A new method for estimating the dispersity of deposited metallic nanoparticles and extent of their interaction with the support matrices

Using a fully relativistic DV cluster method, we study the electronic structure of a large fragment of the crystal lattice of zircon ZrSiO₄ with a plutonium dopant atom replacing a Zr⁴⁺ zirconium atom. Three possible states of the impurity center are considered: Pu⁴⁺ (isovalent substitution), Pu³⁺ (non-isovalent substitution), and Pu³⁺ with an oxygen vacancy in the nearest environment that provides charge compensation. Relaxation of the ZrSiO₄ crystal lattice near a defect is simulated using a semi-empirical method of atomic pair potentials (GULP program). An analysis of overlap populations and effective charges on atoms shows that the chemical bonding of plutonium with a matrix is covalent, while isovalent substitution yields a more stable system than a Pu³⁺ impurity. In the presence of vacancies the structure of chemical bonding is intermediate with respect to substitutions Pu⁴⁺ → Zr⁴⁺ and Pu³⁺ → Zr⁴⁺.     

Photoelectron spectroscopy and diffraction of surface nanoscale NbO/Nb(110) structures

X-ray photoelectron spectroscopy and diffraction (XPS and XPD) are applied to analyze oxygen-induced surface structures on the Nb(110) face formed due to oxygen segregation from the crystal bulk on thermal annealing to 2000 K in vacuum and/or oxygen adsorption in situ at temperatures above 1100 K. The Nb3d, O1s electronic states and valence band spectra of the NbO _x /Nb(110) surface are studied by XPS, and the results are compared with data for NbO, NbO₂, and Nb₂O₅ oxides. It is shown that niobium atoms entering the composition of surface oxide structures on Nb(110), from the standpoint of the nearest environment and chemical bond, are similar to metal states in NbO. The NbO _x layer thickness is estimated to be 0.5 nm. Two chemically inequivalent oxygen states are distinguished on Nb(110), which are, presumably, atomic chemisorbed oxygen on the parts of the clean surface of the Nb monolayer with hexagonal packing and oxygen in the composition of NbO _x -like linear clusters on Nb(110). A model of the NbO _x /Nb(110) surface takes into account a distortion of the structure of NbO _x clusters: a periodic vertical shift of metal atoms in Nb-chains and changes in Nb-O bond angles. Original Russian Text Copyright ? 2009 by M. V. Kuznetsov, A. S. Razinkin, and E. V. Shalaeva __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 3, pp. 536–543, May–June, 2009.     

Electronic structures of mixed sandwich <Emphasis Type="Italic">ansa</Emphasis>-complexes of chromium as studied by gas-phase absorption spectroscopy and quantum chemistry

Gas-phase electronic absorption spectra of ansa-(cycloheptatrienylcyclopentadienyl)-chromium complexes with silicon- and germanium-containing bridges were recorded for the first time. The spectrum of the —(SiMe₂)₂— bridged compound exhibits a Rydberg structure arising from the transitions originating at HOMO. Shortening of the bridge causes the Rydberg bands to broaden beyond detection. Density functional calculations were performed to investigate the electron density distribution in neutral complexes and the corresponding cations. An increase in the angle between the carbocycles on going from the —(SiMe₂)₂— bridged com pound to the —SiMe₂— and —GeMe₂— bridged complexes was shown to cause substantial changes in the composition and energies of the HOMO and Rydberg orbitals. Delocalization of the HOMO in the —SiMe₂— and —GeMe₂— bridged molecules leads to broadening of the Rydberg bands in the gas-phase spectra.     

Dimerization and Coordination Properties of Zinc(II)tetra-4-alkoxybenzoyloxiphthalocyanine in Relation to DABCO in <Emphasis Type="Italic">o</Emphasis>-Xylene and Chloroform

For the first time the interactions between zinc(II)tetra-4-alkoxybenzoyloxiphthalocyanine (Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc) and 1,4-diazabicyclo[2.2.2]octane (DABCO) in o-xylene and chloroform have been studied by calorimetric titration and NMR and electron absorption spectroscopic methods. It has been found that in o-xylene at concentrations of Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc higher than 6×10⁻⁴ mol⋅L⁻¹ π–π dimers species are formed (λ _max= 685 nm). Additions of DABCO to the solution up to mole ratio 1 : 8 (Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc : DABCO) lead to a shift of the aggregation equilibrium towards monomer species due to formation of monoligand axial complexes. Further increasing the DABCO concentration results in formation of Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc—DABCO—Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc sandwich dimers (λ _max= 675 nm).     

Surface Modification of Silicone Rubber by CF<Subscript>4</Subscript> Radio Frequency Plasma Immersion

Silicone rubber samples were treated by CF₄ capacitively coupled plasma at radio frequency (RF) power of 60, 100 and 200 W for a treatment time up to 20 min under CF₄ flow rate of 20 sccm, respectively. Static contact angle, ATR-FTIR and XPS, and AFM were employed to characterize the changes of surface on hydrophobicity, functional groups, and topography. The results indicate the static contact angle is improved from 100.7 to 150.2°, and the super-hydrophobic surface, which corresponds to a static contact angle of 150.2°, appears at RF power of 200 W for a 5 min treatment time. It is suggested that the formation of super-hydrophobic surface is ascribed to the co-action of the increase of surface roughness created by the ablation reaction of CF₄ plasma and the formation of [–SiF _x (CH₃)_2−x –O–] _n (x = 1, 2) structure produced by the direct attachment of F atoms to Si.     

Spectral and electrochemical study of coordination molecules Cu4OX6L4: 3-Methylpyridine and 4-Methylpyridine Cu4OBrnCl(6−n)L4 complexes

The tetranuclear Cu₄OBr_nCl_(6-n)L₄ complexes, where L = 3-methylpyridine (3-Mepy), 4-methylpyridine (4-Mepy) and n=0–6 with trigonal bipyramidal coordination of copper(II) were prepared and their infrared and electronic absorption spectra as well as cyclic voltammograms in nitromethane solutions were measured. The polyhedra in Cu₄OBr_nCl_(6−n) (3-Mepy)₄ molecules are less distorted comparing with those of 4-Mepy analogues as indicated by infrared Cu₄O absorptions, far infrared Cu—Br, Cu—Cl, and Cu—N absorptions, d—d bands in electronic spectra and potentials, measured by cyclic voltammetry. The 3-Mepy complexes exhibit strong single infrared Cu₄O absorptions, while for related 4-Mepy complexes doubly split Cu₄O bands were observed. Two strongly overlapped d—d bands in electronic absorption spectra of the 3-and 4-Mepy complexes in nitromethane were resolved by Gaussian fitting. The 4-Mepy ligand produces slightly stronger ligand field than its 3-Mepy analogue. The maxima of high-energy d—d bands are in a linear correlation with the number of bromide ligands. The correlations for corresponding low-energy bands are considerably deviated from linearity. The halfwave potentials of the complexes in nitromethane correlate with both the number of bromides and the data of electronic absorption spectra suggesting that the reducing electron at the electrode process enters the half-filled d _{z 2} orbital of the copper(II) atom. The origin of a difference between the 3-and 4-Mepy complexes in their spectral and electrochemical properties is also discussed.     

An X-ray photoelectron spectroscopic study of novel SiON glasses

Novel SiON glasses obtained by melting mixtures of crystalline α-SiO₂ and α-Si₃N₄ were investigated by means of X-ray photoelectron spectroscopy (XPS). The incorporation of nitrogen into the SiO₂ network was recently proved by ²⁹Si-MAS-NMR (magic-angle spinning nuclear magnetic resonance) and Si K-XANES (X-ray absorption near edge structure). The Si 2p XPS and the Si KLL XAES (X-ray excited Auger electron spectroscopy) studies of the SiON glasses confirm the formation of mixed structural units (SiO_xN_4-x) by the presence of an additional spectral component energetically located between SiO₂- and Si₃N₄-like signals. The N 1s and O 1s XPS spectra support the conclusion about the incorporation of nitrogen into the SiO₂ network.     

Phase transformations of ammonium tungsten bronzes

This article discusses the formation and structure of ammonium tungsten bronzes, (NH₄) _x WO_3−y . As analytical tools, TG/DTA-MS, XRD, SEM, Raman, XPS, and ¹H-MAS NMR were used. The well-known α-hexagonal ammonium tungsten bronze (α-HATB, ICDD 42-0452) was thermally reduced and around 550 °C a hexagonal ammonium tungsten bronze formed, whose structure was similar to α-HATB, but the hexagonal channels were almost completely empty; thus, this phase was called reduced hexagonal (h-) WO₃. In contrast with earlier considerations, it was found that the oxidation state of W atoms influenced at least as much the cell parameters of α-HATB and h-WO₃, as the packing of the hexagonal channels. Between 600 and 650 °C reduced h-WO₃ transformed into another ammonium tungsten bronze, whose structure was disputed in the literature. It was found that the structure of this phase—called β-HATB, (NH₄)_0.001WO_2.79—was hexagonal.     

Mechanochemical synthesis of some europium diketonates

Results on the influence of mechanoactivation (3–30 min) in a planetary ball mill on the composition, crystal structure, IR spectra and morphology of EuCl₃·6H₂O, dibenzoylmethane (HDBM) and mixtures of EuCl₃·6H₂O — HDBM and EuCl₃·6H₂O — HDBM — 1,10-phenathroline (phen) are presented. Mechanoactivation leads to a decrease of interplanar distances of the EuCl₃·6H₂O and HDBM and partial synthesis of Eu(DBM)₃ and Eu(DBM)₃·phen in the respective mixtures. The fluorescence properties of the products of activation (excitation and emission spectra, lifetime of the excited states) are similar to those of the complexes produced by the conventional “wet” methods, but the strongest excitation of the mechanochemically produced solid state samples is achieved at higher wavelength. Crystals of different forms (prismatic, needle-, long-length-leaf- and rod-like) are formed by mechanoactivation of the mentioned mixtures.     

X-ray photoelectron spectra of heterometallic 3<Emphasis Type="Italic">d</Emphasis>-metal carboxylate complexes

The electronic structure and magnetic states in the heterometallic hexanuclear complex Mn₄^IIFe₂^III (μ₄-O)₂(Piv)₁₀ · MeCN₄ have been studied by X-ray photoelectron spectroscopy (XPS). The substitution of two Mn atoms for two Fe atoms in the hexanuclear complex was found to have an effect on the patterns of iron and manganese X-ray photoelectron spectra. XPS data are evidence of the high-spin paramagnetic state of Mn^II and Fe^III atoms, as well as of the ligand-metal charge transfer upon complex formation. In the heteroatomic complex, the degree of bond covalence increased for both the manganese and iron atoms. The results obtained are in good agreement with X-ray diffraction data.     

Electronic structure of a uranium impurity center in zircon

The electronic structure of a large fragment of the crystal lattice of zircon ZrSiO₄ with a uranium impurity atom replacing the zirconium atom was investigated using the completely relativistic discrete variation (DV) cluster method. The results are compared with the data of a similar calculation of the ideal ZrSiO₄ crystal. An analysis of the overlap populations and effective charges on the atoms of the matrix and impurity showed that chemical binding of uranium with the environment is covalent, and the electron density redistribution caused by this substitution changes not only the impurity and the nearest environment, but also the atoms of the next coordination spheres.     

Physicochemical properties and catalytic performance of Pr2 − x SrxCoO4 ± y mixed oxides for NO reduction by CO

Using the polyglycol gel method, a series of Pr_{2 − x} Sr_xCoO_{4 ± y} (0.2 ≤ x ≤ 1.0) mixed oxides were prepared, and their catalytic activities were studied in the test reaction of NO reduction by CO. The solid-state physicochemical properties, including crystal structure, defect structure, IR spectrum, valence state of B-site ions, nonstoichiometry oxygen (y), oxygen species, and redox properties, were characterized by means of XRD, IR, TPD, TPR, XPS, and chemical analysis. The results show that all mixed oxides display a K₂NiF₄ structure. When x = 0.2 and 1.0, the obtained samples still have little uncertain mixed oxides; however, the mixed oxides (x = 0.4, 0.6, 0.8) all represent a single A₂BO₄ phase. With the increase of x, lattice parameters, unit-cell volume, and average crystalline size decrease gradually, whereas microstrain density, the concentration of Co³⁺, the amounts of lattice oxygen released and the concentration of oxygen vacancy increase. The catalytic activities of Pr_{2 − x} Sr_xCoO_{4 ± y} catalysts for NO reduction by CO are closely correlated with oxygen vacancy and the concentration of Co³⁺. Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 3, pp. 431–437. The text was submitted by the authors in English.     

The vibrational spectra of NbBO4, TaBO4, NaNb3O8 and NaTa3O8

The infrared and Raman spectra of NbBO₄ have been interpreted in terms of the zircon structure in space group I4₁/amd (D¹⁷_4h). Frequency shifts were observed in the Raman bands upon isotopic substitution of the boron atoms and when Nb was replaced by Ta in the crystal lattice. NaTa₃O₈ contains TaO₈ dodecahedra which are almost identical to the ones in TaBO₄ and its Raman spectra are compared with those of NaNb₃O₈ and of NbBO₄ amd TaBO₄ in order to assign metal—oxygen bands. The BO⁵⁻₄ vibrational bands resemble those of the SiO⁴⁻₄ groups rather than the B(OH)⁻₄ ones. However, the BO stretching force constant is much lower than the corresponding SiO one in SiO⁴⁻₄ and it appears as if the metal—oxygen interactions are much stronger in NbBO₄ and TaBO₄ than in ZrSiO₄ and HfSiO₄, respectively.     

Highly Dispersed Ce x Zr1−x O2 Nano-Oxides Over Alumina, Silica and Titania Supports for Catalytic Applications

We have been exploring the utilization of supported ceria and ceria–zirconia nano-oxides for different catalytic applications. In this comprehensive investigation, a series of Ce _x Zr_1−x O₂/Al₂O₃, Ce _x Zr_1−x O₂/SiO₂ and Ce _x Zr_1−x O₂/TiO₂ composite oxide catalysts were synthesized and subjected to thermal treatments from 773 to 1073 K to examine the influence of support on thermal stability, textural properties and catalytic activity of the ceria–zirconia solid solutions. The physicochemical characterization studies were performed using X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HREM), thermogravimetry and BET surface area methods. To evaluate the catalytic properties, oxygen storage/release capacity (OSC) and CO oxidation activity measurements were carried out. The XRD analyses revealed the formation of Ce_0.75Zr_0.25O₂, Ce_0.6Zr_0.4O₂, Ce_0.16Zr_0.84O₂ and Ce_0.5Zr_0.5O₂ phases depending on the nature of support and calcination temperature employed. Raman spectroscopy measurements in corroboration with XRD results suggested enrichment of zirconium in the Ce _x Zr_1−x O₂ solid solutions with increasing calcination temperature thereby resulting in the formation of oxygen vacancies, lattice defects and oxygen ion displacement from the ideal cubic lattice positions. The HREM results indicated a well-dispersed cubic Ce _x Zr_1−x O₂ phase of the size around 5 nm over all supports at 773 K and there was no appreciable increase in the size after treatment at 1073 K. The XPS studies revealed the presence of cerium in both Ce⁴⁺ and Ce³⁺ oxidation states in different proportions depending on the nature of support and the treatment temperature applied. All characterization techniques indicated absence of pure ZrO₂ and crystalline inactive phases between Ce–Al, Ce–Si and Ce–Ti oxides. Among the three supports employed, silica was found to stabilize more effectively the nanosized Ce _x Zr_1−x O₂ oxides by retarding the sintering phenomenon during high temperature treatments, followed by alumina and titania. Interestingly, the alumina supported samples exhibited highest OSC and CO oxidation activity followed by titania and silica. Details of these findings are consolidated in this review.     

Vacuum annealing phenomena in ultrathin TiD y /Pd bi-layer films evaporated on Si(100) as studied by TEM and XPS

Using a combination of TEM and XPS, we made an analysis of the complex high-temperature annealing effect on ultrathin titanium deuteride (TiD _y ) films evaporated on a Si(100) substrate and covered by an ultrathin palladium layer. Both the preparation and annealing of the TiD _y /Pd bi-layer films were performed in situ under UHV conditions. It was found that the surface and bulk morphology of the bi-layer film as well as that of the Si substrate material undergo a microstructural and chemical conversion after annealing and annealing-induced deuterium evolution from the TiD _y phase. Energy-filtered TEM (EFTEM) mapping of cross-section images and argon ion sputter depth profiling XPS analysis revealed both a broad intermixing between the Ti and Pd layers and an extensive inter-diffusion of Si from the substrate into the film bulk area. Segregation of Ti at the Pd top layer surface was found to occur by means of angle-resolved XPS (ARXPS) and the EFTEM analyses. Selected area diffraction (SAD) and XPS provided evidence for the formation of a new PdTi₂ bimetallic phase within the top region of the annealed film. Moreover, these techniques allowed to detect the initial stages of TiSi phase formation within the film–substrate interlayer.     

Resonant emission of UO<Subscript>2</Subscript>, U<Subscript>3</Subscript>O<Subscript>8</Subscript>, and UO<Subscript>2+<Emphasis Type="Italic">x</Emphasis></Subscript> valence electrons under SR excitation near the O<Subscript>4,5</Subscript>(U) absorption edge

The structure of the resonant electron emission (REE) spectra of UO₂ (REE appears under the excitation with synchrotron radiation near the O_4,5(U) absorption edge at ∼100 eV and ∼110 eV) is studied with regard to the X-ray O_4,5(U) absorption spectrum of UO₂ and a quantitative scheme of molecular orbitals based on the X-ray electron spectroscopy data and the results of a relativistic calculation of the electronic structure of UO₂. The structure of the REE spectra of U₃O₈ and UO_2+x is studied for comparison, and the effect of the uranium chemical environment in oxides on it is found. The appearance of such a structure reflects the processes of excitation and decay involving the U5d and electrons of the outer valence MOs (OVMOs, from 0 to ∼13 eV) and inner valence MOs (IVMOs, from ∼13 eV to ∼35 eV) of the studied oxides. It is noted that REE spectra show the partial density of states of U6p and U5f electrons. Based on the structure of REE spectra, it is revealed that U5f electrons directly participate (without losing the f nature) in the chemical bonding of uranium oxides and are delocalized within CMOs (in the middle of the band), which results in the enhancement of the intensity of the REE spectra of CMO electrons during resonances. The U6d electrons are found to be localized near the bottom of the outer valence band and are observed in the REE spectra of the studied oxides as a characteristic maximum at 10.8 eV. It is confirmed that U6p electrons are effectively involved in the formation of IVMOs, which leads to the appearance of the structure in the region of IVMO electron energies during resonances. This structure depends on the chemical environment of uranium in the considered oxides.     

Synthesis and Characterization of Vanadium-Containing ZrSiO4 Solid Solutions from Gels

A procedure is reported for the preparation of vanadium-doped zircon pigmenting system with different vanadia loadings which enabled their complete formation and further characterization. Vanadium-zircon solid solutions were prepared by gelling mixtures of ZrO₂ and V₂O₅ colloidal sols and tetraethylorthosilicate and studied over the temperature range up to the formation of zircon. The reaction sequence of gels was evaluated by X-ray powder diffraction (XRD) and ultraviolet-visible (UV-Vis) diffuse reflectance. It was found that the first crystalline phase detected was a vanadium-containing tetragonal ZrO₂ solid solution where vanadium was stabilized in the reduced V⁺⁴ state. The formation of the V-ZrSiO₄ solid solution occurred by the reaction between the monoclinic form of V⁺⁴-ZrO₂ solid solution and the amorphous silica phase. Energy dispersive X-ray microanalysis (SEM/EDX) data, measurements of lattice parameters and UV-Vis diffuse reflectance of V-ZrSiO₄ solid solutions revealed that vanadium was dissolved as V⁺⁴ replacing Si⁺⁴ in tetrahedral sites in the crystal structure of zircon. The solubility limit of vanadium in ZrSiO₄ was about 0.01 mole of vanadium per mole of zircon (0.5 wt% as V₂O₅).     

Formation of a real structure of perovskites (La1−x , Sr x )CoO3−δ in the region of the morphotropic phase transition

Precision X-ray diffractometry with synchrotron radiation and transmission electron microscopy are used to show that the extent of hexagonal distortion of the perovskite cell of the (La_1−x, Sr _x )CoO₃−δ system decreases and the microstructure of the samples changes when La is substituted by Sr; these changes are due to increased microstrains in the structure and subsequent formation of microunits. The microunit structure of particles in the region of the morphotropic transition 0.3≤x≤0.4, which is a consequence of the metastable state of the system, may be the reason for the high catalytic activity of the samples which we found previously. G. K. Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 1, pp. 92–97, January–February, 1998. This work was supported by RFFR grants 96-03-33103 and 97-03-33497.     

Characterization and catalytic behavior of La2 - x (Sr, Th)xCuO4 ± λ in reaction NO+CO

Two mixed oxide systems La₂-_xSr_xCuO_{4± λ} (0.0⩽x⩽1. 0) and La_2-xTh_xCuO_{4± λ} (O. O⩽x⩽ 0.4) with K₂NiF₄ structure were prepared by varyingx values. Their crystal structures were studied by means of XRD and IR spectra. The average valence of Cu ion at B site, nonstoichiometric oxygen (λ) and the chemical composition in the bulk and on the surface of the catalysts were measured by means of chemical analysis and XPS. The catalytic behavior in reaction CO+NO was investigated under the regular change of average valence of Cu ion at B site and nonstoichiometric oxygen (λ). Meanwhile, the adsorption and activation of the small molecules NO and the mixture of NO+CO over the mixed oxide catalysts were studied by means of MS-TPD. The catalytic mechanism of reaction NO+CO over these oxide catalysts were proposed; and it has been found that, at lower temperatures the activation of NO is the rate determining step and the catalytic activity is related to the lower valent metallic ion and its concentration, while at higher temperatures the adsorption of NO is the rate determining step and the catalytic activity is related to the oxygen vacancy and its concentration. Project supported by the National Natural Science Foundation of China.     

一步醇-水热法合成高效的F掺杂BiVO4光催化剂

以NH₄F为掺杂前体,采用简单的一步醇-水热法制备了F掺杂BiVO₄光催化剂。利用X射线衍射（XRD）、扫描电子显微镜（SEM）、X射线光电子能谱（XPS）、紫外-可见漫反射光谱（UV-Vis）和光致发光光谱（PL）表征了这些光催化剂的物理化学性质。在少量H₂O₂存在条件下,以可见光照射下光催化降解苯酚的反应测定了这些光催化剂的催化活性。研究表明,相较于未掺杂的BiVO₄样品而言,F掺杂BiVO₄样品不仅仍保留了单斜结构,而且有更高的结晶度、表面氧空位密度和光生电荷载流子分离效率,更强的光吸收和更低的带隙能。在这些F掺杂BiVO₄样品中,以n_F/n_Bi的理论值为1.0且带隙能为2.43 eV的F掺杂BiVO₄样品的光催化活性最好（90 min内苯酚的降解率可达95%）。这一优良的光催化性能与其具有最高的结晶度、表面氧空位密度和光生电荷载流子分离效率,最强的光吸收和最低的带隙能有关。