Dispersive X-ray Absorption Spectroscopy Research Articles

Tracking Minority Species in Redox Reactions: A Quantitative Combined XAS and Modulation Excitation Study.

Understanding the nature of intermediates/active species in reactions is a major challenge in chemistry. This is because spectator species typically dominate the experimentally derived data and consequently active phase contributions are masked. Transient methods offer a means to bypass this difficulty. In particular, modulation excitation with phase-sensitive detection (ME-PSD) provides a mechanism to distinguish between spectator and reacting species. Herein, modulation excitation (ME) time-resolved (energy dispersive) X-ray absorption spectroscopy, assisted by phase sensitive detection (PSD) analysis, has been applied to the study of a liquid phase process; in this case the classic ferrocyanide/ferricyanide redox couple. Periodic switches of the electrical potential (anodic/cathodic) enabled the use of the ME approach. Structural changes at fractions as low as 2 % of the total number of electroactive species were detected within the X-ray beam probe volume containing ~30 pmol of Fe(II)/Fe(III).

Bimetallic Gold–Iron Oxide Nanoparticles as Carriers of Methotrexate: Perspective Tools for Biomedical Applications

Bimetallic nanoparticles (BMNPs) combine unique and synergistic properties of two metals, allowing new specific applications. In this study, bimetallic AuFe nanoparticles and their conjugates with methotrexate (MTX) were obtained with an environmentally safe method of metal-vapor synthesis. The composition and electronic structure of the particles were investigated with X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) spectrum and X-ray absorption spectroscopy (XANES and EXAFS). The effects of BMNP-MTX conjugates on human primary cells and tumor cell lines were evaluated with neutral red uptake and MTT in vitro cytotoxicity assays. Bright-field microscopy analyses of tumor spheroid size and evaluations of tumor spheroid vitality based on SFDA AM staining were carried out. In vitro assays for an antibacterial activity evaluation of the generated samples were performed. The influence of BMNP-MTX on cytokine production with normal leukocytes was assessed using ELISA. X-ray analyses of the samples demonstrated that gold was in the ground state Au0 as well as Au+ and Au3+ states are present in small quantities, whereas iron existed as a mixture of non-histometric oxides with states close to Fe2+ and Fe3+. The modification of the AuFe system with MTX is accompanied by a threefold increase in the relative proportion of the Au+ state. BMNP-MTX conjugates demonstrated significant antitumor activity compared to the drug alone, which proves the ability of the generated nanoconjugates to improve the effectiveness of MTX therapy. This was confirmed by a marked reduction in the size and vitality of AuFe-MTX-treated 3D tumor spheroids. In addition to their selective antitumor activity, AuFe-MTX exhibited moderate antibacterial activity and induced sample-specific cytokine production with normal human leukocytes—which points to an immunostimulatory potential. The present findings indicate important and diverse biological properties of BMNP-MTX conjugates and thus highlight perspectives for their biomedical applications and new immune-specific abilities.

Tweaking and collating the structural, optical and magnetic properties of auto combusted lanthanum ferrites - study on effect of precursor concentration

A novel sol-gel auto-combustion technique is utilized to prepare nano-sized, perovskite-structured LaFeO3 powders. The nanoparticles were synthesized for three distinct precursor concentrations (0.5, 1 and 1.5 M) maintaining pH, annealing temperature and time. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, high-resolution scanning electron microscopy (HRSEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray absorption spectroscopy (EDAX), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) study and vibrating sample magnetometer (VSM). XRD revealed that all the prepared samples have shown an orthorhombic phase with space group Pnma. DRS suggested a marginal increase in bandgap and the average band gap was found to be 2.2 eV VSM analysis has shown that all the prepared samples exhibit weak ferromagnetic behaviour due to uncompensated canted spins. All the studies performed revealed a significant modification of structural, optical and magnetic properties with the variation of precursor concentration.

Ultrastable Cu2+ Intercalation Chemistry Based on a Niobium Sulfide Nanosheet Cathode for Advanced Aqueous Storage Devices

Exploring stable and durable cathodes for cost-effective reversible aqueous batteries is highly desirable for grid-scale energy storage applications, but significant challenges remain. Herein, we disclosed an ultrastable Cu2+ intercalation chemistry in mass-produced exfoliated NbS2 nanosheets to build ultralong lifespan aqueous batteries with cost advantages. Anisotropic interplanar expansion of NbS2 lattices balanced dynamic Cu2+ incorporation and the highly reversible redox reaction of Nb4+/Nb(4-δ)+ couple were illuminated by operando synchrotron X-ray diffraction and energy dispersive X-ray absorption spectroscopy, affording an extraordinary capacity of approximately 317 mAh g-1 at 1 A g-1 and a good stability of 92.2% capacity retention after 40000 cycles at 10 A g-1. Impressively, a budget NbS2||Fe hybrid ion cell involving an aqueous electrolyte/Fe-metal anode is established and provides a reliable energy supply of 225.4 Wh kg-1 at 750 W kg-1, providing insights for building advanced aqueous battery systems for large-scale applications.

Determining the proton diffusion coefficient in highly hydrated iridium oxide films by energy dispersive X-ray absorption spectroscopy

Charge transfer reactions in electrodeposited iridium oxide films (EIROF) are investigated by means of operando energy dispersive X-ray absorption spectroscopy (EDXAS), where oxidation and reduction conditions are selected to drive the Ir(III)/Ir(IV) and Ir(IV)/Ir(V) reactions in acidic solutions. The Ir(III)/Ir(IV) couple is related to a well-known electrochromic phenomenon, while the Ir(IV)/Ir(V) couple might play an important role in the catalysis of the oxygen evolution reactions (OER). In the experiments, current intensity and time-resolved X-ray absorption spectroscopy (XAS) are simultaneously recorded upon application of appropriate potential steps, leading to the independent determination of both the relevant reaction rates and the rate-determining steps. This is allowed by the fast acquisition time (∼10−2 s) at the ESRF Energy Dispersive XAS (EDXAS) ID24 beam-line, in combination with the highly hydrated amorphous iridium oxide electrode material, which in turn allows to maximize the fraction of Ir sites participating in the electrochemical processes. If the experimental conditions exclude the possibility of having either oxygen evolution (or reduction), the Degree of Reaction (DoR), determined by both electrochemistry and XAS, exhibits exponential time dependence, clearly pointing to diffusion-controlled processes. Vice versa, under concomitant OER + oxidation of iridium centers or ORR + iridium reduction, the electrochemical and XAS DoRs highlight different phenomena, providing fully complementary information of the ongoing electrode reactions. In all cases, data elaboration allows to determine the diffusion coefficient of H+ ions within the catalyst layer, that is compared and confirmed by data obtained by electrochemical impedance spectroscopy (EIS). The high values of D obtained for EIROF is compared to values obtained on other IrO2 materials can help in explaining the relevant high electrocatalytic activity.

Degradation Analysis by X-ray Absorption Spectroscopy for LiNbO3 Coating of Sulfide-Based All-Solid-State Battery Cathode.

The surface coating of cathode active material in all-solid-state batteries using sulfide-based solid electrolytes is well-known to be a fundamental technology, and LiNbO3 is one of the most representative materials. The half cells using the cathode mixture of Li6PS5Cl/LiNbO3-coated LiNi0.5Co0.2Mn0.3O2 were exposed in harsh conditions at 60 °C and 4.25-4.55 V vs Li/Li+ and analyzed by transmission electron microscope/energy dispersive X-ray spectroscopy (TEM/EDS) and X-ray absorption spectroscopy (XAS). TEM/EDS observation shows that Nb element derived from LiNbO3 coating had remained at the interface, which means that Nb element had not migrated to the solid electrolyte and active material. On the other hand, the XAS spectra of Nb L3-edge changed corresponding to cell performance degradation. From the comparison with the spectra of the reference materials of the Li-Nb-O system, the XAS spectral changes were assigned to the decomposition reaction which released Li and O from the LiNbO3 coating. The side reaction is presumed to cause to the oxidization deterioration of sulfide electrolyte at the interface of Li6PS5Cl/LiNbO3-coated LiNi0.5Co0.2Mn0.3O2.

Time-, space- and energy-resolved in situ characterization of catalysts by X-ray absorption spectroscopy.

A setup for dispersive X-ray absorption spectroscopy (XAS) with spatial, temporal and energy resolution is presented. Through investigation of a Mo/HZSM-5 catalyst during the dehydroaromatization of methane we observed a reduction gradient along the packed bed. Our new method represents an unprecedented addition to the analytical toolbox for in situ characterizations.

Evolution of the perovskite phase in UO2-based samples under conditions representative of a severe nuclear accident by XANES

To understand the fission products behaviour during a Nuclear Severe Accident (NSA), simulated high burnup UO2 fuels produced by sintering at high temperature (SIMFUEL) were submitted to thermal treatments in conditions representative of the beginning of a Pressurized Water Reactor (PWR) severe accident. The samples made of UO2 doped with eleven fission products (FP) surrogates were thus thermally treated from 400 ​°C up to 1000 ​°C at different oxygen potentials (up to −290 ​kJ ​mol(O2)−1 at 1000 ​°C). The samples were characterized before and after the heat treatments by Secondary Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDX) and X-ray Absorption Spectroscopy (XAS) at the MARS beamline, SOLEIL Synchrotron and at the FAME-UHD beamline, ESRF. Initially the SIMFUEL is constituted of a UO2 matrix, a metallic phase composed of Mo, Pd, Ru, Rh and Tc, and an oxide phase with perovskite structure depicted as (Ba, Sr)(Zr, U, RE)O3 where RE stands for Rare Earths. Around 1000 ​°C, it was found that Mo, initially contained in the metallic inclusions, oxidizes into MoO2. In the same conditions, a part of the oxidized Mo interacts with the perovskite phase containing Ba to form BaMoO4. These results will be useful to validate the theoretical models used in calculation codes and to assess thermodynamic databases, which are one of the main sources of errors when calculating a NSA sequence involving molten fuel.

Dispersive x-ray absorption spectroscopy for time-resolved in situ monitoring of mechanochemical reactions.

X-ray absorption spectroscopy (XAS) provides a unique, atom-specific tool to probe the electronic structure of solids. By surmounting long-held limitations of powder-based XAS using a dynamically averaged powder in a Resonant Acoustic Mixer (RAM), we demonstrate how time-resolved in situ (TRIS) XAS provides unprecedented detail of mechanochemical synthesis. The use of a custom-designed dispersive XAS (DXAS) setup allows us to increase the time resolution over existing fluorescence measurements from ∼15minto 2s for a complete absorption spectrum. Hence, we here establish TRIS-XAS as a viable method for studying mechanochemical reactions and sampling reaction kinetics. The generality of our approach is demonstrated through RAM-induced (i) bottom-up Au nanoparticle mechanosynthesis and (ii) the synthesis of a prototypical metal organic framework, ZIF-8. Moreover, we demonstrate that our approach also works with the addition of a stainless steel milling ball, opening the door to using TRIS-DXAS for following conventional ball milling reactions. We expect that our TRIS-DXAS approach will become an essential part of the mechanochemical tool box.

Transient Temperature Response of Supported Rh Nanoparticles in Photothermal Dry Reforming of Methane─An Operando Dispersive X-ray Absorption Spectroscopy Study

Photothermal catalytic conversion of CO2 is an effective strategy for solar energy storage and CO2 utilization. The selective heating of metal nanoparticles (NPs) endows the high-temperature reaction field for CO2 conversion; however, temperatures at the nanoscale under photothermal reaction conditions remain unrevealed. In this study, we performed operando dispersive X-ray absorption spectroscopy (DXAS) under concentrated visible and near-infrared light to evaluate the temperature of the catalytic active sites of Rh NPs on Al2O3 (local temperature) in the photothermal dry reforming of methane. The millisecond-order DXAS measurements demonstrated that the transient change in the local temperature of Rh NPs was affected by the formation process of the surface carbon-containing intermediates. The analysis methodology using operando time-resolved DXAS opens temperature evaluation at the nanoscale under light irradiation, including sunlight.

Hydrogen Adsorption/Desorption Isotherms on Supported Platinum Nanoparticles Determined by in‐situ XAS and ΔXANES Analysis

AbstractHydrogen atoms on supported metal nanoparticles (NPs) play a significant role in heterogeneous catalysis. Despite the extensive previous research, however, the adsorption of hydrogen onto practical supported NP catalysts is still unclear especially in the atmospheric pressure conditions. In this study, adsorption/desorption isotherms of hydrogen on Pt NPs supported on alumina (Al2O3) were obtained in gas‐flow conditions using the analysis of the difference spectra of Pt LIII‐edge X‐ray absorption spectroscopy (XAS) at 303 K. From the analysis of extended X‐ray absorption fine structure (EXAFS), a positive linear relationship was observed between the hydrogen coverage and Pt−Pt bond distance. Additionally, the re‐adsorption experiment of hydrogen after the first adsorption/desorption cycle and the transient change of dispersive XAS spectra in the hydrogen adsorption suggests that the hydrogen adsorption induces the surface reconstruction of Pt NPs on Al2O3 at around room temperature and atmospheric pressure.

NiO/CeO2-Sm2O3 nanocomposites for partial oxidation of methane: In-situ experiments by dispersive X-ray absorption spectroscopy

In this work, we analyze Sm2O3-doped CeO2 (SDC) nanopowders and NiO/SDC nanocomposites in terms of sample reducibility and catalytic activity for partial oxidation of methane. We assess the role of the average crystallite size and specific surface area in Ni and Ce reduction kinetics by in-situ X-ray absorption spectroscopy experiments in diluted H2 and CH4/O2 mixtures. Our results indicate that crystallite size and surface area play a key role in CH4 activation through modification of the sample redox behavior. The oxidation of the metallic phase is the main cause of sample deactivation. A clear relationship is established between the temperature of maximum Ni oxidation rate and grain size. An interplay between Ce atoms from the support and Ni from the active phase was observed during the experiments, evidencing a complex relationship between oxygen vacancy concentration and catalytic activity. A high Ce3+ content in catalyst support was detrimental to catalytic activity

Observation of early ZIF-8 crystallization stages with X-ray absorption spectroscopy

The present study investigates early stages of ZIF-8 crystallization up to 5 minutes post mixing of precursor solutions. Dispersive X-ray Absorption Spectroscopy (DXAS) provides a refined understanding of the evolution of the coordination environment during ZIF-8 crystallization. Linear Combination Analysis (LCA) suggests tetrakis(1-methylimidazole)zinc2+ to be a suitable and stable mononuclear structure analogue for some early stage ZIF-8 intermediates. Our results pave the way for more detailed studies on physico-chemical aspects of ZIF-8 crystallization to better control tailoring ZIF-8 materials for specific applications.

In situ XANES study of the influence of varying temperature and oxygen fugacity on iron oxidation state and coordination in a phonolitic melt

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.

Crystalline Bi2Se3 topological insulator films prepared by dc magnetron sputtering

Topological insulator thin films of Bi2Se3 have been deposited on SrTiO3 (111) substrate by dc magnetron sputtering and annealed in Se environment. X-ray Diffraction (XRD) measurement shows (00l) (l = 3n, where n is an integer) type of reflections over 2θ range of 10–80° without any other peaks indicating that the films are of single crystalline quality along the [001] growth direction confirming that highly c-axis-preferred orientated Bi2Se3 thin films can be obtained by relatively simpler and easily scalable dc magnetron sputtering technique. The results are also confirmed by Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDXS), Photo-electron Spectroscopy (PES) and X-ray absorption spectroscopy (XAS) measurements.

Antibacterial, antibiofilm and cytotoxic activities of biogenic polyvinyl alcohol-silver and chitosan-silver nanocomposites

Using biogenically synthesized silver nanoparticles (AgNPs) by Enterobacter cloacae Ism 26 (KP988024); Polyvinyl Alcohol-Silver (PVA-Ag) and Chitosan-Silver (CS-Ag) nanocomposites were prepared by augmentation. Thermal stability, AgNPs distribution and concentration within nanocomposites were characterized using thermogravimetric analysis (TGA), scanning electron microscope/energy dispersive x-ray (SEM/EDX) and atomic absorption spectroscopy (AAS). Nanocomposites films showed higher thermal stability than pure polymers, different AgNPs concentrations with homogenous distribution. Antibacterial, antibiofilm and cytotoxic activities of nanocomposites films were studied against Multi Drug Resistant (MDR) bacteria including Staphylococcus epidermidis (S.e), Staphylococcus aureus (S.a), Escherichia coli (E.c) and Klebsiella pneumoniae (K.p). PVA-Ag nanocomposite showed larger zones of inhibitions and higher antibiofilm activities than CS-Ag nanocomposite against both Gram-positive and Gram-negative bacteria. AgNPs solution, PVA-Ag and CS-Ag nanocomposites showed low cytotoxic activities against Huh-7 liver cells and IC50 values of 263.20 μg ml−1, 1185.07 μg ml−1 and 119.85 μg ml−1, respectively. PVA-Ag and CS-Ag nanocomposites films showed enhanced thermal stability and biological properties that qualify them for different biomedical applications.

Wide field imaging energy dispersive X-ray absorption spectroscopy

A new energy dispersive X-ray absorption spectroscopy (EDXAS) method is presented for simultaneous wide-field imaging and transmission X-ray absorption spectroscopy (XAS) to enable rapid imaging and speciation of elements. Based on spectral K-Edge Subtraction imaging (sKES), a bent Laue imaging system diffracting in the vertical plane was developed on a bend magnet beamline for selenium speciation. The high flux and small vertical focus, forming a wide horizontal line beam for projection imaging and computed tomography applications, is achieved by precise matching of lattice plane orientation and crystal surface (asymmetry angle). The condition generating a small vertical focus for imaging also provides good energy dispersion. Details for achieving sufficient energy and spatial resolution are demonstrated for both full field imaging and computed tomography in quantifying selenium chemical species. While this system has lower sensitivity as it uses transmission and may lack the flux and spatial resolution of a dedicated focused beamline system, it has significant potential in rapid screening of heterogeneous biomedical or environmental systems to correlate metal speciation with function.

Normalized single-shot X-ray absorption spectroscopy at a free-electron laser.

A setup for dispersive X-ray absorption spectroscopy (XAS), employing a new reference scheme, has been implemented and tested at the soft X-ray free-electron laser (FEL) FLASH in Hamburg. A transmission grating was used to split the FEL beam into two copies (signal and reference). The spectral content of both beams was simultaneously measured for intensity normalization within the FEL bandwidth on a shot-to-shot basis. Excellent correlation between the two beams was demonstrated within a few percent for single bunch operation at 143 eV photon energy. Applying the normalization scheme, an absorption spectrum of a Gd2O3thin film sample was recorded around the Gd N4,5-edge photon energy of 143 eV, showing excellent agreement with a reference spectrum measured at a synchrotron. This scheme opens the door for time-resolved single-shot XAS with femtosecond time resolution at FELs.

Temperature-Programmed Reduction and Dispersive X-Ray Absorption Spectroscopy Studies of CeO<sub>2</sub>-Based Nanopowders for Intermediate-Temperature Solid-Oxide Fuel Cell Anodes

In this work, we study the influence of the average crystallite size and dopant oxide on the reducibility of CeO2-based nanomaterials. Samples were prepared from commercial Gd2O3-, Sm2O3- and Y2O3-doped CeO2 powders by calcination at different temperatures ranging between 400°C and 900°C and characterized by X-ray powder diffraction, transmission electron microscopy and BET specific surface area. The reducibility of the samples was analyzed by temperature-programmed reduction and in situ dispersive X-ray absorption spectroscopy techniques. Our results clearly demonstrate that samples treated at lower temperatures, of smallest average crystallite size and highest specific surface areas, exhibit the best performance, while Gd2O3-doped ceria materials display higher reducibility than Sm2O3- and Y2O3-doped CeO2.

Time-Resolved X-ray Absorption Spectroscopy in (Photo)Electrochemistry

This minireview aims at providing a complete survey concerning the use of X-ray absorption spectroscopy (XAS) for time-resolved studies of electrochemical and photoelectrochemical phenomena. We will see that time resolution can range from the femto-picosecond to the second (or more) scale and that this joins the valuable throughput typical of XAS, which allows for determining the oxidation state of the investigated element, together with its local structure. We will analyze four different techniques that use different approaches to exploit the in real time capabilities of XAS. These are quick-XAS, energy dispersive XAS, pump & probe XAS and fixed-energy X-ray absorption voltammetry. In the conclusions, we will analyze possible future perspectives for these techniques.