANES) spectra at Mn L2,3 edge. Substitution of F− by Cl− ions in anion sites neighboring to Mn2+, leads to a significant rearrangement of the local environment of Mn2+ ions, which results in the long‐wavelength shift of Mn2+ emission spectrum.

Superconductivity related to local electronic and atomic structures in layered chalcogenide 1T-TaS2-xSex

We have performed temperature-dependent synchrotron radiation x-ray absorption fine structure (XAFS) spectra of layered transition metal dichalcogenide 1T-TaS2-xSex to elucidate the local electronic and atomic structure especially associated with the occurrence of superconductivity for the first time. We observed a corresponding temperature-dependent phase transition from nearly commensurate to commensurate charge density wave, as well as a characteristic of p-d hybridization between Ta 5d and Se 4p states, which is favorable to boost superconductivity, determined by x-ray absorption near edge structure (XANES) spectra at the Ta L3-edge and Se K-edge, respectively. And also, the periodic lattice distortion accompanied by the occurrence of charge density wave is clearly demonstrated by extended XAFS (EXAFS) spectra at the Ta L3-edge of the pristine sample 1T-TaS2, which is clearly suppressed in the Se-doping sample 1T-TaSSe with a maximum transition temperature . The present results reveal that the p-d hybridization and the loss of long-range coherence of the CDW state play an important role in manipulating the superconductivity, shedding new light on the physics mechanism of the interplay between superconductivity, charge order, and electron correlation.

Synthesis and electrochemical properties of polymer solution prepared MnCo2O4 nanoparticles

In this work, spinel MnCo2O4 nanoparticles with a particle size of about 40–160 nm were prepared by a simple polymer solution method. The resulting precursor was calcined at 500 °C, 600 °C, 700 °C, and 800 °C to obtain a spinel MnCo2O4 phase. The results of X-ray diffraction and transmission electron microscopy with selected electron diffraction analysis indicated that the MnCo2O4 nanoparticles have a cubic structure. The X-ray absorption near edge structure and X-ray photoelectron spectroscopy spectra have confirmed the mixed valence state of Mn3+/Mn4+ and Co2+/Co3+ in all samples. The electrochemical properties were investigated by using a three-electrode cell system in 6.0 M KOH electrolyte. The sample calcined at 600 °C exhibits the highest specific capacitance value of 282 F/g and 208 F/g at a scan rate of 2 mV/s and at a current density of 1.0 A/g, respectively, and the best capacitance retention with long-term cycling stability over 70% after 1000 cycles. Clearly, calcination temperatures affect to the specific surface area and pore diameter, which can improve the electrochemical performance of the MnCo2O4 nanoparticles.

DL-cysteine and L-cystine formation and their enhancement effects during sulfur autotrophic denitrification

Sulfur autotrophic denitrification has been proved feasible for nitrate removal from aquatic environments and it utilizes elemental sulfur as the electron donor. A maximum denitrification rate of 194.57 mg N/L·d was achieved with biogenic sulfur as electron donor in a mixed culture collected from sulfur packed bed reactors; this rate was considerably higher than that delivered by α-S8 or μ-S in the same mixed culture. The elemental sulfur was also tested in the pure culture of Thiobacillus denitrificans, while a lower denitrification rate was noted than in the mixed culture, bio-S (4.86 mg N/L·d) again outperformed other two elemental sulfur's. X-ray absorption near edge structure spectra were collected to examine possible metabolic intermediates during the sulfur autotrophic denitrification process. The analysis revealed the existence of two major intermediates: DL-cysteine and L-cystine. They were found to not only provide electrons but also play a critical role in promoting the elemental sulfur-mediated sulfur autotrophic denitrification process. In general, we investigated the formation and enhancement effects of sulfur intermediates in the sulfur autotrophic denitrification process.

Molecular Dynamics Simulation of Zinc Ion in Water with an ab Initio Based Neural Network Potential

An artificial neural network provides the possibility to develop molecular potentials with both the efficiency of the classical molecular mechanics and the accuracy of the quantum chemical methods. Here, we develop an ab initio based neural network potential (NN/MM-RESP) to perform molecular dynamics study of zinc ion in liquid water. In this approach, the interaction energy, atomic forces, and atomic charges of zinc ion and water molecules in the first solvent shell are described by a neural network potential trained with energies and forces generated from density functional calculations. The predicted energies and forces from the NN potential show excellent agreement with the quantum chemistry calculations. Using this approach, we carried out molecular dynamics simulation to study the hydration of zinc ion in water. The experimentally observed zinc-water radial distribution function, as well as the X-ray absorption near edge structure spectrum, is well-reproduced by the MD simulation. Comparison of the results with other theoretical calculations is provided, and important features of the present approach are discussed. The neural network approach used in this study can be applied to construct potentials to study solvation of other metal ions, and its salient features can shed light on the development of more accurate molecular potentials for metal ions in other environments such as proteins.

Effect of Beryllium Heat Treatment in Synthetic Ruby

We study the effect of Be atoms in the corundum structure by using UV-Vis–NIR spectroscopy as well as X-ray absorption spectroscopy on synthetic ruby samples obtained by the Verneuil process. From the X-ray absorption near edge structure (XANES) spectra, the Be atoms are shown not to be related to the Cr environment. Furthermore, the UV-Vis–NIR absorption spectra are similar for the unheated, traditionally heated, and Be-heated synthetic ruby samples. However, the Be atoms are able to produce a brown-colored center, and the mixing of the red and the brown colors yields the orange in the Be-heated synthetic ruby samples. We propose that the orange color in the Be-heated synthetic ruby samples is caused by the Be2+ donor state at 475 nm (2.61 eV) in multiple UV-Vis–NIR wavelength excitation spectra.

Mineralogical and geochemical constraints on chromium oxidation induced by birnessite

We have explored redox reactions between dissolved Cr and the phyllomanganate birnessite with high resolution through simultaneous synchrotron X-ray diffraction, X-ray spectroscopy, and fluid analysis at different concentrations of solution pH. Specifically, we collected time-resolved synchrotron X-ray diffraction patterns and X-ray absorption near edge structure (XANES) spectra from triclinic Na-birnessite every 15 min while passing pH controlled 1.0 mM Cr(III) nitrate solutions through a capillary cell. In addition, we quantified Cr(VI) concentrations of the eluate solution every 15 min using spectrophotometry.Consistent with previous studies, we observed an increased rate of Cr(VI) production with decreasing pH. We attribute the comparatively slow kinetics of Cr(III) oxidation at pH 5.0 and 4.0 to a transformation from triclinic to hexagonal birnessite. This solid-state transition reproducibly coincided with a ∼10-fold decline in the extent of oxidation of aqueous Cr(III). Control experiments without Cr(III) revealed no evidence for birnessite transformation within the same time frame, and experiments with hexagonal birnessite as the starting material generated solutions with low fractions (∼3 mol%) of dissolved Cr(VI) from start to finish. At pH 3.0 and 2.0, however, production of Cr(VI) was consistently higher than was observed at pH 5.0 and 4.0. Specifically, at pH 2.0, 80 mol% of the influent Cr(III) was oxidized to Cr(VI) during the experiment compared to 20 mol% at pH 5.0. XANES analyses showed evidence for both Cr(III) and Cr(VI) adsorbing onto the surface of birnessite at all pH values.We propose that Cr(III) is oxidized to Cr(VI) by an electron exchange that reduces Mn(III) in birnessite to Mn(II). At pH 3.5 and higher, the structure of birnessite consequently transforms to hexagonal birnessite. By this pathway, the birnessite crystal structure critically controls the oxidation of dissolved Cr(III) due to the accessibility of reactive Mn(III) in triclinic birnessite relative to hexagonal birnessite. Below pH 3.5, however, birnessite dissolution systematically exposes reactive sites that enable the continuous oxidation of Cr(III) to Cr(VI).

The oxidation state and coordination environment of antimony in silicate glasses

Antimony K-edge X-ray absorption near edge structure (XANES) spectra were recorded for Sb in glasses of five synthetic CaO-MgO-Al2O3-SiO2 (CMAS) compositions and a simplified mid-ocean ridge basalt (MORB). The glasses were quenched from melts equilibrated at 1300 °C, atmospheric pressure, and oxygen fugacities (fO2) from logfO2 = –9 to 0 (ΔQFM from −1.7 to 7.3, where ΔQFM is the fO2 in log units relative to the quartz-fayalite-magnetite buffer), and 1400 °C, 1.0 GPa and logfO2 = +4.7 (ΔQFM+11.0). Comparison with model compounds (Sb, Sb2O3, β-Sb2O4, MnSb2O4 and Zn7Sb2O12) indicates that the oxidation state of Sb changes from Sb3+ to Sb5+ over the range of fO2 investigated. Using the spectra of the most reduced and oxidised glasses as end-members the oxidation state of Sb, Sb5+/ΣSb (where ΣSb = Sb3+ + Sb5+), was determined from the spectra of other samples by linear combination fitting. At terrestrial fO2s nearly all Sb occurs as Sb3+ in these silicate melts. The stability of Sb5+ was found to be positively correlated with the CaO content and optical basicity of the melts. Extended X-ray absorption fine structure (EXAFS) spectra were recorded for glasses prepared at pressures from 1.0 to 3.0 GPa, for which Sb5+/ΣSb = 0 and 1, and for a synthetic Sb-bearing sample of anorthite. The Sb3+O and Sb5+O bond lengths in the glasses are similar (1.938(4) and 1.964(5) Å, respectively) and suggest trigonal pyramidal coordination of Sb3+and octahedral Sb5+. The Sb3+O bond length did not change with pressure. Anorthite (CaAl2Si2O8) was found to readily incorporate Sb as Sb5+ on a tetrahedral site.

The role of cysteine and sulfide in the interplay between microbial Hg(ii) uptake and sulfur metabolism.

Biogenic thiols, such as cysteine, have been used to control the speciation of Hg(ii) in bacterial exposure experiments. However, the extracellular biodegradation of excess cysteine leads to the formation of Hg(ii)-sulfide species, convoluting the interpretation of Hg(ii) uptake results. Herein, we test the hypothesis that Hg(ii)-sulfide species formation is a critical step during bacterial Hg(ii) uptake in the presence of excess cysteine. An Escherichia coli (E. coli) wild-type and mutant strain lacking the decR gene that regulates cysteine degradation to sulfide were exposed to 50 and 500 nM Hg with 0 to 2 mM cysteine. The decR mutant released ∼4 times less sulfide from cysteine degradation compared to the wild-type for all tested cysteine concentrations during a 3 hour exposure period. We show with thermodynamic calculations that the predicted concentration of Hg(ii)-cysteine species remaining in the exposure medium (as opposed to forming HgS(s)) is a good proxy for the measured concentration of dissolved Hg(ii) (i.e., not cell-bound). Likewise, the measured cell-bound Hg(ii) correlates with thermodynamic calculations for HgS(s) formation in the presence of cysteine. High resolution X-ray absorption near edge structure (HR-XANES) spectra confirm the existence of cell-associated HgS(s) at 500 nM total Hg and suggest the formation of Hg-S clusters at 50 nM total Hg. Our results indicate that a speciation change to Hg(ii)-sulfide controls Hg(ii) cell-association in the presence of excess cysteine.

Electrical transport in PEO-NaI-NASICON nanocomposites: An assessment using impedance and X-Ray absorption spectroscopy

Present investigation focuses on conductivity-structure correlation in NaTi2(PO4)3 (NTP) embedded novel hybrid solid polymer composites prepared in a wide range of composition 10NaI-90(PEO1-xNTPx) (wt%), for 0 ≤ x ≤ 0.7. A maximum ionic conductivity of ˜ 4 × 10-5 Ω-1 cm-1 has been achieved with x = 0.7 at 40 °C that is higher than that of the host PEO-NaI (⁓ 5 × 10-7 Ω-1 cm-1) system by at least two orders of magnitude. Elemental mapping during field emission scanning electron microscopy suggests homogeneous distribution of NTP in the compositions. Trends of K-edge energies of oxygen in the X-Ray absorption near edge structure spectra have been found to be useful in proposing a tentative mechanism for ionic transport. Structural and impedance spectroscopy investigations suggest that for low NTP content, salt ions prefer to move through polymer. However, for higher content, surface states of NASICON at polymer-NTP interface facilitate the ionic conduction.

Local Disorder in Ln2Ti2O7 (Ln = Gd, Tb, Dy) Pyrochlores

The temperature dependences of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectra of Ln2Ti2O7 (Ln = Gd, Tb, Dy) geometrically frustrated magnets with a pyrochlore structure are presented. The temperature dependences of the Ln-O and Ti-O interatomic bond lengths and Debye-Waller factors σ2 characterizing the local static and dynamic disordering of bonds have been obtained in the temperature range of 10–300 K. The stiffnesses of metal-oxygen bonds and the parameters of local disordering of the structure have been determined from the dependences σ2(T). The effect of the magnetic state of rare-earth ions on local features of the Ln2Ti2O7 structure has been described. The characteristics of local disorder in pyrochlores under study have been compared to dysprosium zirconate Dy2Zr2O7 having a disordered fluorite structure.

(Arylimido)niobium(V) Complexes Containing 2-Pyridylmethylanilido Ligand as Catalyst Precursors for Ethylene Dimerization That Proceeds via Cationic Nb(V) Species

(Arylimido)niobium(V) complexes containing 2-pyridylmethylanilido ligand Nb(NAr)X2(L) [L = 2-(2,6-Me2C6H3)NCH2(C5H4N); X = NMe2 (2a,b), OCH(CF3)2 (3a–c), Me (4a–c), CH2SiMe3 (5a); Ar = 2,6-Me2C6H3 (a), 2,6-iPr2C6H3 (b), 2-MeC6H4 (c)] have been prepared, and structures of 3a,b, 4b, and 5a were determined by X-ray crystallography. The dimethyl complexes (4a,b) exhibited catalytic activities for ethylene dimerization in the presence of methylaluminoxane (MAO), whereas the activity by 4c was negligible under the same conditions. Complex 4b showed the highest activity, and the activity at 50 °C was higher than those conducted at 25 and 80 °C. The major product was 1-butene, and 1-hexene was formed by subsequent reaction of ethylene with 1-butene accumulated in the reaction mixture. A first-order relationship between the activity [turnover frequency (TOF)] and ethylene pressure was observed, suggesting that the metal-alkyl species would play a role in this catalysis. The activities further increased remarkably upon addition of [Ph3C][B(C6F5)4] at 50 °C; TOF at the initial stage (5 min) of 2 100 000 h–1 (583 s–1) has been attained. Reactions of the dimethyl complexes (4a,b) with 1.0 equiv of [Ph3C][B(C6F5)4] in Et2O afforded [Nb(NAr)Me(L)]+[B(C6F5)4]−(Et2O)2 (6a,b), and the reaction of 6b with ethylene afforded 1-butene and 1-hexene even in the absence of MAO, clearly suggesting that the cationic species play a role in this catalysis. X-ray absorption near edge structure spectra of the catalyst solutions containing 4b (in toluene at 25 °C) and MAO (10 and 50 equiv) showed no significant differences in the pre-edge peak positions and intensities from that in the dimethyl complex (4b), strongly suggesting that both the oxidation states and the basic structures are maintained upon addition of MAO in these catalyst solutions.

Pressure-induced structural changes in α-MoO3 probed by X-ray absorption spectroscopy

Energy-dispersive X-ray absorption spectroscopy at the Mo K-edge was used to study pressure-induced (up to 36 GPa) changes in the local atomic structure of 2D layered oxide α-MoO3. A linear combination analysis based on the low and high-pressure X-ray absorption near edge structure (XANES) spectra shows clear evidence of two high-pressure phases, existing at 18-25 GPa and above 32 GPa. The first transition is due to gradual decrease of the interlayer gap, whereas the second one – to its collapse and oxide structure reconstruction. The local atomic structure around molybdenum atoms at 0.2, 18.5 and 35.6 GPa was determined from the extended X-ray absorption fine structure (EXAFS) using reverse Monte Carlo calculations.

Hierarchical Fe3O4-reduced graphene oxide nanocomposite grown on NaCl crystals for triiodide reduction in dye-sensitized solar cells

Cost-effective reduced graphene oxide sheets decorated with magnetite (Fe3O4) nanoparticles (Fe3O4-rGO) are successfully fabricated via a chemical vapor deposition (CVD) technique using iron (III) nitrate as an iron precursor, with glucose and CH4 as carbon sources, and NaCl as a supporting material. TEM analysis and Raman spectroscopy reveal hierarchical nanostructures of reduced graphene oxide (rGO) decorated with Fe3O4 nanoparticles. Fe K-edge x-ray absorption near edge structure (XANES) spectra confirm that the nanoparticles are Fe3O4 with a slight shift of the pre-edge peak position toward higher energy suggesting that the fabricated Fe3O4 nanoparticles have a higher average oxidation state than that of a standard Fe3O4 compound. The hierarchical Fe3O4-rGO is found to exhibit an excellent catalytic activity toward the reduction of triiodide to iodide in a dye-sensitized solar cell (DSSC) and can deliver a solar cell efficiency of 6.65%, which is superior to a Pt-based DSSC (6.37%).

XANES analysis for cation-vacancy distribution induced by doping Al ions in transition-metal-oxide anodes of lithium battery

We measured an Al K-edge x-ray absorption near edge structure (XANES) spectrum of Al doped NiO for anode materials of lithium ion batteries. We found that the spectrum of the Al doped NiO is similar to that of γ-Al2O3. Calculated site-specific XANES spectra strongly correspond to the coordination nature around the absorbing Al ion, indicating aggregation of cation vacancies surrounded by Al ions in the Al doped NiO. These finding could be useful to understand how Li ions migrate in the anode.