In situ XAFS-XRD study of the Zr-Y2O3 interaction at extra-high temperatures.

The in situ measurement technique for a metal/metal-oxide mixture at extra-high temperature above 2000 K has been desired in the field of nuclear safety engineering. In the present study, we succeeded in simultaneous XAFS-XRD measurements of the Zr oxidation [Zr + O → Zr(O) + ZrO2] up to 1952 K and ZrO2-Y2O3 reaction from 1952 to 2519 K. The chemical shift during Zr oxidation was observed in the absorption spectra around the Zr K-edge, and the interatomic cation-cation and cation-oxygen distances obtained by the fitting analysis of EXAFS during the Y2O3-ZrO2 reaction are explained. Also, the temperature dependency of the anharmonic effect was investigated by comparing the fitted second- and third-order cumulants with the theoretical ones in which the Morse potential was applied as an interatomic potential, giving a good explanation about the local structure dynamics. Finally, the applicability of the developed system to investigation of nuclear fuel materials, such as UO2-Zr, is discussed.

Effect of Surface Freezing of a Cationic Surfactant and n-Alkane Mixed Adsorbed Film on Counterion Distribution and Surface Dilational Viscoelasticity Studied by Total Reflection XAFS and Surface Quasi-Elastic Light Scattering.

When liquid alkane droplets are placed on a surfactant solution surface having a proper surface density, alkane molecules penetrated into the surfactant-adsorbed film to form a mixed monolayer. Such a mixed monolayer undergoes a thermal phase transition from two-dimensional liquid to solid monolayers upon cooling when surfactant tail and alkane have similar chain lengths. We applied the total-reflection XAFS spectroscopy and surface quasi-elastic light scattering to the mixed adsorbed film of cetyltrimethylammonium bromide and hexadecane to elucidate the impact on the surface phase transition on the counterion distribution of the mixed monolayer. The EXAFS analysis verified that a higher percentage of counter Br- ions were localized in the Stern layer than in the diffuse double layer in the surface solid film compared to the surface liquid film, which resulted in a reduction in the surface elasticity measured by the SQELS. The finding that the surface phase transition accompanies the change in the counterion distribution will be important to consider the future applications of the colloidal systems, in which the coexistence of a surfactant and alkane molecules is essential, such as foams and emulsions.

Surface Freezing of Cetyltrimethylammonium Chloride-Hexadecanol Mixed Adsorbed Film at Dodecane-Water Interface.

The surface freezing transition of a mixed adsorbed film containing cetyltrimethylammonium chloride (CTAC) and n-hexadecanol (C16OH) was utilized at the dodecane-water interface to control the stability of oil-in-water (O/W) emulsions. The corresponding surface frozen and surface liquid mixed adsorbed films were characterized using interfacial tensiometry and X-ray reflectometry. The emulsion samples prepared in the temperature range of the surface frozen and surface liquid phases showed a clear difference in their stability: the emulsion volume decreased continuously right after the emulsification in the surface liquid region, while it remained constant or decreased at a much slower rate in the surface frozen region. Compared to the previously examined CTAC-tetradecane mixed adsorbed film, the surface freezing temperature increased from 9.5 to 25.0 °C due to the better chain matching between CTAC and C16OH and higher surface activity of C16OH. This then renders such systems much more attractive for practical applications.

Phase transition kinetics of LiNi0.5Mn1.5O4 analyzed by temperature-controlled operando X-ray absorption spectroscopy.

LiNi0.5Mn1.5O4 (LNMO) is a promising positive electrode material for lithium ion batteries because it shows a high potential of 4.7 V vs. Li/Li(+). Its charge-discharge reaction includes two consecutive phase transitions between LiNi0.5Mn1.5O4 (Li1) ↔ Li0.5Ni0.5Mn1.5O4 (Li0.5) and Li0.5 ↔ Ni0.5Mn1.5O4 (Li0) and the complex transition kinetics that governs the rate capability of LNMO can hardly be analyzed by simple electrochemical techniques. Herein, we apply temperature-controlled operando X-ray absorption spectroscopy to directly capture the reacting phases from -20 °C to 40 °C under potential step (chronoamperometric) conditions and evaluate the phase transition kinetics using the apparent first-order rate constants at various temperatures. The constant for the Li1 ↔ Li0.5 transition (process 1) is larger than that for the Li0.5 ↔ Li0 transition (process 2) at all the measured temperatures, and the corresponding activation energies are 29 and 46 kJ mol(-1) for processes 1 and 2, respectively. The results obtained are discussed to elucidate the limiting factor in this system as well as in other electrode systems.

Communication: Coordination structure of bromide ions associated with hexyltrimethylammonium cations at liquid/liquid interfaces under potentiostatic control as studied by total-reflection X-ray absorption fine structure.

Total-reflection X-ray absorption fine structure (TR-XAFS) technique was applied for the first time to an interface between two immiscible electrolyte solutions under potentiostatic control. The hydration structure of bromide ions was investigated at polarized 2-octanone/water interfaces. TR-XAFS spectra at Br K-edge measured in the presence of hexyltrimethylammonium bromide (C6TAB) were slightly modified depending on the Galvani potential difference (Δ(o)(w)φ). The extended X-ray absorption fine structure analysis exposed hydration structure changes of bromide ions at the polarized interface. The coordination structure of bromide ions at the interface could be analyzed as compared with bromide ions dissolved in aqueous solution and Br(-)-exchanged resin having quaternary ammonium groups. The results indicated that bromide ions were associated with C6TA(+) at the polarized interface. The relative contribution of ion association form of bromide ions with quaternary ammonium groups was enhanced at a potential close to the ion transfer of C6TA(+), where the interfacial concentration of C6TA(+) is increased as a function of Δ(o)(w)φ.

Molecular geochemistry of radium: A key to understanding cation adsorption reaction on clay minerals.

Adsorption reactions of various cations on clay minerals have different effects on their environmental behaviors depending on the molecular-scale adsorption structure. Some cations form outer-sphere complexes via hydration, while others create inner-sphere complexes through dehydration. This preference dictates their environmental impact. However, the factors controlling these complex formations remain unclear. Furthermore, research on the adsorption preferences of radium (Ra) is lacking. Thus, this study conducted the first EXAFS study of Ra2+ adsorbed on clay minerals and showed that Ra2+ forms inner-sphere complexes on vermiculite, which can be surprising because Ra2+ is a divalent cation and prefers to be hydrated. In order to investigate the factors controlling the complex formations, this study conducted systematic EXAFS measurements and DFT calculations for alkali and alkaline earth metal cations. The results showed the importance of the size-matching effect between the adsorbed cation and the cavity of the tetrahedral sheets and that the complex formation can be estimated by the combination of the ionic radius and hydration enthalpy of the adsorbed cation. Furthermore, this study also analyzed environmental core samples. Their results showed the fixation of Ra2+ by clay minerals and the controlling factors can effectively predict cation environmental behavior.

Direct observation of a metastable crystal phase of Li(x)FePO4 under electrochemical phase transition.

The phase transition between LiFePO4 and FePO4 during nonequilibrium battery operation was tracked in real time using time-resolved X-ray diffraction. In conjunction with increasing current density, a metastable crystal phase appears in addition to the thermodynamically stable LiFePO4 and FePO4 phases. The metastable phase gradually diminishes under open-circuit conditions following electrochemical cycling. We propose a phase transition path that passes through the metastable phase and posit the new phase's role in decreasing the nucleation energy, accounting for the excellent rate capability of LiFePO4. This study is the first to report the measurement of a metastable crystal phase during the electrochemical phase transition of LixFePO4.

Population Dynamics of Community Cats Living in a Tourist Area of Onomichi City, Japan, before and after the Trap-Test-Vaccinate-Alter-Return-Monitor Event.

The community cat program (CCP) was recommended by the Ministry of the Environment to reduce cats in local animal shelters and improve stray cat welfare in Japan. It is a non-lethal control measure with stray cats cared for as free-roaming cats for their lifetime in the community, while Trap-Neuter-Return (TNR) or Trap-Test-Vaccinate-Alter-Return-Monitor (TTVARM) activities are carried out. In the CCP, community cat colonies are hypothesized to be closed and static populations. However, it remains unknown whether the cats stay in the colonies, without migration of non-neutered cats following TNR/TTVARM events. We examined the population dynamics of cats before and after a TTVARM event using route censuses (107 days), fixed-point observations, and GPS-tracking in a tourist area in Onomichi. Eleven out of the 30 cats remained in the CCP areas, whereas 13 non-neutered cats immigrated into the CCP areas, within a year, suggesting the CCP program has limited efficacy. Besides, the program cannot support the lifetime management of the cats due rapid turnover of cats. Our results reject the CCP hypothesis, so that the program neither restricts cat breeding nor enhances cat welfare.

Health Status of 'Community Cats' Living in the Tourist Area of the Old Town in Onomichi City, Japan.

The "community cat program (CCP)" is a non-lethal control measure in which stray cats are owned and cared for as community cats at high welfare standards, while the Trap-Neuter-Return (TNR) or Trap-Test-Vaccinate-Alter-Return-Monitor (TTVARM) event is performed. The program is recommended by the Ministry of the Environment in Japan. Here, we evaluated the health status of community cats inhabiting a tourist area in Onomichi City. A medical check was conducted on 30 community cats as a part of the TTVARM event. The following health problems were identified: alopecia, gingivitis, incisor teeth loss, anemia, and urine glucose. An ELISA (the enzyme linked immunosorbent assay) showed that 16.7% of the cats were FIV-positive. The cats were also carriers of zoonoses (Capnocytophaga genus (100%) and Bartonella henselae (ITS, nested; 38.0%)), which pose a risk to tourists and residents. Our findings suggest that most cats require medical treatment. We recommend that friendly cats should be adopted rather than maintained as community cats and that a comprehensive review of the CCP is required.

Extended X-ray absorption fine structure spectroscopy measurements and ab initio molecular dynamics simulations reveal the hydration structure of the radium(II) ion.

Radium is refocused from the viewpoint of an environmental pollutant and cancer therapy using alpha particles, where it mainly exists as a hydrated ion. We investigated the radium hydration structure and the dynamics of water molecules by extended X-ray absorption fine structure (EXAFS) spectroscopy and ab initio molecular dynamics (AIMD) simulation. The EXAFS experiment showed that the coordination number and average distance between radium ion and the oxygen atoms in the first hydration shell are 9.2 ± 1.9 and 2.87 ± 0.06 Å, respectively. They are consistent with those obtained from the AIMD simulations, 8.4 and 2.88 Å. The AIMD simulations also revealed that the water molecules in the first hydration shell of radium are less structured and more mobile than those of barium, which is an analogous element of radium. Our results indicate that radium can be more labile than barium in terms of interactions with water.

In situ two-dimensional imaging quick-scanning XAFS with pixel array detector.

Quick-scanning X-ray absorption fine structure (XAFS) measurements were performed in transmission mode using a PILATUS 100K pixel array detector (PAD). The method can display a two-dimensional image for a large area of the order of a centimetre with a spatial resolution of 0.2 mm at each energy point in the XAFS spectrum. The time resolution of the quick-scanning method ranged from 10 s to 1 min per spectrum depending on the energy range. The PAD has a wide dynamic range and low noise, so the obtained spectra have a good signal-to-noise ratio.

Temperature dependence of multilayering at the free surface of ionic liquids probed by X-ray reflectivity measurements.

The effect of the temperature on the surface layering of ionic liquids has been studied for two ionic liquids, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide([TOMA(+)][C(4)C(4)N(-)]) and trihexyltetradecylphosphonium bis(nonafluorobutanesulfonyl)amide ([THTDP(+)][C(4)C(4)N(-)]), using X-ray reflectivity measurements at 285, 300, and 315 K. Both [TOMA(+)][C(4)C(4)N(-)] and [THTDP(+)][C(4)C(4)N(-)] develop multilayers at the surface. The structure of the multilayers at the [TOMA(+)][C(4)C(4)N(-)] surface shows little temperature-dependent change, whereas that at the [THTDP(+)][C(4)C(4)N(-)] surface clearly becomes diffused with increasing temperature. The different temperature dependence seems to be related to the difference in the recently reported ultraslow dynamics of the interfacial structure of [TOMA(+)][C(4)C(4)N(-)] and [THTDP(+)][C(4)C(4)N(-)] at the ionic liquid|water interface.

µ-XAFS of a single particle of a practical NiO(x)/Ce2Zr2O(y) catalyst.

µ-XAFS analysis using an X-ray µ-beam (1000 nm (h) × 800 nm (v)) was successfully carried out on a single particle of a practical catalyst NiO(x)/Ce(2)Zr(2)O(y) (0 ≤x≤ 1, 7 ≤y≤ 8). The oxidation state and local coordination structure of the NiO(x)/Ce(2)Zr(2)O(y) particle were characterized by Ni K-edge µ-XANES and µ-EXAFS, which showed the catalytically active and inactive phases of a single catalyst particle.

An in situ quick XAFS spectroscopy study on the formation mechanism of small gold nanoparticles supported by porphyrin-cored tetradentate passivants.

We previously reported that a porphyrin-cored tetradentate passivant, which has two disulfide straps over one face of the porphyrin plane, can produce monolayer-protected gold nanoparticles, 2-4 nm in size, by the one-pot reduction of HAuCl(4) in DMF. The resulting nanoparticles are smaller than those prepared using the same S/Au molar ratio of a monodentate passivant. To examine the formation mechanism of small gold nanoparticles, the formation of gold nanoparticles in the presence of porphyrin-cored tetradentate passivants or a structurally related monodentate passivant was studied by time-resolved quick X-ray absorption fine structure spectroscopy. The results demonstrated that all of Au ions in solution are reduced to compose small Au clusters, i.e. nuclei, just after the NaBH(4) reduction of HAuCl(4) in both cases, but their size varied with the initial S/Au molar ratios and structure of the passivants. Thus, the size of Au nuclei was kinetically controlled by the passivants. Interestingly, the porphyrin-cored tetradentate passivant could stabilize smaller gold nanoparticles, 2-4 nm in size, but it was less efficient in trapping the Au nuclei formed at a very early stage, in comparison to the monodentate passivant.

Simultaneous measurement of X-ray specular reflection and off-specular diffuse scattering from liquid surfaces using a two-dimensional pixel array detector: the liquid-interface reflectometer of BL37XU at SPring-8.

An X-ray reflectometer for simultaneous measurement of specular and off-specular reflection of liquid surfaces is described. The reflectometer, equipped with a two-dimensional single X-ray photon-counting pixel array detector obtained the full range of X-ray specular and off-specular reflections in an extremely short time (1 s). Both the specular and off-specular reflection of water exhibited good agreement with the predicted capillary-wave theory within the appropriate instrumental resolution. The approach is also demonstrated on an aqueous solution of 1-dodecyl-3-methylimidazolium chloride. The monolayer in which the dodecyl chain faces upwards and the Cl(-) anion locates next to the imidazolium ring formed on the water surface was found to be laterally homogeneous. The use of a pixel array detector will be particularly powerful for in situ measurements to investigate both out-of-plane and in-plane structures simultaneously, not only for liquid surfaces but also for other thin films.

Ionic multilayers at the free surface of an ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide, probed by x-ray reflectivity measurements.

The presence of ionic multilayers at the free surface of an ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide ([TOMA(+)][C(4)C(4)N(-)]), extending into the bulk from the surface to the depth of approximately 60 A has been probed by x-ray reflectivity measurements. The reflectivity versus momentum transfer (Q) plot shows a broad peak at Q approximately 0.4 A(-1), implying the presence of ionic layers at the [TOMA(+)][C(4)C(4)N(-)] surface. The analysis using model fittings revealed that at least four layers are formed with the interlayer distance of 16 A. TOMA(+) and C(4)C(4)N(-) are suggested not to be segregated as alternating cationic and anionic layers at the [TOMA(+)][C(4)C(4)N(-)] surface. It is likely that the detection of the ionic multilayers with x-ray reflectivity has been realized by virtue of the greater size of TOMA(+) and C(4)C(4)N(-) and the high critical temperature of [TOMA(+)][C(4)C(4)N(-)].

Condensed Film Formation and Molecular Packing in Cationic Surfactant-Cholesterol and Zwitterionic Surfactant-Cholesterol Systems at the Hexane/Water Interface.

A condensed film formation of surfactants with a charged head group at the oil/water interface was achieved by mixing surfactants of different geometric shapes to control molecular packing at the interface. The adsorbed films of mixed tetradecyltrimethylammonium bromide (C14TAB)-cholesterol (Chol) and tetradecylphosphocholine (C14PC)-Chol systems at the hexane/water interface were examined by interfacial tension and X-ray reflectivity measurements. The interfacial tension versus Chol concentration curves have break points because of the expanded-condensed phase transition of the adsorbed film. A two dimensional (2D) phase diagram, phase diagram of adsorption, indicated that 1:1 mixing in the condensed film is energetically favorable because of stronger mutual interaction between different molecules than between the same ones. The electron density profile normal to the interface manifested that the packing of C14TAB (or C14PC) and Chol molecules is like a 2D solid in the condensed state. As C14TAB and C14PC molecules take a corn shape with a large head group (critical packing parameter: CPP ≈ 1/3) and Chol takes an inverted corn shape with a bulky sterol ring (CPP > 1), the mixing of corn shape and inverted corn shape molecules produces well-ordered packing to promote solid-like molecular packing at the interface by energy gain because of vdW interaction between hydrophobic chains in addition to attractive ion-dipole interaction between head groups. Furthermore, the heterogeneous feature in the adsorbed film of the C14TAB-Chol system is explained by an interplay between contact energy and dipole interaction, which contribute to line tension at the domain boundary.

Impacts of chemical amendment and plant growth on lead speciation and enzyme activities in a shooting range soil: an x-ray absorption fine structure investigation.

In situ chemical immobilization is a practical remediation technology for metal-contaminated soils because of its capability to reduce cost and environmental impacts. We assessed the immobilization effects of poultry waste amendment and plant growth (Panicum maximum Jacq.) on Pb speciation and enzyme activities in shooting range soils. Soil contaminated with Pb was obtained from the top 20 cm of a shooting range. To evaluate Pb mobility in the soil profile treated with plants and immobilizing amendment, we used large columns filled with Pb-contaminated soil (0-20 cm, surface soils) and non-contaminated soil (20-75 cm, subsurface soils). The column study demonstrated that the amendment reduced the toxicity characteristic leaching procedure-extractable Pb in the surface soil by 90% of the Control soil. Lead mobility from the surface to subsurface profiles was significantly attenuated by plant growth but was promoted by the amendment without plant application. The extended X-ray absorption fine structure analysis revealed that the amendment reduced the proportion of PbCO(3) and Pb-organic complexes and transformed them into a more geochemically stable species of Pb(5)(PO(4))(3)Cl with 30 to 35% of the total Pb species. Applications of plant and amendment increased activities of dehydrogenase and phosphatase in the surface soil with 2.7- and 1.1-fold greater than those in Control, respectively. The use of amendments in combination with plant growth may have potential as an integrated remediation strategy that enables Pb immobilization and soil biological restoration in shooting range soils.

Solid Film Formation at the Tetradecane/Aqueous Hexadecyltrimethylammonium Bromide Solution Interface Studied by Interfacial Tensiometry and X-ray Reflectometry.

The effect of oil on condensed film formation in the adsorbed film of hexadecyltrimethylammonium bromide (C16TAB) at the tetradecane (C14)/water (W) interface was examined by interfacial tension and X-ray reflectivity measurements. The interfacial tension vs temperature curves have break point due to the expanded?condensed phase transition of the adsorbed film. The partial molar entropy of C16TAB at the interface changes discontinuously, whereas the interfacial density changes almost continuously at the phase transition point. The electron density profile normal to the interface manifested that the condensed film is regarded as a two-dimensional (2D) solid rotator phase in which C16TAB and C14 molecules are densely packed with perpendicular orientation. Combining the interfacial tension and X-ray reflectivity data, the mixing ratio of C16TAB to C14 in the solid film was determined to be 2:3 and thus the film is enriched in oil molecules than surfactant ones. Furthermore, the partial molar entropy change of C14 associated with solid film formation was found to be largely negative and very close to that of surface freezing of liquid alkane, manifesting that C14 molecules are well ordered to form a 2D solid film by mixing with C16TAB molecules at the interface. The solid film formation of the present system is driven by effective vdW interactions between adsorbed C16TAB and intercalated C14 molecules. The morphology of the condensed domain observed during phase transition suggested that the contact energy is more predominant than the dipole repulsion at the domain boundary, which promotes coalescence of small domains into large ones during phase transition.

Three-year route census study on welfare status of free-roaming cats in old-town Onomichi, Japan.

The free-roaming cat population in Japan is increasing, and these cats are regarded as a tourism resource in some areas; however, their welfare status is unknown. Thus, this study assessed the welfare status of free-roaming cats in the old town of Onomichi City, Hiroshima, Japan. Route censuses were conducted 8 times per month for 3 years to estimate cat populations in the uptown and downtown areas of Onomichi. In the 1st year, we found 124 cats and 80 cats in the uptown and downtown areas, respectively. Approximately half the cats in each area were in poor physical condition. By the 3rd year, 99 of the 124 uptown cats and 66 of the 80 downtown cats had disappeared; moreover, uptown cats in poor physical condition disappeared in significantly greater numbers than those in good condition. It was presumed most missing cats died from illness or injury as opposed to having migrated elsewhere. This study suggests the welfare status of free-roaming cats in Onomichi is poor, and organized management of these cats is a matter of great urgency to improve their status.