Reduced organic sulfur (S) functional groups play critical roles in diverse environmental and biological processes, but an enduring analytical challenge is resolving thiols (R-SH) and thioethers (R-S-R') in complex mixtures. Here, we demonstrate the use of S Kα1 high-energy-resolution fluorescence detected (HERFD) X-ray absorption near-edge structure (XANES) spectroscopy to distinguish thiol groups from thioether moieties in complex environmental mixtures as a function of pH. Experiments with model S thiol compounds showed a quantitative decrease in the normalized amplitude of the reduced S peak in spectra with thiol deprotonation (R-SH ↔ R-S- + H+), a phenomenon not observed for other S functionalities. Spectra were collected across a pH range relevant to thiol pKas (3-11) for five well-characterized dissolved organic matter (DOM) samples from natural environments, containing different S content and various mixtures of S functionalities. Using a quantitative relationship between the decrease in the reduced S peak amplitude and thiol deprotonation in composite spectra of model S compounds, the proportions of reduced S as thiols (fRS-) in the five DOM samples were quantified to range from 3% to 41%. For two DOM samples, we quantified thiol pKa distributions and verified reversibility through stepwise, bidirectional pH adjustments. The increase in thiol abundance of one DOM sample following experimental abiotic sulfurization was also quantified to demonstrate method application. We discuss opportunities to optimize S Kα1 HERFD-XANES spectroscopy for enhanced thiol sensitivity in various research applications.

Bimetallic PtNi/CeO2 catalysts were successfully synthesized via a mechanochemical approach, specifically ball milling, and evaluated for methane steam reforming (MSR). A fractional factorial design of experiments was employed to systematically explore the effects of key milling parametersmilling frequency, milling time, and ball-to-powder ratioon the catalysts' structural properties and catalytic performance. The catalysts were characterized by X-ray diffraction, H2 temperature-programmed reduction, transmission electron microscopy, and Raman spectroscopy. Catalytic activity tests were performed in a plug flow reactor under a high gas hourly space velocity (200,000 mL gcat -1 h-1) at a steam-to-carbon ratio of 2 between 700 and 950 °C. The mechanochemically synthesized catalysts were benchmarked against those prepared via incipient wetness impregnation. The most active milled catalysts achieved a methane conversion rate of ca. 22 mol CH4 gNi -1 h-1 at 700 °C (83.5% methane conversion for a PtNi/CeO2 mechanochemically synthesized), outperforming the impregnated counterpart (64% methane conversion under the same reaction conditions). Notably, increasing the milling intensity resulted in enhanced catalytic activity, with milling frequency emerging as the most influential factorcorrelating with the formation of smaller NiO particles. To elucidate the role of Pt addition, in situ X-ray absorption near-edge structure (XANES) and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) measurements were conducted on the most active milled catalysts under MSR conditions. NAP-XPS revealed surface segregation of Pt during MSR, alongside an inhibitory effect on solid carbon deposition, suggesting the potential for a coke-resistant catalyst. These findings highlight the power of mechanochemical synthesis in tuning catalyst properties, offering a scalable and efficient route to high-performance catalysts for methane reforming and hydrogen production.

The increasing demand for phosphorus (P) sources and concerns about surface water quality raise the need to explore safe and efficient secondary P fertilizer sources. This study evaluated the effectiveness of a Ca-based recovered nutrient product (RNP) from synthetic swine wastewater using an innovative anaerobic membrane bioreactor (AnMBR) technology. This study aimed to characterize and compare the dissolution, transformations, and potential bioavailability of P in RNP with conventional P fertilizers (monoammonium phosphate; MAP, triple superphosphate; TSP) in selected soils over time by using short-term laboratory incubation studies in Petri dishes. Soil samples sectioned from the point of application were assessed for pH, total P, resin-extractable P, and selected samples by using X-ray absorption near-edge structure spectroscopy. The RNP treatment showed that over 90%, 70%, and 80% of added P remained in the center section in calcareous, neutral, and acid soils, respectively, where the potential plant-available P was greater than the control in all soils and similar to the MAP treatment only in acid soil after 5 weeks of incubation. The hydroxyapatite-like species dominated P speciation in both RNP and RNP-added soils, leading to less solubility. These results underscore the potential of Ca-based RNP as a P source for tested soils, and process modifications could yield a series of viable secondary P sources for agriculture.

The present work aimed at unravelling if fungal inoculation on grapevine leaves could trigger the dissolution of foliarly deposited Cu (nano)formulations, and how this would impact Cu translocation in planta. Leaves of grapevine seedlings were exposed to 3.3 μg of Cu (5 μg cm-2). Formulations of contrasting solubilities (micro-sized conventional Bordeaux mixture, CuO-nanoparticles (CuO-NPs), and CuSO4) were applied to grapevine leaves, followed by the inoculation of Botrytis cinerea spores on top of the deposited Cu formulations. Nine days after Cu deposition, and six days post inoculation, Cu distribution and transformations were assessed at the leaf surface using micro-X-ray fluorescence and X-ray absorption near-edge structure spectroscopy. Cu was also quantified in non-exposed tissues to evaluate the role of fungal-triggered transformations on Cu translocation. For all non-inoculated formulations, Cu remained largely untransformed at the leaf surface. After inoculation of B. cinerea, Cu was partly found complexed with carboxylate- and thiol-containing compounds, associated with partial Cu reduction, with similar patterns across all (nano)formulations. This was mainly attributed to the presence of fungal metabolites. Despite these transformations, Cu did not significantly translocate in planta, with all the taken-up Cu found on and/or within exposed leaves. This work suggests that these approaches could lead to more efficient plant protection strategies by (i) increasing leaf affinity of Cu-based compounds, while (ii) triggering ionic Cu release thanks to a pathogen-triggered dissolution.

Understanding how protective coatings respond to the harsh low-Earth orbit (LEO) environment is essential for ensuring the safety, longevity, and cost-effectiveness of spacecraft. In particular, identifying environmentally friendly, non-chromate alternatives that can maintain performance under such conditions has both technological and regulatory significance. This study investigates the environmental stability of zirconium-based hybrid conversion coatings with Cu additives (Cu10 and Cu20) applied to cold-rolled steel, tested in the Materials International Space Station Experiment (MISSE) outside the International Space Station (ISS). Chemical and morphological analyses were carried out using a combination of electron microscopy and X-ray spectroscopy techniques, including scanning electron microscopy (SEM), scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (STEM-EDS), X-ray photoelectron spectroscopy (XPS), and X-ray absorption near-edge structure (XANES) spectroscopy. After exposure outside the ISS, all coatings remained structurally intact, with all exhibiting a uniform Zr-rich matrix and embedded Cu-rich clusters, while a thin Si-rich surface layer developed from interaction with space environments. Depth-resolved XPS showed a layered structure with CuO on the surface, Cu2O, and partial Zr(iv) reduction near Cu-rich sites, evidence of Atomic Oxygen (AO)-driven surface oxidation. These results demonstrate that Cu–Zr coatings maintain their chemical integrity and microstructure in harsh space environments, offering a non-chromate alternative for long-term aerospace protection. These insights provide valuable guidance for developing next-generation protective coatings that combine environmental sustainability with the reliability required for future aerospace and orbital applications.

Abstract The redox potential of the pore solution of hardened cements containing ground granulated blast furnace slag (GGBFS) affects reinforcement corrosion and immobilization of radioactive waste. Here, Mn K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy was applied to determine the depth profile of the oxidation state of manganese in hardened GGBFS‐containing cement pastes. Manganese was oxidized in the outer regions of some of the pastes, but the depth to which this occurred was not identical with the ‘blue‐green/white color change front’, usually interpreted as indicating oxidation of sulfur species. For CEM III/B, the color change of the material was gradual and thus unsuitable for a precise determination of the oxidation depth, while for the alkali‐activated slag, a distinct color change front was found, but full oxidation of manganese and sulfur had not occurred in the brighter region. Mn K‐edge XANES spectroscopy is thus a more reliable method than the determination of the visual color change front to follow the ingress of the oxidation front.

Protactinium is one of those long discovered elements with poorly known physico-chemical properties. In aqueous solution, protactinium(V), highly prone to hydrolysis, may or may not display oxo bonding, depending on the medium, in a way that still appears unpredictable due to a critical lack of data. Here, we probe the stability of this bond in hydrochloric acid solutions. Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopy, complemented by ab initio calculations, reveal that a short Pa─Ooxo bond indeed exists at moderate hydrochloric acid concentration 3M and unexpectedly persists even in highly acidic conditions (12M). Our analysis identifies the coexistence of PaO(OH)Cl1, 2 species at moderate acidity and PaOCl4, 5 species at high acidity, with both pairs unambiguously displaying the characteristic mono-oxo bond, with a total coordination number of seven. Notably, EXAFS spectral fitting using geometries obtained from relativistic quantum calculations reveals a Pa─Ooxo bond length of approximately 1.83Å, in excellent agreement with computational predictions. This finding overturns expectations and provides new insight into early actinide bonding behavior in extreme chemical conditions. Understanding such coordination chemistry is critical for advancing nuclear fuel management and more broadly actinidescience.

Iron sulfides (FexSy), including greigite (Fe3S4), are key materials in geological processes and technological applications. However, in the context of colloidal synthesis, the mechanism by which these nanoparticles form remains unexplored. Here, we employ in situ X-ray diffraction and photon-in photon-out spectroscopic studies to elucidate the reaction pathway of Fe(acac)3 and thioacetamide (TAA) in benzyl alcohol (BA), which yields crumpled Fe3S4 nanosheets. Using powder X-ray diffraction (PXRD), we identify FeS (mackinawite) as a crystalline intermediate whose anisotropic growth, driven by its layered crystal structure, governs the crumpled nanosheet-like morphology of Fe3S4 (greigite) through a topotactic transition. By performing high-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopy, we show that the formation of Fe3S4 proceeds through a multistep mechanism involving two intermediates. Supported by density functional theory (DFT), we find that Fe(acac)3 is initially reduced in the presence of TAA in BA, forming a molecular intermediate [Fe(acac)2(BA)2], which subsequently transforms into FeS and ultimately into Fe3S4. Complementary valence-to-core X-ray emission spectroscopy (vtc-XES) reveals the evolution of the coordination environment from Fe-O to Fe-S throughout the reaction. Our work provides a comprehensive understanding of the formation mechanism of Fe3S4 nanosheets in solution, shedding light on how crystal growth dynamics and electronic structure evolution dictate their unique crumpled nanosheet morphology.

Amorphous MoO2-wrapped Mo supported low-crystalline Co nanosheets for enhanced OH bond cleavage: synergistic effect of abundant active sites and robust interfaces.

Abstract X-ray absorption near-edge structure (XANES) spectroscopy enables in situ direct measurements of microscale Fe2+/Fe3+ ratios in minerals and has greatly contributed to the understanding of the redox states during rock formation. Traditionally, the Fe2+/Fe3+ has been quantified based on 1s→3d/4p pre-edge peak features. However, optically anisotropic minerals show significant differences in the absorption of polarized X-rays when measured in different crystallographic orientations, introducing considerable errors in estimates of Fe2+/Fe3+. Multivariate analysis (MVA) utilizing entire X-ray absorption fine structure (XAFS) spectral features combined with appropriate training data, preprocessing, and hyperparameter optimization, offers a potential solution to this issue. This study examines the X-ray absorption anisotropy of clinopyroxene for six distinct crystallographic orientations relative to X-ray propagation and polarization directions using 11 natural single crystals with a wide range of Fe3+/ΣFe (0–0.88) and compositions (diopside, augite, aegirine). We used the full XAFS spectra of the oriented clinopyroxenes to construct MVA models that can accurately estimate Fe3+/ΣFe in unknown orientations. Our measurements reveal that most of the XANES absorption-edge peak features display a clear dependence on the polarization direction of the incident X-ray, suggesting that their absorption anisotropy can mainly be ascribed to dipole-allowed 1s→4p transition processes. On the other hand, the pre-edge peaks exhibit a complex absorption anisotropy that depends on both the propagation and polarization directions, suggesting a complicated nature of quadrupole-allowed 1s→3d transitions enhanced by dipole transitions to mixed 3d–4p orbitals. We found that the conventional pre-edge-based determinations of Fe3+/ΣFe involve large uncertainties of ±13.5–15.3%Fe3+, mainly due to the substantial X-ray absorption anisotropy. Our optimal MVA model, using the least absolute shrinkage and selection operator (Lasso) and trained with autoscaled XANES spectra of oriented clinopyroxenes, can successfully predict %Fe3+ in clinopyroxenes from within the test data set without prior knowledge of the orientation, with a root-mean-squared error of ±7.8%Fe3+. In addition, our results show a good agreement between weighted energy channels of the MVA models and XANES peak features resolved by the polarization-dependent experiment. The MVA coefficients provided in this study offer an effective method for deriving reliable Fe3+/ΣFe from XAFS measurements of clinopyroxene, regardless of orientation. This approach highlights the benefits of using features from the pre-edge, main-edge, and post-edge domains of the spectra to establish the relationships.

Aqueous Zn/MnO2 batteries have garnered significant interests owing to their abundance, high theoretical specific capacity, low cost, and safety. However, the large-scale application of these systems is limited by the lack of understanding of the reaction mechanism of the MnO2 cathode. An electrodeposited polymorph of MnO₂ has been identified as the dominant phase that forms regardless of the initial polymorph in the charge cycles (1.75 V vs Zn/Zn+2). This work investigates the reaction mechanism of the electrodeposited polymorph of MnO₂. A multimodal approach combining synchrotron X-ray diffraction, absorption spectroscopy, and nano-tomography was used to study the structural evolution, reaction chemistry, and the morphological and chemical changes of the electrodeposited cathode. Full-field nano-tomography visualizes these changes in the three-dimensional structure of the electrodeposited cathode after discharge/charge cycle. X-ray absorption near-edge structure (XANES) spectroscopy showed the chemical heterogeneity of the cathode material. Overall, these findings highlight the factors limiting the specific capacity, paving the way for practical applications in grid-scale energy storage systems.

ABSTRACT Spodumene is an important lithium aluminosilicate mineral in the battery supply chain found alongside other silicates with similar surface properties. It can be selectively concentrated by flotation using fatty acid collectors. Historic and modern research has shown how alkaline scrubbing improves spodumene flotation performance, however, its application is inconsistent. This study presents the first use of X-Ray Absorption Near-Edge Structure (XANES) Total Fluorescence Yield (FLY) spectra at the Li K-edge and Al L2,3 edge to evaluate sodium hydroxide treatments of four different spodumene samples. The findings confirmed the spodumene XANES spectra was consistent across all samples and suggested a continuous shift to lower energy occurred along the Li K-edge after alkaline scrubbing, in addition to potential cyclical shifts in peak energy along the Al L2,3 edge. Observed peak shifts were attributed to broken Al–O and Si–O bonds on the spodumene surface. Corresponding batch flotation results revealed selectivity and recovery were improved after scrubbing, with a greater observed improvement for a ‘weathered’ ore. This study demonstrates the potential use of XANES spectroscopy in lithium flotation research and provides further evidence that NaOH scrubbing is beneficial for spodumene flotation performance and should be considered as an integral part of spodumene flotation flowsheets.

Speciation of cesium in a radiocesium-bearing microparticle emitted from Unit 1 during the Fukushima nuclear accident by XANES spectroscopy using transition edge sensor.

Competitive adsorption and molecular interaction study of sulfamethoxazole and trimethoprim on biomass-based activated carbon.

Understanding the oxidation states of transition metals in metalloproteins is critical for elucidating their biochemical functions. Among the available spectroscopic techniques, X-ray Absorption Near Edge Structure (XANES) spectroscopy offers a powerful, element-specific method for probing the electronic environment and oxidation state of metal centers in biological macromolecules. The shape, position, and intensity of the absorption edge in a XANES spectrum can provide direct insights into the valence state and coordination geometry of the metal ion, making it a particularly valuable tool for studying redox-active metalloproteins under near-physiological conditions.In this study, we apply XANES spectroscopy to investigate the copper oxidation states in amicyanin, a well- characterized Type-I copper protein, in its crystalline form. Type-I copper sites are highly conserved among various redox proteins found in bacteria, plants, and animals, and are known for their intense blue color due to strong ligand-to-metal charge transfer transitions. These proteins serve as efficient electron transfer (ET) agents, playing vital roles in biological processes such as respiration and metabolism.Amicyanin, a representative member of the cupredoxins family, features a single copper ion coordinated by a distorted tetrahedral geometry with three strong equatorial ligands (a cysteine and two histidines) and one weak axial ligand, typically methionine. It functions as an electron acceptor for the enzyme methylamine dehydrogenase and transfers it to cytochrome C551i.Our objective is to acquire XANES spectra from single crystals of amicyanin in both oxidized and reduced states. These spectra will be analyzed to determine the oxidation state of the copper center and to detect any associated changes in the local electronic environment. Results from XANES will be compared with structure from single-crystal X-ray crystallography, which provides complementary structural information about the copper coordination sphere.This comparative study aims to deepen our understanding of how changes in oxidation state correlate with local structural features at the active site, enhancing our ability to interpret redox mechanisms in copper proteins at atomic resolution. Results from these complementary techniques will be presented, highlighting how their synergy enables a deeper insight into structure-function relationships in metalloproteins.

Many manganese (Mn) oxide minerals incorporate both Mn 3+ and Mn 4+ in their structures. The ratio of these two Mn valences influences the absorption capacity of metal ions, the mechanisms of redox reaction and topological transformations. Knowledge of the average oxidation state of Mn is also significant in the case of biogenic or purely inorganic formation of these minerals. Enumeration of each oxidation state is still not a common part of their characterization, even though the average oxidation state provides crucial information. In this paper, we describe an accessible titration method based on the standard bismuthic method and we quantify Mn 3+ /Mn 4+ in six secondary manganese oxide natural samples. The titration method was confirmed with X-ray absorption near-edge structure spectroscopy. This method does not require sophisticated laboratory equipment and generates sufficient accuracy and precision (relative error <1%).

Abstract As a redox-sensitive rare-earth element (REE) in apatites, knowledge about the speciation of cerium (Ce) has broad applications, from understanding geochemical and geological processes in the Earth’s crust and mantle to developing sustainable REE extraction techniques. However, Ce speciation in apatites has rarely been determined experimentally but is often inferred from the presence or absence of Ce anomalies in normalized REE patterns. In this contribution, Ce speciation in gem-quality fluorapatite from Durango (Mexico) has been determined by combined X-ray photoelectron spectroscopy (XPS) and synchrotron X-ray absorption near-edge structure (XANES) spectroscopy. The Ce4+/ΣCe (where ΣCe denotes the total Ce = Ce3+ + Ce4+) values in Durango fluorapatite from Ce 3d XPS and bulk Ce L3-edge XANES techniques are similar (0.32–0.34 versus 0.27–0.30). However, microbeam Ce L3-edge XANES (µXANES) spectra measured on oriented sections parallel and perpendicular to the crystallographic c-axis yielded significantly different Ce4+/ΣCe values (0.18–0.21 versus 0.34–0.36), suggesting a marked crystal-orientation effect of the µXANES technique. On the other hand, the Ce4+/ΣCe values of 0.27–0.31 from µXANES measured on an inclined section are similar to those from the XPS and bulk XANES techniques. The mixed Ce3+ and Ce4+ states in Durango fluorapatite are consistent with its formation under oxidizing magmatic-hydrothermal conditions but contradict the general lack of Ce anomalies (CeN/CeN* = 0.86–1.01, where CeN* = Sqrt(LaN × PrN)) in chondrite-normalized REE patterns. This study shows that the lack of Ce anomalies in chondrite-normalized REE patterns of apatites does not guarantee an absence of Ce4+ and that the development of the Ce-in-apatite oxybarometer requires direct determination of Ce speciation in apatites.

Iodine L-edge X-ray absorption near-edge structure (XANES) measurements were performed to characterize each crystal form of the compounds containing iodine atoms. 4-Iode-l-phenylalanine (4ILP) was used as a model compound. Each crystalline form had a distinctive XANES spectral shape. Complementary single-crystal X-ray structure analyses revealed diverse atomic interactions surrounding the iodine atoms, including C···I contacts and I···I halogen bonds. These different interactions influence the electronic states of the iodine atoms of 4ILP, resulting in distinct features in the XANES spectra. Notably, the spectral changes in the L1 absorption edge of iodine atoms were found to be sensitive to van der Waals contacts. On the other hand, those in L2 and L3 were sensitive to the presence or absence of halogen bonds. This research highlights the crucial impact of weak nonconventional atomic interactions on the XANES spectra, providing valuable insights for the development and evaluation of crystalline materials.

Pyrazine (pyz) has been used extensively in coordination chemistry to manifest electron delocalization in mixed-valent compounds and strongly coupled materials. In the current work, using a YbII precursor, [(C5H4Me)2YbII(THF)2] (1), a molecular square [(C5H4Me)2YbIII(pyz•-)]4·1/2(C7H5F3) (2) was synthesized by metal-ligand redox cooperativity. Complex 2 shows evidence of charge transfer from YbII to pyrazine in a range of studies including structural analysis, magnetometry, vibrational spectroscopy, X-ray absorption near-edge structure spectroscopy, and electronic structure calculations. DFT calculations support the assignment of low-energy bands in the UV-vis spectrum as pyrazine-SOMO-to-metal-4f charge transfer. Magnetic studies reveal a Yb-pyz•- exchange coupling of -3.6 cm-1 and pyz•--pyz•- coupling of -18.6 cm-1 for the radical bridged Yb-square complex.

The incorporation of iron (Fe) into calcium carbonate coprecipitates (CCCs) to form Fe-incorporated CCC (CCCFe) widely occurred in CCC-enriched soils and sediments. However, the molecular mechanism of phosphate (P) immobilization on CCCFe remains largely unknown. In this study, batch experiments were conducted to investigate the immobilization mechanisms of P on CCCFe with low and high Fe loadings (CCCFel vs CCCFeh) using P K-edge X-ray absorption near-edge structure (XANES) spectroscopy with surface-sensitive total electron yield (P-XANESTEY) and bulk-sensitive fluorescence yield (P-XANESFLY) modes. Results indicated that the high Fe loading inhibited calcite formation but favored vaterite production in the CCC and enhanced its P retention capacity. Hydroxyapatite (HAP) dominated over ferrihydrite-associated P (Fe-P) in the bulk of P sorbed on the CCCFeh, but amorphous calcium phosphate (ACP) dominated over HAP for the CCC, suggesting Fe-induced transformation of the ACP to the HAP. Furthermore, the P-XANESTEY analysis indicated brushite primarily formed on the surface of the P sorbed on the CCCFeh at high P loading. Consistently, the spherical aberration-corrected scanning transmission electron microscopy analysis directly revealed ferrihydrite coating on the CCC and the presence of Ca-P and Fe-P associations. This study provides new molecular-level insights into Fe-tuned depth-dependent transformation of P on the CCC, thus benefiting P management in the CCC-enriched environmental settings.