Low-oxidation-state Ru sites stabilized in carbon-doped RuO2 with low-temperature CO2 activation to yield methane.

The generation of methane fuel using surplus renewable energy with CO2 as the carbon source enables both the decarbonization and substitution of fossil fuel feedstocks. However, high temperatures are usually required for the efficient activation of CO2. Here we present a solid catalyst synthesized using a mild, green hydrothermal synthesis that involves interstitial carbon doped into ruthenium oxide, which enables the stabilization of Ru cations in a low oxidation state and a ruthenium oxycarbonate phase to form. The catalyst shows an activity and selectivity for the conversion of CO2 into methane at lower temperatures than those of conventional catalysts, with an excellent long-term stability. Furthermore, this catalyst is able to operate under intermittent power supply conditions, which couples very well with electricity production systems based on renewable energies. The structure of the catalyst and the nature of the ruthenium species were acutely characterized by combining advanced imaging and spectroscopic tools at the macro and atomic scales, which highlighted the low-oxidation-state Ru sites (Run+, 0 < n < 4) as responsible for the high catalytic activity. This catalyst suggests alternative perspectives for materials design using interstitial dopants.

Li iontronics in single-crystalline T-Nb2O5 thin films with vertical ionic transport channels.

The niobium oxide polymorph T-Nb2O5 has been extensively investigated in its bulk form especially for applications in fast-charging batteries and electrochemical (pseudo)capacitors. Its crystal structure, which has two-dimensional (2D) layers with very low steric hindrance, allows for fast Li-ion migration. However, since its discovery in 1941, the growth of single-crystalline thin films and its electronic applications have not yet been realized, probably due to its large orthorhombic unit cell along with the existence of many polymorphs. Here we demonstrate the epitaxial growth of single-crystalline T-Nb2O5 thin films, critically with the ionic transport channels oriented perpendicular to the film's surface. These vertical 2D channels enable fast Li-ion migration, which we show gives rise to a colossal insulator-metal transition, where the resistivity drops by 11 orders of magnitude due to the population of the initially empty Nb 4d0 states by electrons. Moreover, we reveal multiple unexplored phase transitions with distinct crystal and electronic structures over a wide range of Li-ion concentrations by comprehensive in situ experiments and theoretical calculations, which allow for the reversible and repeatable manipulation of these phases and their distinct electronic properties. This work paves the way for the exploration of novel thin films with ionic channels and their potential applications.

Investigating the local structure of Ti based MXene materials by temperature dependent X-ray absorption spectroscopy.

The local structures of Ti based MXene-type electrode materials have been studied by Ti K-edge X-ray absorption fine structure measurements as a function of temperature to obtain direct information on the local bond lengths and their stiffness. In particular, the parent MAX phases Ti2AlC and Ti3AlC2 and their etched MXene systems are characterized and their properties compared. We find that selective etching has a substantial effect on the local structural properties of the Ti based MXene materials. It leads to an increase in the interatomic distances, i.e. a decrease in the covalency, and corresponding bond stiffness, that is a likely cause of higher achievable performances. The obtained results underline the importance of the local atomic correlations as limiting factors in the diffusion capacity of ion batteries.

Opportunities and challenges of applying advanced X-ray spectroscopy to actinide and lanthanide N-donor ligand systems.

N-donor ligands such as n-Pr-BTP [2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine] preferentially bind trivalent actinides (An3+) over trivalent lanthanides (Ln3+) in liquid-liquid separation. However, the chemical and physical processes responsible for this selectivity are not yet well understood. Here, an explorative comparative X-ray spectroscopy and computational (L3-edge) study for the An/Ln L3-edge and the N K-edge of [An/Ln(n-Pr-BTP)3](NO3)3, [Ln(n-Pr-BTP)3](CF3SO3)3 and [Ln(n-Pr-BTP)3](ClO4)3 complexes is presented. High-resolution X-ray absorption near-edge structure (HR-XANES) L3-edge data reveal additional features in the pre- and post-edge range of the spectra that are investigated using the quantum chemical codes FEFF and FDMNES. X-ray Raman spectroscopy studies demonstrate the applicability of this novel technique for investigations of liquid samples of partitioning systems at the N K-edge.

Lix(C5H5N)yFe2-zSe2: A Defect-Resilient Expanded-Lattice High-Temperature Superconductor.

Two-dimensional iron chalcogenide intercalates display a remarkable correlation of the interlayer spacing with enhancement of the superconducting critical temperature (Tc). In this work, synchrotron X-ray absorption (XAS; at the Fe and Se K-edges) and emission (XES; at the Fe Κß) spectroscopies allow one to discuss how the important rise of Tc (∼44 K) in the molecule-intercalated Lix(C5H5N)yFe2-zSe2 relates to the electronic and local structural changes felt by the inorganic host upon doping (x). XES shows that widely separated layers of edge-sharing FeSe4 tetrahedra carry low-spin moieties, with a local Fe magnetic moment slightly reduced compared to the parent ß-Fe2-zSe2. Pre-edge XAS expresses the progressively reduced mixing of metal 3d-4p states upon lithiation. Doping-mediated local lattice modifications, probed by conventional Tc optimization measures (cf. the anion height and FeSe4 tetrahedra regularity), become less relevant when layers are spaced far away. On the basis of extended X-ray absorption fine structure, such distortions are compensated by a softer Fe network that relates to Fe-site vacancies, alleviating electron-lattice correlations and superconductivity. Density functional theory (DFT) guided modification of the isolated Fe2-zSe2 (z, vacant sites) planes, resembling the host layers, identify that Fe-site deficiency occurs at low energy cost, giving rise to stretched Fe sheets, in accordance with experiments. The robust high-Tc in Lix(C5H5N)yFe2-zSe2, arises from the interplay of electron-donating spacers and the iron selenide layer's tolerance to defect chemistry, a tool to favorably tune its Fermi surface properties.

Redox Interaction between Selenite and Mackinawite in Cement Pore Water.

In cement-rich radioactive waste repositories, mackinawite (FeS) forms at the steel corrosion interface within reinforced concrete and potentially retards the transport of redox-sensitive radionuclides (e.g., 79Se) in porous cement media. Redox interactions between selenite and mackinawite under hyperalkaline conditions remain unclear and require further investigations. Here, using comprehensive characterization on both aqueous and solid speciation, we successfully monitored the whole interaction process between selenite and mackinawite under hyperalkaline conditions. The results show similar chemical environments for SeO32- and S2-/Sn2- at the mackinawite-water interface, verifying an immediate reduction. After 192 h of reaction, SeO32- was reduced to solid Se0 and SeS2 species, accompanied by the oxidation of S2-/Sn2- to S2O32- and Fe(II) to Fe(III) in mackinawite. Aqueous speciation results showed that ∼99% of aqueous selenium was present as Se4S nanoparticles due to the dissolution of Se from the solid. In parallel, ∼62% of S2-/Sn2- was released into the solution, with mackinawite transforming into magnetite, Fe(OH)3 and FeS2O3+ complexed to Cl- or OH- species, and magnetite subsequently dispersed in the solution. This study provides valuable data about the retardation mechanisms of redox-sensitive radionuclides by soluble iron sulfides, which is critical to advance our understanding of reactive concrete barriers used in nuclear waste disposal systems.

Decoupling the adsorption mechanisms of arsenate at molecular level on modified cube-shaped sponge loaded superparamagnetic iron oxide nanoparticles.

In this study, a commercial cube-shaped open-celled cellulose sponge adsorbent was modified by in-situ co-precipitation of superparamagnetic iron oxide nanoparticles (SPION) and used to remove As(V) from aqueous solutions. Fe K-edge X-ray absorption spectroscopy (XAS) and TEM identified maghemite as the main iron phase of the SPION nanoparticles with an average size 13 nm. Batch adsorption experiments at 800 mg/L showed a 63% increase of adsorption capacity when loading 2.6 wt.% mass fraction of SPION in the cube-sponge. Experimental determination of the adsorption thermodynamic parameters indicated that the As(V) adsorption on the composite material is a spontaneous and exothermic process. As K-edge XAS results confirmed that the adsorption enhancement on the composite can be attributed to the nanoparticles loaded. In addition, adsorbed As(V) did not get reduced to more toxic As(III) and formed a binuclear corner-sharing complex with SPION. The advantageous cube-shape of the sponge-loaded SPION composite together with its high affinity and good adsorption capacity for As(V), good regeneration capability and the enhanced-diffusion attributed to its open-celled structure make this adsorbent a good candidate for industrial applications.

MAP2XANES: a Jupyter interactive notebook for elemental mapping and XANES speciation.

MAP2XANES is an intuitive Jupyter notebook that automatizes the analysis of synchrotron X-ray fluorescence imaging and X-ray absorption spectroscopy for the characterization of complex and heterogeneous samples. The notebook uses basic modules and functions from Numpy, Scipy, Pandas, iPywidgets and Matplotlib libraries for a powerful data reduction process that, in just a few clicks, guides the user through the visualization of elemental maps, space-resolved absorption spectra and their automatized analysis. In particular, by means of linear combination fit of the XANES spectra, the notebook determines the chemical species distribution in the sample under investigation. The direct output of the analysis process is the correlation between the different elemental distributions and the spatial localization of the chemical species detected. An application to mineralogy is thus presented, analyzing the Mn2+, Mn3+ and Mn4+ distribution in a mineral sample of hausmannite (Mn2+Mn23+O4), courtesy of the Museum of Natural Science of Barcelona.

Influence of Silica Coatings on Magnetite-Catalyzed Selenium Reduction.

The reactivity of iron(II/III) oxide surfaces may be influenced by their interaction with silica, which is ubiquitous in aquatic systems. Understanding the structure-reactivity relationships of Si-coated mineral surfaces is necessary to describe the complex surface behavior of nanoscale iron oxides. Here, we use Si-adsorption isotherms and Fourier transform infrared spectroscopy to analyze the sorption and polymerization of silica on slightly oxidized magnetite nanoparticles (15% maghemite and 85% magnetite, i.e., ∼2 maghemite surface layers), showing that Si adsorption follows a Langmuir isotherm up to 2 mM dissolved Si, where surface polymerization occurs. Furthermore, the effects of silica surface coatings on the redox-catalytic ability of magnetite are analyzed using selenium as a molecular probe. The results show that for partially oxidized nanoparticles and even under different Si surface coverages, electron transfer is still occurring. The results indicate anion exchange between silicate and the sorbed SeIV and SeVI. X-ray absorption near-edge structure analyses of the reacted Se indicate the formation of a mixed selenite/Se0 surface phase. We conclude that neither partial oxidation nor silica surface coatings block the sorption and redox-catalytic properties of magnetite nanoparticles, a result with important implications to assess the reactivity of mixed-valence phases in environmental settings.

The rise of X-ray spectroscopies for unveiling the functional mechanisms in batteries.

Synchrotron-based techniques have been key tools in the discovery, understanding, and development of battery materials. In this review, some of the most suitable X-ray spectroscopy related techniques employed for addressing diverse scientific cases connected to battery science are highlighted. Furthermore, current shortcomings, intrinsic limitations, and ongoing challenges of individual techniques are pointed out, providing an outlook of future trends that are relevant to the battery research community. In particular, the ongoing development of next generation synchrotrons, machine learning algorithms for data analysis and combined theoretical/experimental approaches will enhance the already powerful assets of these advanced spectroscopic methods.

Regioselective generation and reactivity control of subnanometric platinum clusters in zeolites for high-temperature catalysis.

Subnanometric metal species (single atoms and clusters) have been demonstrated to be unique compared with their nanoparticulate counterparts. However, the poor stabilization of subnanometric metal species towards sintering at high temperature (>500 °C) under oxidative or reductive reaction conditions limits their catalytic application. Zeolites can serve as an ideal support to stabilize subnanometric metal catalysts, but it is challenging to localize subnanometric metal species on specific sites and modulate their reactivity. We have achieved a very high preference for localization of highly stable subnanometric Pt and PtSn clusters in the sinusoidal channels of purely siliceous MFI zeolite, as revealed by atomically resolved electron microscopy combining high-angle annular dark-field and integrated differential phase contrast imaging techniques. These catalysts show very high stability, selectivity and activity for the industrially important dehydrogenation of propane to form propylene. This stabilization strategy could be extended to other crystalline porous materials.

Gallium- and Iron-Pyoverdine Coordination Compounds Investigated by X-ray Photoelectron Spectroscopy and X-ray Absorption Spectroscopy.

Iron is an essential nutrient for nearly all forms of life, although scarcely available due to its poor solubility in nature and complex formation in higher eukaryotes. Microorganisms have evolved a vast array of strategies to acquire iron, the most common being the production of high-affinity iron chelators, termed siderophores. The opportunistic bacterial pathogen Pseudomonas aeruginosa synthesizes and secretes two siderophores, pyoverdine (PVD) and pyochelin (PCH), characterized by very different structural and functional properties. Due to its chemical similarity with Fe(III), Ga(III) interferes with several iron-dependent biological pathways. Both PVD and PCH bind Fe(III) and Ga(III). However, while the Ga-PCH complex is more effective than Ga(III) in inhibiting P. aeruginosa growth, PVD acts as a Ga(III) scavenger and protects bacteria from Ga(III) toxicity. To gain more insight into the different outcomes of the biological paths observed for the Fe(III) and Ga(III)-siderophore complexes, better knowledge is needed of their coordination geometries that directly influence the metal complexes chemical stability. The valence state and coordination geometry of the Ga-PCH and Fe-PCH complexes has recently been investigated in detail; as for PVD complexes, several NMR structural studies of Ga(III)-PVD are reported in the literature, using Ga(III) as a diamagnetic isosteric substitute for Fe(III). In this work, we applied up-to-date spectroscopic techniques as synchrotron-radiation-induced X-ray photoelectron spectroscopy (SR-XPS) and X-ray absorption fine structure (XAFS) spectroscopy coupled with molecular modeling to describe the electronic structure and coordination chemistry of Fe and Ga coordinative sites in PVD metal complexes. These techniques allowed us to unambiguously determine the oxidation state of the coordinative ions and to gather interesting information about the similarities and differences between the two coordination compounds as induced by the different metal.

Extracellular Albumin Covalently Sequesters Selenocompounds and Determines Cytotoxicity.

Selenocompounds (SeCs) are well-known nutrients and promising candidates for cancer therapy; however, treatment efficacy is very heterogeneous and the mechanism of action is not fully understood. Several SeCs have been reported to have albumin-binding ability, which is an important factor in determining the treatment efficacy of drugs. In the present investigation, we hypothesized that extracellular albumin might orchestrate SeCs efficacy. Four SeCs representing distinct categories were selected to investigate their cytotoxicity, cellular uptake, and species transformation. Concomitant treatment of albumin greatly decreased cytotoxicity and cellular uptake of SeCs. Using both X-ray absorption spectroscopy and hyphenated mass spectrometry, we confirmed the formation of macromolecular conjugates between SeCs and albumin. Although the conjugate was still internalized, possibly via albumin scavenger receptors expressed on the cell surface, the uptake was strongly inhibited by excess albumin. In summary, the present investigation established the importance of extracellular albumin binding in determining SeCs cytotoxicity. Due to the fact that albumin content is higher in humans and animals than in cell cultures, and varies among many patient categories, our results are believed to have high translational impact and clinical implications.

Mineralization-Inspired Synthesis of Magnetic Zeolitic Imidazole Framework Composites.

Metal-organic frameworks (MOFs) capable of mobility and manipulation are attractive materials for potential applications in targeted drug delivery, catalysis, and small-scale machines. One way of rendering MOFs navigable is incorporating magnetically responsive nanostructures, which usually involve at least two preparation steps: the growth of the magnetic nanomaterial and its incorporation during the synthesis of the MOF crystals. Now, by using optimal combinations of salts and ligands, zeolitic imidazolate framework composite structures with ferrimagnetic behavior can be readily obtained via a one-step synthetic procedure, that is, without the incorporation of extrinsic magnetic components. The ferrimagnetism of the composite originates from binary oxides of iron and transition metals such as cobalt. This approach exhibits similarities to the natural mineralization of iron oxide species, as is observed in ores and in biomineralization.

Effects of nanostructuring on the bond strength and disorder in V2O5 cathode material for rechargeable ion-batteries.

We have investigated the nanostructuring effects on the local structure of V2O5 cathode material by means of temperature dependent V K-edge X-ray absorption fine structure measurements. We have found that the nanostructuring largely affects V-O and V-V bond characteristics with a general softening of the local V-O and V-V bonds. The obtained bond strengths correlate with the specific capacity shown by the different systems, with higher capacity corresponding to softer atomic pairs. The present study suggests the key role of local atomic displacements in the diffusion and storage of ions in cathodes for batteries, providing important information for designing new functional materials.

Determination of the local structure of Sr2-xMxIrO4 (M = K, La) as a function of doping and temperature.

The local structure of correlated spin-orbit insulator Sr2-xMxIrO4 (M = K, La) has been investigated by Ir L3-edge extended X-ray absorption fine structure measurements. The measurements were performed as a function of temperature for different dopings induced by substitution of Sr with La or K. It is found that Ir-O bonds have strong covalency and they hardly show any change across the Néel temperature. In the studied doping range, neither Ir-O bonds nor their dynamics, measured by their mean square relative displacements, show any appreciable change upon carrier doping, indicating the possibility of nanoscale phase separation in the doped system. On the other hand, there is a large increase of the static disorder in Ir-Sr correlation, larger for K doping than La doping. Similarities and differences with respect to the local lattice displacements in cuprates are briefly discussed.

Study on the reflectivity properties of spherically bent analyser crystals. Corrigendum.

Corrections to the paper by Honkanen et al. (2014). [J. Synchrotron Rad. 21, 104-110] are made.

Fear of cancer recurrence: a theoretical review and its relevance for clinical presentation and management.

BACKGROUND: There is increasing recognition of the unique physical and psychosocial concerns of the growing population of cancer survivors. An emerging literature demonstrates that fear of cancer recurrence (FCR) is a problematic long-term and late effect for cancer survivors. In fact, FCR is a top concern, and this article provides a necessary synthesis of the extant research evidence and theory. METHODS: Literature searches were conducted using databases including MEDLINE and PsychINFO using specified search terms including 'fear of recurrence' and 'worry about recurrence'. A comprehensive narrative review summarizes early empirical findings on FCR including current definitions, assessment tools, clinical presentations, quality of life impact, prevalence, trajectory and risk factors. This paper also critically reviews the relevant theoretical frameworks to best understand these findings and considers multiple psychosocial treatment models that may have relevance for addressing FCR in the clinical setting. RESULTS: There is evidence of substantial prevalence and quality of life impact of FCR. Several theories (e.g. self-regulation model of illness, a family-based model, uncertainty in illness theory, social-cognitive processing theory, terror management theory) directly or indirectly help conceptualize FCR and inform potential treatment options for those with clinically significant distress or impairment resulting from FCR. CONCLUSIONS: Further investigation into FCR is warranted to promote evidence-based care for this significant cancer survivorship concern.

Microscopic structure of water at elevated pressures and temperatures.

We report on the microscopic structure of water at sub- and supercritical conditions studied using X-ray Raman spectroscopy, ab initio molecular dynamics simulations, and density functional theory. Systematic changes in the X-ray Raman spectra with increasing pressure and temperature are observed. Throughout the studied thermodynamic range, the experimental spectra can be interpreted with a structural model obtained from the molecular dynamics simulations. A spatial statistical analysis using Ripley's K-function shows that this model is homogeneous on the nanometer length scale. According to the simulations, distortions of the hydrogen-bond network increase dramatically when temperature and pressure increase to the supercritical regime. In particular, the average number of hydrogen bonds per molecule decreases to ≈ 0.6 at 600 °C and p = 134 MPa.

Study on the reflectivity properties of spherically bent analyser crystals.

Theoretical and experimental studies are presented on properties of spherically bent analyser crystals for high-resolution X-ray spectrometry. A correction to the bent-crystal strain field owing to its finite surface area is derived. The results are used to explain the reflectivity curves and anisotropic properties of Si(660) and Si(553) analysers in near-backscattering geometry. The results from the calculation agree very well with experimental results obtained using an inelastic X-ray scattering synchrotron beamline.