Synchrotron Radiation X-ray Absorption Spectroscopy Research Articles

Enhanced Electrochemical Performance of Double Perovskites as Cathodes in Reversible Ceramic Electrochemical Cells through Nb Doping

Efficient and cost-effective generation of electricity and hydrogen holds promise through reversible protonic ceramic electrochemical cells (R-PCECs). However, the successful commercialization of R-PCECs depends on the advancement of air electrodes that are both highly active and durable. Here, we made an air electrode material with two phases of double perovskite and single perovskite by doping Nb into B-site of the traditional PrBaCo2O6 double perovskite. The coexistence of the mixed double perovskite and single perovskite phases demonstrates superior electrochemical performance and durability compared to pristine double perovskite and single perovskite materials when employed as cathode materials. X-ray photoelectron spectroscopy (XPS), synchrotron radiation X-ray absorption spectroscopy (XAS) and neutron diffraction analysis reveal that this enhancement is primarily attributed to the introduction of high-valence Nb5+, resulting in an increased number of oxygen vacancies and structural stability. The findings presented in this study contribute valuable insights into the design and development of advanced cathode materials for solid oxide fuel cells and electrolyzers, with the potential for applications in sustainable energy conversion and storage technologies.

Gram-scale synthesis of Ni-Zn diatomic sites catalyst for efficient electrochemical CO2 reduction

Diatomic catalysts inherit the advantages of single atom catalysts and use the adjacent metal-N sites for functional complementary and synergistic effects in electrochemical CO2 reduction (ECR). However, preparation of diatomic catalysts with high yield, Faradaic efficiency and stability together with low overpotential still remains challenging. In this work, we develop a nitrogen-doped carbon supported Ni-Zn diatomic catalyst, whose CO Faradaic efficiency of is higher than 92.0 % in the wide potential range of −0.57 ∼ −1.07 V vs RHE, and the maximum CO Faradaic efficiency is 97.5 % at −0.77 V vs RHE. And also, CN-NiZn performs an extraordinary stability for 30 h in the long-time durability test. More importantly, large-quantities (around 1.66 g) of Ni-Zn diatomic catalysts with remarkable catalytic performance can be prepared by this method. Synchrotron radiation X-ray absorption spectroscopy was tested to reflect the coordination environment and valence states around Ni and Zn atoms. Theoretical calculations further reveal that the synergistic effect between Ni and Zn binary metal sites largely reduces the energy barrier of the reaction to produce the intermediate *COOH, thus effectively increasing the selectivity of ECR. This work indicates that the introduction of another coordination metal can significantly affect the electronic structure of monatomic catalysts, thus improving the electrocatalytic activity and selectivity of ECR.

Insights into the Phase Purity and Storage Mechanism of Nonstoichiometric Na3.4 Fe2.4 (PO4 )1.4 P2 O7 Cathode for High-Mass-Loading and High-Power-Density Sodium-Ion Batteries.

Mixed-anion-group Fe-based phosphate materials, such as Na4 Fe3 (PO4 )2 P2 O7 , have emerged as promising cathode materials for sodium-ion batteries (SIBs). However, the synthesis of pure-phase material has remained a challenge, and the phase evolution during sodium (de)intercalation is debating as well. Herein, a solid-solution strategy is proposed to partition Na4 Fe3 (PO4 )2 P2 O7 into 2NaFePO4 ⋅ Na2 FeP2 O7 from the angle of molecular composition. Via regulating the starting ratio of NaFePO4 and Na2 FeP2 O7 during the synthesis process, the nonstoichiometric pure-phase material could be successfully synthesized within a narrow NaFePO4 content between 1.6 and 1.2. Furthermore, the proposed synthesis strategy demonstrates strong applicability that helps to address the impurity issue of Na4 Co3 (PO4 )2 P2 O7 and nonstoichiometric Na3.4 Co2.4 (PO4 )1.4 P2 O7 are evidenced to be the pure phase. The model Na3.4 Fe2.4 (PO4 )1.4 P2 O7 cathode (the content of NaFePO4 equals 1.4) demonstrates exceptional sodium storage performances, including ultrahigh rate capability under 100 C and ultralong cycle life over 14000 cycles. Furthermore, combined measurements of ex situ nuclear magnetic resonance, in situ synchrotron radiation diffraction and X-ray absorption spectroscopy clearly reveal a two-phase transition during Na+ extraction/insertion, which provides a new insight into the ionic storage process for such kind of mixed-anion-group Fe-based phosphate materials and pave the way for the development of high-power sodium-ion batteries.

X-Ray Absorption Spectroscopy Studies of Ti-Mn Redox Flow Battery to Clarify the Redox Reaction

Redox flow battery (RFB) is a promising candidate of large-scale stationary energy storage which is necessary to utilize renewable energy. For RFBs, the capability to easily increase the capacity by enlarging the electrolyte tank, high charge-discharge cycle performance, and wide flexibility to high- and low-frequency fluctuations are highly advantageous.Nowadays vanadium RFBs are used for practical use, but the material cost of vanadium is problematic to further spread them. An alternative candidate for commercial use is titanium-manganese (Ti-Mn) RFBs [1] whose material cost should be lower. On the other hand, the stability of the electrolyte for positive electrode (catholyte) need to be improved, because precipitates are created by a charge disproportionation reaction of Mn ions in the charged catholyte [2]. The formation of precipitates decreases the energy density and degrades the cyclability. To improve the characteristics, the chemical state and redox reaction of the electrolytes of Ti-Mn RFBs should be clarified by precise analyses.We performed synchrotron radiation X-ray absorption spectroscopy (XAS) for the electrolytes of a Ti-Mn RFB to directly observe the redox reaction [3]. In this study, the same Ti-Mn RFB electrolyte was used for both positive and negative electrodes. The Ti K-edge XAS of the electrolyte for negative electrode (anolyte) revealed gradual reduction reaction of Ti from Ti4+ on the charge process. The Ti L 2,3-edge XAS spectrum for the anolyte at state of charge (SOC) of 80% was mostly attributed to Ti3+ state. The results for Ti are consistent with electrochemical views in previous reports [2]. The Mn K-edge XAS of the catholyte gradually shifted to higher energy-side up to SOC of 50%, indicating a slight oxidation reaction of Mn from Mn2+. However, the Mn L 2,3-edge XAS spectrum for the catholyte solution at SOC of 80% was of Mn2+ state that was not changed from the initial state. Instead, scanning transmission X-ray microscopy (STXM; XAS mapping with a high spatial resolution) at the Mn L 3-edge unveiled that the precipitates mostly consist of Mn4+. Thus, the charge disproportionation reaction of 2Mn3+ -> Mn2+ (solution) + Mn4+ (precipitates) in the charged catholyte was confirmed. In the presentation, the electronic-structure change of the Ti and Mn ions in both catholyte and anolyte will be discussed in detail.

Engineering Phase Transition from 2H to 1T in MoSe2 by W Cluster Doping toward Lithium-Ion Battery.

Phase engineering synthesis strategy is extremely challenging to achieve stable metallic phase molybdenum diselenide for a better physicochemical property than the thermodynamically stable semiconducting phase. Herein, we introduce tungsten atom clusters into the MoSe2 layered structure, realizing the phase transition from the 2H semiconductor to 1T metallic phase at a high temperature. The combination of synchrotron radiation X-ray absorption spectroscopy, Cs-corrected transmission electron microscopy, and theoretical calculation demonstrates that the aggregation doping of W atoms is the factor of MoSe2 structure transformation. When utilizing this distinct structure as an anode component, it demonstrates outstanding rate capability and durability. After 500 cycles, this results in a specific capacity of 1007.4 mAh g-1 at 500 mA g-1. These discoveries could open the door for the future development of high-performance anodes for ion battery applications.

Toward Complete Transformation of Sodium Polysulfides by Regulating the Second-Shell Coordinating Environment of Atomically Dispersed Fe.

Room temperature sodium-sulfur (RT Na-S) batteries are highly competitive as potential energy storage devices. Nevertheless, their actually achieved reversible capacities are far below the theoretical value due to incomplete transformation of polysulfides. Herein, atomically dispersed Fe-N/S active center by regulating the second-shell coordinating environment of Fe single atom is proposed. The Fe-N4S2 coordination structure with enhanced local electronic concentration around the Fermi level is revealed via synchrotron radiation X-ray absorption spectroscopy (XAS) and theoretical calculations, which can not only significantly promote the transformation kinetics of polysulfides, but induce uniform Na deposition for dendrite-free Na anode. As a result, the obtained S cathode delivers a high initial reversible capacity of 1590 mAh g-1, nearly the theoretical value. This work opens up a new avenue to facilitate the complete transformation of polysulfides for RT Na-S batteries.

Ultra-fast surface reconstruction enabled by the built-in electric field in heterostructured CoS2/CuS for water electrolysis

Transition-metal chalcogenides (TMCs) show great potential as highly efficient and cost-effective electrocatalysts for oxygen evolution reaction (OER). Yet the electrochemical conversion into oxides/hydroxides remains poorly understood. In this work, we develop a built-in, electric-field-induced surface reconstruction strategy for ultra-fast self-activation of transition metal sites in self-supporting CoS 2 /CuS heterostructures. The activated CoS 2 /CuS grown on carbon cloth with oxygenated surface species displays an outstanding OER electrocatalytic activity with ultra-low overpotentials of only 136 mV at the current density of 10 mA cm −2 and 266 mV at 100 mA cm −2 in 1.0 M KOH. Comparative studies via synchrotron radiation X-ray absorption spectroscopy and theoretical calculations are employed to elucidate that the built-in electric field within heterointerfaces significantly promotes the reconstruction efficiency by decreasing the formation energy of (oxy)hydroxide species. We believe this work provides new perspectives to conceive catalysts with ultra-low overpotentials and complements the fundamental comprehension of TMCs’ self-reconstruction mechanism. • The nature of metallic site reconstruction upon OER is revealed via combined XAS and DFT • A simplified reconstruction process enabled by the built-in electric field of CoS 2 /CuS • The self-standing electrode shows practical potential for overall water electrolysis A comprehensive perception of the structural transformation and reconstruction of metallic surface sites upon the OER process is essential for the rational design of high-performance OER catalysts. To simplify the energy-consuming activation process and achieve rapid reconstruction, Man et al. report a built-in electric field strategy for modulating surface dynamics of heterostructured CoS 2 /CuS.

Bifunctional OER/NRR Catalysts Based on a Thin-Layered Co3O4-x/GO Sandwich Structure.

Due to ample low-coordinated surface atoms, a distorted lattice endows thin-layered transition metal oxides with a flexible electronic structure, making them the ideal candidates for overall ammonia synthesis. This work proposes a novel and facile method for the controllable synthesis of thin-layered Co3O4 catalysts with graphene as a conductive matrix to further enhance the overall N2 fixation performance. X-ray photoelectron spectroscopy (XPS) and synchrotron radiation X-ray absorption spectroscopy (XAS) demonstrate that the sandwiched Co3O4-x/GO catalysts enable exposure of more coordination unsaturated active sites, resulting in numerous oxygen vacancies. With a higher conductivity and distorted crystalline structure, excellent electrochemical NRR activity is realized with a NH3 production rate of 5.19 mmol g-1 h-1 and a Faradaic efficiency of 10.68% at -0.4 V vs reversible hydrogen electrode (RHE). The density functional theory (DFT) calculation demonstrates that introducing oxygen vacancies in thin-layered cobalt oxides could result in an increased density of states (DOS) near the Fermi level, which would accelerate the NRR rate-determining step. Charge transfer could be accelerated through a weak Co 3d-N 2p σ hybrid bond with a lower energy level. No obvious performance decay could be found after six cycles. Furthermore, the sandwiched Co3O4-x/GO catalyst exhibits a low overpotential of 280 mV@10 mA cm-2 and an outstanding durability for the anode OER, even better than those of the benchmark RuO2. Such an inexpensive sandwiched transition metal oxide catalyst shows great potential in the field of overall N2 fixation.

Tuning the electronic structure of bimetallic CoCu clusters for efficient hydrolysis of ammonia borane

Efficient and low cost catalysts for the hydrogen production from ammonia borane (AB) are highly required to build up the upcoming hydrogen economy. Here we demonstrated that the non-active material could be directly transformed to highly active catalyst for the hydrolysis of AB when the surface parts were stripped to form tiny clusters on graphene oxide (GO), with the presence of strong cluster-support interaction. Moreover, the catalytic activity can be greatly enhanced by further tuning the electronic structure of clusters with various compositions. As a result, the final bimetallic CoCu catalyst on GO can achieve a high total turnover frequency (TOF) value of 72.4 (H2) mol/(Cat-metal) mol·min with an activation energy of 47.8 kJ/mol, which is over 3 times higher than the monometallic clusters on GO. The cluster-support interaction has been clearly identified by synchrotron radiation X-ray absorption spectroscopy. An internal charge transfer from Cu to Co in the clusters can also be identified, which will weaken the B-N bond in AB and then effectively accelerate the hydrolysis of AB to achieve the high performance.

Positively Charged Pt-Based Nanoreactor for Efficient and Stable Hydrogen Evolution.

Positively charged Pt can work as the active center for hydrogen evolution reaction (HER) but the corresponding design of state‐of‐the‐art electrocatalysts at high current densities has never been realized. Here the application of positively charged Pt in an effective Fe‐PtNiPO nanoreactor for highly efficient and stable HER is demonstrated. Synchrotron radiation X‐ray absorption spectroscopy confirms the formation of internal positively charged Pt and the in situ experiments reveal the quick charge transfer in the nanoreactor. Ni‐based materials around Pt are used to tune the electronic structure and promote the water dissociation to form locally enriched H+, while a porous Fe shell can both prevent the loss of active material and allow the efficient material transport. All the beneficial compositions work together to form an effective nanoreactor for HER. As a result, the Fe‐PtNiPO nanoreactor shows a low overpotential of 19 mV to achieve 10 mA cm−2 and exhibits a high mass activity of 10.93 A mgPt −1 (at 100 mV). Most importantly, it only needs an ultra‐low overpotential of 193 mV to achieve a high current density of 1000 mA cm−2 with an excellent stability over 300 h, which represents one of the best electrocatalysts for alkaline HER and might be used for large‐scale industrial application in the future.

Microwave-assisted synthesis and characterization of undoped and manganese doped zinc sulfide nanoparticles

Undoped and Mn-doped ZnS nanocrystals were produced by the microwave-assisted solvothermal method and characterized by X-ray diffraction, photoluminescence spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy. All samples have the cubic zinc blende structure with the lattice parameter in the range of a = 5.406–5.411 Å, and the average size of crystallites is in the range of 6–9 nm. These nanoparticles agglomerate and form large grains with an average size of up to 180 nm. The photoluminescence of the undoped ZnS sample shows a broad emission band located at 530 nm, attributed to the defects at the surface of nanoparticles. In all Mn-doped samples, the emission peak at 598 nm was observed assigned to the characteristic forbidden transition between excited (4T1) and ground (6A1) levels of Mn2+. Synchrotron radiation X-ray absorption spectroscopy at the Zn and Mn K-edges combined with reverse Monte Carlo (RMC) simulations based on the evolutionary algorithm confirms that manganese ions substitute zinc ions. However, the difference in the ion sizes (R(Mn2+(IV)) = 0.66 Å and R(Zn2+(IV)) = 0.60 Å) is responsible for the larger interatomic distances Mn–S (2.40(2) Å) compared to Zn–S (2.33(2) Å). The static structural relaxations in ZnS:Mn nanoparticles are responsible for the large values of the mean-square displacements factors for Zn, S and Mn atoms obtained by RMC simulations.

Structural Characterization of Titanium-Silica Oxide Using Synchrotron Radiation X-ray Absorption Spectroscopy.

In this study, titania–silica oxides (TixSiy oxides) were successfully prepared via the sol–gel technique. The Ti and Si precursors were titanium (IV), isopropoxide (TTIP), and tetraethylorthosilicate (TEOS), respectively. In this work, the effects of pH and the Ti/Si atomic ratio of titanium–silicon binary oxide (TixSiy) on the structural characteristics of TixSiy oxide are reported. 29Si solid-state NMR and FTIR were used to validate the chemical structure of TixSiy oxide. The structural characteristics of TixSiy oxide were investigated using X-ray diffraction, XRF, Fe-SEM, diffraction particle size analysis, and nitrogen adsorption measurements. By applying X-ray absorption spectroscopy (XAS) obtained from synchrotron light sources, the qualitative characterization of the Ti–O–Si and Ti–O–Ti bonds in Ti–Si oxides was proposed. Some Si atoms in the SiO2 network were replaced by Ti atoms, suggesting that Si–O–Ti bonds were formed as a result of the synthesis accomplished using the sol–gel technique described in this article. Upon increasing the pH to alkaline conditions (pH 9.0 and 10.0), the nanoparticles acquired a more spherical shape, and their size distribution became more uniform, resulting in an acceptable nanostructure. TixSiy oxide nanoparticles were largely spherical in shape, and agglomeration was minimized. However, the Ti50Si50 oxide particles at pH 10.0 become nano-sized and agglomerated. The presence of a significant pre-edge feature in the spectra of Ti50Si50 oxide samples implied that a higher fraction of Ti atoms occupied tetrahedral symmetry locations, as predicted in samples where Ti directly substituted Si. The proportion of Ti atoms in a tetrahedral environment agreed with the value of 1.83 given for the Ti–O bond distance in TixSiy oxides produced at pH 9.0 using extended X-ray absorption fine structure (EXAFS) analysis. Photocatalysis was improved by adding 3% wt TiO2, SiO2, and TixSiy oxide to the PLA film matrix. TiO2 was more effective than Ti50Si50 pH 9.0, Ti50Si50 pH 10.0, Ti50Si50 pH 8.0, and SiO2 in degrading methylene blue (MB). The most effective method to degrade MB was TiO2 > Ti70Si30 > Ti50Si50 > Ti40Si60 > SiO2. Under these conditions, PLA/Ti70Si30 improved the effectiveness of the photocatalytic activity of PLA.

Robust ferromagnetic insulating and large exchange bias in LaMnO3:CoO composite thin films

Ferromagnetic insulators (FMIs) have received widespread attention for applications in novel low power consumption spintronic devices. Further optimizing robust ferromagnetic insulation and developing a multifunctional FMI by integrating other magnetic properties can not only ease or pave the way for actual application but also provide an additional degree of freedom for device design. In this work, by introducing antiferromagnetic CoO into the FMI LaMnO3, we constructed (1 − x)LaMnO3:xCoO composite thin films. The films simultaneously show robust FMI characteristics and a large exchange bias (EB). For the x = 0.5 sample, the resistivity is 120 Ω cm at 250 K, the magnetization is 100 emu cm−3, and the EB field is −2200 Oe at 10 K. In particular, the blocking temperature is up to 140 K. Synchrotron radiation x-ray absorption spectroscopy reveals the coexistence of Mn3+, Mn2+, Co2+ and Co3+, arising from interfacial charge transfer and space charge/defect trapping, which should be responsible for the enhanced and integrated multifunctional magnetic properties.

Uniform single atomic Cu1-C4 sites anchored in graphdiyne for hydroxylation of benzene to phenol.

ABSTRACTFor single-atom catalysts (SACs), the catalyst supports are not only anchors for single atoms, but also modulators for geometric and electronic structures, which determine their catalytic performance. Selecting an appropriate support to prepare SACs with uniform coordination environments is critical for achieving optimal performance and clarifying the relationship between the structure and the property of SACs. Approaching such a goal is still a significant challenge. Taking advantage of the strong d-π interaction between Cu atoms and diacetylenic in a graphdiyne (GDY) support, we present an efficient and simple strategy for fabricating Cu single atoms anchored on GDY (Cu1/GDY) with uniform Cu1-C4 single sites under mild conditions. The Cu atomic structure was confirmed by combining synchrotron radiation X-ray absorption spectroscopy, X-ray photoelectron spectroscopy and density functional theory (DFT) calculations. The as-prepared Cu1/GDY exhibits much higher activity than state-of-the-art SACs in direct benzene oxidation to phenol with H2O2 reaction, with turnover frequency values of 251 h−1 at room temperature and 1889 h−1 at 60°C, respectively. Furthermore, even with a high benzene conversion of 86%, high phenol selectivity (96%) is maintained, which can be ascribed to the hydrophobic and oleophyllic surface nature of Cu1/GDY for benzene adsorption and phenol desorption. Both experiments and DFT calculations indicate that Cu1-C4 single sites are more effective at activating H2O2 to form Cu=O bonds, which are important active intermediates for benzene oxidation to phenol.

Synchrotron radiation analysis of root dentin: the roles of fluoride and calcium ions in hydroxyapatite remineralization.

Although the use of fluoride for root caries control is reported to be effective, the mechanism of maintaining hydroxyapatite is still unclear. This study elucidates the roles of fluoride in the recrystallization of hydroxyapatite, and the impact of calcium to maintain the abundance of hydroxyapatite on acid-challenged root dentin with a novel approach - using synchrotron radiation. Root dentin samples obtained from 40 extracted human premolars were subjected to pH challenge in combination with fluoride treatment. The effect of fluoride on hydroxyapatite regeneration on the root was investigated by using a range of fluoride concentrations (1000-5000 p.p.m.) and the EDTA-chelation technique in vitro. Synchrotron radiation X-ray micro-computed tomography and X-ray absorption spectroscopy were utilized to characterize the chemical composition of calcium species on the surface of prepared samples. The percentage of hydroxyapatite and the relative abundance of calcium species were subsequently compared between groups. The absence of calcium or fluoride prevented the complete remineralization of hydroxyapatite on the surface of early root caries. Different concentrations of fluoride exposure did not affect the relative abundance of hydroxyapatite. Sufficient potency of 1000 p.p.m. fluoride solution in promoting hydroxyapatite structural recrystallization on the root was demonstrated. Both calcium and fluoride ions are prerequisites in a caries-prone environment. Orchestration of F- and Ca2+ is required for structural homeostasis of root dentin during acid attack. Sustainable levels of F- and Ca2+ might thus be a strict requirement in the saliva of the population prone to root caries. Fluoride and calcium contribute to structural homeostasis of tooth root, highlighting that routine fluoride use in combination with calcium replenishment is recommended for maintaining dental health. This study also demonstrates that utilization of synchrotron radiation could provide a promising experimental platform for laboratory investigation especially in the dental material research field.

Confined N-CoSe2 active sites boost bifunctional oxygen electrocatalysis for rechargeable Zn–air batteries

Designing highly active electrocatalysts that are inexpensive, highly efficient, and durable for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable zinc–air batteries (ZABs) is vital. A peapod-like CoSe2@NC bifunctional electrocatalyst is successfully fabricated herein by confining CoSe2 nanoparticles (NPs) to one-dimensional (1D) N-doped carbon (NC) nanorods based on a polyaniline encapsulation strategy. The electronic coupling role between NC and CoSe2 is revealed via X-ray photoelectron spectroscopy and synchrotron radiation X-ray absorption spectroscopy. In situ Raman spectroscopy is conducted to examine the structure of CoSe2@NC under the OER in an alkaline electrolyte. The peapod-like CoSe2@NC nanorods exhibit superior activity towards the ORR (E1/2 = 0.83 V) and OER (η = 340 mV @10 mA cm−2) in a 0.1 mol L−1 KOH solution. The as-assembled rechargeable ZAB achieves a large peak power density of 137.1 mW cm−2 and outstanding stability for 500 cycles at 10 mA cm−2. The encapsulation of CoSe2 NPs in the NC shells impedes their aggregation and corrosion during the ORR and OER processes. Experimental and DFT-based computational analyses assist in ascribing the outstanding bifunctional catalytic performance to the formation of N-CoSe2 active sites. These results provide a facile pathway for the development of efficient bifunctional electrocatalysts for high-performance rechargeable metal–air batteries.

Resonant photoemission spectroscopy of the ferromagnetic Kondo system CeAgSb2

We study the electronic structure of single crystal CeAgSb2, a low T c ferromagnetic Kondo system, using synchrotron radiation photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). We have carried out Ce 5s, Ce 5p, Sb 4d core level PES as well as Ce 4d–4f resonant PES of the valence band states of CeAgSb2. We also report the resonant PES behavior of Ce 5s and 5p core-levels and the simultaneous intensity suppression of Sb 4d core-level and Ag 4d valence band states across the Ce 4d–4f threshold. The Ce 4d–4f resonant valence band spectra show typical f 0 and f 1 features associated with Kondo behavior. The constant initial state spectra of the f 0 and f 1 features show maxima at different incident photon energies, arising from different relative contributions of surface and bulk character Ce 4f partial density of states. XAS across the Ce 3d–4f M-edge also shows the corresponding final state f 1 and f 2 features. The weak temperature dependence of the XAS spectra between T = 25 K and 300 K could be simulated using a full multiplet calculation combined with a simplified single-impurity Anderson model approach. The calculations confirm the Kondo screening and allows quantification of the bulk Ce 4f electron count in CeAgSb2. The Ce 5s states show an exchange splitting which reflects the local magnetic moment of Ce 4f states. The overall results characterize the bulk and surface sensitive Ce 4f states, and indicate the role of Kondo effect in forming the moderately enhanced heavy-fermion carriers in CeAgSb2.

Iron adsorption in Cameroon volcanic ashes insights from x-ray absorption spectroscopy

In this study, synchrotron radiation x-ray absorption spectroscopy was used to characterize natural volcanic ash from Mount Cameroon. The latter was employed to remove Fe3+ ions from aqueous solutions, as an option for its application in water treatment. The electronic properties and local structure of Fe adsorbed on the volcanic ash were investigated. The results show that the raw volcanic ashes and those used to adsorb Fe3+ are principally composed of magnetite, Fe(II) sulphate, hematite, and Fe(II) oxide. The volcanic ash materials contain Fe ions coordinated by oxygen atoms with Fe–O bond length provided by magnetite, Fe(II) sulphate, hematite, and Fe(II) oxide. Two types of interactions were suggested: one between oxygen and Fe photo-absorber in the first shell, and the second between another atom of Fe and photo-absorber in the second coordination shell. The adsorption mechanism for Fe3+ removal was attributed to the ion exchange and/or chemisorption processes.

Carbon nanotube supported PtO nanoparticles with hybrid chemical states for efficient hydrogen evolution

The HER activity can be greatly enhanced due to the favorable hybrid chemical states of Pt with both abundant Pt−O active sites and the Pt−C interaction. Efficient electrocatalysts for hydrogen evolution reaction (HER) in alkaline solution are highly required for water splitting. Here we design an ultra-small PtO x nanoparticle with hybrid Pt chemical states on carbon nanotubes as highly efficient alkaline HER catalyst, which shows a low overpotential of 19.4 mV at 10 mA cm −2 , a high mass activity of 5.56 A mg Pt −1 at 0.1 V, and a stable durability for at least 20 h. The HER performance is better than that of the benchmark 20 wt% Pt/C while the Pt content in the catalyst is only about one tenth of that in Pt/C. It also represents one of the best catalysts ever reported for HER in alkaline solution. Synchrotron radiation X-ray absorption spectroscopy reveals that the efficient and stable alkaline HER performance can be attributed to the favorable design of hybrid chemical states of Pt with carbon nanotubes, which exhibits abundant surface Pt–O as active catalytic sites and forms stable Pt–C interfacial interaction to both anchor the NPs and improve the synergistic effect between catalyst and substrate.

Nanosafety evaluation through feces: A comparison between selenium nanoparticles and selenite in rats

Nanosafety evaluation is necessary not only for nanomaterials research and development but also as a cornerstone for legal regulation. In this study, we proposed a non-invasive protocol for nanosafety evaluation through feces using metagenomics and metabolomics together with metallomics. Male SD rats were orally exposed to equal amounts of Se (Se0NPs, 3.14 or Na2SeO3, 6.28 μg/kg bw) and were sacrificed after 24 h. 16S rRNA analysis and LC–MS were used to study the impact of different forms of Se on intestinal microbiota and metabolites in fecal samples. ICP-MS and synchrotron radiation X-ray fluorescence (SR-XRF) and X-ray absorption spectroscopy (XAS) were used to study the concentration and transformation of Se in gastrointestinal track and feces. It was found that Se0NPs brought less alternation to the composition of intestinal microbiota and metabolites related to inflammation, immunity and gut-brain axis related responses than Na2SeO3 did. Besides, the absorbed Se0NPs could be more efficiently converted to organic Se which explained the comparable bioavailability to Na2SeO3. In all, the proposed protocol combined with metagenomics, metabolomics and metallomics in this study can be used for nanosafety evaluation in a non-invasive manner and this may also be used for the screening of the nanosafety of other nanomaterials.