Operando X‐ray absorption spectroscopy (XAS) has undergone a transformation thanks to advances in synchrotron instrumentation and reactor‐cell design, enabling studies of heterogeneous catalysts under working conditions. This topical review surveys these developments and shows how they are implemented on the BM30 (FAME‐PIX) and BM16 (FAME‐UHD) beamlines at the European Synchrotron Radiation Facility (ESRF). Both beamlines now combine high‐flux optics with catalysis‐oriented detection, including a 16‐element Mirion HPGe solid‐state detector (SSD) for sensitive XAS of active sites and a 14‐crystal analyzer spectrometer for high‐energy‐resolution fluorescence detection (HERFD) and X‐ray emission spectroscopy (XES) to track changes in oxidation state and local structure. They also include operando reactor cells capable of operating at temperatures up to 1000°C and pressures up to 100 bar, matching industrial catalytic conditions. We describe the beamline configurations, sample environments and detection modalities, and discuss how their combined use enables real‐time structural and electronic characterization of catalysts. Case studies on methane reforming, ethane dehydrogenation, CO 2 hydrogenation and methane dehydroaromatization demonstrate the scientific impact and versatility of these setups. Collectively, BM30 and BM16 are key tools for operando XAS and help bridge the gap between fundamental understanding and industrial catalytic processes.

The interaction between transition-metal ions and amyloid-β (Aβ) peptides is linked to the pathogenesis of Alzheimer's disease. X-ray absorption spectroscopy is widely used to investigate the coordination of these metal-peptide complexes, but exposure to synchrotron radiation can induce artefacts due to interaction with the X-ray beam. In this work, we examine the effects of X-ray irradiation on Cu(I), Cu(II) and Zn(II) complexes with two truncated Aβ fragments, Aβ1-6 and Aβ1-16. Experiments performed at 10 K reveal a marked photoreduction-associated effect: while the spectra of Cu(I)- and Zn(II)-bound peptides remain unchanged, Cu(II) complexes undergo significant spectral modifications. To probe structural relaxation following reduction, we exposed samples at 10 K, raised the temperature to 200 K and then collected additional spectra upon re-cooling. These experiments reveal that higher temperatures promote relaxation processes that are otherwise kinetically limited, and that the extent of relaxation, depending on the metal-binding mode, differs for Aβ1-6 and Aβ1-16. Overall, our experiments show that major structural modifications only take place in the presence of X-ray-induced metal reduction and that they are modulated by temperature. Thus, X-ray irradiation can be exploited not only as a probe but also as a trigger to study the redox-associated structural dynamics of copper-Aβ complexes and beyond.

Knowledge of the chemical speciation of molybdenum in fluids under hydrothermal conditions is key to understanding the formation of porphyry Cu-Au-Mo deposits, which are the primary economic source of copper, molybdenum and rhenium. However, the chemical identity and thermodynamic stability of aqueous complexes of molybdenum and the role of different ligands on Mo metal transport yet remain inconsistent and incomplete, in particular for sulfur-bearing fluids typical of such environments. We have experimentally studied the role of hydrogen sulfide (H2S and HS-) and the trisulfur radical ion (S3 center dot-) in the transport of molybdenum by hydro-thermal fluids at 300 degrees C and 500 bar as a function of pH, redox conditions as well as sulfur speciation and concentration. We combined solubility measurements of molybdenite in hydrothermal reactors using fluid quenching or sampling, with in situ synchrotron X-ray absorption spectroscopy experiments and thermodynamic and molecular modeling. Our solubility and spectroscopic dataset is consistent with the formation of the tetrathiomolybdate complex, MoS42-, in reduced, H2S/HS--dominated fluids of neutral-to-alkaline pH. In contrast, a mixed-ligand complex with three sulfide ions and one trisulfur radical ion, MoS3(S3)-, prevails in more oxidized and more acidic fluids at the sulfide-sulfate transition where S3 center dot- is far more abundant. In both complexes, Mo is nominally hexavalent and in a first-shell tetrahedral coordination with sulfur atoms. The derived equilibrium constants of the formal solubility reactions (log10K): MoS2(s) + 2H2S0(aq) + 0.5 O2(g) = MoS42- + 2H+ + H2O(liq) and MoS2(s) + H2S0(aq) + S3 center dot- + 0.5 O2(g) = MoS3(S3)- + H2O(liq) at 300 degrees C and 500 bar are 0.5 +/- 0.4 and 14.6 +/- 0.4, respectively. The solubility of MoS2(s) predicted using these constants aligns well with Mo concentrations measured in natural fluid inclusions in quartz that record S-rich fluids from porphyry-epithermal systems. In contrast, other types of Mo complexes invoked so far (molybdates, alkali ion pairs, oxy-chlorides or oxysulfides) are negligible at such conditions. Thus, trisulfur radical ion complexes may be important carriers of Mo in hydrothermal fluids and would require further systematic investigation across a wide range of temperature and pressure.

Abstract Understanding and controlling reaction mechanisms are essential for the rational design of synthesis protocols for colloidal nanoparticles. In the case of luminescent nanocrystals and semiconductor quantum dots, understanding the correlation between structural and optical properties further enables their optimization for specific applications. Silver sulfide (Ag2S) nanocrystals are promising bioimaging probes due to their tunable photoluminescence emission in the NIR-I and NIR-II ranges and the absence of toxicity of bulk Ag2S. We developed an efficient microwave-assisted aqueous synthesis method using glutathione (GSH) as both the sulfur source and the capping agent for the production of directly water-soluble nanocrystals with potential for bioimaging applications. The nucleation and growth of these crystals are investigated using synchrotron-based X-ray absorption and X-ray photoelectron spectroscopies, which do not rely on either a minimum particle size or their crystallinity. We reveal the local structure around the silver atoms and the surface properties of the nanocrystals and relate them back to their optical properties, size, and crystallinity. This comprehensive and multiscale study reveals the different growth mechanisms taking place as a function of the Ag/GSH precursor ratio. In particular, a switch from a reaction-controlled growth regime to aggregative growth occurs in the case of a low precursor ratio, leading to an abrupt shift in the emission wavelength.

Within the ITER project (International Thermonuclear Experimental Reactor) an international project building a magnetic confinement device to achieve fusion as a sustainable energy source, tungsten (W) is planned to serve as a plasma-facing component (PFC) in the tokamak, a magnetic confinement device used to produce controlled thermonuclear fusion power. Post plasma-W interactions, submicron tungsten particles can be released. This study investigated the exposure of lentic freshwater ecosystems to ITER-like tungsten nanoparticles in indoor aquatic mesocosms. Monitoring included tungsten (bio)distribution, (bio)transformation, speciation, and impacts following a relevant exposure scenario (chronic, medium-term, low-dose contamination). Additionally, mechanistic studies using a combination of microfluidic cells and X-ray Absorption Spectroscopy (XAS) provided a time-resolved understanding of tungsten's oxidative dissolution in freshwater. Following contamination, tungsten persisted in the water column (over 90 %), showing significant (∼40 %) and rapid (< 7 days) oxidation-dissolution and polymerization. This led to significant exposure of planktonic niches, strong affinity of polymeric tungsten species for aquatic vegetation, and potential transfer to higher trophic levels like aquatic snails. Over five weeks, the bio-physicochemical parameters of the mesocosms remained stable, and no acute impacts were observed on micro- and macro-organisms.

Hydrothermal-based synthetic methods of quantum dots allow for the exploration of reaction parameters normally inaccessible to typical aqueous-based batch reactions, such as elevated reaction temperatures (>100 °C) and reaction pressures above atmospheric pressure. Coupled with microwave heating, new instantaneously bio-compatible quantum dots (QDs) with enhanced opitcal properties can be yielded. As of today, aqueous-based synthetic methods often lag behind their organic analogues in terms of the photophysical properties of the QDs obtained and the ease of modulation of both the emission wavelength and crystallite size. Using a novel microwave-assisted hydrothermal approach, the synthesis of silver sulphide (Ag2S) QDs exhibiting NIR emission spanning the biological transparency windows via modulation of the reaction parameters has been developed. The intrinsic link between their optical and structural properties is explored via laboratory and synchrotron-based structural analysis techniques. Their toxicity towards a hepatic cell line was assessed, and related back to their structure and size. Overall this work aims to not only further develop the repertoire of synthetic methods for the synthesis of Ag2S QDs, but also paves the way for the development of safer QDs suitable for future clinical applications.

Nickel is generally found in trace amounts in the environment and can be beneficial to living organisms, but it is also an environmental contaminant of high concern, primarily due to anthropogenic releases. Fe oxides play a significant role in the behavior and fate of Ni in the environment, as they can interact with metal cations. However, the interactions between magnetite (Fe3O4) and Ni are not well described, and in particular the effect of magnetite stoichiometry (Fe(ii)/Fe(iii) = R) is not well considered. Ni sorption experiments were performed on stoichiometric (R0.5) and oxidized (R0.1) magnetite as a function of Ni concentration and pH under anaerobic conditions. Samples were analyzed by transmission electron microscopy, X-ray absorption spectroscopy (XAS) and magnetic circular dichroism at the Ni L2,3-edges and XAS at the Ni K-edge. At high Ni concentrations, Ni precipitates as Ni(OH)2 on the magnetite surface, but also as distinct sheet-like particles. At low Ni concentrations, high energy resolution fluorescence detection (HERFD) XAS analyses at the Ni K-edge revealed Ni incorporation into R0.5 magnetite and surface adsorption of Ni onto R0.1 magnetite. The present results were compared with those previously published for Co, which revealed an unexpected distinct behavior of Ni and Co. This element-specific binding mechanism highlights the unique properties of magnetite compared to other naturally occurring iron oxides (e.g. goethite, hematite), for which Ni and Co binding mechanisms are similar. Taken together, these results will help not only to predict the behavior and fate of Ni under environmental conditions in the presence of magnetite but also to synthesize magnetite nanoparticles doped by the addition of Ni with interesting magnetic properties.

ThomX is a compact x-ray source based on Compton scattering, installed at IJCLab (Laboratoire de physique des 2 infinis-Irène Joliot-Curie) in Orsay. The machine uses a small electron storage ring and an intense laser pulse stored in a high-finesse optical cavity. This article describes the various subsystems of the machine and their initial results of the commissioning, which began in mid-2021. This first commissioning phase led to the production of 10^{10} x-rays/s with an on-axis energy of 45 keV. The main steps to be taken to reach the nominal flux are outlined at the end.

Trace element contents in authigenic pyrite (FeS2) are often considered as a reliable geochemical archive of past marine conditions. For instance, cobalt (Co) abundance in marine sedimentary pyrite may track back the extent of past ocean anoxia and is considered as a reverse proxy for the rise of atmospheric oxygen. However, the molecular-scale route of Co incorporation in pyrite at low temperature is not well documented. Thus, any insight on this aspect are expected to help better assess the actual role of pyrite in Co cycling in modern and past subsurface environments. In this study, a series of pyrites were synthesized in solution via the polysulfide pathway under anoxic conditions and at ambient temperature, with various initial aqueous Co concentrations (Co:Fe = 0.13-5). Rietveld refinement analysis of the powder X-ray diffraction (XRD) patterns shows that pyrite is the principal component (69(5) wt%) of the final solid products, with small fractions of marcasite (17(4) wt%) and FeS (10(2) wt%). High Energy Resolution Fluorescence Detected (HERFD) Co K-edge X-ray Absorption Near Edge Structure (XANES) and Extended X-ray absorption fine structure (EXAFS) analysis indicate that a minor fraction (20-36 %) of Co substitutes for Fe in the pyrite structure as compared with a theoretical spectrum of a Co-substituted pyrite supercell calculated using Density Functional Theory (DFT). Besides, in the final products, the major part (64-80 %) of Co persists in the form of an amorphous CoSn-polysulfide precursor phase that represents the whole Co speciation before pyrite nucleation. In this precursor observed at the monosulfide FeS pre-pyrite stage, Co early adopts an octahedral coordination as attested by Co pre-edge data, whereas Co is in tetrahedral coordination in our Co-doped mackinawite FeS reference compound. The local structure of the CoSnpolysulfide precursor is further elucidated by EXAFS shell-by-shell analysis that points to monomeric units (< 1 nm), where Co is octahedrally coordinated to first neighboring S atoms with at least three of these S neighbors belonging to a polysulfide chain of undetermined length. Aggregation of such monomeric units into an amorphous CoSn-polysulfide phase is supported by X-ray scattering-pair distribution function analysis (XRD-PDF) of an analogous amorphous CoSn compound. These results could have important implications on our understanding of pyrite nucleation mechanisms via the polysulfide pathway since the observed octahedral CoSn-polysulfide precursor differs from the generally proposed models of tetrahedral FeS precursors. In addition, the persistence of these peculiar species and the observed delay of Co incorporation in pyrite highlights the importance of trace elements in pyrite formation kinetics at low temperature. Lastly, our results illustrate the high affinity of Co for polysulfides and raise questions on the possible presence and evolution of this non-pyrite CoSn phase in sedimentary archives. In this regard, this study may provide new mechanistic insights that could help explaining the moderate affinity for authigenic pyrite generally reported for Co, in particular in a sedimentary context where other possible bearing phases such as clay minerals and Mn oxides are involved.

Several Cu-ligands, including 1,10-phenanthroline (Phen), have been investigated for anticancer purposes based on their capacity to bind excess Cu in cancer tissues and form redox active complexes able to catalyse the formation of reactive oxygen species (ROS), ultimately leading to oxidative stress and cell death. However, the stability and pro-oxidant activity of Cu-based drugs such as Cu-Phen2 is affected in most cell compartments (e.g. cytosol and nucleus) by the presence of compounds such as glutathione (GSH) and metallothioneins, which can reduce and dissociate Cu(II) from the ligand forming poorly redox-active Cu(I)-thiolate clusters. Here, cell culture studies suggested that lysosomal acidification may play a pivotal role in the anticancer activity of Cu-Phen2. In addition, ROS generation catalysed by Cu-Phen2 in the presence of GSH was shown to be remarkably accelerated at the acidic pH typical of lysosomes. The catalytic mechanism was thoroughly investigated by means of density functional theory (DFT) calculations, which disclose key reaction intermediate species, including a ternary Phen-Cu-GSH complex formed upon dissociation of one Phen ligand. Spectroscopic measurements (including low-temperature luminescence, UV-vis absorption and X-ray absorption spectroscopy) corroborated the formation of such a reactive intermediate ternary complex. Furthermore, they revealed that the faster ROS generation observed at lower pH is due to a pH-dependent competition between Phen and GSH for Cu, which results in a higher stability of Cu-Phen2 against dissociation and de-activation by GSH at lower pH. Overall, this study points to lysosomal targeting as an innovative and effective strategy to improve the stability and cytotoxic activity of Cu-based drugs.

With the increase in laser power and finesse of optical cavities over the last decade, laboratory-size Compton sources are very promising. These sources produce X-rays through interactions between relativistic electrons and laser photons and, in term of brightness, fall between large synchrotron facilities and classical laboratory X-ray sources. The ThomX source is the French project in this field. This article first presents a state of the art of high-intensity Compton sources, then the ThomX source is briefly described, and the first results are detailed, in particular the production of the first X-rays, the acquisition of the first spectrum and the first image of the beam. Finally, the next objectives are discussed.

Acquiring knowledge on the mechanisms of sugar transformation in valuable products is a prerequisite for the optimization of related catalytic processes. In the present work, we study the conversion of glucose and two other related sugars, mannose and erythrose, catalyzed by homogeneous molybdate- and tungstate-based catalysts through a combination of kinetic experiments and in situ X-ray absorption near-edge spectroscopy experiments. The body of results affords shedding light onto the active species and mechanism of the main reactions observed, namely, retro-aldol condensation, a key step to produce short-chain products from biomass-based sugars, and epimerization. In particular, we highlight the very distinct behavior of tungstates and molybdates in terms of reactivity and active species. Tungstates catalyze epimerization and retro-aldol condensation through two different mononuclear bidentate species (O1,O2 and O1,O3, respectively), likely of +VI oxidation state of tungsten. Molybdates promote epimerization through a binuclear, tri-, or tetradentate species (at least O1,O2,O3) and retro-aldol condensation by a mononuclear bidentate species (O1,O3).

Combining nuclear magnetic resonance (NMR), X-ray absorption spectroscopy near-edge structure (XANES), and density functional theory (DFT), we elucidate the structures of tungstate and molybdate with sugars of interest in the conversion of biomass to platform chemicals (glucose, mannose, and erythrose). We highlight a number of complexes, including one nearly isostructural structure that is formed with each metal-sugar combination. We also emphasize the singular reactivity of erythrose that undergoes retro-aldolization at room temperature.

The stability of Fe−N−C oxygen reduction reaction (ORR) electrocatalysts has been considered a primary challenge for their practical application in proton exchange membrane fuel cells (PEMFCs). While several studies have attempted to reveal the possible degradation mechanism of Fe−N−C ORR catalysts, there are few research results reporting on their stability as well as the possible Fe species formed under different voltages in real PEMFC operation. In this work, we employ in‐situ X‐ray absorption near‐edge structure (XANES) to monitor the active‐site degradation byproducts of an atomically dispersed Fe−N−C ORR catalyst under a H2/O2‐operating PEMFC at 90 % relative humidity and 80 °C. For this, stability tests were carried out at two constant cell voltages, namely 0.4 and at 0.8 V. Even though the ORR activity of the Fe−N−C catalyst decreased significantly and was almost identical at the end of the tests for the two voltages employed, the analysis of the XANES recorded under H2/N2 configuration at 0.6 and 0.9 V within the stability test suggests that two different degradation mechanisms occur. They are demetalation of iron cations followed by their precipitation into Fe oxides upon operation at 0.8 V, versus a chemical carbon oxidation close to the active sites, likely triggered by reactive oxygen species (ROS) originated from the H2O2 formation, during the operation at 0.4 V.

We discuss the X-ray absorption spectroscopy (XAS) methods elaborated using the high pressure and high-temperature autoclaves installed at FAME and FAME-UHD beamlines. These methods are based on the in situ acquisition of X-ray transmission and fluorescence spectra of hydrothermal fluids and silicate melts and enable the derivation of both solubility and speciation information about metal complexes. The technological assets of our autoclaves are described across a wide range of experimental conditions spanning from different types of hydrothermal fluids, from liquid-like to vapor-like densities having metal concentrations of <1-10,000 ppm, to magmatic fluid-melt systems at 1000 degrees C. Scientific examples are presented to illustrate the use and the advantages of our spectroscopic 'micro-batch' reactors. Finally, the integration of our autoclave setups on the FAME-UHD crystal analyzer spectrometer and the benefits of this technique are demonstrated.

This paper presents the development of a novel high-pressure/high-temperature reactor cell dedicated to the characterization of catalysts using synchrotron x-ray absorption spectroscopy under operando conditions. The design of the vitreous carbon reactor allows its use as a plug-flow reactor, monitoring catalyst samples in a powder form with a continuous gas flow at high-temperature (up to 1000 °C) and under high pressure (up to 1000 bar) conditions, depending on the gas environment. The high-pressure/high-temperature reactor cell incorporates an automated gas distribution system and offers the capability to operate in both transmission and fluorescence detection modes. The operando x-ray absorption spectroscopy results obtained on a bimetallic InCo catalyst during CO2 hydrogenation reaction at 300 °C and 50 bar are presented, replicating the conditions of a conventional microreactor. The complete setup is available for users and permanently installed on the Collaborating Research Groups French Absorption spectroscopy beamline in Material and Environmental (CRG-FAME) sciences and French Absorption spectroscopy beamline in Material and Environmental sciences at ultra-high dilution (FAME-UHD) beamlines (BM30 and BM16) at the European Synchrotron Radiation Facility in Grenoble, France.

Several copper-ligands, including 1,10-phenanthroline (Phen), have been investigated for anticancer purposes based on their capacity to bind excess copper (Cu) in cancer tissues and form redox active complexes able to catalyse the formation of reactive oxygen species (ROS), ultimately leading to oxidative stress and cell death. Glutathione (GSH) is a critical compound as it is highly concentrated intracellularly and can reduce and dissociate copper(II) from the ligand forming poorly redox-active copper(I)-thiolate clusters. Here we report that Cu-Phen 2 speciation evolves in physiologically relevant GSH concentrations. Experimental and computational experiments suggest that at pH 7.4 mostly copper(I)-GSH clusters are formed, but a minor species of copper(I) bound to one Phen and forming ternary complexes with GSH (GS−Cu-Phen) is the redox active species, oxidizing quite efficiently GSH to GSSG and forming HO⋅ radicals. This minor active species becomes more populated at lower pH, such as typical lysosomal pH 5, resulting in faster GSH oxidation and HO⋅ production. Consistently, cell culture studies showed lower toxicity of Cu-Phen 2 upon inhibition of lysosomal acidification. Overall, this study underscores that sub-cellular localisation can considerably influence the speciation of Cu-based drugs and that minor species can be the most redox- and biologically-active.