•In the series CaCoSinO2n+2 there are no phases with n = 3 and n = 4, despite their similarity to copper based materials,•the chemical shifts of the XPS lines and Si K absorption edges indicates that ...Si has weaker cationic character than in SiO2 despite the same chemical environment,•DFT calculations allowed to interpret spectroscopic data.
In a public space there are several reports of materials with general stoichiometry CaCoSinO2n+2. Pyroxene CaCoSi2O6 is probably the best-known representative for n = 2 but not much is known about materials with n = 3 and n = 4. In this study, attempts were carried out to synthesize those phantom materials and it was found that they do not exist as a single phase. A quantitative XRD analysis revealed that their chemical composition is correct but the formula should be written as CaCoSi2O6 + (n-2)SiO2. Similar qualitative conclusions were drawn from investigation of magnetic (DC magnetometry) and electronic properties using X-ray Photoelectron Spectroscopy (XPS) and Si K edge X-ray Absorption Spectroscopy (XAS). Additionally, the DFT ab initio calculations were carried out to obtain electronic signature from band structure of CaCoSi2O6.
The apparent influence of the excess of SiO2 on magnetic properties of this “series” can be understood in terms of presence and suppression of secondary phases like Ca2CoSi2O7, which form when the starting materials are not homogenized properly. Addition of surplus SiO2 suppresses their formation leaving clear signature from CaCoSi2O6, which also can be synthesized from stoichiometric mixture using proper techniques.
Urban development within watersheds impacts the hydrology and water quality of streams, but changes to groundwater–surface water interactions in this “urban stream syndrome” are not yet well ...understood. This study focused on three stream systems in a northern Virginia (USA) protected area with 14.2, 31.7, and 66.1% developed land in their watersheds. Surface water was sampled weekly for nutrients, dissolved metals, sulfate, ancillary water quality parameters, and discharge over two non-consecutive years with the hyporheic zone sampled during the second year. Concentration–discharge relationships revealed largely chemostatic behavior in surface water solutes in the least urbanized stream, while in the two more urbanized streams, these relationships tended to have significant positive and negative slopes, indicating diverse delivery pathways depending on the constituent. In the least urbanized stream, linear regressions between discharge and solute concentrations in hyporheic water had exclusively negative slopes, indicating source-limited delivery, while the other two urbanized streams maintained largely chemostatic behavior. Average specific conductance and nitrate + nitrite concentrations in stream surface water reflected an urbanization gradient, while sulfate, Ca, K and Sr concentrations suggested a threshold effect: the stream with a mostly forested watershed had the lowest concentrations, while the other two were higher and similar. Specific conductance indicated salinization of both surface and groundwater at the two more urban streams, possibly threatening aquatic organisms. Metal concentrations in surface and subsurface water were often positively correlated with specific conductance and negatively correlated with pH, suggesting that they may originate from road salt and/or be mobilized by acid precipitation. These results indicate the importance of monitoring both baseflow and stormflow as pathways for pollution.
The detection module of the ARDESIA spectrometer, an SDD-based, multichannel X-ray detector is presented. The detector design and experimental characterization are discussed. ARDESIA has been ...optimized for synchrotron radiation applications that require high-rate (>1-Mcps per channel) and high-resolution (better than 200 eV at 6 keV) X-ray detection. The main target applications considered in this development are X-ray fluorescence and X-ray absorption fine structure spectroscopy, in particular for the DAFNE-Light DXR1 beamline at LNF (Frascati, Italy). This detector is based on a compact unit (16 mm <inline-formula> <tex-math notation="LaTeX">\times16 </tex-math></inline-formula> mm) that can be replicated and juxtaposed with several units, thus easily covering different detection configurations. The detector consists of a four-channel monolithic array of SDDs, produced by Fondazione Bruno Kessler (Trento, Italy) connected to a four-channel monolithic CUBE preamplifier mounted on the same carrier. The CUBE preamplifier, compatible with both analog and digital pulse processing, enables reaching high count rates (1-Mcps per channel), while keeping good spectroscopic performances. It is extremely low white series noise guarantees good energy resolution, even at short pulse processing times (below 200 ns).
A proposal for building a new Free Electron Laser facility at the Laboratori Nazionali di Frascati, EuPRAXIA@SPARC_LAB, is at present under consideration. This FEL facility will exploit plasma ...acceleration to produce ultra-bright photon pulses with durations of few femtoseconds down to the wavelengths between 2 and 4 nm, in the so called "water window". The main class of experiments to be performed will include coherent diffraction imaging, soft X-ray absorption spectroscopy, Raman and photofragmentation measurements. In this article we present the updates on the photon beamlines design for the facility.
Wetlands provide essential ecosystem services, including nutrient cycling, flood protection, and biodiversity support, that are sensitive to changes in wetland hydrology. Wetland hydrological inputs ...come from precipitation, groundwater discharge, and surface run-off. Changes to these inputs via climate variation, groundwater extraction, and land development may alter the timing and magnitude of wetland inundation. Here, we use a long-term (14-year) comparative study of 152 depressional wetlands in west-central Florida to identify sources of variation in wetland inundation during two key time periods, 2005–2009 and 2010–2018. These time periods are separated by the enactment of water conservation policies in 2009, which included regional reductions in groundwater extraction. We investigated the response of wetland inundation to the interactive effects of precipitation, groundwater extraction, surrounding land development, basin geomorphology, and wetland vegetation class. Results show that water levels were lower and hydroperiods were shorter in wetlands of all vegetation classes during the first (2005–2009) time period, which corresponded with low rainfall conditions and high rates of groundwater extraction. Under water conservation policies enacted in the second (2010–2018) time period, median wetland water depths increased 1.35 m and median hydroperiods increased from 46 % to 83 %. Water-level variation was additionally less sensitive to groundwater extraction. The increase in inundation differed among vegetation classes with some wetlands not displaying signs of hydrological recovery. After accounting for effects of several explanatory factors, inundation still varied considerably among wetlands, suggesting a diversity of hydrological regimes, and thus ecological function, among individual wetlands across the landscape. Policies seeking to balance human water demand with the preservation of depressional wetlands would benefit by recognizing the heightened sensitivity of wetland inundation to groundwater extraction during periods of low precipitation.
•We measured wetland inundation as a function of social and environmental variables.•Inundation was lowest in periods of high groundwater extraction and low rainfall.•Water conservation policies increased the duration and magnitude of inundation.•Inundation varied among vegetation classes with some not showing signs of recovery.•Wetlandscapes support diverse hydrological regimes in the absence of water stress.
•The Si K and Pd L3 edges of R2PdSi3 (R=Ce, Nd, Tb, Dy, Ho, Er) and HoRh2−xPdxSi2 are reported.•The R–Si bonds possess polar and 4d5s bands of Pd and Rh metallic characters.•There is no indication of ...Ce having a different valence than the other rare earths.•The positions and features of the calculated edges exhibit a fair agreement up to ≈10eV.•The supercell used for Ho2PdSi3 is good enough to reproduce the Si K edge.
We report on the investigation of Si and Pd/Rh chemical environments using X-ray Absorption Near Edge Spectroscopy in two different families of rare earth silicides R2PdSi3 (R=Ce, Nd, Tb, Dy, Ho, Er) and HoRh2−xPdxSi2 (x=0, 0.5, 0.75, 1.0, 1.5, 1.8, 2.0). The Si K, Pd L3 and Rh L3 absorption edges were recorded in order to follow their changes upon the variation of 4f and 4d5s electron numbers. In both cases it was found that the Si K edge was shifted ≈0.5eV toward lower energies, relative to pure silicon. In the first family, the shift decreases with increasing number of f-electrons, while the Si K edge remains constant upon rhodium–palladium substitution.
In all cases the Pd L3 edge was shifted to higher energies relative to metallic Pd. No visible change in the Pd L3 position was observed either with a varying 4f electron count or upon Pd/Rh substitution. Also, the Rh L3 edge did not change.
For two selected members, Ho2PdSi3 and HoPd2Si2, the Wien2K’09 (LDA+U) package was used to calculate the electronic structure and the absorption edges. Si K edges were reproduced well for both compounds, while Pd L3 only exhibited a fair agreement for the second compound. This discrepancy between the Pd L3 theory and experiment for the Ho2PdSi3 sample can be attributed to the specific ordered superstructure used in the numerical calculations.
The observed changes indicate that despite possessing a formal inter-metallic character, the chemical bond between the R–Si and R–Pd interactions are different. The variation and the direction of the chemical shift of the Si K edge suggests a weak ionic character of the R–Si bonds, in agreement with the localized character of the 4f electrons. In turn, the changes of the Pd/Rh edge are consistent with a metallic band that is affected by its long range chemical environment.
Y-doped barium cerate protonic conductors with composition BaCe1-xYxO3-delta (x=0.0,0.,0.,0.3) have been synthesized by sol-gel route, giving by X-ray diffraction tests a homogeneous crystalline ...phase. A commercial sample BaCe0.8Y0.2O3-delta produced by combustion spray pyrolysis was also provided for comparison aim. The local structure around the cations was studied by X-ray absorption spectroscopy at the K-edges of Ba, Ce and Y. It is demonstrated that the insertion of yttrium in the site of cerium produces a remarkable local distortion of the dopant first-shell octahedral environment that affects also the next coordination shells by a static disorder increasing with dopant amount. For a dopant concentration estimated as x > 0.17, a poorly crystallized yttrium oxide phase that cannot be detected by X-ray diffraction is segregated. The static disorder around Y noticeably increases in the protonated samples and can be related to a preferential location of protons near the dopant.
Gold metallodrugs form a class of promising antiproliferative agents showing a high propensity to react with proteins. We exploit here X-ray absorption spectroscopy (XAS) methods both X-ray ...absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) to gain insight into the nature of the adducts formed between three representative gold(I, III) metallodrugs (i.e., auranofin, Au(2,2′-bipyridine)(OH)₂(PF₆), Aubipy, and dinuclear Au₂(6,6′-dimethyl-2,2′-bipyridine)₂(μ-O)₂(PF₆)₂, Auoxo6) and two major plasma proteins, namely, bovine serum albumin (BSA) and human serum apotransferrin (apoTf). The following metallodrug-protein systems were investigated in depth: auranofin/apoTf, Aubipy/BSA, and Auoxo6/apoTf. XANES spectra revealed that auranofin, upon protein binding, conserves its gold(I) oxidation state. Protein binding most probably takes place through release of the thiosugar ligand and its subsequent replacement by a thiol (or a thioether) from the protein. This hypothesis is independently supported by EXAFS results. In contrast, the reactions of Aubipy with serum albumin and of Auoxo6 with serum apoTf invariantly result in gold(III) to gold(I) reduction. Gold(III) reduction, clearly documented by XANES, is accompanied, in both cases, by release of the bipyridyl ligands; for Auoxo6 cleavage of the gold-gold dioxo bridge is also observed. Gold(III) reduction leads to formation of protein-bound gold(I) species, with deeply modified metal coordination environments, as evidenced by EXAFS. In these adducts, the gold(I) centers are probably anchored to the protein through nitrogen donors. In general, these two XAS methods, i.e., XANES and EXAFS, used here jointly, allowed us to gain independent structural information on metallodrug/protein systems; detailed insight into the gold oxidation state and the local environment of protein-bound metal atoms was achieved in the various cases.
Using an innovative procedure known as metal vapor synthesis (MVS) to prepare bimetallic catalysts, starting from Au and Pd vapors, AuPd co-evaporated and AuPd separately evaporated bimetallic ...catalysts were achieved. After being tested, the catalytic activity and selectivity of the AuPd catalyst turned out to be higher than the AuPd ones. Using EXAFS spectroscopy it was shown that, in the AuPd samples, small bimetallic AuPd nanoparticles were present, having an Au rich core surrounded by an AuPd alloyed shell while in the AuPd sample there was the presence of monometallic Au and Pd nanoparticles showing some alloying only in the boundary regions. The EXAFS results were also qualitatively confirmed by the XANES spectra.
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