Characterisation of Sonochemically Produced PdO Nanoparticles by X‐ray Absorption Near Edge Structure Spectroscopy

Brij‐35 [polyoxyethylene(23) lauryl ether] stabilised palladium nanoparticles, obtained on attempted sonochemical reduction of PdCl₂ by sodium sulfite in water under Argon, instantaneously oxidized to PdO. The particles obtained were stable and have narrow size distribution with an average size of 10 nm diameter. PdO nanoparticles were reduced to Pd nanoparticles in an autoclave by treatment with 50 bar hydrogen at 140 °C. The catalytic behaviour of Pd nanoparticles, thus obtained, is unusual in comparison with conventional Pd catalysts. The nanoparticles were characterized by UV‐Vis spectroscopy, TEM and their X‐ray Absorption Near Edge Structure (XANES) at the Pd‐L‐III edge.     

Study of lead levels in soils by weathering of metallic Pb bullets used in dove hunting in Córdoba,Argentina

A study of level of Pb in soils of the center‐north of the Province of Córdoba, a worldwide recognized tourist region for dove hunting, was performed in this work. The native forest of the region has a great population of doves associated with the grain‐productive fields of the surrounding. Contamination of soils due to hunting activities is regulated by national and local norms. The Córdoba Environmental Secretary by resolution no. 1115/2011 approved a new regulation that categorizes this activity as generator of Y31 (Pb) industrial waste. Lead from pellets alloy is deposited on the soil of the shooting fields. Samples were taken at depth of 50 mm from 315 pits referenced by GPS in accordance with local environmental authorities as well as the hunting outfitters companies. Sampling sites are distributed between parallels 31 °S (S31) up to 30 °S (S30) and between meridians W64 up to W63. Soils samples were analyzed by X‐ray fluorescence spectroscopy while Pb bullets were analyzed by scanning electron microscopy (SEM) and X‐ray diffraction (XRD). The average concentration obtained for Pb in dry soil sieved (200 mesh) was 80 ppm. Powder XRD patterns of crust material removed from the corroded surface of weathered bullets were obtained. Three Pb mineral compounds were identified by XRD analysis and also studied by optical microscopy and SEM. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and characterization of S-Au interaction in gold nanoparticle bound polymeric beads

A detailed X-ray Absorption Spectroscopic examination of S-Au interaction in gold nanoparticle bound to Polystyrene-Divinyl Benzene (PS-DVB) micro beads was carried out. Gold nanoparticles were bound to the surface of the commercially available PS-DVB beads using a simple one step procedure. Influence of polystyrene backbone on the electronic structure of the gold nanoparticles was observed through X-ray Absorption Near Edge Structure (XANES) spectra of Au at L III edge. An additional structure in the white line of the S K-edge XANES spectrum confirmed the presence of S-Au bonding. Transmission Electron Microscopy (TEM) studies coupled with Selected Area Electron Diffraction Pattern and X-ray Diffraction studies revealed the morphology of the Au nanoparticles bound to the micro beads.     

Tetrahedral versus octahedral Mn site coordination in wurtzite and rocksalt Zn1−xMnxO investigated by means of XAS experiments under high pressure

We present the results of x-ray absorption measurements carried out in Zn_1−xMn_xO thin films under high pressure. The Mn environment remains essentially the same for nominal Mn concentrations given by x=0.05, 0.1, 0.15 and 0.25. Both the XANES (X-ray Absorption Near Edge Structure) and EXAFS (Extended X-ray Absorption Fine Structure) indicate that Mn occupies the Zn site, being surrounded by four oxygen atoms at 2.02±0.01 Å. The substitutional hypothesis is reinforced by comparing the differences between the ambient (wurtzite) and high pressure (rocksalt) spectra, which correspond to tetrahedral and octahedral Mn environments.     

A new method to study complex materials in solid state chemistry: application to chalcogenide materials

We show that a combined application of Mössbauer spectroscopy and other experimental tools such as X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy and nuclear magnetic resonance provides a coherent picture of the local electronic structure in chalcogenide materials. In order to develop this idea we propose an analysis of the Sn, Sb and Te local electronic structures for three different systems of materials. The first example concerns the In–Sn–S system. We show that Li insertion in In₁₆Sn₄S₃₂ leads to changes of the Sn oxidation states from Sn(IV) to Sn(II). The second example concerns materials of the Tl–Sb–S system. We show that variations of the ¹²¹Sb Mössbauer isomer shift and surface of the first peak of the X‐ray absorption spectra at the Sb L_III edge can be linearly correlated because of the main influence of the Sb 5s electrons. This is explained by changes in the local environment of the Sb atoms. The last example concerns the crystalline phases of the Tl–Sn–Te system. The formal oxidation numbers of the Te atoms are determined from ¹²⁵Te Mössbauer spectroscopy and X‐ray photoelectron spectroscopy. They are related to the different types of bonds involving the Te atoms in the Tl–Sn–Te compounds.     

The photodegradation of cadmium yellow paints in Henri Matisse’s Le Bonheur de vivre (1905–1906)

Evidence for the alteration of the yellow paints in Henri Matisse’s Le Bonheur de vivre (1905–1906, The Barnes Foundation) has been observed since the 1990s. The changes in this iconic work of Matisse’s Fauvist period include lightening, darkening, and flaking of the yellow paints. Handheld X-ray fluorescence (XRF) and multispectral imaging surveys reveal that the degradation is confined to cadmium yellow (CdS) paints. The discoloration of cadmium yellow paints in Impressionist, Post-Impressionist and early modernist work from the 1880s through the 1920s has been ascribed to the photo-oxidative degradation of CdS. Preliminary investigations of the degraded yellow paints in this work involved Cd L_III-edge X-ray Absorption Near Edge Spectroscopy (XANES) at the Stanford Synchrotron Radiation Light Source (SSRL Menlo Park, California) and Scanning Electron Microscopy-energy dispersive X-ray analysis (SEM-EDS) at the Winterthur Museum Scientific Research and Analysis Laboratory. To determine if the visual changes in the paints did in fact indicate photo-oxidative degradation and if different chemistries could be observed for the lightened versus darkened regions, synchrotron radiation-micro Fourier Transform InfraRed (SR-μFTIR) spectroscopy, X-ray Fluorescence (SR-μXRF) mapping and micro X-ray Absorption Near Edge Spectroscopy (μXANES) mapping at the Cd L_III-edge of the altered paint cross-sections were carried out at the European synchrotron radiation facility (ESRF, Grenoble, France) beamline ID-21. The goal is to elucidate the discoloration mechanisms observed in the paint using elemental and speciation mapping. The μXANES mapping and SR-FTIR imaging showed a substantial enrichment of CdCO₃ in the off-white surface crust of the faded/discolored CdS paint. This suggests that the CdCO₃ is present as an insoluble photodegradation product rather than solely a paint filler or starting reagent. Additionally, oxalates and sulfates were found to be concentrated at the alteration surface.     

X‐ray fluorescence determination of the manganese valence state and speciation in manganese ores

This work concerns determination of the manganese valence state and speciation by wavelength‐dispersive X‐ray fluorescence analysis. The authors investigated the effect of the manganese valence state and speciation on the intensity of some К‐series lines of the X‐ray emission spectrum for the samples of manganese compounds. The intensities of MnKβ₅ line and MnKβ′ satellite are least influenced by speciation, and they may be used for evaluating the manganese valence state for the samples containing low iron. The intensities of MnKβ″ and MnKβ^x satellites may be employed for assessing the manganese speciation. The results of X‐ray fluorescence determination of the manganese valence state and speciation in the manganese ores of the South Ural deposits agree with the X‐ray diffraction data. The X‐ray fluorescence method is definitely advantageous, because it does not require a complicated process of sample preparation and allows to receive fast information on the manganese valence state and speciation with the purpose to assess the quality of manganese ores. Copyright © 2015 John Wiley & Sons, Ltd.     

Beam‐induced redox transformation of arsenic during As K‐edge XAS measurements: availability of reducing or oxidizing agents and As speciation

During X‐ray absorption spectroscopy (XAS) measurements of arsenic (As), beam‐induced redox transformation is often observed. In this study, the As species immobilized by poorly crystallized mackinawite (FeS) was assessed for the susceptibility to beam‐induced redox reactions as a function of sample properties including the redox state of FeS and the solid‐phase As speciation. The beam‐induced oxidation of reduced As species was found to be mediated by the atmospheric O₂ and the oxidation products of FeS [e.g. Fe(III) (oxyhydr)oxides and intermediate sulfurs]. Regardless of the redox state of FeS, both arsenic sulfide and surface‐complexed As(III) readily underwent the photo‐oxidation upon exposure to the atmospheric O₂ during XAS measurements. With strict O₂ exclusion, however, both As(0) and arsenic sulfide were less prone to the photo‐oxidation by Fe(III) (oxyhydr)oxides than NaAsO₂ and/or surface‐complexed As(III). In case of unaerated As(V)‐reacted FeS samples, surface‐complexed As(V) was photocatalytically reduced during XAS measurements, but arsenic sulfide did not undergo the photo‐reduction.     

XANES of the AuLIII edge in gold metal and in two compounds AuCN and AuCl3

The X-ray Absorption Near Edge Structure (XANES) of the AuL_III edge in gold metal and in its two compounds AuCN and AuCl₃ have been recorded. The observed chemical shifts of the edge and the fine structure peaks in the compounds are discussed. It is observed that the energy shifts ΔE of the AuL_III due to chemical effects in aurous cyanide (AuCN) and auric chloride (AuCl₃) with respect to the pure Au edge is 2.9 eV in AuCN and 0.7eV in AuCl₃. The edge widths in AuCN and AuCl₃ are found to be almost the same for both the compounds, presumably because electronegativities of CN and Cl are not very different. The observed fine structure peaks of the discontinuities of AuCN and AuCl₃ are displaced progressively away from the main edge.     

XAS analysis of iron and palladium bonded to a polysaccharide produced anaerobically by a strain of Klebsiella oxytoca

Klebsiella oxytoca BAS‐10 ferments citrate to acetic acid and CO₂, and secretes a specific exopolysaccharide (EPS), which is able to bind different metallic species. These biomaterials may be used for different biotechnological purposes, including applications as innovative green biogenerated catalysts. In production of biogenerated Pd species, the Fe(III) as ferric citrate is added to anaerobic culture of K. oxytoca BAS‐10, in the presence of palladium species, to increase the EPS secretion and improve Pd‐EPS yield. In this process, bi‐metallic (FePd‐EPS) biomaterials were produced for the first time. The morphology of bi‐metallic EPS, and the chemical state of the two metals in the FePd‐EPS, are investigated by transmission electron microscopy, Fourier transform infra‐red spectroscopy, micro‐X‐ray fluorescence, and X‐ray absorption spectroscopy methods (XANES and EXAFS), and compared with mono‐metallic Pd‐EPS and Fe‐EPS complexes. Iron in FePd‐EPS is in the mineralized form of iron oxides/hydroxides, predominantly in the form of Fe³⁺, with a small amount of Fe²⁺ in the structure, most probably a mixture of different nano‐crystalline iron oxides and hydroxides, as in mono‐metallic Fe‐EPS. Palladium is found as Pd(0) in the form of metallic nanoparticles with face‐centred cubic structure in both bi‐metallic (FePd‐EPS) and mono‐metallic (Pd‐EPS) species. In bi‐metallic species, Pd and Fe nanoparticles agglomerate in larger clusters, but they remain spatially separated. The catalytic ability of bi‐metallic species (FePd‐EPS) in a hydrodechlorination reaction is improved in comparison with mono‐metallic Pd‐EPS.     

Iron speciation in ancient Attic pottery pigments: a non‐destructive SR‐XAS investigation

The present work reports a detailed investigation on the speciation of iron in the pigments of decorated pottery fragments of cultural heritage relevance. The fragments come from the Gioiosa Guardia archaeological site in the area of the `Strait of Messina' (Sicily, Southern Italy), and date back to VI–V century BC. The purpose of this study is to characterize the main pigmenting agents responsible for the dark‐red coloration of the specimens using non‐destructive analytical techniques such as synchrotron radiation X‐ray absorption spectroscopy (SR‐XAS), a well established technique for cultural heritage and environmental subjects. Absorption spectra were collected at the Fe K‐edge on the Italian beamline for absorption and diffraction (BM8‐GILDA) at the European Synchrotron Radiation Facility in Grenoble (France). In order to determine the speciation of Fe in the samples, principal component analysis and least‐squares fitting procedures were applied to the near‐edge part of the absorption spectra (XANES). Details on the local structure around the Fe sites were obtained by analyzing the extended part of the spectra (EXAFS). Furthermore, an accurate determination of the average Fe oxidation state was carried out through analysis of the pre‐edge peaks of the absorption spectra. Samples resulted composed of an admixture of Fe₂O₃ (hematite or maghemite) and magnetite (Fe₃O₄), occurring in different relative abundance in the dark‐ and light‐colored areas of the specimens. The results obtained are complementary to information previously obtained by means of instrumental neutron activation analysis, Fourier transform infrared absorbance and time‐of‐flight neutron diffraction.     

Characterization of surface carbon films on weathered Japanese roof tiles by soft x‐ray spectroscopy

The effects of weathering on carbon films deposited on Japanese smoked roof tiles were investigated by soft x‐ray absorption and emission spectroscopy using synchrotron radiation. X‐ray absorption measurements revealed that weathering oxidizes the carbon films and that partial carboxy chemical bonding occurs. Incident angle‐dependent x‐ray absorption spectra in the C K region confirmed that the degree of the orientation at the surface of the oxidized carbon films decreases with weathering. However, the take‐off angle‐dependent C K x‐ray emission spectra showed that the orientation of the layered carbon structure is maintained in the bulk portion when weathered. Therefore, it is confirmed that oxidation proceeds from the surface of the carbon films. Weathering degrades and oxidizes the surface carbon films, which causes the metallic silver color to change to darker gray. Copyright © 2005 John Wiley & Sons, Ltd.     

Theoretical study of electronic structure, chemical bonding, and X-ray absorption near edge spectroscopy in niobium and niobium monoxide

In this work, we calculate band structures, the density of state and chemical bonding of the metallic niobium (Nb) and its mono-oxide (NbO) crystals in their solid states using the Density Functional Theory and X-ray Absorption Near Edge Spectroscopy. The electronic properties of Nb and NbO are investigated using the Finite Difference Method. These theoretical results are found in good agreement with the most recent experimental data. Our calculations reveal that the NbO crystal behaves like a superconductor.     

The pH dependence of Am(III) complexation with acetate: an EXAFS study

The complexation of acetate with Am(III) is studied as a function of the pH (1–6) by extended X‐ray absorption fine‐structure (EXAFS) spectroscopy. The molecular structure of the Am(III)–acetate complexes (coordination numbers, oxygen and carbon distances) is determined from the raw k³‐weighted Am L_III‐edge EXAFS spectra. The results show a continuous shift of Am(III) speciation with increasing pH value towards the complexed species. Furthermore, it is verified that acetate coordinates in a bidentate coordination mode to Am(III) (Am—C distance: 2.82 ± 0.03 Å). The EXAFS data are analyzed by iterative transformation factor analysis to further verify the chemical speciation, which is calculated on the basis of thermodynamic constants, and the used structural model. The experimental results are in very good agreement with the thermodynamic modelling.     

The molecular orientation of DNA bases on H-passivated Si(1 1 1) surfaces investigated by means of near edge X-ray absorption fine structure spectroscopy

Layers of the DNA bases adenine, cytosine, and guanine were deposited onto hydrogen passivated Si(1 1 1) surfaces. The average tilt angles of these molecules with respect to the substrate surface were determined by the angular dependence of the Near Edge X-ray Absorption Fine Structure (NEXAFS) of the carbon K-edge. The interpretation of the NEXAFS spectra was assisted by a semi-empirical approach to the calculation of the π^∗-transition region which employs density functional theory calculations and core level photoemission data.     

An EXAFS spectroscopic study of Am(III) complexation with lactate

The pH dependence (1–7) of Am(III) complexation with lactate in aqueous solution is studied using extended X‐ray absorption fine‐structure (EXAFS) spectroscopy. Structural data (coordination numbers, Am—O and Am—C distances) of the formed Am(III)–lactate species are determined from the raw k³‐weighted Am L_III‐edge EXAFS spectra. Between pH 1 and pH 6, Am(III) speciation shifts continuously towards complexed species with increasing pH. At higher pH, the amount of complexed species decreases due to formation of hydroxo species. The coordination numbers and distances (3.41–3.43 Å) of the coordinating carbon atoms clearly point out that lactate is bound `side‐on' to Am(III) through both the carboxylic and the α‐hydroxy function of lactate. The experimentally determined coordination numbers are compared with speciation calculations on the basis of tabulated thermodynamic stability constants. Both EXAFS data and thermodynamic modelling are in very good agreement. The EXAFS spectra are also analyzed by iterative transformation factor analysis to further verify the determined Am(III) speciation and the used structural model.     

Direct chromium speciation using X‐ray spectrometry and chemometrics

Chromium is a chemical element that occurs in two principal distinct forms: trivalent (Cr(III)) and hexavalent (Cr(VI)). As chromium toxicity depends on its oxidation state, the concentrations of both the species should necessarily be determined, and not only that of total chromium. Using X‐ray spectrometry allied to chemometrics, this work presents a new method for chromium speciation, with no prior separation and/or preconcentration of Cr(III) and Cr(VI) species. Spectra of several solutions containing different concentrations of Cr(III) and Cr(VI) were obtained. The data were treated through principal component analysis and partial least squares regression. The results obtained show that direct speciation using a conventional X‐ray spectrometer is possible, with calculated limits of detection and quantification for Cr(III) and Cr(VI) being lower than 17 and 50 µg g^?1, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

Solid‐phase cadmium speciation in soil using L3‐edge XANES spectroscopy with partial least‐squares regression

Cadmium (Cd) has a high toxicity and resolving its speciation in soil is challenging but essential for estimating the environmental risk. In this study partial least‐square (PLS) regression was tested for its capability to deconvolute Cd L₃‐edge X‐ray absorption near‐edge structure (XANES) spectra of multi‐compound mixtures. For this, a library of Cd reference compound spectra and a spectrum of a soil sample were acquired. A good coefficient of determination (R²) of Cd compounds in mixtures was obtained for the PLS model using binary and ternary mixtures of various Cd reference compounds proving the validity of this approach. In order to describe complex systems like soil, multi‐compound mixtures of a variety of Cd compounds must be included in the PLS model. The obtained PLS regression model was then applied to a highly Cd‐contaminated soil revealing Cd₃(PO₄)₂ (36.1%), Cd(NO₃)₂·4H₂O (24.5%), Cd(OH)₂ (21.7%), CdCO₃ (17.1%) and CdCl₂ (0.4%). These preliminary results proved that PLS regression is a promising approach for a direct determination of Cd speciation in the solid phase of a soil sample.     

Speciation of inclusions and precipitates in steel by means of XRF and LEEIXS

Fundamentals of x‐ray fluorescence spectrometry and X‐ray emission spectrometry in the case of electron probe x‐ray microanalysis and low‐energy electron induced x‐ray spectrometry are compared. The different aluminum and titanium compounds occurring in steel can be investigated by examining soft x‐ray spectra, arising from valence shell orbitals. The non‐metallic inclusions were isolated by galvanometric electrolysis. In the case of the speciation of titanium, direct electron bombardment of the sample is used to generate soft x‐rays. By investigating the Ti L lines, titanium carbide, nitride and sulfide can be distinguished. To specify aluminum compounds, the Kβ transition in the x‐ray fluorescence spectrum was examined. The concentration of aluminum oxide and nitride in precipitates of special steel qualities can be determined with a satisfactory determination limit. Finally, pre‐operational studies for the determination of different silicon inclusions using electron excitation were carried out. Copyright © 2003 John Wiley & Sons, Ltd.     

X-PEEM/NEXAFS and AFM of polypyrrole and copper micro-patterns on insulating fluoropolymer substrates

Micro-patterns (80 μm and 10 μm) of copper and semi-conducting polypyrrole on insulating fluorinated ethylene propylene substrates were characterized using synchrotron-based X-ray Photoemission Electron Microscopy (X-PEEM), Near Edge X-ray Absorption Fine Structure (NEXAFS), and Atomic Force Microscopy (AFM). Electronic states in the polypyrrole are verified using the NEXAFS data, and sample degradation upon irradiation is addressed. X-PEEM images show homogeneous distributions of the corresponding elements in the patterns. They do not exhibit dichroic effects and give information about the growth of copper and polypyrrole (i.e. nucleation of Cu, overgrowth of PPy, formation of PPy granules). AFM results are used to verify the topography of the patterns and support the findings on pattern growth.