XANES Spectroscopy Research Articles

Alkaline-Earth Rhodium Hydroxides: Synthesis, Structures, and Thermal Decomposition to Complex Oxides.

The rhodium(III) hydrogarnets Ca3Rh2(OH)12 and Sr3Rh2(OH)12 crystallize as polycrystalline powders under hydrothermal conditions at 200 °C from RhCl3·3H2O and either Ca(OH)2 or Sr(OH)2 in either 12 M NaOH or KOH. Rietveld refinements against synchrotron powder X-ray diffraction (XRD) data allow the first crystal structures of the two materials to be determined. If BaO2 is used as a reagent and the concentration of hydroxide increased to hydroflux conditions (excess NaOH), then single crystals of a new complex rhodium hydroxide, BaNaRh(OH)6, are formed in a phase-pure sample, with sodium included from the flux. Structure solution from single-crystal XRD data reveals isolated octahedral Rh centers that share hydroxides with 10-coordinate Ba and two independent 8-coordinate Na sites. 23Na magic-angle spinning NMR confirms the presence of the two crystallographically distinct Na sites and also verifies the diamagnetic nature of the sample, expected for Rh(III). The thermal behavior of the hydroxides on heating in air was investigated using X-ray thermodiffractometry, showing different decomposition pathways for each material. Ca3Rh2(OH)12 yields CaRh2O4 and CaO above 650 °C, from which phase-pure CaRh2O4 is isolated by washing with dilute nitric acid, a material previously only reported by high-pressure or high-temperature synthesis. Sr3Rh2(OH)12 decomposes to give a less crystalline material with a powder XRD pattern that is matched to the 2H-layered hexagonal perovskite Sr6Rh5O15, which contains mixed-valent Rh3+/4+, confirmed by Rh K-edge XANES spectroscopy. On heating BaNaRh(OH)6, a complex set of decomposition events takes place via transient phases.

Evaluation of the Use of Wetlands in Arsenic Sequestration of Mine-Influenced Effluent using Synchrotron XRF and XANES Spectroscopy

Evaluation of the Use of Wetlands in Arsenic Sequestration of Mine-Influenced Effluent using Synchrotron XRF and XANES Spectroscopy

Accurate predictions of microscale oxygen barometry in basaltic glasses using V K-edge X-ray absorption spectroscopy: A multivariate approach

This research was supported by the Remote, In Situ, and Synchrotron Studies for Science and Exploration (RIS4 E) node of the NASA SSERVI program and NASA grants NNX16AR18G and NNX17AL07G. XANES spectroscopy data were collected at GeoSoilEnviroCARS (Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation, Earth Sciences (EAR-1128799) and Department of Energy, Geosciences (DE-FG02-94ER14466). Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357. King was supported by an Australian Research Council Future Fellowship (FT130101524).

Phosphorus removal by slag depends on its mineralogical composition: A comparative study of AOD and EAF slags

Electric arc furnace slag (EAF) and argon oxygen decarburization slag (AOD) were investigated in column experiments to determine the effect of mineralogical composition on their P removal performance and lifespan. Polyethylene glycol (PEG) and NaOH solutions were used for pretreatment of the slags to adjust their dissolution properties. The modified slags exhibited better P removal performance at the beginning of the experiment, but had shorter lifespan than the unmodified slags. AOD and EAF modified with PEG and NaOH achieved 100% P removal during the first 84 and 60 pore volumes, respectively, which were ≥20 pore volumes longer than virgin AOD and EAF. However, virgin EAF and AOD both had a P removal efficiency above 90% during the first 280 pore volumes. Possibly, soluble minerals such as free lime are lost during the modification step, causing a decreased long-term P removal capacity. The XRD results showed that the high P removal ability of AOD and EAF was attributed to the dissolution of beta dicalcium silicate (β-C2) and gamma dicalcium silicate (γ-C2S), which were dominant mineral phases in the slags. Results from SEM-EDS analysis revealed significant P accumulation on the slag surface. Cracks on the EAF slag surface contributed to its longer lifespan. Analysis with P K-edge XANES spectroscopy showed that the P retained on the slag surface was dominated by amorphous calcium phosphate, with a substantial amount of carbonate apatite (around 30%). Amorphous calcium phosphate was transformed to crystalline apatite as the slag aged with column operating time.

Mn-bearing eleonorite from Hagendorf South pegmatite, Germany: crystal structure and crystal-chemical relationships with other beraunite-type phosphates

Abstract 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 R 1=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.

Chromium(VI) removal by siderite (FeCO3) in anoxic aqueous solutions: An X-ray absorption spectroscopy investigation

Chromium(VI) is an environmental contaminant of priority concern, which can be treated by reduction of toxic Cr(VI) to non-toxic Cr(III). Siderite (FeCO3), an Fe(II)-containing mineral, occurs in many anaerobic sediments and groundwater systems and is extremely reactive, thus making it a potentially important host-phase in governing the fate and transport of Cr(VI) in a range of anoxic aqueous environments. Here, we investigate the fate of Cr(VI) during sorption and reduction by siderite, as well as speciation of Cr(VI)-reacted siderite as a function of varying pH (4–10) and initial Cr(VI) concentrations (0.5–10 mM) under strictly oxygen-free conditions. Notably, up to 97% and 91% of initial added aqueous Cr(VI) (0.5–10 mM) was reduced to Cr(III) at pH 4 and 5, respectively. However, the reduction efficiency of Cr(VI) by siderite slightly decreased in the pH range from 6 to 10 (~90% Cr(III)), only at 0.5–1.5 mM initial Cr(VI) concentrations. Chromium K-edge XANES spectroscopy confirmed the complete reduction of sorbed Cr(VI) to Cr(III) after equilibration of siderite with low (2 mM) and high (10 mM) initial Cr(VI) concentrations at pH 5, 7 and 9. In addition, Fe K-edge XANES and EXAFS spectra of solid-phase samples showed that 74–78% and 78–89% of Fe remained as siderite, respectively, after equilibration with Cr(VI) at pH 7 and 9, whereas only 24% remained for the low Cr(VI) treatment at pH 5. The results imply that under anoxic aqueous conditions, siderite can help immobilize and detoxify Cr(VI) with the extent of these coupled sorption and redox reactions being controlled by initial Cr(VI) concentrations and pH.

Investigating the surface electronic structures of retired components and irradiated KDP crystals with different fluences by XANES spectroscopy

The electronic structure of phosphorus is essential to the understanding of the laser-induced damage of potassium dihydrogen phosphate (KDP) crystals. The surface electronic structure of retired components and KDP crystals irradiated with different fluences are studied by X-ray absorption near-edge structure. Results indicate that the A/C ratios (the peaks A and C corresponding to the electron transition from 2p→3s and 2p→3p, respectively) in the L2,3-edge spectra are up to 0.9 for the retired samples, and the damage is inhomogeneous on the surface. Furthermore, the electronic structure of phosphorus is associated with laser induced damage.

Phosphorus speciation in a prairie soil amended with MBM and DDG ash: Sequential chemical extraction and synchrotron-based XANES spectroscopy investigations

Sequential chemical extraction and synchrotron-based XANES spectroscopy techniques were used to identify P species in two ashes before and after addition to a prairie soil. The used ashes were: meat and bone meal ash (MBMA) and dried distillers grains ash (DDGA) plus mineral P fertilizer (MP) for comparison. Soil treated with MP contained higher content of resin-Pi and NaHCO3-Pi followed by DDGA and MBMA. The MBMA amended soil had the highest (47%) proportion of the soil P contained in recalcitrant HCl extractable fraction, reflecting more Ca-bound P present and being formed in soil after application. Analysis of both ashes with XANES spectroscopy before application to soil revealed that MBMA had strong spectral features consistent with hydroxyapatite (Ca5(PO4)3(OH)). DDGA exhibited spectral features consistent with a mixture of several Mg and K phosphate salts rather than a single mineral species. The distinctive features in the XANES spectra of both ashes largely disappeared after amendment to the soil, suggesting transformation to different P forms in the soil after application. It is also possible that the added amount of P to the studied soil via DDGS or MBMA was small enough so that P speciation is not different from the background P level.

Phosphorus speciation in a long-term manure-amended soil profile – Evidence from wet chemical extraction, 31P-NMR and P K-edge XANES spectroscopy

Long-term application of manure can lead to an enrichment of phosphorus (P) in agricultural soils. To which extent this P leaches into drainage systems and thereby potentially contributing to eutrophication of surface waters, depends on the distribution and speciation of P present in the soil. In this study the P speciation and related soil characteristics were investigated for a sandy loam soil that had been receiving manure for >40 years. A combination of solution-state 31P-NMR, P K-edge XANES and wet chemical extractions was applied.Topsoil P contents were with 42 mmol kg−1 more than twice as high as in the sub soil (14–18 mmol kg−1). Linear combination fitting (LCF) of P K-edge XANES spectra indicated that P accumulation in the topsoil occurred predominantly via adsorption of inorganic P to Fe/Al hydroxide surfaces, resulting in substantial P saturation of these mineral phases. Up to 76% of the topsoil P was associated with Al or Fe. The organic P content was low (5–10%), but an additional important topsoil P pool identified with XANES-LCF was amorphous calcium phosphate (30%), which may have been added with manure or formed in situ. Towards the deeper subsoil the relative portion of primary apatite increased progressively and reached 80% of total P at a depth of 70 to 80 cm. These results highlight the importance of Fe and Al mineral phases for P retention in long-term manure-amended soils also under non-acidic conditions.

Zincovelesite-6N6S, Zn3(Fe3+,Mn3+,Al,Ti)8O15(OH), a new högbomite-supergroup mineral from Jacupica mountains, Republic of Macedonia

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, hydroxycalcioromeite, 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 Mossbauer 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) A, c = 55.86(1) A, V = 1684.8(9) A3, Z = 6. The strongest lines of the powder X-ray diffraction pattern [d, A (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 hogbomite 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.

Phosphorus Speciation and Solubility in Aeolian Dust Deposited in the Interior American West.

Aeolian dust is a significant source of phosphorus (P) to alpine oligotrophic lakes, but P speciation in dust and source sediments and its release kinetics to lake water remain unknown. Phosphorus K-edge XANES spectroscopy shows that calcium-bound P (Ca-P) is dominant in 10 of 12 dust samples (41-74%) deposited on snow in the central Rocky Mountains and all 42 source sediment samples (the fine fraction) (68-80%), with a lower proportion in dust probably because acidic snowmelt dissolves some Ca-P in dust before collection. Iron-bound P (Fe-P, ∼54%) dominates in the remaining two dust samples. Chemical extractions (SEDEX) on these samples provide inaccurate results because of unselective extraction of targeted species and artifacts introduced by the extractions. Dust releases increasingly more P in synthetic lake water within 6-72 h thanks to dissolution of Ca-P, but dust release of P declines afterward due to back adsorption of P onto Fe oxides present in the dust. The back sorption is stronger for the dust with a lower degree of P saturation determined by oxalate extraction. This work suggests that P speciation, poorly crystalline minerals in the dust, and lake acidification all affect the availability and fate of dust-borne P in lakes.

Vanadium, sulfur, and iron valences in melt inclusions as a window into magmatic processes: A case study at Nyamuragira volcano, Africa

This study describes microscale sulfur (S), vanadium (V), and iron (Fe) K-edge X-ray absorption near edge structure (µ-XANES) spectroscopy measurements on olivine-hosted melt inclusions (MI) preserved in tephras (1986 and 2006) and lavas (1938 and 1948) erupted from Nyamuragira volcano (D.R. Congo, Africa). The S, V, and Fe spectroscopic data are used to constrain the evolution of oxygen fugacity (fO2) and sulfur speciation for the entrapped melts. Melt inclusions from lavas show evidence of post-entrapment crystallization and were thus reheated prior to µ-XANES analysis. The MI from tephra show no evidence of post-entrapment crystallization and were, therefore, not reheated. Sulfur, V, and Fe µ-XANES results from 1938, 1948, and 2006 eruptive materials are all similar within analytical uncertainty and provide similar average calculated melt fO2’s based on XANES oxybarometry. However, olivine-hosted MI from the 1986 tephras yield significantly different S, V, and Fe XANES spectra when compared to MI from the other eruptions, with disagreement between calculated fO2’s from the three valence state oxybarometers beyond the uncertainty of the calibration models. Their V µ-XANES spectra are also significantly more ordered and yield more reduced average V valence. The S µ-XANES spectra display a significantly more intense low-energy spectral resonance, which indicates differences in Fe-S bonding character, and greater variability in their measured sulfate content. These V and S spectroscopic features are best explained by crystallization of sub-micrometer magnetite and sulfide crystallites within the 1986 inclusions. The sensitivity of XANES spectroscopy to short-range order allows these crystallites to be recognized even though they are not easily detected by imaging analysis. This shows that V and S µ-XANES are potentially highly sensitive tools for identifying the presence of volumetrically minor amounts of spinel and sulfide within inclusions extracted from rapidly-cooled samples of tephra. Additionally, the observation that rehomogenized 1938 and 1948 inclusions from lava yield similar S, V, and Fe XANES spectra to the 2006 inclusions from tephra may be an encouraging indication that rehomogenization appears to have enabled the successful recovery of their pre-eruptive fO2, despite their complex post-eruptive histories.

Effects of Mineral Compositions on Matrix Diffusion and Sorption of 75Se(IV) in Granite.

Exploring the migration behaviors of selenium in granite is critical for the safe disposal of radioactive waste. The matrix diffusion and sorption of 75Se(IV) (analogue for 79Se) in granite were systematically studied to set reliable parameters in this work. Through-diffusion and batch sorption experiments were conduct with four types of Beishan granite. The magnitudes of the obtained apparent diffusion coefficient (Da) values are of the following order: monzogranite > granodiorite-2 > granodiorite-1, which is opposite to the sequence of the Kd values obtained from both the diffusion model and batch sorption experiments. The EPMA results of the granitic flakes showed that there was no obvious enrichment of Se(IV) on quartz, microcline and albite. Only biotite showed a weak affinity for Se(IV). Macroscopic sorption behaviors of Se(IV) on the four types of granite were identical with the sequence of the granitic biotite contents. Quantitative fitting results were also provided. XPS and XANES spectroscopy data revealed that bidentate inner-sphere complexes were formed between Se(IV) and Fe(III). Our results indicate that biotite can be representative of the Se(IV) sorption in complex mineral assemblages such as granite, and the biotite contents are critically important to evaluate Se(IV) transport in granite.

Chemical state changes of Nafion in model polymer electrolyte fuel cell under oxygen/hydrogen gas atmosphere observed by S-K XANES spectroscopy.

Changes in the chemical states of the sulfonic groups of Nafion in a model polymer electrolyte fuel cell under an oxygen/hydrogen gas atmosphere were studied using sulfur K-edge XANES spectroscopy. First, the chemical state changes in the sulfonic acid groups of both cathode and anode electrodes due to humidity under oxygen/hydrogen gas flow were observed. Reversible spectral changes ascribed to the hydration and dehydration of the sulfonic acid group were observed at both electrodes. This result is similar to the experimental results obtained without introducing oxygen (helium/hydrogen). On the anode, some of the sulfonic acid groups were decomposed to atomic sulfur adsorbed on platinum (Sad) and the amount increased with time. On the cathode, the formation of Sad was suppressed under the oxygen atmosphere. Next, the effects of oxygen gas introduction onto Sad were examined. Sad was at once formed on both electrodes under dry conditions without an oxygen supply. By supplying oxygen gas, Sad on the cathode disappears. Therefore, the catalyst of the cathode has the ability to recover against the poisoning Sad, while that on the anode accumulates.

X-ray spectroscopic analysis of stochastic, periodic precipitation in Co–Fe-Based Prussian blue analogues

Stochastic, ripening-induced, periodic precipitation of Co–Fe-based Prussian blue analogues in water-glass gels was analyzed by XRF and XANES spectroscopies.

Probing hydrogen bonding interactions and impurity intercalation in gibbsite using experimental and theoretical XANES spectroscopy.

The Al and O K-edge XANES spectra of Bayer process gibbsite are examined, both experimentally and with plane wave density functional theory, and transition assignments are made. We confirm that the broad transitions in Al K-edge spectra are fundamentally the same as those in more ordered and well-studied corundum, and typical of octahedrally coordinated aluminium. Analysis of O K-edge spectra reveals that while much of the initial edge transition structure (535-548 eV) is due to O 2p hybridization with Al orbitals, the lowest energy region (∼535-539 eV) is particularly influenced by O-H states which are heavily perturbed by hydrogen bonding interactions. We therefore tentatively suggest that an unexplained structure at 539 eV in O K-edge spectra of corundum may be due to surface hydroxylation. Finally, we examined Na K-edge spectra, as sodium is the major impurity in these materials and implicated in perturbation of the evolution of materials properties with calcination through the transition aluminas. Density functional theory calculations find sodium replacement of in-sheet H-atoms is the most thermodynamically stable site for sodium inclusion. We subsequently confirm this assignment spectroscopically, explicitly demonstrating the precise location of Na+ impurities for the first time.

Диагностика 3D локальной атомной структуры наноструктурированных материалов на основе спектроскопии XANES

Диагностика 3D локальной атомной структуры наноструктурированных материалов на основе спектроскопии XANES

A re-assessment of the oxidation state of iron in MORB glasses

The oxidation state of Fe, Fe/3+ΣFe (where ΣFe=Fe2++Fe3+), in glass samples of mid-ocean ridge basalt (MORB), from a wide range of localities, was determined by XANES spectroscopy to be 0.10(2) (n=42). This value is lower than that reported previously by XANES, 0.16(1) (n=103), but consistent with the most recent value determined by redox titrations, 0.11(2) (n=104), all for similar sets of samples. We attribute the anomalously high XANES value of 0.16 to a calibration error resulting from the interpretation of Mössbauer spectra and the resulting Fe/3+ΣFe values of the standards. Our alternative interpretation removes the problem of resolving Fe/3+ΣFe values <∼0.1 in basaltic glasses, produces isomer shift and quadrupole splitting values for Fe3+ that are independent of Fe3+/ΣFe (as is the case for Fe2+), and gives Fe/3+ΣFe values that are consistent with the thermodynamically expected dependence on oxygen fugacity (fO2). Fe/3+Fe2+ is related to fO2 for our synthetic MORB composition by the temperature independent expression ΔQFM=4log⁡(Fe3+/Fe2+)+4.23(5), where ΔQFM is the fO2 in log units relative to the quartz–fayalite–magnetite buffer. The average fO2 of natural MORB was estimated to be QFM+0.1.

Application of XANES spectroscopy to investigate Sb species in corroded bullets crust material oriented to evaluate the potential toxic effects in the environment

Lead, antimony, and other toxic metals from pellets alloy are dispersed in the soil of the shooting fields. As long as the corroding bullets are present in soil, secondary Pb and Sb phases appear in the weathering crusts being an important source of bioavailable Pb and Sb. Knowledge about the corrosion mechanism of Sb from the bullet is limited, and reports on Sb speciation in crust and soils are still scarce. Considering that Sb species have different toxicological properties in the environment, this work has focused attention in X‐ray Absorption Near Edge Structure measurements at the Sb L‐edges in order to identify its chemical speciation in crust (Sb(0), Sb(III), and Sb(V)).X‐ray Absorption Near Edge Structure measurements were carried out at the D04A Soft X‐ray Spectroscopy beamline at the LNLS. Samples consisted of dust crust taken from physically deformed and strongly corroded metallic bullets retained in soil samples sieving from shooting fields of the North and East region of Córdoba, Argentina.The results showed that the main species found in all samples were Sb(V)(Sb2O5) followed by Sb(0) (metallic). Sb(III) was not observed, and it is known that Sb(III) is more toxic than Sb(V). The results suggested that in these environmental conditions, pentavalent Sb was the predominant species after weathering of metallic Sb from corroding bullets.

Nickel(II) complexes with cytosine and threonine: Synthesis and structure

Mono-and mixed-ligand complexes with the composition [Ni(Cyt)2(H2O)2]Cl2, [Ni(Thr–)2(H2O)2] and [Ni(Thr–)(Cyt)(H2O)2]Cl are synthesized and studied. Using IR spectroscopy it is determined that in the complex compounds, cytosine is bidentate (C=O group oxygen and heterocycle N3), threonine interacts with the Ni(II) ion due to amino and carboxyl groups. The models of the atomic structure of the studied compounds are proposed based on the EXAFS and XANES spectroscopy results.