O. G. Ellert

Mechanochemical activation of starting oxide mixtures for solid-state synthesis of BiFeO3

We have studied the effect of mechanochemical activation on the reactivity of Bi2O3 + Fe2O3 oxide mixtures, assessed the temperature effect on the kinetics of BiFeO3 formation in the oxide mixtures before and after mechanochemical activation, and optimized the conditions of bismuth ferrite synthesis by solid-state reaction. A material with a BiFeO3 content of at least 98.3 wt % has been obtained, and its magnetic properties have been investigated.

Synthesis of high-purity nanocrystalline BiFeO3

The kinetics of BiFeO3 formation from xerogel prepared by reverse coprecipitation were studied at different synthesis temperatures. We examined the influence of annealing temperature on the morphology of the reaction products and optimized synthesis conditions, which allowed us to obtain 99.7 wt % pure BiFeO3 consisting of crystalline grains less than 50 nm in size. Its magnetic properties were investigated.

Study of the formation mechanism of complex oxides obtained by the sol–gel method: influence of the structure of iron, aluminium and yttrium acetylacetonate precursors on the phase composition of the ZrO2 ceramics

To obtain new effective basic reagents for single-phase ceramic production with the use of alkoxosynthesis methods, three heterometallic iron–yttrium acetylacetonate complexes were originally synthesized by electrochemical anodic dissolution in acetylacetone. By means of X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), magnetic susceptibility and Mossbauer methods, the structure and properties of the new complex oxides were studied. It was shown that for the iron-containing gels and oxides, Fe3+/Y3+ ions participate in the oxide formation mechanism. The sets of interatomic distances found by means of EXAFS in the new iron–yttrium precursor and in the zirconium gel are practically equal. The presence of structure fragments formed by these bonds and especially direct Fe–Y in the precursors allow the formation of single-phase triple ceramic oxides.

Study of iron-alumina cluster catalysts for synthesis of alkylaromatic hydrocarbons from CO and H2

New selective catalysts for alkylaromatic synthesis from CO and H2 were studied. The catalysts were obtained by the hydrolysis of Fe(acac)3 with Al(OR)3 with the following activation in O2 and H2. The selective catalysts were found to contain tiny ferromagnetic clusters indiscernible by Mössbauer spectroscopy. The formation of the larger metallic clusters led to the alkan production.

Platinum acetate blue: synthesis and characterization.

Platinum acetate blue (PAB) of the empirical formula Pt(OOCMe)2.5±0.25, a byproduct in the synthesis of crystalline platinum(II) acetate Pt4(OOCMe)8, is an X-ray amorphous substance containing platinum in the oxidation state between (II) and (III). Typical PAB samples were studied with X-ray diffraction, differential thermal analysis-thermogravimetric, extended X-ray absorption fine structure, scanning electron microscopy, transmission electron microscopy, magnetochemistry, and combined quantum chemical density functional theory-molecular mechanics modeling to reveal the main structural features of the PAB molecular building blocks. The applicability of PAB to the synthesis of platinum complexes was demonstrated by the preparation of the new homo- and heteronuclear complexes Pt(II)(dipy)(OOCMe)2 (1), Pt(II)(μ-OOCMe)4Co(II)(OH2) (2), and Pt(III)2(OOCMe)4(O3SPhMe)2 (3) with the use of PAB as starting material.

SYNTHESIS AND STRUCTURE OF COMPLEX METAL OXIDES PRODUCED BY INTERACTION OF IRON AND NICKEL ACETYLACETONATES WITH HYDROLYSIS PRODUCTS OF TITANIUM AND ZIRCONIUM ALCOHOLATES

The interaction of nickel and iron acetylacetonates with hydrolysis products of titanium and zirconium alcoholates and their mixture has been studied. It was shown that chemical synthesis of organometallic gels followed by heat treatment makes it possible to form complex single-phase binary or ternary oxides. For the first time single-phase metal-containing titanate, zirconate, and titanate-zirconate oxides have been produced and their structure and magnetic and local electronic properties characterized.

Magnetic properties of Pr2–xFe1 + xSbO7 and Bi2–xLnxFeSbO7 (Ln = La, Pr) pyrochlore solid solutions

The Bi–La–Fe–Sb–O, Pr–Fe–Sb–O, and Bi–Pr–Fe–Sb–O systems have been shown to contain pyrochlore solid solutions. We have determined the limits of the Pr2–xFe1 + xSbO7 and Bi2–xLnxFeSbO7 (Ln = La, Pr) solid solutions and shown that there is no compound corresponding to the “ideal” composition Pr2FeSbO7. Analysis of the magnetic properties of the synthesized compounds indicates that rare earth substitution for bismuth ions has no effect on the spin glass transition and that the spin glass state is only determined by the interaction between the Fe3+ spins on the octahedral site. The Pr3+ paramagnetic ion in Pr2–xFe1 + xSbO7 does not participate in the formation of the spin glass state but makes a paramagnetic contribution to the total magnetic susceptibility, which is especially significant at low temperatures.

Fe-containing nanoparticles used as effective catalysts of lignin reforming to syngas and hydrogen assisted by microwave irradiation

AbstractActive iron-containing nanosized components have been formed on the lignin surface. The metal was deposited on the lignin from an ethanol solution of Fe(acac)3 and from a colloid solution of iron metal particles obtained beforehand by metal vapor synthesis. These active components are able to absorb microwave radiation and are suitable for microwave-assisted high-rate dehydrogenation and dry reforming of lignin without addition of a carbon adsorbent, as a supplementary radiation absorbing material, to the feedstock. The dependence of the solid lignin heating dynamics on the concentration of supported iron particles was investigated. The threshold Fe concentration equal to 0.5xa0wt.%, providing the highest rate of sample heating up to the reforming and plasma generation temperature was identified. The microstructure and magnetic properties of iron-containing nanoparticles supported on lignin were studied before and after the reforming. The Fe3O4 nanoparticles and also core-shell Fe3O4@γ-Fe-С nanostructures are formed during the reforming of lignin samples. The catalytic performance of iron-based nanoparticles toward the lignin conversion is manifested as increasing selectivity to hydrogen and syngas, which reaches 94% at the Fe concentration of 2xa0wt.%. It was found that with microwave irradiation under argon, hydrogen predominates in the gas. In the СО2 atmosphere, dry reforming takes place to give syngas with the СО/Н2 ratio of ~u20090.9. In both cases, the degree of hydrogen recovery from lignin reaches 90–94%.n Graphical abstractThe microwave-supported deposition of iron on the lignin surface gives active well defined nanoparticles Fe3O4 and also core-shell Fe3O4@γ-Fe-С nanostructures. These nanocomponents provide for high-rate microwave-assisted dehydrogenation and dry reforming of lignin.

Hybrid materials based on polymethylsilsesquioxanes containing Fe, Pt, and Fe–Pt metallic nanoparticles

New hybrid materials based on Pt, Fe, and Pt–Fe nanoparticles stabilized in a matrix of polymethylsilsesquioxane nanogel and ultrahigh molecular weight polyethylene (UHMWPE) were prepared. Metal vapor synthesis was used to produce mono- and bimetallic nanoparticles. It was shown that organosilicon nanogel effectively stabilizes Pt nanoparticles with an average size of 0.9 nm. Using the nanogel results in the formation of superparamagnetic Fe particles 3–5 nm in size that consist of ferromagnetic Fe0 core and antiferromagnetic shells of Fe oxides. It is established that using an organosilicon matrix in the formation of Pt-Fe/UHMWPE systems helps reduce the average particle size of Fe in the material from 6.5 to 4.5 nm and narrow their particle size distribution. The composition, magnetic and electronic characteristics of the nanocomposites are studied via transmission electron microscopy, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, XANES, and EXAFS.

Fluorination of Bi1.8Fe1.2SbO7 pyrochlore solid solutions

A technique has been developed for fluorinating the pyrochlore oxide Bi1.8Fe0.2FeSbO7, and a compound with the composition Bi1.8Fe1.2SbO7–x/2Fx has been obtained. The synthesized oxyfluoride also has the pyrochlore structure (sp. gr. Fd3m), with a lattice parameter a = 10.4443(1) Å (Rwp = 5.2). It has been shown that the charge balance upon fluorine substitution for oxygen is maintained not through partial reduction of Fe3+ to Fe2+ but through the incorporation of fluorine into oxygen vacancies. The magnetic behavior of the fluorinated pyrochlore phase is determined by the persisting frustration of the octahedral sublattice, which is responsible for the development of a spin glass state below Tf = 12 K. The fluorination-induced changes in the anion sublattice led to an increase in the antiferromagnetic exchange interaction between neighboring Fe3+ ions and changes in the dynamic properties of the spin glass phase.