Synchrotron X-ray Absorption Near-edge Structure Research Articles

K3V3(PO4)4/C: A new carbon-coated layered structure cathode material for potassium-ion batteries

The emergence of layered structure materials has positioned itself as a focal point in the progress of potassium-ion battery (KIBs) cathode materials, as it faces challenges concerning cycling-induced structural stability. In this particular investigation, the successful synthesis of a carbon-coated polyanionic layered composite denoted as K3V3(PO4)4/C has been achieved. K3V3(PO4)4/C was subsequently employed as a novel positive electrode material for KIBs. Upon subjecting it to 100 cycles at a current density of 200 mA g−1, the discharge specific capacity exhibited a remarkable value of 37 mAh g−1, thus showcasing a capacity retention of 88%. Impressively, even after undergoing 300 cycles at a high current density of 400 mA g−1, the capacity retention remained constant at 85%. The superior long-term cycling performance and high capacity retention observed in K3V3(PO4)4/C can be attributed to the inherent stability of the polyanionic layered structure and the dual contributions derived from the carbon coating. Furthermore, the application of characterization techniques such as synchrotron X-ray absorption near-edge structure spectroscopy (XANES) revealed a V valence state of + 3 within the synthesized sample. By establishing a structural model for K3V3(PO4)4/C and conducting first-principles calculations on its band structure and density of states, it was confirmed that the material facilitates electron transfer. An investigation into potassium ion migration and diffusion elucidated the involvement of tetrahedral site hopping (TSH). The successful synthesis of K3V3(PO4)4/C material not only provides valuable insights but also serves as a reference for the development of KIBs cathode materials.

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.

Pseudocapacitive Deionization of Saltwater by Mn3O4@C/Activated Carbon.

Capacitive deionization (CDI), a m ethod with notable advantages of relatively low energy consumption and environmental friendliness, has been widely used in desalination of saltwater. However, due to the weak electrical double-layer electrosorption of ions from water, CDI has suffered from low throughput capacity that may limit its commercial applications. Thus, it is of importance to develop a high-efficiency and engineering-feasible CDI process. Manganese and cobalt and their oxides, being faradic materials, have a relatively high pseudocapacitance, which can cause an increase of positive and negative charges on opposing electrodes. However, their low conductivity properties limit their electrochemical applications. Pseudocapacitive Mn3O4 nanoparticles encapsulated within a conducting carbon shell (Mn3O4@C) were prepared to enhance charge transfer and capacitance for CDI. Desalination performances of the Mn3O4@C (5-15 wt %) core-shell nanoparticles on activated carbon (AC) (Mn3O4@C/AC) serving as CDI electrodes have thus been investigated. The pseudocapacitive Mn3O4@C/AC electrodes with relatively low diffusion resistances have much greater capacitance (240-1300 F/g) than the pristine AC electrode (120 F/g). In situ synchrotron X-ray absorption near-edge structure spectra of the Mn3O4@C/AC electrodes during CDI (under 1.2 and -1.2 V for electrosorption and regeneration, respectively) demonstrate that reversible faradic redox reactions cause more negative charges on the negative electrode and more positive charges on the positive electrode. Consequently, the pseudocapacitive electrodes for CDI of saltwater ([NaCl] = 1000 ppm) show much better desalination performances with a high optimized salt removal (600 mg/g·day), electrosorption efficiency (48%), and electrosorption capacity (EC) (25 mg/g) than the AC electrodes (288 mg/g·day, 23%, and 12 mg/g, respectively). The Mn3O4@C/AC electrode has a maximum EC of 29 mg/g for CDI under +1.2 V. Also, the Mn3O4@C/AC electrodes have much higher pseudocapacitive electrosorption rate constants (0.0049-0.0087 h-1) than the AC electrode (0.0016 h-1). This work demonstrates the feasibility of high-efficiency CDI of saltwater for water recycling and reuse using the low-cost and easily fabricated pseudocapacitive Mn3O4@C/AC electrodes.

Incipient metal and sulfur extraction during melting of metasomatised mantle

A long-standing debate on the genesis of magmatic-hydrothermal Cu-Au deposits is whether the elevated oxygen fugacity (fO2) and metal endowment of their parental magmas are inherited from the mantle source or acquired during fractionation within the crust. This debate is built mainly on the composition of magmas emplaced into the upper crust that underwent varying degrees of differentiation and assimilation, which inevitably obscure their relationship to mantle processes. Here, we approach this debate from a new perspective by studying melt generation directly in mantle samples. This opportunity is provided by xenoliths from Lake Bullen Merri (Australia), which record partial melting of a pre-existing metasomatic assemblage. Melting occurred when the xenoliths were incorporated in hot basalts and carried towards the surface, where quenching upon eruption froze-in the melt-restite relationships. These samples preserve patches and interconnected networks of silicate glass along grain boundaries, caught in the act of undergoing melting and melt extraction. Melting consumed mainly metasomatic hornblende, phlogopite, and clinopyroxene, generating shoshonitic compositions that can be sulfide-rich, or have negligible sulfide content. We use four independent approaches to estimate the fO2 of glass, including sulfide content, oxybarometry based on spinel-olivine pairs, Fe3+/Fetot of glass determined by synchrotron X-ray absorption near-edge structure (XANES) spectroscopy, and Cu/Fe ratio of the sulfide assemblage. Sulfide-rich melt had higher fO2 compared to the sulfide-poor melt, and these characteristics were inherited from the metasomatic assemblage; the oxidation state of the melts controlled their sulfide content. Subduction-modified mantle can thus store elevated oxidation state, sulfur, and metal content for hundreds of millions of years before low-degree partial melting generates oxidised, sulfur- and metal-enriched high-K/shoshonitic melts in post-collisional settings.

Temperature Dependence of Yb Valence in an Au–Al–Yb Intermediate-Valence Quasicrystal Investigated by Yb <i>L</i><sub>3</sub>-Edge X-ray Absorption Near-Edge Structure Spectroscopy

In this paper, we investigate the temperature dependence of Yb valence in an Au–Al–Yb intermediate-valence quasicrystal by Yb L3-edge synchrotron X-ray absorption near-edge structure spectroscopy. The Yb valence of 2.61+ at room temperature decreases monotonically as the temperature decreases, indicating that the Yb ionic radius increases as the temperature decreases and is consistent with the anomalous suppression of the thermal shrinkage of this quasicrystal by cooling, as previously reported. The Yb valence changes by −0.053 on cooling from 298 to 2 K, and its change is more gradual on the high-temperature side than on the low-temperature side with the boundary around 200 K. Additionally, the effect of the changes in the Yb valence on the volume is quantitatively examined. The ratio of the volume changes due to the change in Yb valence per Yb atom, ΔVYb, to the amount of change in Yb valence, Δν, which is expressed as ΔVYb/Δν, was evaluated. The value of ΔVYb/Δν was estimated to be −2.8 Å3/unit Yb valence/Yb atom, whose value was close to that evaluated for YbInCu4.

Selecting High Zinc Wheat Cultivars Increases Grain Zinc Bioavailability.

Improving the concentration and bioavailability of zinc (Zn) in cereal grains is an important way to solve the problem of Zn deficiency in human body. The bioavailability of Zn is related to both its distribution and speciation in grains. In the current study, we examined the differences of Zn concentration, distribution, and speciation within grains among wheat cultivars with similar high grain yield but contrasting grain Zn concentration using synchrotron micro X-ray fluorescence (μ-XRF) and X-ray absorption near-edge structure (XANES). Results showed that compared to the low-Zn cultivar, the Zn concentration was 103, 50, 76, 33, and 64% higher in the crease region, aleurone layer, scutellum, embryonic axis, and endosperm of the high-Zn cultivar, respectively. Zinc mainly colocalized with phosphorus (P) in the aleurone layer and the scutellum, but less colocalization of Zn with P and a much lower concentration ratio of P/Zn were found in the high-Zn cultivar. Sulfur (S) is present in the form of scattered spots in the endosperm in accord with Zn, but the colocalization of Zn with S was predominant in the modified aleurone layer and the nucellar projection of the high-Zn cultivar. XANES results showed the lower proportion of Zn-phytate in the high-Zn cultivar. Findings indicated that it is possible to select the high-yield wheat cultivar with both high grain Zn concentration and high bioavailability, which provide a new perspective for genetic Zn biofortification.

The representation of skin colour in medieval stained glasses: The role of manganese

The present study concerns a corpus of 17 glass pieces representing character heads, originating from 11 major cathedrals and churches from North Western France and which constitute the masterpiece of stained glass windows. Skin complexion ranges from colourless to flesh-tone and purple. These glasses have been investigated using non-destructive and non-invasive techniques. Particle Induced X-ray Emission and Particle Induced Gamma Emission analyses at AGLAE show that these glass pieces show potassic plant ash glass compositions, typical to 12th −15th centuries. The compositional variability of the major glass components remains limited, similar to that found for single monuments, despite the diversity of geographic origins. The Mn and Ba concentrations follow a different trend in flesh-coloured or purple glasses and in colourless glasses, suggesting that the sources of Ba and Mn in these two kinds of glasses originated from different raw materials. Purple and flesh tone glasses contain more manganese than colourless glasses with an almost similar iron content. Synchrotron X-ray absorption near-edge structure spectroscopy (XANES) and portable UV–visible-NIR optical absorption spectroscopy indicate that glass colour varies with results from Fe2+, Fe3+, Mn2+ and Mn3+. The thickness of the glasses, about 3 mm, has been measured using ultrasound techniques. Its dispersion is similar in the various coloured glasses. This parameter mostly influences the colour saturation but not the hue. Obtaining flesh-coloured or purple glasses requires some control of the oxidation state of manganese during glass making. Divalent manganese is largely prevalent and the colour change from flesh-tone to purple hues is driven by small variations in the Mn3+ content. As these variations are not related to the Fe/Mn ratio, the resulting glass colour is difficult to predict on the only basis of glass composition. Due to the low kinetics for obtaining a redox equilibrium state between furnace atmosphere and the silicate melt, using Mn4+- and Mn3+-oxide minerals made it possible to favour oxidized melts, provided the glasses be taken out of the oven before redox equilibrium be reached: the shorter the melting time, the more oxidized will be resulting glass. This shows that medieval glassmakers were able to overcome the challenge of making glasses under highly oxidizing conditions to retaining enough oxidized manganese to favour flesh-tone and purple colours in wood-fuelled furnaces.

Synchrotron XANES and EXAFS evidences for Cr+6 and V+5 reduction within the oil shale ashes through mixing with natural additives and hydration process

Solid friable residues (i.e. Ash) from combusted oil shale are a major environmental issue because they are highly enriched with toxic elements following combustion. The synchrotron based techniques X-ray Absorption Fine Structure (XAFS) were used for determining the changes in speciation of Chromium (Cr) and Vanadium (V) in the ash and its mixtures with Red soil and Phosphogypsum as additives, through one-year period of hydration process. The X-ray Absorption Near Edge Structure (XANES) qualitative results indicate that all mixtures exhibits similar patterns showing that Vanadium has remain as pentavalent state, on the contrary Chromium has dramatic decreased from hexavalent to trivalent. This change in Cr speciation became clearer with increasing hydration period. Therefore, the results confirmed the advantage of the hydration process in the Cr(VI) reduction which might be due the domination of carbonate phase within all mixtures, thus hydration caused carbonate dissolution that increase the pH toward more alkaline which caused the Cr(IV) reduction into less-harmful and less mobile Cr(III). This increase in pH was not in favor of changing the V(V) into V(IV) due to its large stability field V(V). The Extend X-ray Absorption Fine Structure (EXAFS) analysis showed that Cr exhibiting a coordination shell of C-atoms as first nearest neighbors backscattering atoms around Cr, and at C-atoms backscattering at medium range order. This confirmed the domination of carbonate media through the best fitting of Cr–C. Which might be attributed to the more alkaline conditions developed during saturation of water (hydration), that accelerates of the reduction of Cr(VI) into Cr(III). This means simply that hydration of the ash can reduce the presence of harmful Cr(VI) in these ash tailings.

Resolving the Evolution of Atomic Layer-Deposited Thin-Film Growth by Continuous In Situ X-Ray Absorption Spectroscopy

In situ synchrotron X-ray absorption near-edge structure characterization of thin-film titania growth by atomic layer deposition (ALD) over ZnO nanowires reveals persistent low-coordinated Ti motifs leading to a new picture of ALD growth. Through the design of growth and measurement cycles, Ti K-edge spectral data are continuously recorded so as to characterize the film evolution as a function of ALD cycle number and the surface changes within the time scale of the ALD cycle. A unified set of analysis tools is developed to interpret the time-series of spectral data. A prenucleation stage of growth, a transition region, and then a steady-state growth stage are observed with distinguishable features. Multivariate curve resolution analysis, that is physically constrained, demonstrates two specific spectral components with associated, time-dependent concentrations. The bulk-film component tracks the stages of growth. The surface and interface components, present throughout the stages of growth, reveal a significant coverage of relatively isolated or loosely networked tetrahedrally coordinated Ti atomic motifs. Finally, spectral signatures for the intra-cycle growth kinetics are reconstructed at a time resolution of ∼ 1 s and demonstrate that the transient Ti motifs on the growing surface stabilize within a few seconds of the Ti precursor pulse.

A primordial 15N-depleted organic component detected within the carbonaceous chondrite Maribo

We report on the detection of primordial organic matter within the carbonaceous chondrite Maribo that is distinct from the majority of organics found in extraterrestrial samples. We have applied high-spatial resolution techniques to obtain C-N isotopic compositions, chemical, and structural information of this material. The organic matter is depleted in 15N relative to the terrestrial value at around δ15N ~ -200‰, close to compositions in the local interstellar medium. Morphological investigations by electron microscopy revealed that the material consists of µm- to sub-µm-sized diffuse particles dispersed within the meteorite matrix. Electron energy loss and synchrotron X-ray absorption near-edge structure spectroscopies show that the carbon functional chemistry is dominated by aromatic and C=O bonding environments similar to primordial organics from other carbonaceous chondrites. The nitrogen functional chemistry is characterized by C-N double and triple bonding environments distinct from what is usually found in 15N-enriched organics from aqueously altered carbonaceous chondrites. Our investigations demonstrate that Maribo represents one of the least altered CM chondrite breccias found to date and contains primordial organic matter, probably originating in the interstellar medium.

In Operando X-ray Studies of High-Performance Lithium-Ion Storage in Keplerate-Type Polyoxometalate Anodes.

Polyoxometalates (POMs) have emerged as potential anode materials for lithium-ion batteries (LIBs) owing to their ability to transfer multiple electrons. Although POM anode materials exhibit notable results in LIBs, their energy-storage mechanisms have not been well-investigated. Here, we utilize various in operando and ex situ techniques to verify the charge-storage mechanisms of a Keplerate-type POM Na2K23{[(MoVI)MoVI5O21(H2O)3(KSO4)]12 [(VIVO)30(H2O)20(SO4)0.5]}·ca200H2O ({Mo72V30}) anode in LIBs. The {Mo72V30} anode provides a high reversible capacity of up to ∼1300 mA h g-1 without capacity fading for up to 100 cycles. The lithium-ion storage mechanism was studied systematically through in operando synchrotron X-ray absorption near-edge structure, ex situ X-ray diffraction, ex situ extended X-ray absorption fine structure, ex situ transmission electron microscopy, in operando synchrotron transmission X-ray microscopy, and in operando Raman spectroscopy. Based on the abovementioned results, we propose that the open hollow-ball structure of the {Mo72V30} molecular cluster serves as an electron/ion sponge that can store a large number of lithium ions and electrons reversibly via multiple and reversible redox reactions (Mo6+ ↔ Mo1+ and V5+/V4+↔ V1+) with fast lithium diffusion kinetics (DLi+: 10-9-10-10 cm2 s-1). No obvious volumetric expansion of the microsized {Mo72V30} particle is observed during the lithiation/delithiation process, which leads to high cycling stability. This study provides comprehensive analytical methods for understanding the lithium-ion storage mechanism of such complicated POMs, which is important for further studies of POM electrodes in energy-storage applications.

Adsorption and oxidation of SO2 on the surface of TiO2 nanoparticles: the role of terminal hydroxyl and oxygen vacancy-Ti3+ states.

Herein, the absorption and oxidation reactions of SO2 on TiO2 nanoparticles (TiO2 NPs) at 296 K under various environmental conditions (humidity, UV irradiation, and ozone copresence) were investigated by using a flow chamber reaction system, synchrotron X-ray absorption near-edge structure (XANES) and high resolution synchrotron X-ray photoelectron spectroscopy (XPS) measurements. The results showed that oxidation of SO2 to sulfate via TiO2 NP catalysis happened at a very rapid rate. The appropriate relative humidity, UV irradiation and co-presence of ozone all markedly promoted SO2 oxidation on TiO2 NPs. High resolution XPS unraveled that the terminal hydroxyl (OHt) and oxygen vacancy (VO)-Ti3+ states on TiO2 NPs were the active sites for SO2 adsorption and oxidation. The data of XPS measurements suggest that SO2 was adsorbed on a OHt next to a Ti3+ VO and reacted to form HSO3-. HSO3- can then transform into SO32-via transfer of a proton. The resulting adsorbed SO32- could bind to a surface bridging O (Ob) atom and transform into SO42-. A H2O molecule could dissociate on VO-Ti3+ into two bridging hydroxyl (OHb) groups, subsequently forming new Ob, which provides an active O site for the adsorbed HSO3-/SO32- and oxidizes them into HSO4-/SO42- on the surface of the TiO2 NPs. The copresence of O3 could promote H2O dissociation into OHb, promoting the formation of Ob. The copresence of O3 may also promote the dissociation of adsorbed H2O into TiO2-O2- and hydroxyl radicals (˙OH) on VOs, facilitating the oxidation of adsorbed HSO3-/SO32-. Under UV irradiation, new VOs were created via oxidation of lattice O by photo-generated holes, resulting in increased Ob and subsequently enhanced oxidation of adsorbed HSO3-/SO32- on TiO2 NPs.

On the Germanium Incorporation in Cu2ZnSnSe4 Kesterite Solar Cells Boosting Their Efficiency

The presence of Ge during the synthesis of thin film kesterite Cu2ZnSnSe4 (CZTSe) solar cell absorbers boosts their power conversion efficiency, especially due to an improved open circuit voltage. The mechanism underlying this beneficial effect of Ge is still under debate. We gained deep insights into the role of Ge by applying advanced synchrotron nanoprobe-based X-ray fluorescence spectroscopy and X-ray absorption near-edge structure spectroscopy to cross-sectional lamellas taken from high efficiency devices. We observe that Ge remains in the CZTSe absorber layer after the synthesis process with a specific heterogeneous distribution. Different grains contain different Ge concentrations. Moreover, Ge depletion exists at random grain boundaries but not at symmetric Σ3-boundaries, leading to different band alignments. The incorporated Ge occupies Sn lattice sites in the CZTSe crystal structure; however, the concentration is only 0.1 to 0.5 at %. Also Ge aggregates in nanoscale inclusions, which we could id...

Lanthanum chromite for visible light-driven photocatalytic hydrogen evolution

Lanthanum chromite (LaCrO3) photocatalysts have been successfully prepared via a sol-gel route followed by thermal treatment through calcination in air atmosphere. The structures and properties of the as-prepared samples are examined with various techniques, including synchrotron X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Their photocatalytic activity on hydrogen evolution from aqueous methanol solution is investigated under visible light (λ > 400 nm). Results show that the local structures and chemical states of the cations, La3+ and Cr3+, are insensitive to the calcination temperature, as confirmed by XANES and EXAFS. The highest hydrogen evolution rate is achieved by the LaCrO3 sample calcined at 1100 °C and loaded with 0.01 wt% Pt co-catalyst, which is 2.11 μmol/h.

Root-induced soil deformation influences Fe, S and P: rhizosphere chemistry investigated using synchrotron XRF and XANES.

Rhizosphere soil has distinct physical and chemical properties from bulk soil. However, besides root-induced physical changes, chemical changes have not been extensively measured in situ on the pore scale. In this study, we couple structural information, previously obtained using synchrotron X-ray computed tomography (XCT), with synchrotron X-ray fluorescence microscopy (XRF) and X-ray absorption near-edge structure (XANES) to unravel chemical changes induced by plant roots. Our results suggest that iron (Fe) and sulfur (S) increase notably in the direct vicinity of the root via solubilization and microbial activity. XANES further shows that Fe is slightly reduced, S is increasingly transformed into sulfate (SO42- ) and phosphorus (P) is increasingly adsorbed to humic substances in this enrichment zone. In addition, the ferrihydrite fraction decreases drastically, suggesting the preferential dissolution and the formation of more stable Fe oxides. Additionally, the increased transformation of organic S to sulfate indicates that the microbial activity in this zone is increased. These changes in soil chemistry correspond to the soil compaction zone as previously measured via XCT. The fact that these changes are colocated near the root and the compaction zone suggests that decreased permeability as a result of soil structural changes acts as a barrier creating a zone with increased rhizosphere chemical interactions via surface-mediated processes, microbial activity and acidification.

Amorphous calcium phosphate in the pupal cuticle of Bactrocera dorsalis Hendel (Diptera: Tephritidae): A new discovery for reconsidering the mineralization of the insect cuticle

It is now widely accepted that Hexapoda emerged from Crustacea. Compared to the ubiquitous calcified exoskeleton in crustaceans, a mineralized cuticle in insects is extremely rare. Catecholamine-driven protein cross-links play a leading role in the sclerotization of insect cuticle. In this study, mineralization was discovered in the pupal cuticle of Bactrocera dorsalis (Diptera: Tephritidae), a common pest of fruit farms. We mainly profiled the features of mineralized pupal cuticles from B. dorsalis and its white mutant B. dorsaliswh and unmineralized cuticle from Musca domestica using high-resolution field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) combined with structural analysis involving infrared (IR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and synchrotron X-ray absorption near-edge structure (XANES) spectroscopy. We also compared the thermodynamic and mechanical properties of different pupal cuticles. The results showed that the pupal cuticles of B. dorsalis contain a phase of stable amorphous calcium phosphate (ACP) with a high level of magnesium, which is mainly distributed in the exocuticle and assists in the formation of a graded, stiffened cuticle structure. Unexpectedly, this ACP possesses a very low Ca/P ratio and has a composition similar to that of CaHPO4·2H2O. The degree of mineralization in the pupal cuticle of B. dorsaliswh (approximately 22 wt%) is significantly greater than that of wild-type B. dorsalis (approximately 12 wt%), which indicates that there may be a connection between the biomineralization and tyrosine-mediated tanning pathways. These findings provide new evidence for the mineralization of the insect cuticle, which may shed new light on the evolutionary mechanism underlying the divergence of cuticle sclerotization between insects and crustaceans.

Steeping and germination of wheat (Triticum aestivum L.). II. Changes in spatial distribution and speciation of iron and zinc elements using pearling, synchrotron X-ray fluorescence microscopy mapping and X-ray absorption near-edge structure imaging

Iron (Fe) and zinc (Zn) in wheat are mainly present as insoluble phytates in the aleurone cells. Phytate breakdown during steeping and germination of wheat enhances their bio-accessibility. However, the accompanying redistribution within the grain and changes in speciation are still unclear. We unravelled these changes using a combination of wheat fractionation by pearling, X-ray fluorescence microscopy mapping and X-ray absorption near-edge structure imaging. A significant fraction of Zn and Fe migrates to radicles and coleoptiles during germination. The remainder has low water extractability (≤8%). The high water extractability (26–27%) of Zn in the radicle and coleoptile indicates its mobility in the seedling. Zn migrates from the aleurone to the pericarp and embryonic tissues, while Fe is dominantly present in the scutellum tissue attached to the seedling. The co-localisation of Zn and sulfur (S) in the developing embryo suggests that translocated Zn is bound to S-containing peptides. In aleurone cells Fe remains phytate bound and although Zn is phytate and S-bound, slight changes in its speciation occur during germination. This study partially explains the impact of steeping and germination on mineral bio-accessibility and opens possibilities for enhancing nutritional quality during food processing.

Effects of composition and heat treatment on manganese–bismuth magnets

Synchrotron X-ray absorption near-edge structure (XANES) spectra are used to complement X-ray diffractometry (XRD) in the phase identification of pressed manganese–bismuth (MnBi) pellets. The heat treatment at 1000°C for 10 min after the synthesis improves the ferromagnetic properties. The magnetisation and coercive field are further enhanced when the Mn:Bi ratio is raised to 2:1. The obtained magnetic properties are related to the MnBi peaks in XRD patterns as well as the Mn-edge XANES spectra. Although the spectra in the case of Mn:Bi ratio of 2:1 and 3:1 resemble that of MnO reference, the pre-edge is shifted by the contribution of zero valent Mn and the peak intensity is reduced. A variety of phases in MnBi alloys dictate their magnetic properties required for permanent magnets and desirable ferromagnetic properties are governed by the increase of MnBi phase at the expense of MnO.

Pseudo-equilibrium equation of calcium phosphate precipitation from aqueous solution.

An X-ray amorphous phase is frequently present at the early stage of calcium phosphate crystallization, and the relevant solution chemistry is essential for understanding the mechanism of reaction. Here, we report a quantitative study of a series of reaction systems at pseudo-equilibrium states. We determined the composition of solutions and the quantities of the precipitate samples, and characterized the long- and short-range order of the precipitate using X-ray diffraction and synchrotron X-ray absorption near-edge structure spectroscopy, respectively. We found that, in a particle with multiple structural units, only a fraction of the units was able to reach pseudo-equilibrium with the solution composition, which represents the average number of surficial clusters per unit. These findings enabled us to propose a general form of the equilibrium constant equation. The equation fits the pseudo-equilibrium data well, and it converts to the "solubility product (Ksp)" and the conventional "reaction quotient" in two limit cases, respectively. Further, using a cube model, we derived a "particle equation" that reveals the connection between the particle structure and the form of equilibrium constant equation. The dependency of the form of pseudo-equilibrium equation on the structure and size of the precipitate reveals a fundamental relation in chemistry, and its applicability remains to be examined in other reaction systems, such as those involving nanocrystals and porous materials.

Ex vivo detection of calcium phosphate and calcium carbonate in rat blood serum

The total calcium (tCa) in blood serum comprises free Ca2+ ions (fCa), protein-bound calcium (prCa), and complexed calcium by small anions (cCa). The cCa fraction, in addition to fCa, has been indicated to have some physiological activity. However, there is little evidence for the structure of its constituents. Here we report an ex vivo detection of the cCa constituents by synchrotron X-ray absorption near-edge structure spectroscopy. We collected the data directly on rat blood serum and, by making use of the reference samples, derived a spectrum that exhibits the features of cCa constituents. Among the features are those of the complexes of calcium phosphate and calcium carbonate. The detected complexes in the cCa fraction are mainly Ca(η2-HPO4)(H2O)4 and Ca(η1-HCO3)(H2O)5+, in which HPO42− and HCO3− serve as bidentate and unidentate ligands, respectively. The remained H2O molecules on the coordination sphere of Ca2+ enable these complexes to behave partially like aquated Ca2+ ions in protein-binding. Besides, as the dominant part of prCa, albumin-bound calcium (albCa) exhibits a spectrum that closely resembles that of fCa, indicating weak interactions between the protein carboxyl groups and calcium. The weak-bound cCa and albCa, along with fCa and the relevant anions, compose a local chemical system that could play a role in maintaining the calcium level in blood.