X-ray Absorption Spectroscopy Results Research Articles

Self-Assembled Fe-Phenolic Acid Network Synergizes with Ferroptosis to Enhance Tumor Nanotherapy.

Natural polyphenolic compound rosmarinic acid (RA) has good antitumor activity. However, the distinctive tumor microenvironment, characterized by low pH and elevated levels of glutathione (GSH), enhances the tolerance of tumors to the singular anti-tumor treatment mode using RA, resulting in unsatisfactory therapeutic efficacy. Targeting nonapoptotic programmed cell death processes may provide another impetus to inhibit tumor growth. RA possesses the capability to coordinate with metal elements. To solve the effect restriction of the above single treatment mode, it is proposed to construct a self-assembled nanocomposite, Fe-RA. Under tumor microenvironment, Fe-RA nanocomposite exerts the characteristics of POD-like enzyme activity and depletion of GSH, producing a large amount of hydroxyl radical (·OH) while disrupting the antioxidant defense system of tumor cells. Moreover, due to the enhanced permeability and retention effect (EPR), Fe-RA can transport Fe2+ to a greater extent to tumor cells and increase intracellular iron content. Causing an imbalance in iron metabolism in tumor cells and promoting cell ferroptosis. The results of the synchrotron X-ray absorption spectroscopy (XAS) and high-resolution mass spectrometry (HRMS) prove the successful complexation of Fe-RA nanocomposite. Density functional theory (DFT) explains the efficient catalytic mechanism of its peroxide-like enzyme activity and the reaction principle with GSH.

Directed Electron Delivery from a Pb-Free Halide Perovskite to a Co(II) Molecular Catalyst Boosts CO2 Photoreduction Coupled with Water Oxidation.

The development of high-performance photocatalytic systems for CO2 reduction is appealing to address energy and environmental issues, while it is challenging to avoid using toxic metals and organic sacrificial reagents. We here immobilize a family of cobalt phthalocyanine catalysts on Pb-free halide perovskite Cs2AgBiBr6 nanosheets with delicate control on the anchors of the cobalt catalysts. Among them, the molecular hybrid photocatalyst assembled by carboxyl anchors achieves the optimal performance with an electron consumption rate of 300±13 μmol g-1 h-1 for visible-light-driven CO2-to-CO conversion coupled with water oxidation to O2, over 8 times of the unmodified Cs2AgBiBr6 (36±8 μmol g-1 h-1), also far surpassing the documented systems (<150 μmol g-1 h-1). Besides the improved intrinsic activity, electrochemical, computational, ex-/in situ X-ray photoelectron and X-ray absorption spectroscopic results indicate that the electrons photogenerated at the Bi atoms of Cs2AgBiBr6 can be directionally transferred to the cobalt catalyst via the carboxyl anchors which strongly bind to the Bi atoms, substantially facilitating the interfacial electron transfer kinetics and thereby the photocatalysis.

Modeling manganese lithium borate-based glass using a combination of X-ray absorption spectroscopy and computer simulations

This work presents a comprehensive study on the structural analysis of manganese lithium borate-based glass, which is of significant interest in energy storage device technology. The glass, denoted as xMnO2-(1-x)(Li2O–2B2O3), with varying MnO2 compositions (x = 0.2, 0.25, and 0.3), was thoroughly investigated through a combination of X-ray Absorption Spectroscopy (XAS), Molecular Dynamics (MD) simulations, and Reverse Monte Carlo (RMC) refinement to delve into its atomic-level structure. Insights into the coordination environments were obtained from XAS results, while MD simulations revealed the structural characteristics and dynamics. RMC refinement facilitated the creation of realistic glass structures by fitting experimental constraints, establishing a solid foundation for simulated structures validated against experimental findings. This study also determined an optimal Mn2+/Mn3+ ratio of 60:40, which is instrumental in enhancing the electrochemical performance of the material, thereby contributing to a better understanding of the structural and electronic properties of the manganese lithium borate-based glass. These findings have significant implications for energy storage applications and offer directions for further studies on this interesting glass system.

Structural and electronic transformations of GeSe2 glass under high pressures studied by X-ray absorption spectroscopy

Pressure-induced transformations in an archetypal chalcogenide glass (GeSe2) have been investigated up to 157 GPa by X-ray absorption spectroscopy (XAS) and molecular dynamics (MD) simulations. Ge and Se K-edge XAS data allowed simultaneous tracking of the correlated local structural and electronic changes at both Ge and Se sites. Thanks to the simultaneous analysis of extended X-ray absorption fine structure (EXAFS) signals of both edges, reliable quantitative information about the evolution of the first neighbor Ge-Se distribution could be obtained. It also allowed to account for contributions of the Ge-Ge and Se-Se bond distributions (chemical disorder). The low-density to high-density amorphous-amorphous transformation was found to occur within 10 to 30 GPa pressure range, but the conversion from tetrahedral to octahedral coordination of the Ge sites is completed above [Formula: see text] 80 GPa. No convincing evidence of another high-density amorphous state with coordination number larger than six was found within the investigated pressure range. The number of short Ge-Ge and Se-Se "wrong" bonds was found to increase upon pressurization. Experimental XAS results are confirmed by MD simulations, indicating the increase of chemical disorder under high pressure.

Engineering a PtCu Alloy to Improve N2 Selectivity of NH3-SCO over the Pt/SSZ-13 Catalyst.

Improving the N2 selectivity is always a great challenge for the selective catalytic oxidation of ammonia (NH3-SCO) over noble-metal-based (especially Pt) catalysts. In this work, Cu as an efficient promoter was introduced into the Pt/SSZ-13 catalyst to significantly improve the N2 selectivity of the NH3-SCO reaction. A PtCu alloy was formed in the PtCu/SSZ-13 catalyst, as confirmed by X-ray diffraction, transmission electron microscopy, energy dispersive spectrometry mapping, and X-ray absorption spectroscopy results. As indicated by the X-ray photoelectron spectroscopy analysis, the Pt species in the alloyed PtCu nanoparticle was mainly present in the electron-rich state on PtCu/SSZ-13, while the electron-deficient Cu and isolated Cu2+ species were both present on the surface of PtCu/SSZ-13. Due to such a unique alloyed structure with an altered oxidation state, the N2 selectivity of NH3-SCO on the PtCu/SSZ-13 catalyst was remarkably improved, while the NH3-SCO activity was kept comparable to that on Pt/SSZ-13. The reaction path was changed from the NH mechanism on Pt/SSZ-13 to both NH and internal selective catalytic reduction mechanisms on the PtCu/SSZ-13 catalyst, which was considered the main reason for the enhanced N2 selectivity. This work provides a new route to synthesize efficient alloy catalysts for optimizing the N2 selectivity of NH3-SCO for NH3 slip control in diesel exhaust purification.

Magnetic properties and electron oxidation state transition of immunomagnetic nanoparticles specifically captured with the target bacteria

Immunomagnetic nanoparticles (IMNPs) have been widely applied for the capture and concentration in the rapid detection of target bacteria. In this research, the focus was on studying the changes in magnetic properties changes of the IMNPs when they were attached to bacterial cells. These alterations in properties could facilitate an even rapid detection of the target bacteria and eliminate the need for culturing on plating media. The variation of magnetizing values, including saturated magnetization (Ms), remanent magnetization (Mr), coercivity force (Hc), and magnetic susceptibility (χm), was analysed through M-H loops. It was observed that the magnetizing properties of the IMNPs underwent changes based on the concentrations of Salmonella Typhimurium cells in the test solution. The correlation of this phenomenon was confirmed by the results of synchrotron x-ray absorption spectroscopy (XAS), which revealed electronic transition changes in the IMNPs after capturing the bacteria cells. Additionally, the electronic bands of the magnetite nanoparticle [Fe(II) and Fe(III)] were detected, indicating an electronic transformation between the Salmonella cells and the bound IMNPs. The XAS change was further verified using different cell types, such as Campylobacter jejuni which also showed electronic transformation after attaching to IMNPs. These findings suggest that IMNP-cell attachment triggered the change in the magnetic properties of IMNPs. Such insights could serve as valuable information for the development of novel rapid bacteria detection assays/devices using magnetic sensing techniques.

Investigating intrinsic and extrinsic defects in an inorganic hybrid system (BaTiO3–CaF2) via vacuum ultraviolet-excited low-temperature luminescence

Investigations into the luminescence of undoped and Eu-doped BaTiO3@CaF2 hybrid compound, as well as its individual components, were performed at both room and low temperatures, and the findings were discussed in the context of intrinsic and extrinsic defects present in both matrices. The synthesis process employed an eco-friendly method, capable of producing crystalline phases in just 1 min of plateau time at temperatures as low as 140 °C. The microwave-hydrothermal method can provide free oxygen ions at the surface, allowing them to interact with the ions from the precursor solution of CaF2. For Eu-doped samples, while the isolated CaF2 showed the characteristic 4f65d1-4f7 Eu2+ transition, BaTiO3@CaF2 hybrid compound showed the association of two defects, resulting in emissions related to defects from oxygen ions as well as Eu2+. The evidence of intrinsic defects was confirmed by comparing the samples measured at 60 K, where the influence of lattice vibrations was reduced, leading to a decrease in non-radiative processes. Another difference observed was the presence of the 4f-4f transitions associated with the presence of Eu3+ in this sample. Discussions were further supported by X-ray Absorption Spectroscopy (XAS) results, performed at the Ti K-edge and Eu L3-edge. EXAFS parameters were estimated based on the incorporation of Eu into the CaF2 structure and replacing Ca sites. For the BaTiO3@CaF2:Eu system, both EuBa and EuTi had to be included in the fitting process, indicating that some of the Eu dopant is either in the lattice of CaF2 or in BaTiO3.

Sorption of metal elements by single-walled carbon nanotubes and x-ray absorption spectroscopy analysis

Single-walled carbon nanotubes (SWCNTs) were used for the sorption of monovalent K(I), divalent Pb(II), Zn(II), and Cd(II) in addition to hexavalent Cr(VI) metal elements from aqueous solutions. X-ray absorption spectroscopy (XAS) was employed for the preliminary characterization of the metals sorbed SWCNTs materials. The adsorption capacities of the investigated metals are associated with the functional groups involved in the sorption mechanism. The sorption and XAS results revealed that hexavalent Cr(VI) was highly adsorbed by SWCNTs. The sorption mechanism of Cr(VI) is associated with the reduction of Cr(VI) to trivalent Cr(III). XAS also suggested that in the environment nearest to the sorbed metals Cr, Pb, Zn, and K, the existing binding interactions are Cr–O, Pb–O, Zn–O, and K–O respectively.

Bench-scale processing of TiBOx/h-BN ceramics for alkaline water splitting applications

ABSTRACT: The successful development of novel materials for widespread alkaline water splitting has the potential to significantly reduce costs and accelerate industrialization. In this study, the commercialized materials ceramic structure TiBOx/h-BN was processed with a bench-scale facility, reaching the 480 mV overpotential at the current density of 10 mA cm−2 in oxygen evolution reaction (OER). Notably, this modified structure demonstrated stability in harsh industrial environments (6 M KOH, 60 °C), maintaining a current density of 580 mA cm−2 for 640 h, which suggests its potential to replace existing nickel-based anode materials. During the laboratory modification process, we selectively leached the OER unfavorable structures in the multicomponent ceramics based on the excellent properties of the narrow bandgap of the conductive ceramic bulk. As a result, an interfacial amorphous structure and a highly conductive bulk that synergistically achieves high OER performance were formed. The effectiveness of this method was corroborated by both X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) results. This study provides a new strategy for developing stable and cost-effective OER materials for industrial alkaline water electrolysis (AWE) applications.

Modulation of the Work Function of TiO2 Nanotubes by Nitrogen Doping: Implications for the Photocatalytic Degradation of Dyes

The work function engineering in metal-oxide nanostructures by judicious doping of impurities is not straightforward as it introduces multiple defects in the system. In this regard, understanding the nitrogen (N) doping-induced modulation of Fermi levels in TiO2 nanotubes (TNTs) is challenging for visible-range photocatalytic applications. Here, 50 keV N ions are implanted in TNTs with a fluence range of 1014–1016 ions/cm2. X-ray diffraction and micro-Raman analyses demonstrate the formation of anatase-TiO2 in pristine TNTs, while the crystalline quality is significantly affected by increasing ion fluence. The evolution of Ti3+ is also established by X-ray photoelectron spectroscopy, whereas ultraviolet photoelectron spectroscopy reveals the reduction in work function due to the formation of oxygen vacancies, in good agreement with X-ray absorption spectroscopy and photoluminescence results. The electron paramagnetic resonance study further identifies the evolution of Ti3+/N-substitutional defect centers. Finally, an enhancement in visible-light-assisted methylene blue and Rhodamine B dye degradation is recorded up to a fluence of 1 × 1015 ions/cm2, and it is correlated with the N-ion implantation-induced formation of electrochemically active states near the conduction band minimum and the valence band maximum. The decrease in degradation efficiency beyond a critical fluence of 1015 ions/cm2 is discussed on the ground of ion-beam-mediated amorphization and the subsequent increase in electron–hole recombination in the defect states.

Anion-induced robust ferroelectricity in sulfurized pseudo-rhombohedral epitaxial BiFeO3 thin films via polarization rotation.

Polarization rotation caused by various strains, such as substrate and/or chemical strain, is essential to control the electronic structure and properties of ferroelectric materials. This study proposes anion-induced polarization rotation with chemical strain, which effectively improves ferroelectricity. A method for the sulfurization of BiFeO3 thin films by introducing sulfur anions is presented. The sulfurized films exhibited substantial enhancement in room-temperature ferroelectric polarization through polarization rotation and distortion, with a 170% increase in the remnant polarization from 58 to 100.7 μC cm-2. According to first-principles calculations and the results of X-ray absorption spectroscopy and high-angle annular dark-field scanning transmission electron microscopy, this enhancement arose from the introduction of S atoms driving the re-distribution of the lone-pair electrons of Bi, resulting in the rotation of the polarization state from the [001] direction to the [110] or [111] one. The presented method of anion-driven polarization rotation might enable the improvement of the properties of oxide materials.

Effect of cobalt content on point defects and local structure in activated Ca3(VO4)2 single-crystal solid solutions

Doping-induced structural changes of Co-activated calcium orthovanadate Ca3(VO4)2 (CVO) single crystals and specific local behavior of cobalt ions depending on the dopant content are presented in this paper. CVO is activated with over-stoichiometric Co3O4 of different concentration (CVO:xCo; x ​= ​0.1, 0.5, 1.0, 1.5, 2.0 ​wt %) during the Czochralski growth. Single-crystal synchrotron X-ray diffraction study shows gradual increase in the number of Ca crystallographic sites occupied by cobalt ions with increasing dopant concentration: from Ca3 site for CVO:0.1Co to additionally Ca2 and Ca4 sites for CVO:0.5–1.5Co, and also to Ca1 site for CVO:2.0Co. Vacancies in the tetrahedral vanadium V2 site are detected for all samples, and those in the tetrahedral V1 site are additionally found for CVO:2.0Co. Disordering of O1, O4, O7 oxygen sites is observed in all structures. Combined results of X-ray diffraction analysis and X-ray absorption spectroscopy showed that the formal charge of Co ions is mixed between 2+ and 3+ with the prevalence of 2+. A trend towards a decrease in formal charge with an increase in Co concentration is observed. The coordination number of Co(2+δ)+ ions is found to be 4.6 and polyhedron is intermediate between tetrahedral and octahedral.

Pd/BEA hydrocarbon traps: Effect of hydrothermal aging on trapping properties and Pd speciation

Interest in Pd/zeolites as automobile exhaust catalysts has driven research focused on understanding the chemical environment of Pd active centers. Here, we studied the effects of hydrothermal deactivation on a Pd/BEA hydrocarbon trap. Hydrothermal aging (HTA) led to decreased ethylene storage capacity and oxidation activity. Characterization by x-ray absorption spectroscopy (XAS) and NOx adsorption indicated that for lower Si/Al ratio samples, the amount of ion exchanged Pd increased after HTA. Temperature programmed desorption of NOx after NO exposure revealed two desorption peaks, with a high temperature peak that increased in area with increased aging temperature. Based on infrared spectroscopy, XAS and reactor results, the high temperature desorption peak is consistent with NO stored on Pd+. The Pd+ formed during NO adsorption, existing originally as [Pd(OH)]+. This species was less active in ethylene storage and oxidation than the original Pd2+ species. [Pd(OH)]+ stored NOx to a higher temperature than Pd2+.

Speciation and thermodynamic properties of La(III)-Cl complexes in hydrothermal fluids: A combined molecular dynamics and in situ X-ray absorption spectroscopy study

Chlorine is the most common ligand in geofluids, and one of the most important complexing agents for rare earth elements. The geometry and thermodynamic properties of La(III)-Cl complexes determined by previous experimental studies show inconsistency especially at temperature over 350 °C. Here, ab initio molecular dynamics (MD) simulations were employed to determine the nature and thermodynamic properties of La(III)-Cl complexes at temperature up to 500 °C and pressure up to 30kbar. The simulations were ground proofed by in situ X-ray absorption spectroscopy (XAS) results (400 bar, 25 to 500 °C). Both MD and XAS show an increase in the relative stabilities of chloride complexes with increasing temperature. The formation constants of LaCln3-n (n = 1–3) complexes were calculated using trmodynamic integration method that is within ab initio MD. The calculated formation constants of LaCl2+ and LaCl2+ at temperatures below 400 °C agree with Migdisov et al.’s (2009) extrapolations from the Helgeson-Kirkham-Flowers (HKF) equation-of-state. We fitted the HKF equation-of-state parameters of LaCln3-n (n = 1–3) within the Deep Earth Model (DEW, Sverjensky et al., 2014) to enable the calculations of the formation constants up to 1200 °C, 60 kbar, based on the previous experimental data and the new results. The predictions confirm the increased stability of chloride complexes with increasing temperature and further underline the effect of pressure on La speciation: while LaCl3(aq) becomes important in Cl-rich metamorphic and magmatic hydrothermal fluids (T > 350 °C; P < 5kbar) circulating in the upper crust, LaCl2+ and LaCl2+ appear to be the dominant complexes under higher pressure characteristic of the lower crust or subducting slab environments.

Interaction of Zn with ferrihydrite and its cooperative binding in the presence of PO4

In nature, zinc (Zn) ions interact with natural organic matter and soil metal (hydr)oxides. The resulting solid-solution partitioning is of major importance for the geochemical cycling and environmental risks of toxicity and deficiency. Ferrihydrite (Fh) is an important proxy for the natural metal (hydr)oxide fraction in soils. At its surfaces, Zn2+ ions have multi-component interactions, for instance with phosphate (PO43−). In nature, the latter is particularly relevant in topsoils since PO4 is omnipresent and has a high affinity for Fh. Zinc and phosphate ions may bind cooperatively by electrostatic forces and/or by ternary complex formation. This was studied presently with batch adsorption experiments using freshly prepared and well-characterized Fh nanoparticles. The data have been interpreted using the charge distribution (CD) model combined with a surface structural model for Fh that includes site heterogeneity. The CD coefficients have been derived independently by optimization of the surface geometries with molecular orbital calculations applying density functional theory (MO/DFT/B3LYP/6-31+G**). These computations confirm that upon adsorption Zn can change spontaneously its coordination number from 6 to 4. In agreement with literature results from X-ray absorption spectroscopy (XAS), Zn is bound at low loading as a double-corner bidentate complex. At higher loading, the number of ions in the second shell of Zn decreases according to published XAS results. Our model with the formation of surface complexes with single corner-sharing can quantitatively predict this decrease. Zn polymerization only occurs at a very high molar Zn/Fe ratio (>0.1), which can be described using a neutral, hydrolyzed Zn-dimer species. The presence of PO4 enhances the Zn adsorption, especially in the pH range 5–6. At the Zn and PO4 levels studied, no ternary Zn-P surface complexes can be revealed. For comparison, we re-interpreted copper (Cu)-PO4-Fh adsorption literature data with similar metal and PO4 loadings. In line with the results for Zn, no ternary Cu-P surface complexes were found. We conclude that electrostatic interactions explain metal adsorption at background levels in multi-component systems, and that ternary complexes may form only at rather extreme metal or PO4 loading conditions.

X-ray absorption spectroscopy and actinide electrochemistry: a setup dedicated to radioactive samples applied to neptunium chemistry.

A spectroelectrochemical setup has been developed to investigate radioactive elements in small volumes (0.7 to 2 ml) under oxidation-reduction (redox) controlled conditions by X-ray absorption spectroscopy (XAS). The cell design is presented together with in situ XAS measurements performed during neptunium redox reactions. Cycling experiments on the NpO22+/NpO2+ redox couple were applied to qualify the cell electrodynamics using XANES measurements and its ability to probe modifications in the neptunyl hydration shell in a 1 mol l-1 HNO3 solution. The XAS results are in agreement with previous structural studies and the NpO22+/NpO2+ standard potential, determined using Nernst methods, is consistent with measurements based on other techniques. Subsequently, the NpO2+, NpO22+ and Np4+ ion structures in solution were stabilized and measured using EXAFS. The resulting fit parameters are again compared with other results from the literature and with theoretical models in order to evaluate how this spectroelectrochemistry experiment succeeds or fails to stabilize the oxidation states of actinides. The experiment succeeded in: (i) implementing a robust and safe XAS device to investigate unstable radioactive species, (ii) evaluate in a reproducible manner the NpO22+/NpO2+ standard potential under dilute conditions and (iii) clarify mechanistic aspects of the actinyl hydration sphere in solution. In contrast, a detailed comparison of EXAFS fit parameters shows that this method is less appropriate than the majority of the previously reported chemical methods for the stabilization of the Np4+ ion.

Efficiency and mechanisms of Sb(III/V) removal by Fe-modified biochars using X-ray absorption spectroscopy

Fe-modified biochars (FeBC) are effective antimony (Sb) removal materials; however, the removal mechanisms require further investigation. In this study, aqueous Sb(III) and Sb(V) removal by FeBC (300, 600, and 900 °C) was evaluated, with the adsorption mechanisms investigated using X-ray absorption spectroscopy (XAS). Screening results (based on removal efficiencies) using different types of FeBC indicated the 900 °C FeCl3-modified biochar (FeCl3BC900) achieved the best Sb(III/V) removal performance. The kinetics of the Sb(III/V) removal process were best fitted by a pseudo-second-order model. Additionally, the isothermal results were described by Langmuir and Redlich-Peterson models. Aqueous analysis and X-ray absorption near-edge structure data fitting indicated Sb(III) was oxidized to Sb(V) in the Sb(III)-spiked system, and the oxidation extent increased with increasing pyrolysis temperature. The oxidation process rapidly occurred in both the solution and biochar. No Sb(V) was reduced to Sb(III) in the Sb(V)-spiked system. The XAS results of the isothermal experiment indicated the oxidation capacity of FeCl3BC900 was limited for high initial Sb(III) concentrations. The Sb-Fe1 and Sb-Fe2 bonding distances were 3.05–3.10 and 3.47–3.54 Å, respectively, indicating inner-sphere complexes were formed during the Sb(III/V) removal processes. The Sb(III/V) removal mechanisms included electrostatic adsorption, inner-sphere complexes, and coprecipitation. Oxidation was also involved in Sb(III) removal.

Elucidation of Operating Mechanism of BiFeO3 As a Negative Electrode for Na-Ion Batteries Using in Operando XAS Investigation

Sodium-ion batteries (SIBs) are gaining much attention in the global market of rechargeable batteries especially in the field of large-scale electrical energy storage systems. Considering the increasing demand for the efficient energy storage systems, it is necessary to design new electrode materials, which are capable to deliver higher reversible capacity. A wide spectra of positive electrode materials were employed in sodium ion batteries, whereas more development is required in the field of negative electrodes. Anode materials of sodium-ion batteries were mainly classified under insertion, conversion and alloying type materials1. Among the conversion type materials, Perovskite materials have gained significant attention as conversion type anode materials in sodium-ion batteries, owing to the high theoretical capacity possessed by these materials2,3.BiFeO3 is one such perovskite which possess the potential to deliver higher reversible capacity through conversion and alloying reactions4.In the present work, BiFeO3 was synthesized using a sol-gel method. Structural and morphological characterizations were done with X-ray diffraction and Field emission scanning electron microscopy techniques. Further, electrochemical studies were carried out in a sodium half-cell in the voltage range 0.01-3.00 V vs. Na+/Na. In the cyclic voltammogram, pronounced difference is observed between the first and subsequent cycles and to understand the reason behind this, elucidation of operating mechanism is required. In situ/ex situ XRD techniques are usually not sufficient to get information regarding the operating mechanism of conversion type electrode materials as these converts into metallic nanoclusters (without a long-range order) distributed in Na2O matrix during the insertion of Na+ ions. Hence, in this work, element specific X-ray absorption spectroscopic (XAS) technique was applied to elucidate the oxidation state and coordination environment changes of BiFeO3 during cycling in a sodium half-cell. Evidences for the electrochemical activity of Bi through conversion reaction (Bi3+ - Bi0) and alloying reaction (with metallic Na) during first discharge was obtained from XAS results. Further, involvement of Fe in the charge storage mechanism through conversion of its oxidized (Fe3+) form to metallic Fe was also observed, which is absent in previous literature reports. In the subsequent charging, reversible dealloying and subsequent oxidation of Bi and oxidation of Fe were noted. The Bi LIII edge and Fe K edge XAS results during second discharge reveals that similar conversion and alloying reactions occur as in the case of first discharge by reduction of Bi and Fe oxides. However, Fe and Bi oxides exists in different oxidation states at the end of first charge than in pristine BiFeO3.In addition to the elucidation of operating mechanism, the electrochemical performance of BiFeO3 was optimized by varying binder and electrolyte compositions. The best electrochemical performance was obtained when Fluoroethylene carbonate was used as an electrolyte additive. Acknowledgement A. Bhaskar gratefully acknowledge financial support from “DST-IISc Energy Storage Platform on Supercapacitors and Power Dense Devices” through the MECSP-2K17 program under grant no. DST/TMD/MECSP/2K17/20”. D. Dixon acknowledges the financial support from funding agency, Science and Engineering Board (SERB), New Delhi, India through Ramanujan Fellowship, under the grant number SB/S2/ RJN-162/2017. A. Surendran is grateful to UGC New Delhi (Ref. no.:63/CSIR-UGC NET DEC. 2017) for the UGC SRF grant and Academy of Scientific and Innovative Research (AcSIR), Ghaziabad- 201002, India. A.T acknowledges the Council of Scientific and Industrial Research (CSIR) for a senior research fellowship and Innovative Research (AcSIR), Ghaziabad- 201002. DESY, Hamburg, Germany is acknowledged for the beamtime allocation at the P65 beamline at PETRA III and we acknowledge the beamline scientist Dr. Edmund Welter for the support. The CIF, CSIR-CECRI is acknowledged for technical support with material characterization. Reference [1] Wu, C., Dou, S. X. & Yu, Y. The State and Challenges of Anode Materials Based on Conversion Reactions for Sodium Storage. Small 14, 1–20 (2018).[2] M. Nakayama, H. Ikuta, Y. Uchimoto, M. Wakihara, Changes in local structure during electrochemical Li insertion into A-site deficient perovskite oxides, La1/3NbO3, J. Phys. Chem. B,107(2003)10715-10721[3] M. Kong, K. Liu, J. Ning, J. Zhou, H. Songa, Perovskite framework NH4FeF3/carbon composite nanosheets as a potential anode material for Li and Na ions storage, J. Mater. Chem. A, 5(2017)19280-19288[4] X. Dinga, Y.Liub, Hollow bismuth ferrite combined graphene as advanced anode material for sodium-ion batteries, 30(2020)153-159

Precise Construction of Stable Bimetallic Metal–Organic Frameworks with Single-Site Ti(IV) Incorporation in Nodes for Efficient Photocatalytic Oxygen Evolution

Precise Construction of Stable Bimetallic Metal–Organic Frameworks with Single-Site Ti(IV) Incorporation in Nodes for Efficient Photocatalytic Oxygen Evolution

Exploring the structure of atom-precise silver-palladium bimetallic clusters prepared via improved single-pot co-reduction synthesis protocol.

Designing atom-precise bimetallic clusters with a relatively cost-effective and more abundant metal than Au (i.e., Ag) is desirable for the development of heterogeneous bimetallic cluster catalysts for industrial applications. Atom-precise Ag-based bimetallic clusters, which are analogs of the well-studied Au based clusters, are yet to be fully explored as catalysts. Establishing the Pd loading limit and the position of the Pd dopant in AgPd bimetallic clusters will further give an insight into the structure-activity relationships for these atom-precise AgPd heterogeneous catalysts. In this study, an improved single-pot co-reduction strategy was employed to prepare the bimetallic clusters, which were then characterized by mass spectrometry, x-ray photoelectron spectroscopy (XPS), and x-ray absorption spectroscopy (XAS) to identify the loading and position of the dopant metal. Our results show that only a single dopant Pd atom can be incorporated, and in comparison with monometallic Ag25 clusters, the absorption peaks of Ag24Pd1(SPhMe2)18 2- bimetallic clusters are blue shifted due to the incorporation of Pd. The XPS and XAS results show that the Ag24Pd1(SPhMe2)18 2- bimetallic clusters have multivalent Ag(0) and Ag(I) atoms and surprisingly show Pd(II) species with significant Pd-S bonding, despite the prevailing wisdom that the Pd dopant should be in the center of the cluster. The XAS results show that the singly doped Pd atom predominantly occupies the staple position, albeit we cannot unambiguously rule out the Pd atom in an icosahedral surface position in some clusters. We discuss the ramifications of these results in terms of possible kinetically vs thermodynamically controlled cluster formation.