X-ray Absorption Near-edge Structure Spectroscopy Research Articles

Structural Studies and Thermal Analysis in the Cs2MoO4–PbMoO4 System with Elucidation of β-Cs2Pb(MoO4)2

The quaternary compound Cs2Pb(MoO4)2 was synthesized and its structure was characterized using X-ray and neutron diffraction from 298 to 773 K, while thermal expansion was studied from 298 to 723 K. The crystal structure of the high-temperature phase β-Cs2Pb(MoO4)2 was elucidated, and it was found to crystallize in the space group R3̅m (No. 166), i.e., with a palmierite structure. In addition, the oxidation state of Mo in the low-temperature phase α-Cs2Pb(MoO4)2 was studied using X-ray absorption near-edge structure spectroscopy. Phase diagram equilibrium measurements in the Cs2MoO4-PbMoO4 system were performed, revisiting a previously reported phase diagram. The equilibrium phase diagram proposed here includes a different composition of the intermediate compound in this system. The obtained data can serve as relevant information for thermodynamic modeling in view of the safety assessment of next-generation lead-cooled fast reactors.

Electronic Structure and Ultrafast Electron Dynamics in CuO Photocatalysts Probed by Surface Sensitive Femtosecond X-ray Absorption Near-Edge Structure Spectroscopy

CuO is often employed as a photocathode for H2 evolution and CO2 reduction, but observed efficiency is still far below the theoretical limit. To bridge the gap requires understanding the CuO electronic structure; however, computational efforts lack consensus on the orbital character of the photoexcited electron. In this study, we measure the femtosecond XANES spectra of CuO at the Cu M2,3 and O L1 edges to track the element-specific dynamics of electrons and holes. Results show that photoexcitation represents an O 2p to Cu 4s charge transfer state indicating the conduction band electron has primarily Cu 4s character. We also observe ultrafast mixing of Cu 3d and 4s conduction band states mediated by coherent phonons, with Cu 3d character of the photoelectron reaching a maximum of 16%. This is the first observation of the photoexcited redox state in CuO, and results provide a benchmark for theory where electronic structure modeling still relies heavily on model-dependent parametrization.

High-Temperature Syngas Desulfurization and Particulate Filtration by ZnO/Ceramic Filters.

Combustible gas (e.g., gasification syngas) cleaning at high temperatures can obtain further gains in energy efficiency for power generation and importantly leads to a simplified process and lower cost as a commercially viable source of clean energy. Thus, a feasibility study for high-temperature desulfurization (HTDS) and additional high-temperature particulate filtration (HTPF) of a raw syngas using ZnO sorbent-dispersed Raney CuO (ZnO/R-CuO) and ceramic filter (ZnO/CF) has been carried out. By synchrotron X-ray absorption near-edge structure (XANES) spectroscopy, mainly Zn(II) and Cu(II) are found in the ZnO/R-CuO sorbents. Both ZnO and R-CuO in the sorbents are involved in HTDS (1% H2S) at 873 K to form ZnS, Cu2S, and a small amount of CuS and reach relatively high HTDS efficiencies (82-90%). In addition, regeneration of the sulfurized sorbent by oxidation with O2 at 873 K (HTRG) for 1 h can restore ZnO and CuO for continuous and repetitive HTDS-HTRG cycles. To facilitate the HTDS engineering applications by the ZnO/R-CuO sorbents, their reaction rate constant (8.35 × 104 cm3/g/min) and activation energy (114.8 kJ/mol) at 873 K have also been determined. Furthermore, the ZnO/CF sorbent/filter can perform HTDS and additional HTPF at 873 K with very high particulate removal efficiencies (>98%). This demonstrates the feasibility for hot-syngas cleaning with a much better energy efficiency and lesser cost for cleaner power generation.

Exploring the Depths of Corrosion: A Novel GE-XANES Technique for Investigating Compositionally Complex Alloys.

In this study, we propose the use of nondestructive, depth-resolved, element-specific characterization using grazing exit X-ray absorption near-edge structure spectroscopy (GE-XANES) to investigate the corrosion process in compositionally complex alloys (CCAs). By combining grazing exit X-ray fluorescence spectroscopy (GE-XRF) geometry and a pnCCD detector, we provide a scanning-free, nondestructive, depth-resolved analysis in a sub-micrometer depth range, which is especially relevant for layered materials, such as corroded CCAs. Our setup allows for spatial and energy-resolved measurements and directly extracts the desired fluorescence line, free from scattering events and other overlapping lines. We demonstrate the potential of our approach on a compositionally complex CrCoNi alloy and a layered reference sample with known composition and specific layer thickness. Our findings indicate that this new GE-XANES approach has exciting opportunities for studying surface catalysis and corrosion processes in real-world materials.

Aluminum speciation in forest soils and forest floor density fractions using synchrotron-based XANES spectroscopy

The speciation of aluminum (Al) in soils is important for Al cycling and Al toxicity in terrestrial ecosystems. Current soil Al speciation methods are mostly wet-chemical, discriminating among operationally defined fractions rather than distinct Al species. We performed synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy at the Al K-edge (1560 eV) for Al speciation in different horizons of three forest soil profiles and O layer density fractions. We deconvoluted the spectra by linear combination fitting (LCF; 1550–1690 eV), using reference spectra of 22 diluted inorganic and organic Al-bearing soil constituents. Our first time application of Al XANES spectroscopy + LCF for soil Al speciation revealed methodological challenges and difficulties. Thus, a minimum sample Al content of 5 mg g−1 was necessary to yield spectra with satisfactory signal-to-noise ratio in reasonable acquisition time, and Al contents > 15 mg g−1 resulted in spectrum distortion by self absorption, requiring adequate sample dilution prior to XANES analysis. Nevertheless, Al K-edge XANES spectroscopy allowed for estimating the relative contribution of different Al species to total Al in our soil and density fraction samples. The Al XANES spectra of different Al carboxylates were very similar. The same was true for different Al phenol species, different 2:1 clay minerals (illite, montmorillonite, chlorite), different 1:1 clay minerals (kaolinite, halloysite), and different feldspars (orthoclase, anorthite), jeopardizing a reliable differentiation and quantification of these specific compounds. We therefore combined these compounds into the groups SOM carboxyl(ate)-bound Al, SOM phenol-bound Al, 1:1 clay mineral-bound Al, 2:1 clay mineral-bound Al, and feldspar-bound Al. XANES results showed a decreasing contribution of organically bound Al to total soil Al with soil depth (O layers 20–43 %; Ah horizons 10–22 %; B horizons 0–12 %). Major inorganic Al-bearing constituents in the fine earth of all soils were 2:1 clay minerals and feldspars, followed by 1:1 clay minerals (kaolinite), and Fe oxyhydroxides with partial Al substitution. Gibbsite or allophane did contribute only marginally to fine-earth Al in our soils. Different Oa layer density fractions with different SOM content and SOM decomposition status also differed in Al content and Al speciation, indicating the existence of spatially separated forest floor constituents with different Al speciation. Aluminum in the mineral-dominated density fraction > 1.6 g cm−3 with advanced SOM decomposition, comprising about 50 % of total Oa mass, was entirely bound in clay minerals (65–70 % of total Al) and feldspars (30–35 % of total Al). In contrast, Al in the mineral-poor density fraction < 1.0 g cm−3 was entirely bound to SOM as Al-organo complex, with Al bound to SOM phenol groups (>75 % of total Al) being more relevant than Al bound to SOM carboxyl(ate) groups. However, the latter density fraction comprised only 4 % of total Oa mass in both soils. Aluminum K-edge XANES spectroscopy, particularly when combined with total element analysis and XRD, is a promising novel tool for speciation of Al in soils and in SOM-mineral associations, with a great potential to promote our understanding of Al biogeochemistry in terrestrial ecosystems.

Vanadium Speciation in Ancient Shales Revealed through Synchrotron-Based X-ray Spectroscopy

Redox-sensitive trace elements, such as vanadium, are frequently used as paleoredox proxies to infer the redox status of ancient marine depositional environments. When applied to vanadium, this approach relies on an accurate understanding of vanadium geochemistry in marine sediments. This, in turn, requires the application of analytical techniques capable of providing reliable chemical information on vanadium host phases of vanadium and thus the ability to distinguish authigenic from detrital phases. The increasing availability of synchrotron-based X-ray spectroscopic techniques capable of providing chemical speciation information at both the bulk and micro-scale presents an opportunity to refine our understanding of vanadium geochemistry in ancient marine sediments. Here, we show the utility of synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy and scanning X-ray fluorescence microscopy (SXFM) for investigating vanadium host phases in ancient marine sediments. The studied samples from the 1400 Ma Xiamaling Formation came from strongly contrasting depositional settings (ranging from oxic to euxinic) with a wide range of vanadium enrichments (enrichment factors from 0.7 to 9.6), yet vanadium speciation determined by XANES was consistently found to be phyllosilicate-hosted vanadium (III). High-resolution elemental imaging by SXFM coupled with global statistical colocalization analyses revealed strong associations between vanadium and potassium, consistent with vanadium hosted by potassium-rich clay minerals. These findings, while demonstrating the power of synchrotron-based X-ray methods, imply that differentiating authigenic and detrital vanadium in ancient marine sediments is unlikely to be possible given that post-depositional processes result in similar chemical speciation for both fractions. This will also limit the reliability of vanadium isotope system studies that depend on differentiating authigenic and detrital fractions using selective extraction procedures.

Biodegradation of vulcanized rubber by a gut bacterium from plastic-eating mealworms

The disposal of vulcanized rubber waste is difficult due to the presence of three-dimensional crosslinking network structure. Here, we report that a bacterium Acinetobacter sp. BIT-H3, isolated from the gut of plastic-eating mealworm, can grow on and degrade vulcanized poly(cis-1,4-isoprene) rubber (vPR). Scanning electronic microscopy (SEM) shows that strain BIT-H3 can penetrate into the vPR and produce craters and cracks. The tensile strength and the crosslink density of vPR decreased by 53.2% and 29.3% after ten weeks’ incubation, respectively. The results of Horikx analysis, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and X-ray absorption near-edge structure (XANES) spectroscopy reveal that strain BIT-H3 can break down both sulfide bridges and double bonds of polymeric backbone within vPR. Sulfate and oligo(cis-1,4 isoprene) with terminal aldehyde and keto groups were identified as metabolic products released during vPR degradation. Through genomic and transcriptional analyses, five enzymes of dszA, dszC1, dszC2, Laccase2147, and Peroxidase1232 were found to be responsible for vPR degradation. Based on the chemical structure characterizations and molecular analyses, a vPR biodegradation pathway was proposed for strain BIT-H3. These findings pave a way for exploiting vulcanized rubber-degrading microorganisms from insect gut and contribute to establish a biodegradation method for vulcanized rubber waste disposal.

Spectromicroscopy Studies of Silicon Nanowires Array Covered by Tin Oxide Layers.

The composition and atomic and electronic structure of a silicon nanowire (SiNW) array coated with tin oxide are studied at the spectromicroscopic level. SiNWs are covered from top to down with a wide bandgap tin oxide layer using a metal-organic chemical vapor deposition technique. Results obtained via scanning electron microscopy and X-ray diffraction showed that tin-oxide nanocrystals, 20nm in size, form a continuous and highly developed surface with a complex phase composition responsible for the observed electronic structure transformation. The "one spot" combination, containing a chemically sensitive morphology and spectroscopic data, is examined via photoemission electron microscopy in the X-ray absorption near-edge structure spectroscopy (XANES) mode. The observed spectromicroscopy results showed that the entire SiNW surface is covered with a tin(IV) oxide layer and traces of tin(II) oxide and metallic tin phases. The deviation from stoichiometric SnO2 leads to the formation of the density of states sub-band in the atop tin oxide layer bandgap close to the bottom of the SnO2 conduction band. These observations open up the possibility of the precise surface electronic structures estimation using photo-electron microscopy in XANES mode.

Removal of toxic arsenic(iii) from an old endemic black-foot disease groundwater by oxidative electrosorption

Environmental context Naturally occurring arsenic was the likely cause of endemic black foot disease in groundwaters in Taiwan, and levels still exceed Taiwan EPA water quality standards. A method for the clean-up of these groundwaters that is both feasible and environmentally friendly is urgently needed. Oxidation of As(III) as H3AsO3 to the less toxic As(V)− and removal of As in groundwater was performed quantitatively by electrosorption using materials derived from agricultural wastes; this shows that this method has the potential to be a novel, green remediation method. Rationale Naturally occurring arsenic in the groundwater caused black-foot disease (BFD) in the 1950s on the southwest seashore of Taiwan. Recently, we found that the concentration of arsenic in groundwater taken from currently sealed wells in areas previously affected by BFD remained higher than the Taiwan (EPA) water quality standard. Although clean tap water is available in that area, removal of arsenic from the groundwater is of great importance to expand possible utilisation. Methodology Removal of arsenic from two old endemic BFD groundwaters with activated carbon (AC) electrodes recycled from agricultural wastes by electrosorption using capacitive deionisation (CDI) processes was studied. A better understanding of arsenic electrochemistry involved in electrosorption was investigated by in situ X-ray absorption near-edge structure spectroscopy. Results Arsenic removal efficiencies (61–93%) remained high across concentrations (5 and 196 mg/L). A high oxidation rate constant (0.93 h−1) for As(III)0 to As(V)− was found, allowing the electrosorption of As(V)− onto the meso- and micro-pores of the AC CDI electrodes with rate constants of 0.021 and 0.0013 h−1, respectively. Removal of arsenic from contaminated groundwater for drinking water was achieved with six CDI reactors in series. Moreover, in the presence of other ions (such as Na+, Mg2+ and Ca2+), 60–73% of As(III)0 and As(V)− ions were removed from the groundwaters by electrosorption. Discussion We have developed an engineering-feasible method for converting As(III)0 to less toxic As(V)−, enabling its removal by electrosorption, which demonstrates the feasibility for green remediation of BFD waters as well as other arsenic-contaminated groundwaters.

State-of-charge of individual active material particles in lithium ion batteries: a perspective of analytical techniques and their capabilities.

The state-of-charge (SOC) is an essential parameter for battery management systems to reflect and monitor the remaining capacity of individual battery cells. In addition to its application at the cell level, the SOC also plays an important role in the investigation of redox processes of cathode active materials (CAMs) in lithium ion batteries (LIBs) during electrochemical cycling. These processes can be influenced by a large variety of factors such as active material properties, inhomogeneities of the electrode, degradation phenomena and the charge/discharge protocol during cycling. Consequently, non-uniform redox reactions can occur, resulting in charge heterogeneities of the active material. This heterogeneity can translate into accelerated aging of the CAM and a reduction in reversible capacity of the battery cell, since the active material is not fully utilized. To understand and monitor the SOC heterogeneity at the mesoscale, a wide range of techniques have been implemented in the past. In this perspective an overview of current state-of-the-art techniques to evaluate charge heterogeneities of CAMs in LIBs is presented. Therefore, techniques which utilize synchrotron radiation like X-ray absorption near-edge structure (XANES) and transmission X-ray spectroscopy (TXM) are presented as well as Raman spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Next to these established techniques, classification single particle inductively coupled plasma optical emission spectroscopy (CL-SP-ICP-OES) as a new approach is also discussed in this perspective. For these techniques, the areas of application, advantages as well as drawbacks are highlighted and discussed.

High-sensitive XANES analysis at Ce L2-edge for Ce in bauxites using transition-edge sensors: Implications for Ti-rich geological samples

Accurate determination of cerium (Ce) valence state is important for interpreting the Ce anomaly in geological archives for (paleo)redox reconstruction. However, the routine application of Ce L3-edge X-ray absorption near-edge structure (XANES) spectroscopy for detecting trace Ce in geological samples can often be restricted by coexisting titanium (Ti) due to the proximity of their fluorescence emission lines. Therefore, the signal-to-noise ratio of Ce L3-edge XANES spectra may not be sufficiently high for high-quality spectroscopic analysis. This study introduces a semi-quantitative approach appropriate for Ti-rich, Ce-dilute geological materials by synchrotron-based X-ray measurement at the Ce L2-edge. First, the results confirm that Ce L2-edge XANES spectra are able to avoid overlapping Ti Kβ emissions and provide more reliable information on the Ce valence state in Ti-rich materials relative to L3-edge XANES. Moreover, the application of transition-edge sensor (TES) could reach the higher sensitivity with better energy resolution than conventional silicon drift detector (SDD) to detect fluorescence X-ray (Ce Lβ1). The investigation on bauxites developed from the Columbia River Basalts shows that combining Ce L2-edge XANES and TES allows for resolving weak Ce fluorescence lines at the L2-edge from Ti-rich, Ce-dilute samples (Ti/Ce mass ratio up to ∼6000, tens of ppm Ce). The outcome emphasizes the practical possibility of investigating Ce redox state in Ti-rich geological samples.

Zinc speciation and desorption kinetics in a mining waste impacted tropical soil amended with phosphate

Mining is an important component of the Brazilian economy. However, it may also contribute to environmental problems such as the pollution of soils with zinc and other potentially toxic metals. Our objective was to evaluate changes in the chemical speciation and mobility of Zn in a soil amended with phosphate. Soil samples were collected from a deactivated mining area in the state of Minas Gerais, Brazil, and amended with NH4H2PO4 saturated with deionized water to 70 % of maximum water retention and incubated at 25 ± 2 °C in open containers for 60 days. The soil was chemically and mineralogically characterized, and sequential extraction, desorption kinetics, and speciation were carried out using synchrotron bulk-sample and micro–X-ray Absorption Near-Edge Structure (XANES/μ-XANES) spectroscopy at the Zn K-edge, and X-ray fluorescence microprobe analysis (μ-XRF). The combination of μ-XRF and μ-XANES techniques made it possible to identify Zn hotspots in the main species formed after phosphate remediation. The best fit combination for bulk XANES and μ-XANES was observed in Zn-montmorillonite, Zn-kerolite, Zn-ferrihydrite, and gahnite. In the course of phosphate treatment, gahnite, Zn layered double hydroxides (Zn-LDH), Zn3(PO4), and ZnO were identified by bulk XANES, while Zn-ferrihydrite, Zn-montmorillonite, and scholzite were identified by μ-XANES. Zinc in the phosphate-amended soil had the strongest partial correlations (r′ > 0.05) with Ni, Co, Fe, Cr, Mn, Si, P, Cd, Pb, and Cd, while the unamended soil showed the strongest correlation with Cu, Pb, Fe, and Si. The application of NH4H2PO4 altered Zn speciation and favored an increase in Zn desorption. The most available Zn contents after phosphate amendment were correlated with the release of exchangeable Zn fractions, associated with carbonate and organic matter.

Uptake and incorporation of Al, Cr, V, Zn and Mo in hematite: Competition, synergies and influence on structural properties

This study investigated multiple (di-, tri- and tetra-)incorporation of selected minor and trace elements (Al3+, Cr3+, V3–5+, Zn2+, Mo6+ and As5+) into hematite. The purpose was to improve understanding of how hematite may control trace element mobility in the environment, and how physical and chemical properties of hematite are impacted by multi-element incorporation at x/Fe molar ratios of up to 10%. Simultaneous structural incorporation of Al±Cr±V±Zn into hematite was achieved, with both synergistic and antagonistic effects occurring between certain element combinations. Cr+Al had synergistic effects on their co-incorporation, while V negatively affected Al incorporation, and both V and Zn negatively affected Cr incorporation. In contrast, Mo was minimally associated with hematite, and As prevented hematite formation completely. X-ray diffraction indicated contraction and expansion of the hematite unit-cell upon substitution was related to the ionic radius of the substituting element in single-element samples, while V predominantly controlled the direction of deviation in multi-element samples. X-ray absorption near-edge structure spectroscopy indicated V was present as a mixture of V3+-V5+, with a higher average V oxidation state associated with multi-element samples. Results provide new insights into trace element geochemistry within hematite, and highlight the importance of multi-element studies to better understand natural and anthropogenic systems.

Synthesis and Structure Stabilization of Disordered Rock Salt Mn/V-Based Oxyfluorides as Cathode Materials for Li-Ion Batteries

The demand for high-performance lithium-ion batteries and thus efficient cathode materials is steadily increasing. In addition to a high energy density and long lifetime, these should also be cost-effective and environmentally benign. Manganese-based materials have particular potential because manganese is available in sufficient quantities and can be supplied at a comparatively low cost. Hence, in this study, manganese-based disordered rock salt oxyfluorides Li2Mn1–xVxO2F (0 ≤ x ≤ 0.5) are synthesized as cathode materials for lithium-ion batteries using high-energy mechanochemical ball-milling. The effect of partial vanadium substitution on the sample properties is analyzed, focusing on the electrochemical properties. Furthermore, a heat treatment process for stabilization of the samples is followed, where the morphology and structure of the samples are studied by powder X-ray diffraction and electron microscopy (SEM/TEM). The oxidation states of the transition metals in the synthesized compositions are further investigated using X-ray absorption near-edge structure spectroscopy. The data analysis reveals that the heat treatment resulted in increased symmetry and reduced defects of ball-milled compounds, but it may also affect the local fluorination degree in the structure. However, the results show that this treatment process has a beneficial effect on capacity retention of the formulated electrodes (∼81% after 100 cycles), a faster response to the change of cycling rate, and less increase in charge-transfer resistance of the samples during cycling. Such a structural improvement attributed to mitigation of the surface/bulk defects is an additional input to the series of cathode candidates of low temperature stability.

Transition-Metal Catalysts for Methane Dehydroaromatization (Mo, Re, Fe): Activity, Stability, Active Sites, and Carbon Deposits

The most studied catalysts for methane dehydroaromatization (MDA)─Mo/ZSM-5─are not commercialized yet due to the rapid deactivation and insufficient activity. Catalytic systems based on Fe and Re are potential alternatives to Mo-containing zeolites. Here, we compare the catalytic performance of these catalysts as a function of metal type and its loading in ZSM-5 zeolite. The results show that the catalytic activity decreases in the order of Re/ZSM-5 > Mo/ZSM-5 > Fe/ZSM-5, while the catalyst stability decreases in the opposite order: Fe/ZSM-5 > Mo/ZSM-5 > Re/ZSM-5. The active metal species in the working catalysts were determined by operando X-ray absorption near-edge structure spectroscopy combined with mass spectrometry. We found that Re0 and Fe2+ species are the most likely active species for the catalytic dehydroaromatization of CH4 to aromatics in respective catalysts. Combining the pulse reaction technique with operando thermogravimetry analysis–mass spectrometry experiments, we demonstrate that the length of the induction period strongly correlates to the activity of the catalyst. The longer induction period of the Fe/ZSM-5 catalyst indicates the slow growth of hydrocarbon pool intermediates inside the zeolite pores and thus explains its poor catalytic performance. Finally, both the formation of hydrocarbon pool species and the activity of Fe/ZSM-5 can be improved by increasing the Fe loading, reaction pressure, and space velocity.

Rhombohedral and Turbostratic Boron Nitride Polytypes Investigated by X-ray Absorption Spectroscopy

The electronic structure of rhombohedral sp2-hybridized boron nitride (r-BN) is characterized by X-ray absorption near-edge structure spectroscopy. Measurements are performed at the boron and nitrogen K-edges (1s) and interpreted with first-principles density functional theory calculations, including final state effects by applying a core hole. We show that it is possible to distinguish between different 2D planar polytypes such as rhombohedral, twinned rhombohedral, hexagonal, and turbostratic BN by the difference in chemical shifts. In particular, the chemical shift at the B 1s-edge is shown to be significant for the turbostratic polytype. This implies that the band gap can be tuned by a superposition of different polytypes and stacking of lattice planes.

Ca Minerals and Oral Bioavailability of Pb, Cd, and As from Indoor Dust in Mice: Mechanisms and Health Implications.

Elevating dietary calcium (Ca) intake can reduce metal(loid)oral bioavailability. However, the ability of a range of Ca minerals to reduce oral bioavailability of lead (Pb), cadmium (Cd), and arsenic (As) from indoor dust remains unclear. This study evaluated the ability of Ca minerals to reduce Pb, Cd, and As oral bioavailability from indoor dust and associated mechanisms. A mouse bioassay was conducted to assess Pb, Cd, and As relative bioavailability (RBA) in three indoor dust samples, which were amended into mouse chow without and with addition of , , Ca gluconate, Ca lactate, Ca aspartate, and Ca citrate at . The mRNA expression of Ca and phosphate (P) transporters involved in transcellular Pb, Cd and As transport in the duodenum of mice was quantified using real-time polymerase chain reaction. Serum 1,25-Dihydroxyvitamin D3 [], parathyroid hormone (PTH), and renal CYP27B1 activity controlling synthesis were measured using ELISA kits. Metal(loid) speciation in the feces of mice was characterized using X-ray absorption near-edge structure (XANES) spectroscopy. In general, mice exposed to each of the Ca minerals exhibited lower Pb-, Cd-, and As-RBA for three dusts. However, RBAs with the different Ca minerals varied. Among minerals, mice fed dietary did not exhibit lower duodenal mRNA expression of Ca transporters but did have the lowest Pb and Cd oral bioavailability at the highest Ca concentration (; 51%-95% and 52%-74% lower in comparison with the control). Lead phosphate precipitates (e.g., chloropyromorphite) were observed in feces of mice fed dietary . In comparison, mice fed organic Ca minerals (Ca gluconate, Ca lactate, Ca aspartate, and Ca citrate) had lower duodenal mRNA expression of Ca transporters, but Pb and Cd oral bioavailability was higher than in mice fed . In terms of As, mice fed Ca aspartate exhibited the lowest As oral bioavailability at the highest Ca concentration (; 41%-72% lower) and the lowest duodenal expression of P transporter (88% lower). The presence of aspartate was not associated with higher As solubility in the intestine. Our study used a mouse model of exposure to household dust with various concentrations and species of Ca to determine whether different Ca minerals can reduce bioavailability of Pb, Cd, and As in mice and elucidate the mechanism(s) involved. This study can contribute to the practical application of optimal Ca minerals to protect humans from Pb, Cd, and As coexposure in the environment. https://doi.org/10.1289/EHP11730.

Phosphorus speciation along a soil to kettle hole transect: Sequential P fractionation, P XANES, and 31P NMR spectroscopy

Phosphorus (P) is an essential element for all living organisms but can also be an important factor in the eutrophication of aquatic/marine ecosystems. Kettle holes are often situated in regions under intense agricultural land use where there is a high risk of nutrient transfer to larger waterbodies. The chemical speciation of soil P influences its rate of transfer from arable fields to aquatic environments. However, there is a paucity of information on the P speciation in kettle holes and their effect on the P cycle. Thus, we investigated the P composition of arable soils and kettle hole sediments in surface and subsurface layers along a transect of an agricultural field. Multiple P analyses were carried out including modified sequential Hedley P fractionation, P K-edge X-ray absorption near edge structure (XANES) spectroscopy, and 31P nuclear magnetic resonance (NMR) spectroscopy. The Pt concentrations ranged from 680 to 1123 mg kg−1 in the soils and 797 to 2591 mg kg−1 in the sediments. A predominance of the residual-P fraction, characterized as not extractable P, occluded P or stable forms of organic P (Po) was determined by sequential fractionation, ranging from 37 to 67 % followed by 3 to 38 % H2SO4-Pi and 3 to 16 % NaOH-Po of total P (Pt) in the soils and sediments. Analyses with P K–edge XANES spectroscopy assigned 61 to 100 % Fe- and Al-P, 0 to 14 % Ca-P, and 0 to 39 % Po in the arable soils and 46 to 74 % Fe- and Al-P, 14 to 43 % Ca-P, and 0 – 38 % Po in the adjoining kettle hole sediments. Solution 31P NMR spectra on alkaline extracts revealed a broad signal in the phosphomonoester region, which was the most abundant form of organic P across all samples. Besides, the proportion of ‘complex’ phosphomonesters (broad signal) to that of total extractable P was about 2-fold greater in the kettle hole sediments than in soils. Complex forms of organic P are known to be strongly associated with organic matter (OM) and appear to accumulate on a decadel timeframe. Therefore, it is desirable that kettle hole sediments are conserving P (and carbon), which will help reduce the transfer of P from agricultural fields to other, more vulnerable aquatic/marine ecosystems.

Formation of oriented layered MoS2 from amorphous thin film revealed by polarized x-ray absorption spectroscopy

MoS2 is a prototypical two-dimensional van der Waals (vdW) solid, where covalently bonded S–Mo–S triplets are held together by weaker vdW forces. In this work, we have studied structural transformation from a three-dimensional amorphous phase of MoS2 into a layered vdW crystal using S L2,3 edge x-ray absorption near-edge structure (XANES) spectroscopy with in-plane and out-of-plane polarized x-ray beam. The crystallization process, which starts from an isotropic amorphous phase, is accompanied by the establishment of vdW interaction between covalently bonded layers, resulting in the anisotropic nature of the crystalline phase. We have disclosed that the preferential growth of MoS2 layers along the (200) Bragg reflection commences immediately from the amorphous phase with no intermediate crystal orientations. We have additionally identified a unique signature in the S L2,3 edge spectrum that is associated with vdW bonds and can be possibly used to determine sulfur-based single-layered and multi-layered transition metal dichalcogenides.

Molecular-Level Insights into Phosphorus Transformation Mechanisms in Entisol Soils under Multiple Long-Term Fertilization Regimes

Improving phosphorus (P) fertilization strategies benefits mitigating future global P shortage and reducing legacy P loss risk in agricultural lands. In this study, the molecular transformation mechanisms of P in Entisol soils under multiple long-term fertilization regimes including PK; NK; NPK; NPK with pig manure (NPKM); and NPK with rice straw return (NPKS) were investigated by sequential fractionation (SF), synchrotron-based P K-edge X-ray absorption near-edge structure (P-XANES) and solution 31P nuclear magnetic resonance (P-NMR) spectroscopy. Compared with conventional NPK fertilization, a higher accumulation of total P occurred in soils under the PK, NPKM and NPKS treatments. By SF, there were relatively higher contents of NaHCO3-extracted inorganic P (Pi) fractions for the soils under PK (52.5 mg/kg) and NPKM (35.5 mg/kg) fertilization relative to the NPK (23.3 mg/kg) treatment. Consistently, P-XANES analysis revealed that there was a higher proportion of brushite, as a bioavailable P form, in soil under the PK and NPKM treatments compared with the NPK treatment, indicating higher P availability in the Entisol soils under PK and NPKM fertilizations. By P-NMR, long-term PK fertilization resulted in relatively a higher ratio of orthophosphate diesters to orthophosphate monoesters after correction compared with the NPK fertilization, which strongly suggested that N deficiency enhanced the biodegradability of soil organic P (Po) pools, thus providing new molecular-level insights into soil Po transformation. Collectively, these results, obtained from a long-term experimental study, facilitates the comprehensive understanding of P availability and transformation mechanisms in Entisol soils under multiple fertilization regimes, and thus benefits the improvement of fertilization strategies in agricultural soils.