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The lanthanide (Ln) elements are critical materials that are typically extracted/mined together. Their separation by use of solvent extraction from acidic media is well known; however, there are few studies in basic media with carbonate anions. We investigated the complexation of Eu(III) and Tb(III) carbonates as solids and solutions in alkaline K2CO3, wherein we sought to access a Tb(IV) carbonate complex through ozonolysis. L3‐edge XANES of Eu and Tb carbonate solids, colorless solutions, and a red‐hued Tb solution (obtained by ozonolysis) all showed Ln(III) cations. The absence of evidence for a Tb(IV) complex was confirmed through XAS and EPR analyses, despite the solution exhibiting a deep red color. For solids and solutions, EXAFS results indicate molecular Ln(III)‐carbonato anions. In terms of the Eu(III) carbonate coordination number, the coordination does not change upon dissolution of the solid sample. Furthermore, EXAFS for the solutions revealed evidence for the association of potassium cations with the Ln(III)‐carbonato anions. This direct observation of contact ion pairing by EXAFS at room temperature is rare. The insights into Ln(III) carbonate complexation and solution speciation afforded by XANES‐EXAFS, FT‐IR, and EPR provides perspectives that serve as benchmarks for future computational and experimental efforts focused on caustic‐side solvent extraction of Ln(III) ions. [ABSTRACT FROM AUTHOR]

The viscosities of Ce‐free and Ce‐bearing (∼1.3 mol%, ∼6.5 wt.% Ce2O3) soda lime silicate (window glass) melts were measured with respect to oxidation state. Experiments were performed isothermally using a concentric‐cylinder viscometer on melts equilibrated with successively reducing CO–CO2 gas mixtures within a gas tight vertical tube furnace at 1 atm. Viscosity measurement and sampling were performed at the end of each melt reduction step. Further, viscosities in the glass transition temperature range were estimated using the shift factor method applied to glass transition temperature values determined using differential scanning calorimetry (DSC) measurements on quenched glasses. The Ce speciation at each stepwise melt reduction was probed using Ce L3‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy, while structural information upon Ce addition and reduction was provided by Raman spectroscopy. The viscosities of these materials remain constant at this level of Ce addition and do not vary significantly with redox state at high temperature. Conversely, viscosity values in the glass transition temperature range increase upon both Ce addition and reduction. Our analysis, based on the glass composition analyses obtained via electron probe microanalyzer (EPMA), viscosity calculations, and observations of silicate structural changes, leads to the conclusion that the observed viscosity increase around the glass transition temperature is explained by the high ionic field strength of Ce ions as well as the polymerization behavior of the silicate matrix occurring during reduction of Ce. Because of its low concentration, resulting from its low solubility, Ce redox changes exert only minimal effects on the viscosity of this melt. [ABSTRACT FROM AUTHOR]

The interaction of NiO clusters with a graphene layer of a nanotube in NiOx/CNT composites is simulated based on a theoretical analysis of Ni K-edge XANES spectra. Various cases of orientation of crystallographic planes relative to the nanotube wall are considered. It was determined that Ni in the composite is predominantly in the 2+ state, NiO particles are oriented towards the tube wall by the (200) plane. Accounting for carbon atoms even in the first sphere of the nickel environment makes it possible to achieve good agreement between the theoretical spectrum and experiment. [ABSTRACT FROM AUTHOR]

Plants rely on potassium for many critical biological processes, but most soils are potassium limited. Moving potassium from the inaccessible, mineral-bound pool to a more bioavailable form is crucial for sustainably increasing local potassium concentrations for plant growth and health. Here, we use a synthetic soil habitat (mineral doped micromodels) to study and directly visualize how the saprotrophic fungus, Fusarium sp. DS 682, weathers K-rich soil minerals. After 30 days of fungal growth, both montmorillonite and illite (secondary clays) had formed as surface coatings on primary K-feldspar, biotite, and kaolinite grains. The distribution of montmorillonite differed depending on the proximity to a carbon source, where montmorillonite was found to be associated with K-feldspar closer to the carbon (C) source, which the fungus was inoculated on, but associated with biotite at greater distances from the C source. The distribution of secondary clays is likely due to a change in the type of fungal exuded organic acids; from citric to tartaric acid dominated production with increasing distance from the C source. Thus, the main control on the ability of Fusarium sp. DS 682 to weather K-feldspar is proximity to a C source to produce citric acid via the TCA cycle. [ABSTRACT FROM AUTHOR]

Herein, we describe the synthesis, crystal structure, and electronic properties of {[K2(dmso)(H2O)5][Ni2(H2mpba)3]·dmso·2H2O}n (1) and [Ni(H2O)6][Ni2(H2mpba)3]·3CH3OH·4H2O (2) [dmso = dimethyl sulfoxide; CH3OH = methanol; and H4mpba = 1,3-phenylenebis(oxamic acid)] bearing the [Ni2(H2mpba)3]2− helicate, hereafter referred to as {NiII2}. SHAPE software calculations indicate that the coordination geometry of all the NiII atoms in 1 and 2 is a distorted octahedron (Oh) whereas the coordination environments for K1 and K2 atoms in 1 are Snub disphenoid J84 (D2d) and distorted octahedron (Oh), respectively. The {NiII2} helicate in 1 is connected by K+ counter cations yielding a 2D coordination network with sql topology. In contrast to 1, the electroneutrality of the triple-stranded [Ni2(H2mpba)3] 2− dinuclear motif in 2 is achieved by a [Ni(H2O)6]2+ complex cation, where the three neighboring {NiII2} units interact in a supramolecular fashion through four R22(10) homosynthons yielding a 2D array. Voltammetric measurements reveal that both compounds are redox active (with the NiII/NiI pair being mediated by OH– ions) but with differences in formal potentials that reflect changes in the energy levels of molecular orbitals. The NiII ions from the helicate and the counter-ion (complex cation) in 2 can be reversibly reduced, resulting in the highest faradaic current intensities. The redox reactions in 1 also occur in an alkaline medium but at higher formal potentials. The connection of the helicate with the K+ counter cation has an impact on the energy levels of the molecular orbitals; this experimental behavior was further supported by X-ray absorption near-edge spectroscopy (XANES) experiments and computational calculations. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an indispensable nutrient for arable crops, but at the same time, contributes to excessive eutrophication in aquatic ecosystems. Knowledge about P is essential to assess the possible risks of P being transported towards vulnerable aquatic ecosystems. Our objective was to characterize P along a catena from arable and wetland soils towards aquatic sediments of a shallow lagoon of the Baltic Sea. The characterization of P in soil and sediment samples included a modified sequential P fractionation and P K-edge X-ray absorption near edge structure (XANES) spectroscopy. The concentrations of total P ranged between 390 and 430 mg kg−1 in the arable soils, between 728 and 2258 mg kg−1 in wetland soils and between 132 and 602 mg kg−1 in lagoon sediments. Generally, two sinks for P were revealed along the catena. The wetland soil trapped moderately stable P, Al-P and molybdate-unreactive P (MUP), which are most likely organically bound phosphates. Sediments at the deepest position of the catena acted as a sink for, MUP compounds among the lagoon sediments. Thus, wetlands formed by reed belts can help to prevent the direct transfer of P from arable soils to adjacent waters and deeper basins and help to avoid excessive eutrophication in shallow aquatic ecosystems. [ABSTRACT FROM AUTHOR]

We present an extensive study of the luminescence characteristics of Mn impurity ions in a YAl3(BO3)4:Mn crystal, in combination with X-ray fluorescence analysis and determination of the valence state of Mn by XANES (X-ray absorption near-edge structure) spectroscopy. The valences of manganese Mn2+(d5) and Mn3+(d4) were determined by the XANES and high-resolution optical spectroscopy methods shown to be complementary. We observe the R1 and R2 luminescence and absorption lines characteristic of the 2E ↔ 4A2 transitions in d3 ions (such as Mn4+ and Cr3+) and show that they arise due to uncontrolled admixture of Cr3+ ions. A broad luminescent band in the green part of the spectrum is attributed to transitions in Mn2+. Narrow zero-phonon infrared luminescence lines near 1060 nm (9400 cm−1) and 760 nm (13,160 cm−1) are associated with spin-forbidden transitions in Mn3+: 1T2 → 3T1 (between excited triplets) and 1T2 → 5E (to the ground state). Spin-allowed 5T2 → 5E Mn3+ transitions show up as a broad band in the orange region of the spectrum. Using the data of optical spectroscopy and Tanabe–Sugano diagrams we estimated the crystal-field parameter Dq and Racah parameter B for Mn3+ in YAB:Mn as Dq = 1785 cm−1 and B = 800 cm−1. Our work can serve as a basis for further study of YAB:Mn for the purposes of luminescent thermometry, as well as other applications. [ABSTRACT FROM AUTHOR]

Two sodium vanadium phosphates, synthetic analogues of the minerals kosnarite, Na3V2(PO4)3, and yurmarinite, Na7V4(PO4)6, were obtained by hydrothermal synthesis simulating a natural hydrothermal solution. While the Na3V2(PO4)3 phase belongs to the NASICON family and is well-known for its high-ionic conductivity, the new Na7V4(PO4)6 compound is a rare case of V2+-containing oxosalts, which are hard to prepare due to their instability in air. Here we report the crystal structure of heterovalent vanadium phosphate studied by single crystal X-ray diffraction, XANES spectroscopy, and topological ion migration modelling. A discussion of divalent vanadium compounds of both natural and synthetic origin is also given, with a review of the methods for their synthesis and a comparative analysis of V–O bond lengths. [ABSTRACT FROM AUTHOR]

Constraints on marine phosphate availability and cycling directly inform our understanding of long‐term biological evolution. However, early Earth phosphate records are sparse, biased toward siliciclastic samples, and susceptible to post‐depositional modification. Well‐preserved shallow marine inorganic carbonate precipitates provide a complementary yet understudied record of phosphate cycling. We combined micro‐X‐ray fluorescence mapping, X‐ray absorption, and Nuclear Magnetic Resonance spectroscopy on samples of Precambrian syndepositional herringbone calcite (HBC) and microspar to characterize phosphorus speciation and distribution in these carbonate fabrics. Phosphorus spectroscopy from synthetic calcite, HBC, and microspar, is qualitatively consistent with a disordered distribution of phosphate. These characteristics are diagnostic of calcite‐hosted phosphate, which is pervasive at low concentrations in HBC and microspar. This study provides evidence that ancient, well‐preserved carbonate fabrics retain phosphate sourced from seawater and highlights the potential for an unaltered archive of marine phosphate concentration over geologic time. Plain Language Summary: Phosphorus is a critical nutrient to sustain life on Earth as we know it. Understanding the form and source of phosphorus on the early Earth will enhance our knowledge of the origins and early evolution of life. However, there is no way to directly measure the source, form and abundance of phosphorus in the environment when life was evolving over 2.5 billion years ago. The rock record provides a potential archive to indirectly measure phosphorus from ancient marine environments, yet there are a number of considerations, for example; (a) which minerals are able to record information about marine phosphorus? (b) How do we know those minerals have not been altered over time? In this work, we have identified well‐preserved, unaltered carbonate minerals from ∼2.5 billion and 800 million years ago, that preserve marine phosphate within their mineral structure using micron‐scale techniques. The characterization of this form of phosphorus is important to our understanding of the evolution of the phosphorus cycle over Earth's history. Key Points: Synchrotron analyses identify calcite‐hosted phosphate in well‐preserved Precambrian carbonate fabricsHerringbone calcite and synsedimentary microspar serve as an unaltered archive for ancient marine dissolved inorganic phosphateMicrite retains abundant apatite mineral micro‐inclusions that may bias bulk calcite‐hosted phosphate or P/Ca records [ABSTRACT FROM AUTHOR]

Platelets and their subcellular components (e.g., dense granules) are essential components in hemostasis. Understanding their chemical heterogeneities at the sub-micrometer scale, particularly their activation during hemostasis and production of platelet-derived extracellular vesicles, may provide important insights into their mechanisms; however, this has rarely been investigated, mainly owing to the lack of appropriate chemical characterization tools at nanometer scale. Here, the use of scanning transmission X-ray microscopy (STXM) combined with X-ray absorption near edge structure (XANES) to characterize human platelets and their subcellular components at the carbon K-edge and calcium L2,3-edge, is reported. STXM images can identify not only the spatial distribution of subcellular components in human platelets, such as dense granules (DGs) with sizes of ~200 nm, but also their granule-to-granule chemical heterogeneities on the sub-micrometer scale, based on their XANES spectra. The calcium distribution map as well as the principal component analysis of the STXM image stacks clearly identified the numbers and locations of the calcium-rich DGs within human platelets. Deconvolution of the carbon K-edge XANES spectra, extracted from various locations in the platelets, showed that amide carbonyl and carboxylic acid functional groups were mainly found in the cytoplasm, while ketone-phenol-nitrile-imine, aliphatic, and carbonate functional groups were dominant in the platelet DGs. These observations suggest that platelet DGs are most likely composed of calcium polyphosphate associated with adenosine triphosphate (ATP) and adenosine diphosphate (ADP), with significant granule-to-granule variations in their compositions, while the cytoplasm regions of platelets contain significant amounts of proteins. [ABSTRACT FROM AUTHOR]

Modeling metal sorption in soils is of great importance to predict the fate of heavy metals and to assess the actual risk driven from pollution. The present study focuses on adsorption of HM ions on two types of hydromorphic soils, including calcaric fluvisols loamic and calcaric fluvic arenosols. The individual and competitive adsorption behaviors of Cu and Zn on soils and soil constituents are evaluated comprehensively. It is established that the sorption processes were best described with the Langmuir model. The results suggest that the calcaric fluvic arenosols are more vulnerable to heavy metal input compared to fluvisols loamic. In all cases, Cu had a higher range of values of the adsorption process parameters relative to Zn. The Zn is likely to be the most critical environmental factor in such soils since it exhibited a decreased sorption under competitive conditions. The retention mechanisms of HM in hydromorphic soils are considered. Based on theoretical calculations of ion activity in soil solutions using solubility diagrams of Cu and Zn compounds, the possibility of precipitation of Cu hydroxide and Zn carbonate in the studied soils is shown. Direct physical methods of nondestructive testing (XAFS and XRD) are applied to experimentally prove the formation of these HM compounds on the surface of montmorillonite, the dominant mineral in hydromorphic soils, and calcite. Thus, the combination of both physicochemical methods and direct physical methods can provide a large amount of real information about the mechanisms of HM retain with solid phases. [ABSTRACT FROM AUTHOR]

Limonitic layers of the regolith, which are often stockpiled as waste materials at laterite mines, commonly contain significant concentrations of valuable base metals, such as nickel, cobalt, and manganese. There is currently considerable demand for these transition metals, and this is projected to continue to increase (alongside their commodity values) during the next few decades, due in the most part to their use in battery and renewable technologies. Limonite bioprocessing is an emerging technology that often uses acidophilic prokaryotes to catalyse the oxidation of zero-valent sulphur coupled to the reduction of Fe (III) and Mn (IV) minerals, resulting in the release of target metals. Chromium-bearing minerals, such as chromite, where the metal is present as Cr (III), are widespread in laterite deposits. However, there are also reports that the more oxidised and more biotoxic form of this metal [Cr (VI)] may be present in some limonites, formed by the oxidation of Cr (III) by manganese (IV) oxides. Bioleaching experiments carried out in laboratory-scale reactors using limonites from a laterite mine in New Caledonia found that solid densities of ∼10% w/v resulted in complete inhibition of iron reduction by acidophiles, which is a critical reaction in the reductive dissolution process. Further investigations found this to be due to the release of Cr (VI) in the acidic liquors. X-ray absorption near edge structure (XANES) spectroscopy analysis of the limonites used found that between 3.1 and 8.0% of the total chromium in the three limonite samples used in experiments was present in the raw materials as Cr (VI). Microbial inhibition due to Cr (VI) could be eliminated either by adding limonite incrementally or by the addition of ferrous iron, which reduces Cr (VI) to less toxic Cr (III), resulting in rates of extraction of cobalt (the main target metal in the experiments) of >90%. [ABSTRACT FROM AUTHOR]

Zinc K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy of Zn adsorbed to silica and Zn‐bearing minerals, salts and solutions was conducted to explore how XANES spectra reflect coordination environment and disorder in the surface to which a metal ion is sorbed. Specifically, XANES spectra for five distinct Zn adsorption complexes (Znads) on quartz and amorphous silica [SiO2(am)] are presented from the Zn–water–silica surface system: outer‐sphere octahedral Znads on quartz, inner‐sphere octahedral Znads on quartz, inner‐sphere tetrahedral Znads on quartz, inner‐sphere octahedral Znads on SiO2(am) and inner‐sphere tetrahedral Znads on SiO2(am). XANES spectral analysis of these complexes on quartz versus SiO2(am) reveals that normalized peak absorbance and K‐edge energy position generally decrease with increasing surface disorder and decreasing Zn–O coordination. On quartz, the absorption‐edge energy of Znads ranges from 9663.0 to 9664.1 eV for samples dominated by tetrahedrally versus octahedrally coordinated species, respectively. On SiO2(am), the absorption‐edge energy of Znads ranges from 9662.3 to 9663.4 eV for samples dominated by tetrahedrally versus octahedrally coordinated species, respectively. On both silica substrates, octahedral Znads presents a single K‐edge peak feature, whereas tetrahedral Znads presents two absorbance features. The energy space between the two absorbance peak features of the XANES K‐edge of tetrahedral Znads is 2.4 eV for Zn on quartz and 3.2 eV for Zn on SiO2(am). Linear combination fitting of samples with a mixture of Znads complex types demonstrates that the XANES spectra of octahedral and tetrahedral Znads on silica are distinct enough for quantitative identification. These results suggest caution when deciphering Zn speciation in natural samples via linear combination approaches using a single Znads standard to represent sorption on a particular mineral surface. Correlation between XANES spectral features and prior extended X‐ray absorption fine structure (EXAFS) derived coordination environments for these Znads on silica samples provides insight into Zn speciation in natural systems with XANES compatible Zn concentrations too low for EXAFS analysis. [ABSTRACT FROM AUTHOR]

Background: The phosphorus (P) stocks of arable subsoils not only influence crop production but also fertilizer P sequestration. However, the extent of this influence is largely unknown. This study aimed to (i) determine the extent of P sequestration with soil depth, (ii) analyze P speciation after long-term P fertilization, and (iii) compare soil P tests in predicting crop yields. We analyzed four long-term fertilizer trials in Germany to a depth of 90 cm. Treatments received either mineral or organic P, or a combination of both, for 16 to 113 years. We determined inorganic and organic P pools using sequential extraction, and P speciation using 31P nuclear magnetic resonance (NMR) and X-ray absorption near edge structure (XANES) spectroscopy. In addition, we applied three P soil tests, double-lactate (DL), calcium acetate lactate (CAL), and diffusive gradients in thin films (DGT). Results: The results suggested that plants are capable of mobilizing P from deeper soil layers when there is a negative P budget of the topsoil. However, fertilization mostly only showed insignificant effects on P pools, which were most pronounced in the topsoil, with a 1.6- to 4.4-fold increase in labile inorganic P (Pi; resin-P, NaHCO3–Pi) after mineral fertilization and a 0- to 1.9-fold increase of organic P (Po; NaHCO3–Po, NaOH–Po) after organic P fertilization. The differences in Po and Pi speciation were mainly controlled by site-specific factors, e.g., soil properties or soil management practice rather than by fertilization. When modeling crop yield response using the Mitscherlich equation, we obtained the highest R2 (R2 = 0.61, P < 0.001) among the soil P tests when using topsoil PDGT. However, the fit became less pronounced when incorporating the subsoil. Conclusion: We conclude that if the soil has a good P supply, the majority of P taken up by plants originates from the topsoil and that the DGT method is a mechanistic surrogate of P plant uptake. Thus, DGT is a basis for optimization of P fertilizer recommendation to add as much P fertilizer as required to sustain crop yields but as low as necessary to prevent harmful P leaching of excess fertilizer P. [ABSTRACT FROM AUTHOR]

The oxidation state of Cr, Cr2+/ΣCr (where ΣCr = Cr2+ + Cr3+ = 0.35 wt%), in Fe-free silicate glasses quenched from melts equilibrated as a function of pressure to 3.5 GPa at 1500 °C, and as a function of temperature to 1500 °C at atmospheric pressure, and at oxygen fugacities (fO2, in log units relative to the quartz-fayalite-magnetite (QFM) buffer) between ∆QFM = − 1 and − 2, was determined by XANES spectroscopy. Increasing temperature stabilises Cr2+ and increasing pressure stabilises Cr3+. A general expression for Cr3+/Cr2+ in silicate melts was derived: log(Cr3+/Cr2+) = 1/4(∆QFM + 8.58 − 25,050/T + 940P/T − 0.02P) + 9770/T − 7.69 + 6.22Λ + (900P − 172P2)/T, where P is pressure in GPa, T is temperature in K, and Λ is the optical basicity of the composition. This equation reproduces 213 Cr2+/ΣCr values reported here and in the literature with an average ΔCr2+/ΣCr of 0.02. A MORB melt at 1400 °C and QFM is predicted to have Cr2+/ΣCr ~ 0.35 at the surface but Cr2+/ΣCr ~ 0 at a depth of ~ 60 km. Although Cr2+ is an important oxidation state in silicate melts it is not preserved at low temperatures due to an electron exchange reaction with Fe3+. [ABSTRACT FROM AUTHOR]

Calcium (Ca) plays a crucial role for plant nutrition, soil aggregation, and soil organic matter (SOM) stabilization. Turnover and ecological functions of Ca in soils depend on soil Ca speciation. For the first time, we used synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy at the Ca K-edge (4038 eV) to investigate Ca speciation in soils. We present Ca K-edge XANES spectra of standard compounds with relevance in soils (e.g. calcite, dolomite, hydroxyapatite, anorthite, clay mineral-adsorbed Ca; Ca oxalate, formate, acetate, citrate, pectate, phytate). Calcium XANES spectra with good signal-to-noise ratios were acquired in fluorescence mode for Ca concentrations between 1 and 10 mg g−1. Most standard spectra differed markedly among each other, allowing the identification of different Ca species in soils and other environmental samples as well as Ca speciation by linear combination fitting. Calcium XANES spectra obtained for samples from different horizons of twelve temperate forest soils revealed a change from dominating lithogenic Ca to clay mineral-bound and/or organically bound Ca with advancing pedogenesis. O layer Ca was almost exclusively organically bound. With increasing SOM decomposition, shares of oxalate-bound Ca decreased. Oxalate-bound Ca was absent in calcareous, but not in silicate subsoil horizons, which can be explained by microbial decomposition in the former vs. stabilization by association to pedogenic minerals in the latter soils. Synchrotron-based Ca XANES spectroscopy is a promising novel tool to investigate the fate of Ca during pedogenesis and—when performed with high spatial resolution (µ-XANES), to study aggregation and SOM stabilization mechanisms produced by Ca. [ABSTRACT FROM AUTHOR]

The synthesis of carbon nanotubes (CNTs) is usually done by metallic catalysts with a gaseous carbon precursor at high temperature. Yet, mild synthesis conditions can broaden the application of CNTs and their composites. In the present work, it is unraveled why partially substituted Fe ions in 2D MnO2 nanosheets lead to the growth of CNTs at low temperatures of 400−500 °C. The local formation of Fe3C by carbon precursor explains the unusually high catalytic activity of 2D FexMn1−xO2 nanosheets for preparing CNTs. Finally, Fe3C is oxidized to Fe3C/FeOx yolk/shell morphology in ambient atmosphere after the CNT formation reaction. These results shed light on the development of novel catalyst materials that allow for efficiently prepare CNTs under mild conditions for their wider use in energy‐harvesting applications. [ABSTRACT FROM AUTHOR]

Iron oxidation state and environment in magmas affect their phase diagram and their properties, including viscosity and density, which determine magma mobility and eruptive potential. In turn, magma composition, pressure, temperature and oxygen fugacity affect iron oxidation state and coordination, potentially leading to complex feedbacks associated with magma ascent, degassing and eruption. While equilibrium experiments and models have led to a deep understanding of the role of iron in melts, our knowledge of the effects of disequilibrium processes on iron oxidation state and its structural role in lavas and magmas remains limited. Accordingly, we performed a series of dynamic disequilibrium experiments on a natural melt composition (a phonolite lava from Erebus volcano, Antarctica) at atmospheric pressure, in which oxygen fugacity and temperature were controlled and varied. During the experiments, we continuously measured iron oxidation and coordination using Fe K-edge dispersive X-ray Absorption Spectroscopy (XAS). We found that iron oxidation state changes in the phonolite melt are reversible and well reproduced by existing models. Changes in iron oxidation state are driven by joint diffusion of alkali cations and oxygen anions at magmatic temperatures (~ 1000 °C for Erebus phonolite). However, redox diffusion timescales are too slow for any significant oxygen exchange with the atmosphere at the lava/air interface or via air entrainment. Turning to iron coordination, while Fe2+ and Fe3+ are present mostly in an average five-fold coordination, complex coordination variations decoupled from redox changes were detected. The data suggest transitions between Fe3+ in four-fold and six-fold coordination prior to reduction or as a consequence of oxidation. This questions the possible implication of Fe coordination changes in triggering crystallisation of magnetite nanolites upon magma ascent, and, through such crystallisation events, in promoting magma explosivity. [ABSTRACT FROM AUTHOR]

X-ray absorption near-edge structure (XANES) spectroscopy is a powerful technique to quantitatively investigate sulfur speciation in geologically complex materials such as minerals, glasses, soils, organic compounds, industrial slags, and extraterrestrial materials. This technique allows nondestructive investigation of the coordination chemistry and oxidation state of sulfur species ranging from sulfide (2- oxidation state) to sulfate (6+ oxidation state). Each sulfur species has a unique spectral shape with a characteristic K-edge representing the s → p and d hybridization photoelectron transitions. As such, sulfur speciation is used to measure the oxidation state of samples by comparing the overall XANES spectra to that of reference compounds. Although many S XANES spectral standards exist for terrestrial applications under oxidized conditions, new sulfide standards are needed to investigate reduced (oxygen fugacity, fO2, below IW) silicate systems relevant for studies of extraterrestrial materials and systems. Sulfides found in certain meteorites (e.g., enstatite chondrites and aubrites) and predicted to exist on Mercury, such as CaS (oldhamite), MgS (niningerite), and FeCr2S4 (daubréelite), are stable at fO2 below IW-3 but rapidly oxidize to sulfate and/or produce sulfurous gases under terrestrial surface conditions. XANES spectra of these compounds collected to date have been of variable quality, possibly due to the unstable nature of certain sulfides under typical (e.g., oxidizing) laboratory conditions. A new set of compounds was prepared for this study and their XANES spectra are analyzed for comparison with potential extraterrestrial analogs. S K-edge XANES spectra were collected at Argonne National Lab for FeS (troilite), MnS (alabandite), CaS (oldhamite), MgS (niningerite), Ni1-xS, NiS2, CaSO4 (anhydrite), MgSO4, FeSO4, Fe2(SO4)3, FeCr2S4 (daubréelite), Na2S, Al2S3, Ni7S6, and Ni3S2; the latter five were analyzed for the first time using XANES. These standards expand upon the existing S XANES end-member libraries at a higher spectral resolution (0.25 eV steps) near the S K-edge. Processed spectra, those that have been normalized and "flattened," are compared to quantify uncertainties due to data processing methods. Future investigations that require well-characterized sulfide standards, such as the ones presented here, may have important implications for understanding sulfur speciation in reduced silicate glasses and minerals with applications for the early Earth, Moon, Mercury, and enstatite chondrites. [ABSTRACT FROM AUTHOR]

X-ray absorption spectroscopy (XAS) is a new highly effective nondestructive technique for diagnostics of the local atomic and electronic structure of materials, including those that do not have long-range order in their atomic arrangement. In particular, X-ray absorption near edge structure (XANES) spectroscopy makes it possible to identify materials, to assess the oxidation states of atoms, and to find the parameters of the full 3D local structure around absorbing atoms with a high degree of accuracy, up to 1 pm for bond lengths and several degrees for bond angles. This review describes the current state and capabilities of XAS spectroscopy and, in particular, XANES in studying terrestrial and extraterrestrial natural materials. Modern synchrotron centers allow the acquisition of XAS spectra of materials with high energy and time resolutions, with microfocusing and nanofocusing, and spectral measurements under real conditions (for example, directly under high pressures and temperatures). These broad possibilities make X-ray absorption spectroscopy a unique highly effective technique for the diagnostics of geological materials. [ABSTRACT FROM AUTHOR]

Synchrotron X-ray absorption near edge spectroscopy (XANES) and extended X-ray fine structure (EXAFS) are used to study the effect of temperature in the co-precipitation synthesis of iron oxides. Nanoparticles are rod-like and agglomerate into microscale aggregates. XANES spectra complement X-ray diffractometry in the phase identification of inverse spinel structured maghemite (γ-Fe2O3). In addition to the smallest crystallite size, EXAFS analysis revealed the highly distorted structure in the sample synthesized at 90°C. The samples synthesized at lower temperatures (25OC, 60OC) are ferrimagnetic with much larger magnetizations. The variation in magnetic properties with the synthetic temperature is related to the differences in crystallite size and distortion in the structure of γ-Fe2O3 nanoparticles. [ABSTRACT FROM AUTHOR]

Palaeontology relies on the description of fossil morphologies to understand the evolutionary history of life on Earth. Yet much remains unknown about the impact of fossilization processes, even though these may introduce biases into palaeobiological interpretations. Here, we report the characterization of fossilized remains of the earliest known woody plant Armoricaphyton chateaupannense preserved either in 2D (as flat carbonaceous films) or in 3D (as organo‐mineral structures) in early Devonian shales (c. 407 Ma) of the Armorican Massif on the northern margin of Gondwana. To document the fine‐scale structure and the chemistry of the tracheids of this ancient plant, we used propagation phase contrast synchrotron radiation X‐ray microcomputed tomography (PPC‐SRμCT), transmission electron microscopy (TEM) and synchrotron‐based scanning transmission X‐ray microscopy (STXM) coupled with X‐ray absorption near edge structure (XANES) spectroscopy. PPC‐SRμCT enables digital visualization of cell walls in unprecedented detail for the specimens preserved in 3D revealing structures similar to those observed in extant lignified cells, thereby strongly suggesting that the earliest woody plant A. chateaupannense originally contained lignin compounds. STXM‐based XANES and TEM data show that, whatever the preservation modes (3D vs 2D), the remaining organic matter has a chemical composition rather typical of pyrobitumen compounds, raising the possibility of an original source other than lignin. The pyrobitumen compounds also contains automorphic Ti‐nanominerals interpreted as a diagenetic feature. Altogether, the present study illustrates that anatomical and chemical preservations may not always be correlated. [ABSTRACT FROM AUTHOR]

Refined data on the crystal structure, chemical composition and properties of jouravskite, ideally Ca3Mn4+(SO4)(CO3)(OH)6·12H2O, have been obtained on a sample from N'Chwaning 3 Mine, Kuruman, Kalahari manganese field, Northern Cape Province, South Africa. The chemical composition determined using a combination of different methods (including ICP-OES, gas chromatography of products of ignition and electron microprobe) is (wt%): CaO 25.88, SrO 0.19, BaO 0.23, B2O3 0.39, Fe2O3 1.01, MnO2 12.00, SiO2 0.06, CO2 6.8, SO3 12.44, H2O 41.8, total 100.80, which corresponds to the empirical formula (Z = 2): (Са2.98Sr0.01Ba0.01)Σ3.00(Mn4+0.89Fe3+0.08Si0.01)Σ0.98{(SO4)1.00(CO3)1.00[B(OH)4]0.07}Σ2.07(OH)5.78·11.94H2O. Tetravalent state of Mn was confirmed by Mn K-edge XANES spectroscopy. The IR spectrum of jouravskite contains characteristic bands of Mn4+(OH)6 octahedra, CO32− and SO42− anions, and H2O molecules. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.0332. Jouravskite is isostructural with thaumasite. The parameters of the hexagonal (space group P63) unit cell are: a = 11.07129(14) Å, c = 10.62650(14) Å, V = 1128.02(3) Å3 and Z = 3. Investigation of other samples of ettringite-group minerals from N'Chwaning 3 Mine demonstrates wide variations of the contents of manganese, iron and boron, and possible existence of a Mn4+-dominant analogue of sturmanite with the presumed idealized formula Са6Mn4+2(SO4)2[B(OH)4](OH)10O2·nH2O. [ABSTRACT FROM AUTHOR]

A comprehensive study of the Jiddat Al Harasis 055 (L4-5 type) ordinary chondrite is conducted using 2D X-ray fluorescence spectroscopy, Mössbauer spectroscopy, X-ray absorption near edge structure (XANES) spectroscopy, X-ray diffraction, and vibrating sample magnetometry. The content of Fe, Ni, Si, Mg, S, Ca, Al, Mn, Ti, and Cr is determined; several components and areas with increased content of S, Ti, Cr, and Ni are detected along with several Ca-Al inclusions. According to XANES data, the Jiddat Al Harasis 055 sample contains iron with the average oxidation state 2.4+. This result is consistent with the data of Mössbauer spectroscopy used to identify iron phases which testifis that 46% and 54% of iron ions appear in Fe2+ and Fe3+ states, respectively. By comparing the pre-edge energy position and the area under the preedge peak of XANES spectra with literature data reported for geological materials, the average coordination number in the first coordination sphere of iron is found to be 5.3. According to the data of Xray diffraction and Mössbauer spectroscopy, the iron-containing meteorite phases consist mainly of olivine, pyroxene, hematite, and goethite. The observed magnetic properties of the sample can be attributed to small inclusions of ferromagnetic phases such as nickel nanoparticles, which cannot be reliably identified using laboratory spectral methods. [ABSTRACT FROM AUTHOR]

A review of current works on XANES spectroscopy applied for the determination of parameters of a threedimensional local atomic structure of nanostructured materials is given. Special attention is paid to a new method based on the theoretical analysis of XANES spectra by means of multivariate interpolation. The uniqueness of the technique consists not only in the highly accurate (up to 0.01 Å) determination of interatomic distances in materials without a long-range order in the atomic arrangement but also the estimation of the angular distribution of atoms (i.e. chemical bond angles) in any condensed materials. Several types of nanostructured materials, including coordination compounds, semiconductor quantum dots, nanosized structures in quasicrystals and extraterrestrial materials are given as examples. [ABSTRACT FROM AUTHOR]

A new mineral species zincovelesite-6N6S with the simplified formula Zn3(Fe3+,Mn3+,Al,Ti)8O15(OH) was discovered in the orogenetic zone related to the “Mixed Series” metamorphic complex near the Nežilovo village, Jacupica Mountains, Pelagonia mountain range, Republic of Macedonia. In oxide Zn-Fe-Mn ore, zincovelesite-6N6S forms lenticular aggregates up to 2 × 2 × 0.5 mm consisting of thin near-coplanar platelets up to 70 × 70 × 1 µm3 and associated with franklinite, gahnite, hetaerolite, zincochromite, ferricoronadite, baryte, As-rich fluorapatite, dolomite, Zn-bearing talc, almeidaite, hydroxycalcioroméite, zircon, quartz, and scheelite. In silicate-baryte zones of the metasomatic rock, uniaxial intergrowths of zincovelesite-6N6S with nežilovite are observed. The new mineral is opaque, black, with brownish-black streak. The lustre is strong submetallic to metallic. The micro-indentation hardness is 1118 kg/mm2 which corresponds to Mohs’ hardness ca. 6½. Zincovelesite-6N6S is brittle, with uneven fracture. No cleavage or parting is observed. The density calculated from the empirical formula is 5.158 g/cm3. In reflected light zincovelesite-6N6S is light grey. The reflectance values [Rmax/Rmin, % (λ, nm)] are: 17.1/13.4 (470), 16.5/12.8 (546), 16.2/12.6 (589), 15.6/12.2 (650). The IR spectrum shows the presence of OH groups. According to the Mössbauer spectrum, all iron is trivalent. The Mn K-edge XANES spectroscopy shows that Mn is predominantly or completely trivalent. The average chemical composition is (wt%; electron microprobe, H2O determined by gas chromatography of ignition products): MgO 0.97, CuO 0.50, ZnO 30.80, Al2O3 8.17, Mn2O3 21.31, Fe2O3 29.44, TiO2 5.28, Sb2O5 3.74, H2O 1.1, total 101.31. The empirical formula based on 16 O atoms is H1.05Zn3.26Mg0.21Cu0.05Fe3+3.18Mn3+2.32Al1.38Ti0.57Sb0.20O16. Zincovelesite-6N6S is trigonal, probable space group P-3m1, a = 5.902(2) Å, c = 55.86(1) Å, V = 1684.8(9) Å3, Z = 6. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 2.952 (62) (110), 2.881 (61) (1.0.16), 2.515 (100) (204), 2.493 (88) (1.1.12), 2.451 (39) (1.0.20), 1.690 (19) (304, 2.1.16), 1.572 (19) (2.0.28), 1.475 (29) (221). Zincovelesite-6N6S is the first Fe3+-dominant member of the högbomite supergroup and, thus, can be considered as a parent species of a new mineral group. The rootname velesite is given for the discovery locality near the city of Veles. [ABSTRACT FROM AUTHOR]

Mn2+-bearing eleonorite from the Hagendorf South pegmatite situated south of Waidhaus, Upper Palatinate, Bavaria, Germany was study based on single crystal X-ray analysis, Mn and Fe K-edge XANES spectroscopy, as well as IR spectroscopy. According to spectroscopic data, all Mn is bivalent, and all Fe is trivalent. The empirical formula of the mineral is (Mn2+0.58Zn0.13Mg0.04 Fe3+5.24)Σ5.98(PO4)4(H2O,OH,O)11. The monoclinic unit-cell parameters are: a=20.832(3) Å, b=5.1569(3) Å, c=19.200(2) Å, β=93.01(1)°; space group C2/c. The structure was refined to R1=5.20% in anisotropic approximation using 1994 reflections with I>3σ(I). Despite in most beraunite-group minerals M1-site demonstrates selective accumulation of bivalent cations, in Mn-bearing eleonorite Mn2+-cations are disordered between octahedral sites without statistical predominance anywhere; all octahedral M(1–4)-sites are predominantly occupied by Fe3+. M1-site is half-occupied by Fe3+ and contains subordinate Mn2+ and minor Zn2+ and Mg2+. Based on the new data we suppose that Mn-bearing eleonorite was formed as a secondary phase as a result of oxidation of a primary Mn-bearing beraunite-group mineral in with Mn2+ was initially distributed between different M sites. [ABSTRACT FROM AUTHOR]

The antimicrobial properties of copper ions have been known for a long time. However, the exact mechanism of action of the transition metal on microorganisms has long been unclear. X-ray absorption near-edge structure (XANES) spectroscopy at the Cu K edge allows the determination of copper speciation in Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa that have been treated with Cu(II) and Cu(I) solutions. The death/inactivation of the bacteria was observed using plate counting and light microscopy. The Cu K-XANES spectra of the two Gram-negative bacteria are different than those of the Gram-positive strain. The results clearly show that the Cu+-S bond contributes to the antibacterial activity of copper, as in the case of silver. The detailed evaluation of the differentiated absorption spectra shows that Cu+ (not Cu2+) is the dominant ion that binds to the bacteria. Because Cu+ is not the most common copper ion, copper is not as effective an antibacterial agent as silver, whose common valency is actually + 1. Any reaction of copper with phosphorus from the bacteria can be excluded after the evaluation of the absorption spectra. [ABSTRACT FROM AUTHOR]

The microwave synthesis of quantum dots (QDs) based on zinc and manganese sulfides and oxides in a water-ethanol medium is proposed. The sample synthesized is characterized by X-ray diffraction (XRD), photoluminescence, X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The XRD analysis shows the presence of the hexagonal ZnS phase of wurtzite type with an average nanocrystal size of 4.5 nm and manganese oxide Mn3O4 (hausmannite phase) with an average particle size of 12.5 nm in the sample under study, but does not provide the unambiguous conclusion about the doping of ZnS nanoparticles with Mn atoms. Although the analysis of the zinc and manganese K-edge XANES spectra suggests that the synthesized QD sample is a ZnMnS solid solution (~11%), a significant amount of a by-product (manganese oxide Mn3O4 of the hausmannite phase, ~89%) is formed. [ABSTRACT FROM AUTHOR]

The synthesis of zinc sulfide (ZnS) quantum dots (QDs) by microwave heating in a water-ethanol medium is proposed. The effect of the synthesis temperature (80 °C, 100 °C, 120 °C, and 150 °C) on the QD characteristics is examined. Based on the analysis of X-ray diffraction profiles the conclusion is drawn that the hexagonal ZnS phase of wurtzite type with an average nanocrystal size of 2.6-3.7 nm forms in the synthesized QDs. The nanocrystallite size is found to increase with the QD synthesis heating temperature. The analysis of X-ray absorption spectra (XANES) at the zinc K-edge indicates a higher crystallinity of the QD samples prepared at higher synthesis temperatures. The combined analysis of X-ray diffraction profiles, optical diffuse reflectance spectra, and X-ray absorption spectra implies the following possible QD structure: the pure hexagonal ZnS phase of wurtzite type in the bulk of nanoparticles and the amorphous ZnO phase in the surface layer of nanoparticles. [ABSTRACT FROM AUTHOR]

A colloidal solution of gold nanoparticles is synthesized with the use of sodium tetrachloroaurate(III) as a precursor, oleylamine as a reducer and surfactant, and 1-octadecene as a solvent. Reaction stages are analyzed in situ by optical (UV-vis) absorption spectroscopy with a simultaneous analysis of particle sizes by dynamic light scattering and X-ray absorption near edge spectroscopy for the analysis of the gold oxidation state. After the synthesis the size of obtained nanoparticles is determined by transmission electron microscopy. The analysis of the obtained experimental data reveals the presence of three main steps in the reduction reaction mechanism, corresponding to Au, Au, Au, which enables the construction of the reaction model. The reaction mechanism involves the formation of gold(I) complexes with oleylamine, followed by polymerization and the formation of gold nanoclusters coated with oleylamine. [ABSTRACT FROM AUTHOR]

X-ray absorption near edge structure (XANES) spectroscopy was used on zoned sphalerites (ZnS) from two world-class Mississippi Valley Type deposits, the Central and Eastern Tennessee Mining district, USA, in order to investigate germanium oxidation states. Due to the low germanium concentrations of these samples, it was necessary to perform the X-ray absorption spectroscopy (XAS) in fluorescence mode. The overlapping of the Zn K βand Ge K αemission lines meant that a high energy-resolution was required. This was achieved using crystal analysers and allowed a bandwidth of 1.3 eV to be obtained. Experimental spectra were compared to XANES calculations and three configurations of germanium incorporation into sphalerite were identified. The first two, the most prevalent, show germanium (II) and (IV) surrounded by sulphur atoms in tetrahedral coordination, suggesting the replacement of Zn by Ge. In the third configuration, germanium (IV) is surrounded by oxygen atoms. This third configuration is unexpected for a zinc sulphide mineral and it resembles that of argutite (GeO2). [ABSTRACT FROM AUTHOR]

Interaction of Cu (II) ions with the matrix of soil and mineral phases of layered silicates was assessed by the Miller method of selective sequential fractionation and a set of synchrotron X-ray methods, including X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XANES). It was shown that the input of Cu into Calcic Chernozem in the form of monoxide (CuO) and salt (Cu(NO3)2) affected the transformation of Cu compounds and their affinity for metal-bearing phases. It was found that the contamination of soil with a soluble Cu(II) salt increased the bioavailability of the metal and the role of organic matter and Fe oxides in the fixation and retention of Cu. During the incubation of soil with Cu monoxide, the content of the metal in the residual fractions increased, which was related to the possible entry of Cu in the form of isomorphic impurities into silicates, as well as to the incomplete dissolution of exogenic compounds at the high level of their input into the soil. A mechanism for the structural transformation of minerals was revealed, which showed that ion exchange processes result in the sorption of Cu (II) ions from the saturated solution by active sites on the internal surface of the lattice of dioctahedral aluminosilicates. Surface hydroxyls at the octahedral aluminum atom play the main role. X-ray diagnostics revealed that excess Cu(II) ions are removed from the system due to the formation and precipitation of coarsely crystalline Cu(NO3)(OH)3. [ABSTRACT FROM AUTHOR]

Solid solutions of zinc sulfide with manganese and cobalt are synthesized. Based on the analysis of X-ray diffraction profiles the conclusion is drawn about the formation of a hexagonal wurtzite type structure in the synthesized quantum dot (QD) solutions. The average crystallite sizes are 8 nm and 22 nm for the samples with manganese and cobalt respectively. Results of IR and optical spectroscopy are consistent with the powder X-ray diffraction and X-ray fluorescence data. The question about particle aggregation in isopropanol and DMF solutions is considered. The QD structures based on ZnS particles doped with Mn and Co transition metal atoms are modeled. The possibility to apply X-ray absorption near edge structure (XANES) spectroscopy to verify the atomic structure parameters around the positions of doping transition metal atoms in QDs of the ZnS family is shown. Partial densities of ZnS:Mn and ZnS:Co electronic states are calculated. [ABSTRACT FROM AUTHOR]

The coordination chemistry of d10s2 metal ions is strongly affected by an (at least partially) occupied d10s2 metal ion-ligand atom antibonding orbital, which may cause a void in the coordination sphere due to repulsion between the electrons in the antibonding orbital on the metal ion and those on the ligands. The character of the formed d10s2 metal ion-ligand atom bond plays an important role in the electron density in the antibonding orbital and thereby also in the coordination chemistry. The hydrated tin(II) ion, [Sn(H2O)3]2+, and the trihydroxidostannate ion, [Sn(OH)3]−, have very different mean Sn−O bond lengths (2.21 and 2.08 Å, respectively) and O-Sn-O angles (ca. 78 and 90°, respectively) both in the solid state and in solution. On increasing the covalency of the tin(II)-ligand bonds, the repulsion decreases and higher coordination numbers are obtained, as seen in the dimethylsulfoxide- and N,N-dimethylthioformamide-solvated tin(II) ions, both of which are five-coordinate with square-pyramidal structures. [ABSTRACT FROM AUTHOR]

In this paper, a study of pure and doped samarium magnetite nanoparticles synthesized using a microwave synthesis in aqueous solution was performed. The shape, size and structure of the pure and samarium doped magnetite nanoparticles were determined by X-ray diffraction, transmission electron microscopy, X-ray absorption spectroscopy and Mössbauer spectroscopy. The magnetic properties of the nanoparticles were investigated using a vibrating sample magnetometer. It was found that the samarium doped magnetite nanoparticles were superparamagnetic with high saturation magnetization. The doping with a small amount of samarium allowed to reduce the size of nanoparticles, their size distribution, increase resistance to oxidation and improve their magnetic characteristics. [ABSTRACT FROM AUTHOR]

A local atomic structure around titanium positions in Ti-bearing hibonite (CaAlO) has been studied. The structural models of substitution of different substitution defects Ti-Al in hibonite by titanium atoms have been considered. Optimization of structural models of hibonite has been done by means of density functional theory calculations using pseudopotential approximation as implemented in VASP 5.3 code. Gibbs free energies analysis has shown that models of substitution of M2 and M4 aluminum positions by titanium atoms are the most probable. For the most probable structural models of Ti-bearing hibonite theoretical X-ray absorption near-edge structure (XANES) spectra near the titanium K edge have been calculated. Significant differences in theoretical XANES spectra calculated for different structural models with non-optimized and optimized atomic structure have been demonstrated. Changes in the intensity of pre-edge structure of Ti K XANES spectra for different substitution models of aluminum by titanium have been observed which relate to different titanium coordination in structural models. Energy shift of spectral features towards lower energy for optimized models implies increase of interatomic distances in local surroundings of Ti absorbing atoms. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots of the CdSe family have been studied by X-ray absorption near edge structure (XANES) spectroscopy and computer modelling. Cd K edge XANES spectra in colloidal quantum dots based on varisized CdSe nanoparticles have been recorded. Atomic structure of CdSe particles and also CdSe particles doped by transition metal atoms Mn and Co has been modelled based on the density functional theory. The embedding of the doping atoms is shown to result in considerable changes in the local atomic structure of CdSe particles. XANES spectra have been calculated above the Cd K edge in CdSe particles, above the Mn K edge in CdSe:Mn particles, above the Co K edge in CdSe:Co particles. The sensitivity of XANES spectroscopy to small changes in structural parameters of the nanoparticles of CdSe family has been demonstrated that furnishes an opportunity to apply it for the verification of atomic structure parameters around positions of cadmium and doping atoms of transition metals in quantum dots based on CdSe. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) based on zinc sulfide are synthesized by a microwave method in an aqueous medium using dioctyl sodium sulfosuccinate (DS) or 4,4′-bipyridine (BP). Based on the analysis of X-ray diffraction profiles the conclusion is drawn that QDs obtained have a structure of cubic zinc blende with an average particle size of 5.6 nm for the ZnS sample and 4.8 nm for ZnS. Transmission electron microscopy images show the presence of spherical aggregates of particles only for ZnS. FTIR data indicate the presence of sulfate ions in both samples; DS remains in the sample, facilitating the QD agglomeration, while BP is effectively washed out. From the optical diffuse reflectance spectra the band gap is estimated, which turns out to be larger than the expected one due to the presence of elemental sulfur in the samples and partial oxidation of the QD surface. The QD structure based on ZnS particles is also modeled in the work. The possibility to employ X-ray absorption near-edge spectroscopy for the verification of atomic structural parameters around zinc sites in QDs based on zinc sulfide is demonstrated. [ABSTRACT FROM AUTHOR]

Long-term soil and ecosystem development involves predictable changes in nitrogen (N) and phosphorus (P) availability and limitation, but far less is known about comparable changes in sulfur (S) despite its importance as an essential plant macronutrient and component of soil organic matter. We used a combination of elemental analysis, X-ray absorption spectroscopy, hydrolytic enzyme assays, and stable S isotope ratios to examine S in soil and leaf tissue along the 120,000-year Franz Josef chronosequence, New Zealand. Total soil S concentrations increased during the early stages of pedogenesis and then declined as soils aged. There was little variation in soil N:S ratios along the chronosequence other than in the youngest (5 year old) soil, although the carbon (C):S ratio increased markedly in the oldest soils and the P:S ratio decreased continuously along the chronosequence. Foliar S concentrations and N:S ratios varied widely among common plant species but did not change consistently with increasing soil age, although foliar P:S declined for several species in the older stages of the chronosequence. The chemical nature of soil organic S extracted from mineral and organic horizons and determined by S K-edge X-ray absorption near-edge fine-structure (XANES) spectroscopy was dominated by C-bonded S distributed approximately equally in highly-reduced and intermediate oxidation states, although ester-bonded S was also abundant throughout the chronosequence. Soil sulfatase activity expressed on a soil C basis was highest in young soils, indicating low S availability in the early stage of pedogenesis. Enzymatic C:S and N:S ratios varied little during ecosystem development, although the enzymatic P:S ratio increased continuously along the chronosequence. Stable S isotope ratios (δS) increased along the chronosequence, particularly in the early stages of pedogenesis, reflecting a shift in S inputs from primary mineral S to oceanic sulfate in atmospheric deposition. Overall, this first comprehensive assessment of S along a long-term soil chronosequence suggests that S availability is low in the earliest stage of pedogenesis, but then remains stable throughout the progressive and retrogressive phases of ecosystem development, despite pronounced shifts in the chemistry and dynamics of other nutrients. [ABSTRACT FROM AUTHOR]

A new mineral ferricoronadite with the simplified formula Pb(Mn Fe )O was discovered in the orogenetic zone related to the 'Mixed Series' metamorphic complex near the Nežilovo village, Pelagonian massif, Republic of Macedonia. Associated minerals are franklinite, gahnite, hetaerolite, roméite, almeidaite, Mn-analogue of plumboferrite, zincohögbomite analogue with Fe > Al, zincochromite, Zn-bearing talc, Zn-bearing muscovite, baryte, quartz and zircon. Ferricoronadite is a late hydrothermal mineral forming veinlets up to 8 mm thick in granular aggregate predominantly composed by zinc-dominant spinels. The new mineral is opaque, black, with brownish black streak. The luster is strong submetallic to metallic. The micro-indentation hardness is 819 kg/mm. Distinct cleavage is observed on (100). Ferricoronadite is brittle, with uneven fracture. The density calculated from the empirical formula is 5.538 g/cm. In reflected light, ferricoronadite is light gray. The reflectance values [ R / R , % ( λ, nm)] are: 28.7/27.8 (470), 27.6/26.6 (546), 27.2/26.1 (589), 26.5/25.5 (650). The IR spectrum shows the absence of HO and OH groups. According to the Mössbauer spectrum, all iron is trivalent. The Mn K-edge XANES spectroscopy shows that Mn is predominantly tetravalent, with subordinate Mn. The chemical composition is (wt%; electron microprobe, Mn apportioned between MnO and MnO based on the charge-balance requirement): BaO 5.16, PbO 24.50, ZnO 0.33, AlO 0.50, MnO 9.90, FeO 11.45, TiO 4.19, MnO 44.81, total 100.84. The empirical formula based on 8 cations Mn + Fe + Ti + Al + Zn pfu is PbBa(MnFeMnTiAlZn)O. The crystal structure was determined using single-crystal X-ray diffraction data. The new mineral is tetragonal, space group I4/ m, a = 9.9043(7), c = 2.8986(9) Å, V = 284.34(9) Å, Z = 1. In ferricoronadite, double chains of edge-sharing (Mn, Fe, Ti)-centered octahedra are connected via common vertices to form a pseudo-framework with tunnels containing large cations Pb and Ba. The strongest lines of the powder X-ray diffraction pattern [ d, Å ( I, %) ( hkl)] are: 3.497 (33) (220), 3.128 (100) (−130, 130), 2.424 (27) (−121, 121), 2.214 (23) (240, −240), 2.178 (17) (031), 1.850 (15) (141, −141), 1.651 (16) (060), 1.554 (18) (−251, 251). Ferricoronadite is named as an analogue of coronadite Pb(Mn Mn )O with the major charge-compensating octahedral cation Fe instead of Mn. [ABSTRACT FROM AUTHOR]

An in silico study of semiconductor quantum dots of the CdTe family doped with atoms of rare earth elements is performed based of density functional theory. An ab initio computer design of quantum dots based on CdTe nanoparticles doped with Eu и Gd atoms is carried out. Partial densities of states of CdTe:Eu and CdTe:Gd quantum dots are calculated and analyzed. X-ray absorption near edge (XANES) spectra near the Eu K-, L-, and L- and Gd K-, L-, and L-edges of CdTe:Eu and CdTe:Gd quantum dots are calculated. The sensitivity of XANES spectroscopy for the verification of parameters of a nanosized atomic structure of quantum dots based on CdTe particles doped with atoms of rare earth elements and the determination of the local atomic structure around the atoms of rare earth elements in quantum dots is demonstrated. [ABSTRACT FROM AUTHOR]

The fine structure of X-ray absorption spectra near the K edge and the extended fine structure of X-ray absorption for titanium, copper, and chromium in nanocrystalline coatings based on titanium nitride doped with copper, chromium, and silicon are experimentally studied. The samples are prepared by the evaporation of composite cathodes using the vacuum arc plasma-assisted method. The parameters of the local environment of titanium, copper, and chromium atoms in the structures of the samples under study are calculated. It is established that the presence of a copper impurity in the coating of no more than 12% in amount leads to a slight increase in the Ti-N distance in comparison with the titanium sample, whereas doping with silicon leads, on the contrary, to a decrease in the bond length. The measurement results for the K absorption edges of copper and chromium confirm that the doping elements are concentrated at the edges of the growing titanium-nitride crystallite and determine its size, which corresponds to the sizes of the coherent-scattering region of 40-50 nm. [ABSTRACT FROM AUTHOR]

The ab initio computer design of the CdS-based quantum dots and the cobalt doped CdS quantum dots is carried out. The characteristics features of the atomic and electronic structures of semiconductor colloidal quantum dots on CdS of different sizes are studied, and the effect of cobalt impurity atoms is estimated. We have proved the sensitivity of the X-ray absorption near-edge structure (XANES) method for the verification of the nanosized atomic structural parameters calculated by the methods of computer modeling for small-scale quantum dots of the CdS family, and for the determination of the local environment parameters of the cobalt atom in the quantum dot. [ABSTRACT FROM AUTHOR]

The catalytic conversion of a mixture of ethanol and glycerol over the Re-W/AlO catalysts was studied. The Re-W binary system exhibits a non-additive cocatalytic effect in the conversion of ethanol and its mixture with glycerol into the fraction of olefins С-С. The non-additive increase in the catalytic activity is associated with the specific structure of the binuclear metallocomplex precursors, due to which the supported metals are arranged in the immediate vicinity from each other on the support surface and intensively interact to form Re. The study of the combined conversion of ethanol and glycerol made it possible to find an optimum ratio of the reactants in the initial mixture. The yield of target hydrocarbons attains 50 wt.% based on the amount of carbon passed through the reactor. [ABSTRACT FROM AUTHOR]

BACKGROUND Pyrolysis of slaughterhouse waste could promote more sustainable phosphorus (P) usage through the development of alternative P fertilizers. This study investigated how pyrolysis temperature (220, 350, 550 and 750 °C), rendering before pyrolysis, and wood or corn biomass additions affect P chemistry in bone char, plant availability, and its potential as P fertilizer. RESULTS Linear combination fitting of synchrotron-based X-ray absorption near edge structure spectra demonstrated that higher pyrolysis temperatures decreased the fit with organic P references, but increased the fit with a hydroxyapatite ( HA) reference, used as an indicator of high calcium phosphate ( CaP) crystallinity. The fit to the HA reference increased from 0% to 69% in bone with meat residue and from 20% to 95% in rendered bone. Biomass additions to the bone with meat residue reduced the fit to the HA reference by 83% for wood and 95% for corn, and additions to rendered bone by 37% for wood. No detectable aromatic P forms were generated by pyrolysis. High CaP crystallinity was correlated with low water-extractable P, but high formic acid-extractable P indicative of high plant availability. Bone char supplied available P which was only 24% lower than Triple Superphosphate fertilizer and two- to five-fold higher than rock phosphate. CONCLUSION Pyrolysis temperature and biomass additions can be used to design P fertilizer characteristics of bone char through changing CaP crystallinity that optimize P availability to plants. © 2014 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The features of ethanol conversion into hydrocarbons C-C in the presence of the novel catalyst Pd-Zn/γ-alumina and pilot zeolite system Pd-Zn/MFI/γ-alumina were studied (MFI is high-siliceous zeolite with ZSM-5 type structure). The structure of active sites changes noticeably in the course of preliminary activation and catalytic reaction. High selectivity and stability of the zeolite-containing Pd-Zn catalyst in alcohol conversion into hydrocarbon components of fuels is related to the stable composition of the alloy that forms clusters PdZn. At the same time, the alumina-based catalyst loses stability due to zinc diffusion from the alloy into γ-AlO to form the spinel structure. [ABSTRACT FROM AUTHOR]

The chemical composition of tissues can influence their form and function. As a prime example, the lattice-like arrangement of collagen fibrils required for corneal transparency is controlled, in part, by sulfated proteoglycans, which, via core proteins, bind to the collagen at specific locations along the fibril axis. However, to date, no studies have been able to directly identify and characterize sulfur (S) in the cornea as a function of tissue location. In this study, X-ray absorption near-edge structure spectroscopy and micro-beam X-ray fluorescence (μ-XRF) chemical contrast imaging were employed to probe the nature of the mature (bovine) cornea as a function of position from the anterior sub-epithelial region into the deep stroma. Data indicate an inhomogeneity in the composition of S species in the first ≈50 μm of stromal depth. In μ-XRF chemical contrast imaging, S did not co-localize with phosphorous (P) in the deep stroma where sulfates are prominent. Rather, P is present only as isolated micrometric spots, presumably identifiable as keratocytes. This study lends novel insights into the elemental physiology of mature cornea, especially in relation to its S distribution; future studies could be applied to human tissues. Moreover, it defines an analytical protocol for the interrogation of S species in biological tissues with micrometric resolution. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Estimation of Fe/ΣFe ratios in materials at the submicrometre scale has been a long-standing challenge in the Earth and environmental sciences because of the usefulness of this ratio in estimating redox conditions as well as for geothermometry. To date, few quantitative methods with submicrometric resolution have been developed for this purpose, and most of them have used electron energy-loss spectroscopy carried out in the ultra-high vacuum environment of a transmission electron microscope (TEM). Scanning transmission X-ray microscopy (STXM) is a relatively new technique complementary to TEM and is increasingly being used in the Earth sciences. Here, we detail an analytical procedure to quantify the Fe/ΣFe ratio in silicates using Fe L-edge X-ray absorption near edge structure (XANES) spectra obtained by STXM, and we discuss its advantages and limitations. Two different methods for retrieving Fe/ΣFe ratios from XANES spectra are calibrated using reference samples with known Fe content by independent approaches. The first method uses the intensity ratio of the two major peaks at the L-edge. This method allows mapping of Fe/ΣFe ratios at a spatial scale better than 50 nm by the acquisition of 5 images only. The second method employs a 2-eV-wide integration window centred on the L maximum for Fe, which is compared to the total integral intensity of the Fe L-edge. These two approaches are applied to metapelites from the Glarus massif (Switzerland), containing micrometre-sized chlorite and illite grains and prepared as ultrathin foils by focused ion beam milling. Nanometre-scale mapping of iron redox in these samples is presented and shows evidence of compositional zonation. The existence of such zonation has crucial implications for geothermometry and illustrates the importance of being able to measure Fe/ΣFe ratios at the submicrometre scale in geological samples. [ABSTRACT FROM AUTHOR]

The atomic structure of copper(II) complexes based on diacetyl monoxime 1′-phthalazinyl hydrazone is studied by XANES spectral analysis and magnetochemistry. The XANES spectra at the Cu K-edge are measured in CHNCuO and CHNCuO complexes. The calculations of the Cu K-XANES spectra of the complexes in question are performed for a few structural models based on the full-potential finite difference method. By low-temperature magnetochemistry magnetic exchange parameters are determined, and a quantum chemical simulation of the exchange interaction is carried out within the broken symmetry approximation. Based on a combined analysis of the XANES spectra and magnetic exchange parameters, the most probable structural models of CHNCuO and CHNCuO complexes are found. [ABSTRACT FROM AUTHOR]