A. V. Kozinkin

Iron(III) Oxide Nanoparticles in a Polyethylene Matrix

A method is proposed for the preparation of iron(III) oxide nanoparticles via thermal decomposition of iron(III) acetate in a high-temperature solution of polyethylene. The nanoparticles were characterized by EXAFS, EPR, and Mössbauer spectroscopy. The nearest neighbor environment of Fe in the nanoparticles was shown to be similar to that in the structure of γ-Fe2O3 . According to the Mössbauer results, the material contains iron(III) oxide in superparamagnetic and ferromagnetic states similar to γ-Fe2O3 . The particle size determined by high-resolution transmission electron microscopy is consistent with x-ray diffraction data. Experimental data are presented on the field-dependent magnetization of the material.

Cobalt-Containing Core-Shell Nanoparticles on the Surface of Poly(tetrafluoroethylene) Microgranules

Cobalt-containing nanoparticles have been prepared via thermal decomposition of cobalt acetate on the surface of poly(tetrafluoroethylene) (PTFE) microgranules forming a fluidized bed over the surface of hot mineral oil. Using transmission electron microscopy, the average size of the cobalt-containing nanoparticles has been determined to be 3.6 nm. The composition and structure of the nanoparticles have been determined by x-ray diffraction, extended x-ray absorption fine structure spectroscopy, and electron paramagnetic resonance, and the magnetic properties of the synthesized nanomaterial have been studied. The results indicate that the nanoparticles have a core-shell structure, with a metallic cobalt core (≃10 vol%) and a shell consisting of three phases: Co3O4 (≃80%) and small amounts of CoO and CoF2 (≃10%). The fluoride phase results from the interaction of the nanoparticles with surface fluorine atoms of the PTFE microgranules.

Copper Nanoparticles in a Polyethylene Matrix

The composition and structure of Cu-containing nanoparticles stabilized in a polyethylene matrix were studied. The nearest neighbor environment of Cu in the 15-nm particles is similar to that in metallic Cu. In contrast to Fe nanoparticles, the Cu nanoparticles embedded in polyethylene do not oxidize during storage in air.

Mechanisms of formation of near-edge fine structure of K X-ray absorption spectra of metallic Cu, Ni, Co (HCP and FCC phases), and Cr

The K X-ray absorption near-edge fine structure spectra of metallic Cu, Ni, Co (hexagonal close-packed and face-centered cubic phases), and Cr have been studied. The experimental spectrum of cobalt has been measured in the high-temperature face-centered cubic phase. The calculations have been performed by the full multiple scattering method in the cluster approximation using the semiempirical muffin-tin potential. The spectra have been calculated for clusters containing from 13 to 935 atoms. It has been demonstrated that the spectra cease to depend on the cluster size for clusters containing about 400 atoms. It has been established that the intensity ratio of two peaks located at the fundamental edge of all the spectra under investigation sharply changes with a variation in the atomic potential strength. The mechanisms responsible for the formation of the near-edge structure of the spectra have been revealed using the results of the model calculations. The studies resulted in good agreement of the calculated spectra with the experiment.

Electronic and atomic structure of platinum-cobalt nanocatalysts

X-ray diffraction in combination with X-ray emission and EXAFS spectroscopy were used to study the electronic and atomic structure of metal nanoparticles stabilized on a carbon support in novel PtxCo/C catalysts of different composition with the molar ratio Pt:Co (x) of 1 to 3. Cobalt atoms in nanoparticles, which average size was 2–4 nm, were shown to form chemical bonds both with platinum atoms and carbon atoms of the support material.

Copper Nanoparticles on the Surface of Ultradispersed Polytetrafluoroethylene Nanograins

Nanosized copper-containing particles stabilized on the surface of polymer nanograins were obtained by thermal decomposition of copper-containing precursors in a fluidized bed of ultradispersed polytetrafluoroethylene. Transmission electron microscopy showed that the average size of nanoparticles is 10–12 nm. The structure of the particles was determined by EXAFS, EPR, and X-ray powder diffraction. The copper nanoparticles consist of a core and a shell and are well structured. The core is copper metal, whereas the surface layer, which constitutes no more than 2% of the nanoparticle weight, is copper oxide.

Rhenium Compounds with Metal–Metal Multiple Bonds: X-Ray Spectral Study of the Electronic Structure

The electronic structures of the binuclear complexes [(NH4)2Re2Cl8)] · 2H2O and Re2(CH3COO)4Br2 were studied using ReLβ5 X-ray emission spectra. The distribution of the Re 5d AOs and Cl 3p AOs in the MOs of these complexes was analyzed. The ReLβ5 spectra of the complexes exhibit components corresponding to the metal–metal δ-bond. The contribution of the rhenium 5d AOs to the δ bond in [(NH4)2Re2Cl8)] · 2H2O is almost twice as low as in Re2(CH3COO)4Br2.

The electronic structure of iron carbonyl complexes as probed by X-ray emission spectroscopy and quantum-chemical calculations

The electronic structure of the polynuclear iron carbonyl complexes [Et2N][Fe4N(CO)12], [Et4N]2[Fe5C(CO)14], and [Et4N]2[Fe6C(CO)16] has been studied by X-ray emission spectroscopy and quantum-chemical calculations. The fine structure of the FeKβ5 X-ray emission spectra characterizes the distribution of iron valence p electrons over the molecular orbitals of the compounds. Comparison of the fine structure of the FeKβ5 X-ray emission spectra with the densities of states of all atoms in the molecules has made it possible to determine in detail the character and specific features of chemical bonding in the complexes.

Atomic structure of gold nanoparticles stabilized in polyethylene

Transmission electron microscopy, X-ray powder diffraction, and X-ray absorption spectroscopy techniques were used to study the atomic structure of gold nanoparticles involving 1, 5, 10, and 20 wt % of Au which were stabilized in a high-pressure polyethylene matrix. The average sizes of the Au-containing nanoparticles amounted to 7 and 50 nm. The atomic structure of the Au-containing nanoparticles was similar to that of metallic gold in the bulk state. When the Au concentration in polyethylene was equal to 1 wt %, gold atoms were found on the surface of nanoparticles, which interacted with light atoms C/O.

Determination of the melting temperature of palladium nanoparticles by X-ray absorption spectroscopy

The anharmonicity parameters of the interatomic potential in ~4-nm palladium nanoparticles deposited on poly(tetra)fluoroethylene microgranules 0.2–0.5 μm in average size were studied by X-ray absorption spectroscopy from an analysis of temperature-dependent EXAFS Pd K edges. The parameters of the interatomic potential obtained were used to calculate melting temperature Tmelt = 1591 K and Debye temperature ΘD = 257 K of palladium nanoparticles; these temperatures are significantly lower than those in metallic palladium: 277 K and 1825 K, respectively.