L3-edge XANES Research Articles

Constructing 2D Polyphenols-Based Crosslinked Networks for Ultrafast and Selective Uranium Extraction from Seawater.

The role of tannins (TA), a well-known abundant and ecologically friendly chelating ligand, in metal capture has long been studied. Different kinds of TA-containing adsorbents are synthesized for uranium capture, while most adsorbents suffer from unfavorable adsorption kinetics. Herein, the design and preparation of a TA-containing 2D crosslinked network adsorbent (TANP) is reported. The ≈1.8-nanometer-thick TANP films curl up into micrometer-scale pores, which contribute to fast mass transfer and full exposure of active sites. The coordination environment of uranyl (UO2 2+) ions is explored by integrated analysis of U L3-edge XANES and EXAFS. Density functional theory calculations indicate the energetically favorable UO2 2+ binding. Consequently, TANP with excellent adsorption kinetics presents a high uranium capture capacity (14.62mg-Ug-Ads-1) and a high adsorption rate (0.97mgg-1day-1) together with excellent selectivity and biofouling resistance. Life cycle assessment and cost analysis demonstrate that TANP has tremendous potential for application in industrial-scale uranium extraction from seawater.

Crystal chemical design, synthesis and characterisation of U(IV)-dominant betafite phases for actinide immobilisation

Crystal chemical design principles were applied to synthesise novel U4+ dominant and titanium excess betafite phases Ca1.15(5)U0.56(4)Zr0.17(2)Ti2.19(2)O7 and Ca1.10(4)U0.68(4)Zr0.15(3)Ti2.12(2)O7, in high yield (85–95 wt%), and ceramic density reaching 99% of theoretical. Substitution of Ti on the A-site of the pyrochlore structure, in excess of full B-site occupancy, enabled the radius ratio (rA/rB = 1.69) to be tuned into the pyrochlore stability field, approximately 1.48 ≲ rA/rB ≲ 1.78, in contrast to the archetype composition CaUTi2O7 (rA/rB = 1.75). U L3-edge XANES and U 4f7/2 and U 4f5/2 XPS data evidenced U4+ as the dominant speciation, consistent with the determined chemical compositions. The new betafite phases, and further analysis reported herein, point to a wider family of actinide betafite pyrochlores that could be stabilised by application of the underlying crystal chemical principle applied here.

(Digital Presentation) Molybdenum-Promoted Intermetallic PtCo ORR Catalyst

Molybdenum (Mo)-promoted intermetallic platinum-cobalt (Pt-Co) oxygen reduction reaction (ORR) catalyst with significantly enhance ORR activity was obtained through impregnation and thermal treatments using MoCl5 as a precursor. With an optimized coverage of the Mo promoters, X-ray absorption spectroscopy reveals the cluster-like Mo-Ox species effectively lowered the white line intensity of Pt in its near edge structure (Pt L-edge XANES), suggesting the further weakening of its affinity towards oxygen. The Mo-promoted intermetallic Pt-Co catalyst thus exhibited a high ORR mass activity of 0.89 A/mgPt compared to 0.22 A/gmPt for pure Pt and 0.62 A/mgPt for its parent Pt-Co respectively under RDE testing conditions. The Mo-promoted catalyst showed compelling durability losing only 29 % of its initial 0.95 V mass activity which is even higher than the non-promoted fresh PtCo catalyst (0.32 A/mgPt vs 0.24 A/mgPt). When tested under membrane electrode assembly (MEA) conditions, the high ORR activity further enabled the operation of the fuel cell under low cathode relative humidities (RH) with minimal penalties in ionic transport resistance at low current regions. Density functional theory calculations reveal the beneficial role of molybdenum oxide cluster species in lowering the d-band energy surface Pt atoms, particularly at Pt segregated regions with no Pt-Co phase in proximity to induce the strain or ligand effects.

Synthesis and characterisation of Ce-doped zirconolite Ca0.80Ce0.20ZrTi1.60M0.40O7 (M\u2009=\u2009Fe, Al) formed by reactive spark plasma sintering (RSPS)

Reactive spark plasma sintering has been utilised as a high-throughput processing route for the synthesis of two simulant zirconolite wasteform materials, targeting Ca0.80Ce0.20ZrTi1.60M0.40O7 (M = Fe3+ and Al3+). Materials were processed under 15 MPa uniaxial pressure, with heating/cooling rates of 100 °C/min to 1320 °C, maintained under vacuum. Despite moderate yield (> 80 wt%) of zirconolite-2M, a considerable Ce-rich perovskite phase was formed in both formulations, attributed to complete reduction of the Ce inventory to Ce3+, as determined by Ce L3-edge XANES analysis. The composition charge balanced with Al3+ was favoured on the basis of lower accompanying perovskite fraction.Graphical abstract

Understanding Degradation Mechanism between Garnet Solid Electrolyte Li7La3Zr2O12 and LiNi0.6Mn0.2Co0.2O2 Cathode

All-solid-state Li-ion batteries (ASSLBs) using oxide based solid electrolytes have been considered as a promising candidates for the next generation batteries due to their excellent thermal and electrochemical stability. Especially, garnet-type Li7La3Zr2O12 (LLZO) has gained much attention due to its good conductivity and large electrochemical window. Since the electrochemical window of LLZO allows usage of high voltage cathodes such as NMC (LiNixMnyCo1-x-yO2) and Li anode, it is possible to design high voltage, high capacity and safe energy storage medium using the eletrolyte.However, current attempts on exploiting LLZO as a solid electrolyte have been hindered by high resistance at the interface, especially between cathode and the solid electrolyte. Even though the importance of the issue is well known, there has not been a comprehensive understanding yet on the topic. The lack of understanding comes from the difficulty of characterizing buried interface. It is difficult to study thin interfacial region between cathode and solid electrolyte with conventional techniques since the signal from the interface is often overwhelmed by the bulk, and destructive characterization techniques ruin the signal itself.We developed model system by sputtering thin-film cathode on top of pre-prepared solid state electrolyte pellets to overcome this problem. Samples were annealed afterwards to simulate sintering process. Since the interfacial region is near surface, we could use XANES and EXAFS which are surface-sensitive and non-destructive. Those techniques gave us valuable information regarding oxidation state and local chemical environment of each element, which were used to evaluate migration tendency. Moreover, those results can be used to precisely characterize secondary phases by complementing complex XRD results. Results obtained from those characterization techniques were correlated with electrochemical analysis techniques such as EIS and chronovoltammetry to evaluate the effect of the interfacial degradation on cell performance.In this work, we aimed to obtain fundamental understanding on the instability of cathode|electrolyte interface during two different stages: manufacturing stage and operation stage. We systematically varied variables related to manufacture (Sintering temperature, sintering time, gas environment during sintering), and operation (Electrochemical potential, current density). We chose NMC622 (LiNi0.6Mn0.2Co0.2O2) as a cathode, and Al-doped cubic LLZO (Li7La3Zr2O12) as a solid electrolyte.To study degradation of NMC622|LLZO during manufacturing stage, we varied temperature condition (300°C, 500°C, 700°C for 4h respectively) and gas environment (air, O2, humidified O2, N2, CO2) during annealing. Samples annealed in air showed high interfacial resistance and poor performance, which are signs for interfacial degradation. At 700°C, formation of detrimental phase such as La2Zr2O7 and La(Ni,Co)O3 led to complete blockage of Li ions. XANES and EXAFS showed severe change of oxidation state and chemical environment of Ni and Co, which indicated that those species escaped out of the cathode and participate in the secondary phase formation. In contrast, NMC622|LLZO interface remained chemically stable up to 700°C with no formation of detrimental phase when the sample was annealed in O2. On the other hand, when the sample was annealed in humidified O2 at 700°C, detrimental phase(La2Zr2O7) could be found. In addition, we could characterize substantial amount of Li2CO3 from samples annealed in humidified O2, which could have formed by reaction between LiOH and CO2 during sample characterization done in air. Annealing in CO2 condition led to the crystallization of detrimental phases such as Li2CO3, La2O2CO3, NiCO3 at 500°C. In addition, we could see formation of La2Zr2O7 and La2(Ni,Co)O4 from the sample annealed at 700°C. In both air and CO2 environment, we could find La-(Ni,Co)-O secondary phase from annealed samples, which indicates interdiffusion at the interface. However, extent of the degradation was much higher in CO2 environment. This could be seen by the intensity of XRD peaks corresponding to secondary phases, which overwhelmed the ones corresponding to bulk LLZO. Co L-edge XANES and XRD data for samples annealed at 700°C in different gas conditions could be seen in the attached figure.These findings suggest that interfacial degradation is strongly dependent on the sintering temperature and gas environment. Sintering temperature should be kept as low as possible to avoid formation of detrimental phase. In terms of gas environment, O2 environment is the most promising since the sample remained stable up to 700°C. On the other hand, we found that CO2 and H2O(vapor) are detrimental to the sample. This could be because that they could both form phases which could extract Li out of the system, which led to formation of delithiated secondary phases such as La2Zr2O7. Findings from the work can be used to design optimal conditions to manufacture and operate all solid Li-batteries using LLZO with minimal interfacial degradation. Figure 1

Competitive Reaction of Neptunium(V) and Uranium(VI) in Potassium-Sodium Carbonate-Rich Aqueous Media: Speciation Study with a Focus on High-Resolution X-ray Spectroscopy.

Neptunium(V) and uranium(VI) are precipitated from an aqueous potassium-sodium-containing carbonate-rich solution, and the solid phases are investigated. U/Np M4,5-edge high-energy resolution X-ray absorption near edge structure (HR-XANES) spectroscopy and Np 3d4f resonant inelastic X-ray scattering (3d4f RIXS) are applied in combination with thermodynamic calculations, U/Np L3-edge XANES, and extended X-ray absorption fine structure (EXAFS) studies to analyze the local atomic coordination and oxidation states of uranium and neptunium. The XANES/HR-XANES analyses are supported by ab initio quantum-chemical computations with the finite difference method near-edge structure code (FDMNES). The solid precipitates are also investigated with powder X-ray diffraction, scanning electron microscopy-energy dispersive X-ray spectroscopy, and Raman spectroscopy. The results strongly suggest that K[NpVO2CO3](cr), K3[NpVO2(CO3)2](cr), and K3Na[UVIO2(CO3)3](cr) are the predominant neptunium and uranium solid phases formed. Despite the 100 times lower initial neptunium(V) concentration at pH 10.5 and oxic conditions, neptunium(V)-rich phases predominately precipitate. The prevailing formation of neptunium(V) over uranium(VI) solids demonstrates the high structural stability of neptunium(V) carbonates containing potassium. It is illustrated that the Np M5-edge HR-XANES spectra are sensitive to changes of the Np-O axial bond length for neptunyl(V/VI).

A Pseudotetrahedral Uranium(V) Complex.

A series of uranium amides were synthesized from N, N, N-cyclohexyl(trimethylsilyl)lithium amide [Li][N(TMS)Cy] and uranium tetrachloride to give U(NCySiMe3) x(Cl)4- x, where x = 2, 3, or 4. The diamide was isolated as a bimetallic, bridging lithium chloride adduct ((UCl2(NCyTMS)2)2-LiCl(THF)2), and the tris(amide) was isolated as the lithium chloride adduct of the monometallic species (UCl(NCyTMS)3-LiCl(THF)2). The tetraamide complex was isolated as the four-coordinate pseudotetrahedron. Cyclic voltammetry revealed an easily accessible reversible oxidation wave, and upon chemical oxidation, the UV amido cation was isolated in near-quantitative yields. The synthesis of this family of compounds allows a direct comparison of the electronic structure and properties of isostructural UIV and UV tetraamide complexes. Spectroscopic investigations consisting of UV-vis, NIR, MCD, EPR, and U L3-edge XANES, along with density functional and wave function calculations, of the four-coordinate UIV and UV complexes have been used to understand the electronic structure of these pseudotetrahedral complexes.

Electronic behaviour of Au-Pt alloys and the 4f binding energy shift anomaly in Au bimetallics- X-ray spectroscopy studies

The electronic structure and charge redistribution of 6s conduction charge and 5d charge in Au and Pt alloys, Au9Pt and AuPt9 have been investigated using a charge compensation model. It is found that, both the Au and Pt 4f binding energy (BE) exhibits a negative shift in the alloys relatively to the pure metal in apparent disagreement with electroneutrality considerations (Au is the most electronegative metallic element); more interestingly, the negative Au 4f BE shift in Au-Pt alloy is in contrast to previous observations for a large number of Au bimetallic systems with more electropositive hosts in which the more electropositive the host„ the more positive the Au 4f BE shift. This anomaly is counter intuitive to electronegativity considerations. This dilemma was resolved by the charge compensation model in which both electronegativity and charge neutrality can be satisfied and the overall charge flow δ, onto Au is small and positive and δ arises from charge flow of 6s conduction charge, Δnc onto Au site, which is partially compensated by the depletion of 6d charge Δnd at the Au site (δ = Δnc+ Δnd ∼0.1 >0). The much larger Coulomb interaction between 4f and 5d than that between 4f and 6s results in positive 4f BE shifts. The Au 4f BE shift in Au-Pt alloys together with 193Au Mössbauer data were used in the charge compensation model analysis which shows that the model is still valid in that the Au 4f shift in Au-Pt alloy arises from mainly conduction charge gain with little depletion of d charge at the Au site. The model also works for Pt. The Au and Pt 5d character in the alloys have been examined with valence band spectra which show both maintain their d characteristic in dilute alloys with Pt d piling up at the Fermi level, and the top of the Au valence band being pushed toward the Fermi level; this is confirmed with DFT densities of state calculations. When Pt is diluted in Au, it gains d charge as evident from the reduction in whiteline intensity at the Pt L3-edge XANES. What emerges from this work is a picture in which the s-d charge compensation in Au bimetallic alloys is triggered by electronegativity difference between Au and the host. For Au-Pt and Au-Pd systems, the difference in electronegativity is very small, conduction charge transfer dominates, and the Au 4f shift is negative whereas in most Au bimetallics, the larger the electronegativity difference, the larger the compensation and the larger the Au 4f shifts.

CO2 Hydrogenation over Pt-Containing UiO-67 Zr-MOFs—The Base Case

CO2 hydrogenation was carried out over Pt-containing UiO-67 Zr-MOFs at T = 220–280 °C and ambient pressure, with H2/CO2 = 0.2–9 and contact times, τ = 0.004–0.01 gcat·min·mL–1. The catalysts were characterized by XRD, N2 adsorption, FESEM, TEM and HRTEM, Pt L3-edge XANES and EXAFS, dissolution-NMR, CO chemisorption, IR spectroscopy, and TGA. A positive correlation was observed between the degree of Pt reduction and CO2 conversion. Contact time variation experiments showed that CO is a primary product of reaction, while CH4 is a secondary product. Testing of catalyst crystals with 0.15 and 2.0 μm crystal size, respectively, revealed no influence of diffusion on the reaction rate. Comparison to a conventional Pt/SiO2 catalyst showed very similar activation energy, with Eapp = 50 ± 3 kJ·mol–1. However, the turnover frequency over Pt/SiO2 was significantly lower, and Pt/SiO2 did not yield methane as a product. The Pt-containing UiO-67 Zr-MOF catalyst showed stable activity during 60 h of testing.

Correlated XANES, TEM, and NanoSIMS of presolar graphite grains

We report correlated XANES, TEM, and NanoSIMS measurements of twelve presolar graphite grains extracted from primitive meteorites and for which isotopic data indicate predominantly Type-II supernovae origins. We find continued evidence for isotopic heterogeneities in presolar graphite grains, including the first observation of a radial gradient in the inferred initial 26Al/27Al within a presolar graphite grain. The XANES spectra of these samples show a variety of minor absorbances near the C K-edge, attributable to vinyl-keto, aliphatic, carboxyl, and carbonate molecules, as well as possible damage during sample preparation. Each sample exhibits homogeneous C K-edge XANES spectra within the graphite, however, showing no correlation with isotopic heterogeneities. Gradients in the isotope ratios of C, N, O, and Al could be due to both processes during condensation, e.g., mixing in stellar ejecta and granular transport, and post-condensation effects, such as isotope dilution and exchange with isotopically normal material in the early Solar System or laboratory, the latter of which is a significant issue for high-density presolar graphite grains. It remains unknown whether the mechanisms behind isotope exchange would also affect the local chemistry and therefore the XANES spectra. Ti L-edge XANES from most Ti-rich subgrains match standard spectra for TiC and potentially TiCN. A rare rutile (TiO2) subgrain has been identified, though it lacks the lowest energy L3 peak typically seen in standard spectra. Ca has also been identified by EDXS in TiC subgrains, likely due to the decay of live 44Ti at the time of formation. Future NanoSIMS measurements will determine the variability of initial 44Ti in TiC subgrains, an important constraint on mixing in the ejecta of the grains’ parent supernovae.

Near-surface Regions of Electrochemically Polarized Chalcopyrite (CuFeS2) as Studied Using XPS and XANES

Characteristics of the non-stoichiometric near-surface layers formed at reacted chalcopyrite are important for understanding its behavior as the main mineral of copper and for various materials applications. Here, we measured Cu L-, Fe L-, and S L-edge TEY XANES, and conventional XPS from chalcopyrite electrochemically polarized in 1M HCl solution. The spectra of copper, in contrast to those of Fe and S, remain almost unchanged on the first potential cycle despite strongly varying composition of the Fe-depleted near-surface regions. The Cu L-XANES spectra of chalcopyrite electrochemically pre-reduced and then anodized, and of that first anodized and then cathodically reduced, show the same leading peak but post-edge features indicative of covellite CuS and bornite Cu5FeS4, respectively. We suggest that the invariability of the Cu L-edge XANES and Cu 2p spectra is due to tetrahedral coordination CuS4 units stable even in the highly distorted non-stoichiometric structures.

Nature of WO4 tetrahedra in blue light emitting CaWO4 probed through the EXAFS technique

Blue emission due to self trapped exciton recombination in CaWO4 is believed to be very sensitive to the nature of the WO4 structural units. The present manuscript deals with the probing of structural differences existing in WO4 tetrahedra of CaWO4 particles having varying average crystallite sizes and different blue light emission characteristics. Based on XRD, W L1 edge XANES and W L3 edge EXAFS studies, it is inferred that factors like average W–O and Ca–O bond lengths, average number of oxygen atoms around W6+ ions and disorder in WO4 tetrahedra do not have any effect on the blue luminescence intensity from the samples. The lifetime value of excitons is lower for the nanocrystals/nanoparticles of CaWO4 compared to the bulk sample. The lower lifetime of self trapped excitons and the associated decrease in blue luminescence intensity for nanoparticles/nanocrystals (compared to bulk) has been explained based on competing non-radiative processes involving the interaction of holes with surface hydroxyl groups and an associated decrease in the extent of radiative exciton recombination.

Sol–gel produced sodium calcium phosphosilicates for bioactive applications: Synthesis and structural characterisation

A series of phosphosilicates P 2O 5 (45 mol%)–CaO (20–40 mol%)–Na 2O (5–20 mol%)–SiO 2 (10–15 mol%) has been synthesised by the sol–gel route using PO(OH) 3− x (OC 2H 5) x ( x = 1, 2) as the phosphorus precursor. Evolution of the gels with temperature was studied using thermogravimetric analysis and differential thermal analysis. These phosphosilicates show good stability against crystallisation remaining fully amorphous even after calcination at 400 °C. The short-range structure of the stabilised sol–gel glasses and the effect of adding modifier oxides to the network structure have been investigated using a combination of techniques: FT-IR spectroscopy, 31P magic angle spinning NMR, high energy XRD and P L-edge XANES.

Nd L3-edge x-ray absorption near-edge structure spectroscopy of nanocrystal-dispersed soft-magnetic alloys containing very small amounts of Nd

The Nd L3-edge XANES spectra of Nd-added FINEMET type soft magnetic alloys were characterized. Meltspun amorphous metallic alloys with compositions of Fe73.5Si13.5B9Cu0.5Nb3Nd0.5 and Fe73.5Si13.5B9Nb3Nd1 were heart-treated at 850 K for various durations up to 1 h in order to induce crystallization of nanocrystalline phases inside the alloys. The introduction of small amounts of Nd to the FINEMET-type alloys resulted in enhanced crystallization temperatures. The structural evolution of Nd over time was inferred based on changes of the Nd L3-edge x-ray absorption near-edge structure spectra. When coexisting with Cu atoms, Nd atoms clustered at the early stage of heat treatment and generally remained unaltered over time. In the absence of Cu atoms, however, the neighboring atoms of Nd changed over time. Magnetic properties of the heat-treated samples were discussed in connection with such local structural changes occurring at Nd sites in addition to the typical role of Cu atoms in crystallization behaviors.

Polarized X-ray absorption spectroscopy and XPS of TiS3: S K- and Ti L-edge XANES and S and Ti 2p XPS

Sulfur and Ti 2p XPS and polarized S K- and L2,3- and Ti L2,3-edge XANES spectra have been obtained from oriented ribbon-like crystals of TiS3 grown by vapor transport. The S 2p XPS spectrum for (001) crystal faces has line widths of 0.53eV and is completely accounted for by partially overlapped 2p3/2/2p1/2 doublets for sulfide (S2−) and disulfide (S22-) species, which are separate and independent entities in TiS3. Evidence of unsaturated surface states is lacking, consistent with a surface monolayer for the (001) growth face of disulfide atoms oriented with their charge-neutral sides outward. The S K-edge XANES spectra show pronounced anisotropy in the (001) plane of TiS3 crystals, associated with the photoelectron transition channel S 1s→3pxσu∗ with the electric vector (E) parallel the a-axis (and the S–S bond of the disulfide group), and transitions to unoccupied antibonding orbitals of S–Ti bonds with E parallel to the b-axis (the direction of the well-known quasi-one-dimensional character of TiS3). The XPS and ultrasoft and soft X-ray region XANES spectra confirm the surface and near-surface structural integrity of TiS3.

Electronic Structure of LaCuO3: X-Ray Absorption Fine Structure Theoretical Analysis

Oxygen K-edge and copper L2,3-edge X-ray absorption spectra of LaCuO3 have been analyzed theoretically on the basis of a full multiple scattering formalism in the real space. Combined oxygen K-edge and Cu L3-edge XANES is shown to be a useful tool for the study of the electronic structure of LaCuO3. The full multiple scattering approach is found to be successful to analyze experimental oxygen K-edge XANES in LaCuO3, while the single scattering approximation is not valid in this case. It is found that unoccupied oxygen p-states interact with Cu 3d ones in a specific resonant manner.

Sulfur L-edge XANES study of zinc-, cadmium-, and mercury-containing metallothionein and model compounds

Sulfur L-edge XANES study of zinc-, cadmium-, and mercury-containing metallothionein and model compounds