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A comparative analysis of the structure and magnetic properties of nanoparticles of Fe-Ni and Fe-Co alloys without carbon and encapsulated in carbon obtained by gas-condensation synthesis is carried out. Particular attention is paid to the study of the formation of a solid solution in nanoparticles with carbon. X-ray analysis and magnetic properties convincingly demonstrate that a disordered supersaturated solid solution of carbon in FeNi@C and FeCo@C nanoparticles is formed.

The absorption spectra of cobalt-doped anatase TiO2 nanopowders in the infrared and visible ranges have been studied after various oxidative and reductive treatments. The annealing leads to the appearance of the Drude-like contribution in the infrared region and significant change in the absorption in an visible range due to the formation of defects of the oxygen-vacancy-type and Ti3+ ions. The observed additional contribution in the absorption spectra of TiO2:Co nanopowders as compared to the spectra of undoped powders is ascribed to the d–d transitions in ions Co2+. The change in the absorption related to cobalt after annealing is explained by a change in the local environment of Co ions from the octahedral to the tetrahedral environment.

Out of many functionalities of zinc oxide, its magnetic properties are only sparsely explored. Herein we report on the evolution of ferromagnetism of undoped ZnO nanoparticles, depending on the zinc source used for the synthesis. We started from mechanochemical synthesis of phase pure nanocrystalline hydrozincite, Zn5(CO3)2(OH)6 (ZnHC) by milling a mixture comprising either Zn(NO3)2·6H2O or ZnCl2, and Na2CO3 for 10 min. Zinc oxide nanoparticles with specific surface over 70 m2/g were obtained by subsequent heating of ZnHC up to 300 °C. Ferromagnetism was observed only for ZnO nanoparticles derived from Zn(NO3)2, while those from ZnCl2 were conventionally diamagnetic. X-ray photoelectron, Raman, as well as electron paramagnetic resonance spectrograms consistently showed significantly higher concentration of oxygen vacancies in the Zn(NO3)2-derived ZnO. We also referred to the difference in the charging states of oxygen vacancies by detailed observation of EPR spectra. Since the formation of ZnO from ZnHC is topotactic, the difference in the lattice imperfection was discussed in terms of the hydration energy of the coexisting NO3− or Cl− anion. The present simple mechanochemical – thermal procedure offers a facile method for obtaining well-dispersed active ZnO nanoparticles. More importantly, the new synthesis method offers possibility of controlling their magnetic properties by choosing anionic species of the starting zinc source.

In this work, we developed and optimized conjugates of carbon-coated iron nanoparticles (Fe@C) with streptavidin and monoclonal antibodies. The conjugation procedure included two stages. First, amino groups were grafted onto the carbon shell to facilitate noncovalent sorption of bovine serum albumin (BSA). Further, the covalent attachment of proteins to the BSA layer via glutaraldehyde coupling was performed. It was established and confirmed that the synthesis procedure is reproducible and allows preparation of stable conjugates. The resulting nanoparticles are clusters of Fe@C particles coated by proteins. The size of the clusters is in the range of 100–190 nm and can be controlled via the tuning of conjugation conditions, including pH, BSA-to-Fe@C ratio, etc. Conjugates of Fe@C with streptavidin and monoclonal antibodies (sizes of approximately 140–150 nm) were synthesized. Proton T2 relaxometry was used to detect these conjugates with very high sensitivity due to the magnetic markers, Fe@C. The relaxivity (r2) of different conjugates varied within the range of 290–450 1/s*mM. Conjugate applicability for relaxometry-based assay was confirmed by direct detection of streptococcal protein G and biotinylated BSA in a dot immunoassay.

Nanopowders Ni@C synthesized by gas condensation have a core-shell structure. The size of the core is 2–10 nm and the thickness of the shell is 1–3 nm. The changes in the magnetic properties and the structure of these particles upon annealing in the 100–1100°C temperature range are investigated in this work. Analysis of changes in the magnetic properties, the structure, and the chemical stability shows that the core of the particles in the initial state after synthesis is a supersaturated solid solution of carbon in nickel, which decomposes into nickel and carbon upon high-temperature annealing. Rather slow cooling of nickel particles causes the carbon shell to form. The shell ensures their chemical stability.

Core–shell CoFe@C and NiFe@C nanocomposites were prepared by gas-condensation synthesis. CoFe@C and NiFe@C particles had bcc and fcc cores, respectively. The treatment of these nanocomposites with hydrochloric acid revealed that they are more chemically stable than Fe@C composites. The maximum specific magnetization of CoFe@C and NiFe@C nanocomposites at room temperature in the field with a strength of 27 kOe was 125 and 58 G cm3/g, respectively. The processes of longitudinal and transverse relaxation of nuclear proton spins of aqueous suspensions of nanocomposites in various magnetic fields (0.5, 1, and 2 kOe) were studied. NiFe@C and CoFe@C nanocomposites have high transverse relaxivity values and can be used as magnetic markers for detection of low concentrations of bioobjects by NMR relaxometry.

The research was supported by the Russian Science Foundation (project 16-12-10004). The authors are grateful for the contributions made by our colleagues G. S. Zakharova, A. S. Konev, K. I. Borodin, Z. A. Phatakhova, A. M. Murzakaev, and V. S. Gaviko. The X-ray investigation and magnetic measurements have been performed in the Collaborative Access Center of M. N. Mikheev Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences, Yekaterinburg, Russia.

Co-doped TiO2 is one of the most extensively studied oxides for applying as dilute magnetic semiconductors due to its room temperature magnetism. Here we present results of the studies of Ti0.97Co0.03O2 nanopowders synthesized by hydrothermal method by means of X-ray diffraction, soft X-ray absorption spectroscopy (Ti L2,3 and Co L2,3 spectra), hard X-ray absorption spectroscopy (Co K spectra), and 1s3p resonant inelastic X-ray scattering at the Co K edge. According to X-ray diffraction data and Ti L2,3 X-ray absorption spectra, all the samples before the thermal treatment exhibit anatase structure with substantial amount of amorphous phase. After annealing the Ti0.97Co0.03O2 samples in vacuum or hydrogen at 700oC, the anatase structure persists while amorphous phase contribution is eliminated. Surface sensitive soft X-ray absorption Co L2,3 spectroscopy revealed only Co2+ ions tetrahedrally coordinated by oxygen ions and no sign of metallic Co. Co2+ tetrahedral sites (instead of typical octahedral ones) ...

The charge states of the cobalt ions in TiO2 nanopowders with the anatase lattice are studied by soft X-ray absorption spectroscopy. It is found that, at a low cobalt impurity concentration (1.8 at %), the cobalt ions with an oxidation state 2+ are mainly located in the tetrahedral (T d ) environment of oxygen ions. Amorphous titanium dioxide exists on the sample surface before heat treatment. Annealing in vacuum or hydrogen leads to the enrichment of the nanoparticle surfaces with Co2+ ions, a change in the coordination of the remaining part of cobalt ions from octahedral to tetrahedral, stabilization of the anatase structure, and the disappearance of the amorphous phase. The crystal lattice of the samples with a relatively high cobalt concentration (12 at %) is distorted, and annealing does not cause the disappearance of the amorphous phase of TiO2. Cobalt is reduced to its metallic state upon hydrogen annealing of the samples with a high cobalt concentration.

Rapid synthesis of delafossite CuAlO 2 using a mechanically activated mixture of microcrystalline Cu 2 O and nanocrystalline Al 2 O 3 powder was achieved after subsequent annealing under argon atmosphere. The results were analyzed by using X-ray diffractometry, thermal analysis, transmission and scanning electron microscopy, Raman and X-ray photoelectron spectroscopy and SQUID magnetometry. The presence of core–shell configuration of Cu 2 O nanoparticles with the thickness of the non-crystalline surface shell of about 1.0 nm associated with partial oxidation of Cu 2 O was evident. By calcining the precursor in the temperature range of 300–800 °C for 4 h under Ar flow, CuO and CuAl 2 O 4 were observed as main phases. At 900 °C, CuAlO 2 became a main phase. At 1100 °C, CuAlO 2 delafossite with a small admixture of α-Al 2 O 3 was observed. Paramagnetism was observed on our CuAlO 2 at room temperature with a weak ferromagnetism. In the 10 min activated mixture, a contamination with Fe was detected. A unique weak ferromagnetic feature of CuAlO 2 may be associated with the structural paramagnetic Cu 2+ and Fe 3+ ions. Antiferromagnetic short-range-order was developed below 60 K. This was ascribed to the mixed state of Cu + and Cu 2+ in the Cu O sub-lattice with a high amount of oxygen vacancies, similar to the states in the Cu 2- x O.

Cobalt-doped anatase Ti1–xCoxO2 (0 < x ≤ 0.04) nanopowders (with a particle size of 30–40 nm) were produced by the hydrothermal synthesis method. Morphology, structure, and thermal stability of the synthesized compounds were examined using transmission electron microscopy, infrared spectroscopy, and X-ray diffraction analysis. Using X-ray photoelectron spectroscopy, cobalt ions are shown to have an oxidation state of 2+, with titanium ions having a tetravalent state of Ti4+. In the as-prepared state, all investigated compounds of Ti1–xCoxO2 are paramagnetic, with the value of paramagnetic susceptibility growing in proportion to cobalt content; with the spin of cobalt ion equal to S = 3/2. Analysis of the electron paramagnetic resonance spectra reveals that doping TiO2 with cobalt (up to 2%) is accompanied by a significant increase in the concentration of F+ centers. Further growth of the cobalt content results in a relatively wide line (nearly 600 Oe) in the spectrum, with a g-factor of about 2.005, demon...

The surface functionalization of magnetic nanoparticles improves their physicochemical properties and applicability in biomedicine. Natural polymers, including proteins, are prospective coatings capable of increasing the stability, biocompatibility, and transverse relaxivity (r2) of magnetic nanoparticles. In this work, we functionalized the nanoclusters of carbon-coated iron nanoparticles with four proteins: bovine serum albumin, casein, and gelatins A and B, and we conducted a comprehensive comparative study of their properties essential to applications in biosensing. First, we examined the influence of environmental parameters on the size of prepared nanoclusters and synthesized protein-coated nanoclusters with a tunable size. Second, we showed that protein coating does not significantly influence the r2 relaxivity of clustered nanoparticles, however, the uniform distribution of individual nanoparticles inside the protein coating facilitates increased relaxivity. Third, we demonstrated the applicability of the obtained nanoclusters in biosensing by the development of a nuclear-magnetic-resonance-based immunoassay for the quantification of antibodies against tetanus toxoid. Fourth, the protein coronas of nanoclusters were studied using SDS-PAGE and Bradford protein assay. Finally, we compared the colloidal stability at various pH values and ionic strengths and in relevant complex media (i.e., blood serum, plasma, milk, juice, beer, and red wine), as well as the heat stability, resistance to proteolytic digestion, and shelf-life of protein-coated nanoclusters.

Nanopowder TiO2-0.73 % Mn was synthesized by the sol-gel method. Thermal treatment of the samples was carried out in vacuum at a temperature of 500°C. Magnetic properties were studied in the temperature range from 2 to 850 K. The effects of electron irradiation and vacuum annealing on the EPR spectra and magnetic properties of TiO2-Mn powder are discussed. It was established that a part of manganese ions in the anatase crystal lattice interacts antiferromagnetically, which causes a decrease in magnetization as compared to the result of the calculation for non-interacting ions. Vacuum annealing leads to the formation of oxygen vacancies and, at the same time, to a noticeable increase in the ferromagnetic contribution to magnetization, especially, after preliminary electron irradiation. We assume that the ferromagnetic contribution to the magnetization appears either due to incomplete compensation of antiferromagnetically directed moments of manganese ions, or due to positive exchange interactions of Mn ions via defects in the TiO2 lattice. It is shown that the temperature of magnetic disordering in samples with a spontaneous magnetic moment exceeds 600°C. © 2019, Institute for Metals Superplasticity Problems of Russian Academy of Sciences. All rights reserved.

The report is devoted to an analysis of the structural and magnetic state of the nanocrystalline diluted magnetic semiconductors based on TiO2 doped with Fe and Co atoms. Structural and magnetic characterization of samples was carried out using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR) spectroscopy, SQUID magnetometry, and the density functional theory (DFT) calculations. Analysis of the experimental data suggests the presence of non-interacting paramagnetic Fe3+ and Co2+ ions in the high-spin state and negative exchange interactions between them. The important conclusions is that the distribution of dopants in the TiO2 matrix, even at low concentrations of 3d-metal dopant (less than one percent), is not random, but the 3d ions localization and dimerization is observed both on the surface and in the nanoparticles core. Thus, in the paper the quantum mechanical model for describing the magnetic properties of TiO2:(Fe, Co) was suggested. The model operates only with two parameters: paramagnetic contribution of non-interacting 3d-ions and dimers having different exchange interactions between 3d magnetic carriers.

Electromagnetic properties of complex oxide solid solutions containing Ce and Y attract increasing interests due to their high application potential. Their properties are known to be dependent on many factors including grain size and crystal defects. Here we focus on unique features of nanocrystalline Ce$_{1-x}$Y$_{x}$O$_{2-δ}$ (x ≤ 0.3) solid solutions prepared via a mechanosynthesis. Mechanically activated CeO$_{2-δ}$ and mechanosynthesized Ce$_{1-x}$Y$_{x}$O$_{2-δ}$ exhibit room-temperature ferromagnetism. The saturation magnetization reaches maximum for the Ce$_{0.9}$Y$_{0.1}$O$_{2-δ}$ solid solution. XPS and Raman spectra show that Ce$^{Zahl}$4+s are partially reduced to Ce$^{3+}$, with simultaneous introduction of oxygen vacancies accumulated on surface of the solid solutions. An analysis of the experimental magnetization data and the determination of both the spin state and the concentration of magnetic carriers revealed that a small part of the Ce$^{3+}$ spins (

High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) analysis, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), magnetic methods, and density-functional theory (DFT) calculations were applied for the investigations of Co-doped anatase TiO2 nanoparticles ( ∼ 20 nm). It was found that high-spin Co2+ ions prefer to occupy the interstitial positions in the TiO2 lattice which are the most energetically favourable in compare to the substitutional those. A quantum mechanical model which operates mainly on two types of Co2+ – Co2+ dimers with different negative exchange interactions and the non-interacting paramagnetic Co2+ ions provides a satisfactorily description of magnetic properties for the TiO2:Co system.

NiPd bimetallic systems were for the first time synthesized by laser electrodispersion (LED) of the Ni77Pd23 alloy target followed by the deposition of produced bimetallic particles on a TEM copper grid and alumina granules. Selective area energy-dispersive analysis confirms the bimetallic nature of NiPd particles deposited on a TEM copper grid. Their mean size is 1.0 nm according to TEM. XPS data demonstrate that under deposition on alumina granules (total metal content of 0.005 wt.%), nickel in bimetallic particles nearly completely oxidizes to Ni2+ species predominantly in the form of aluminate. At the same time major part of palladium (84%) exists in Pd0 but oxidizes to Pd2+ (80%) during 6 months storage in air. Both metals are deposited on the external surface of alumina granules and localized in the same areas. In situ reduction of both metals by H2 in the catalytic cell of XPS spectrometer is hindered. Nickel is not reduced even at 450°C, confirming the formation of NiAlOx, whereas palladium is reduced at higher temperatures compared to a similar monometallic catalyst. Nevertheless, NiPd/Al2O3 catalyst is more efficient in gas-phase chlorobenzene hydrodechlorination at 150–350°C than Ni/Al2O3 and even Pd/Al2O3, and much more stable. The difference may be caused by the formation of new active sites due to the contact between Pd0 and NiAlOx-modified support, and the protective action of spinel reacting with HCl by-product.

Nickel nanoparticles coated with few layers of carbon have been embedded into the polydimethylsiloxane (PDMS) matrix in concentrations up to 11 vol %. Dielectric and magnetic properties of composite materials have been studied in wide frequency (20 Hz–1 MHz) and temperature (130–430 K) ranges. It was demonstrated that the temperature behavior of dielectric properties is determined by glass transitions in the PDSM matrix below 200 K and the Maxwell–Wagner relaxation above room temperature. The possibility of using fabricated composites on the basis of the PDMS matrix for producing a wide range of passive electromagnetic components, such as frequency-selective filters, wide-band detectors/sensors of a bolometric type, and even electromagnetic “black holes” is also discussed.

This paper presents the results of investigations of the structural state and magnetic properties of nanocrystalline cupric oxide samples with average particle sizes of approximately 40 and 13 nm, which were synthesized by the electric explosion and gas phase methods, respectively. The samples have been studied using X-ray diffraction, neutron diffraction, magnetic measurements, high-resolution transmission electron microscopy, and copper nuclear magnetic resonance. It has been shown that, in the initial state, regardless of the synthesis method, CuO nanoparticles are characterized by a heterogeneous magnetic state, i.e., by the existence of long-range antiferromagnetic order, spontaneous magnetization, especially at low temperatures, and paramagnetic centers in the material. The ferromagnetic contribution is probably caused by the formation of magnetic polaron states due to the phase separation induced in the system by excess charge carriers as a result of the existence of point defects (vacancies in the anion sublattice) in the nanocrystalline state. In this state, there is an inhomogeneously broadened nuclear magnetic resonance spectrum, which is a superposition of the spectrum of the initial antiferromagnetic matrix and the spectrum of ferromagnetically ordered regions. At high concentrations of ferromagnetically ordered regions, the antiferromagnetic matrix exhibits a nuclear magnetic resonance spectrum of CuO nanoparticles, predominantly from regions with the ferromagnetic phase. The appearance of magnetization can also be partly due to the frustration of spins in CuO, and this state is presumably localized near the most imperfect surface of the nanoparticles. The magnetic susceptibility of nanoparticles in the initial state in strong magnetic fields is significantly higher than that for the annealed samples, which, most likely, is associated with the influence of the high concentration of magnetic polarons. No correlation between the ferromagnetic contribution and the size of particles is found. In the CuO samples annealed at 400°C in air, when the average size of CuO nanoparticles remains unchanged, the ferromagnetic contribution completely disappears, and the magnetic behavior of the nanoparticles becomes qualitatively similar to the magnetic behavior of bulk CuO.

Sedimentation dynamics of magnetite (γ-Fe3O4) nanopowders (10 - 20 nm) in water in the presence of a gradient magnetic field was studied by optical and Nuclear Magnetic Resonance (NMR) relaxometry methods. The magnetic field B ≤ 0.3 T, dB/dz ≤ 0.13 T/cm was produced by the system of permanent strip magnets. The initial sedimentation rate of the nanoparticles in water and under magnetic fields is higher for less concentrated suspensions (c0 = 0.1 g/l) than for more concentrated ones (c0 = 1 g/l). This might be connected with the formation of gel structures due to strong magnetic attraction between ferromagnetic nanoparticles. In the gravitation field, the suspensions of the particles (10 - 20 nm) remain stable for over 20 hours. The sedimentation process can be greatly accelerated by the action of a vertical gradient magnetic field, reducing the sedimentation time down to several minutes. In a gradient magnetic field enhanced by a steel grid, sedimentation of the nanopowder (c0 = 0.1 g/l) for 180 minutes resulted in reduction of the iron concentration in water down to 0.4 mg/l. In flowing water regime, the residual iron concentration in water 0.3 mg/l is reached after 80 minutes.

Ni@C nanocomposites and the carbon shells extracted by etching Ni@C in nitric acid have been characterized by means of soft X-ray absorption and X-ray photoelectron spectroscopies. It was found on the base of Ni 2p X-ray absorption spectra and atomic multiplet calculations that Ni traces in the carbon-shell sample are in the Ni2+ state formed probably by nickel nitrate hexahydrate, Ni(NO3)2·6H2O. Second derivatives of C 1s of X-ray absorption spectra and C 1s X-ray photoelectron spectra were used for characterization of functional groups linked to carbon shells of nanocomposites. The application of second derivatives of C 1s of X-ray absorption spectra allowed to confirm AA stacking of carbon layers for highly oriented pyrolytic graphite. The low-energy features in C 1s XAS spectra of Ni@C and carbon-shell samples are found to be of a different nature. Most likely, the low-energy C 1s XAS feature of the carbon-shell sample is formed due to hydrogenation of carbon atom.

Me@C nanocomposites were prepared by evaporation of overheated liquid drop of Me in the flow of inert gas containing a hydrocarbon. The resulting carbon-coated nickel and iron nanoparticles contain metal cores of about 5 nm in size that are wrapped in a few layers of graphene-like carbon. Experimental data and theoretical results give evidence of the ability of carbon coating in nanocomposites Fe@C and Ni@C to H2 activation by dissociative adsorption due to the presence of space and structure defects and/or the presence of transition metal in subsurface layer. Since molecular hydrogen dissociation is the key step of hydrogenation reactions, both Ni@C and Fe@C provide high conversion of phenylacetylene (PA) (about 100%) during hydrogenation at the temperatures above 150 and 300 °C, respectively. Fe@C provides excellent styrene (ST) selectivity: 86% at 99% PA conversion at 300 °C. ST selectivity is moderate on Ni@C (about 60%) in the temperature range of 100–150 °С and low at higher temperatures.

Nanocomposites based on iron and nickel particles encapsulated into carbon (Fe@C and Ni@C), with an average size of the metal core in the range from 5 to 20 nm and a carbon shell thickness of approximately 2 nm, have been prepared by the gas-phase synthesis method in a mixture of argon and butane. It has been found using X-ray diffraction, transmission electron microscopy, and Mossbauer spectroscopy that iron nanocomposites prepared in butane, apart from the carbon shell, contain the following phases: iron carbide (cementite), α-Fe, and γ-Fe. The phase composition of the Fe@C nanocomposite correlates with the magnetization of approximately 100 emu/g at room temperature. The replacement of butane by methane as a carbon source leads to another state of nanoparticles: no carbon coating is formed, and upon subsequent contact with air, the Fe3O4 oxide shell is formed on the surface of nanoparticles. Nickel-based nanocomposites prepared in butane, apart from pure nickel in the metal core, contain the supersaturated metastable solid solution Ni(C) and carbon coating. The Ni(C) solid solution can decompose both during the synthesis and upon the subsequent annealing. The completeness and degree of decomposition depend on the synthesis regime and the size of nickel nanoparticles: the smaller is the size of nanoparticles, the higher is the degree of decomposition into pure nickel and carbon. The magnetization of the Ni@C nanocomposites is determined by several contributions, for example, the contribution of the magnetic solid solution Ni(C) and the contribution of the nonmagnetic carbon coating; moreover, some contribution to the magnetization can be caused by the superparamagnetic behavior of nanoparticles.

H1 NMR relaxometry is a method that is extremely sensitive to the presence of magnetic nanoparticles, which significantly affect the transverse relaxation time of the water proton. Accordingly, the use of magnetic nanoparticles as labels allows detection of even extremely small amounts of the test substance. This paper analyzes the prospects for applying the method of solid-phase NMR-relaxometric determination of biologically active molecules. The nitrocellulose membranes are chosen as a solid phase and nanoparticles based on iron core with a carbon shell are used as magnetic labels. The possibility of detecting small concentrations of magnetic particles in porous medium is demonstrated. Finally, the ability to detect extremely low concentrations of an analyte, in this case, streptavidin protein (0.5 ng/ml to 100 ng/ml), which is actively used in various fields of biology and medicine, is demonstrated. © Published under licence by IOP Publishing Ltd. Russian Science Foundation, RSF: 17-15-01116 The work was carried out within the Russian Science Foundation project 17-15-01116. equipment of the Ural Center for Shared Use Modern nanotechnology UrFU was used.

TiO2-Co nanopowders were synthesized by the sol-gel method and gas condensation method. The structure of powders and its change during various heat treatments in air and hydrogen was investigated. The samples obtained by the gas condensation method contain ferromagnetic regions in the as-prepared state. This ferromagnetism does not disappear when annealed in air at 773 K. The magnetization curves of these powders are measured in the temperature range from 2 up to 773 K and the temperature dependence of the ferromagnetic contribution is analyzed.

The 61Ni, 13C NMR spectra of carbon encapsulated nickel nanoparticles have been obtained. It has been shown that the cores of the particles consist of metallic nickel with face-centered cubic structure, nickel carbide Ni3C and carbon-nickel solid solution. The carbon shell of nanoparticles is a highly defective structure and close to an amorphous glassy-like carbon. © Published under licence by IOP Publishing Ltd. Ural Branch, Russian Academy of Sciences, UB RAS: 18-10-2-37. The study was performed within the state assignments of the Mikheev Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences: state program «Function» No АААА-А19-119012990095-0; state program «Magnit» No АААА-А18-118020290129-5 and state program «Alloys». The research also was supported by the project of the complex program of Ural Branch of Russian Academy of Sciences № 18-10-2-37.

Nickel-containing metal-carbon nanocomposites (Ni@C) synthesized by levitation melting in a flow of an inert gas-hydrocarbon mixture were used as catalysts of the hydrogenation of phenylacetylene (PA). The nanocomposites were characterized by X-ray photoelectron spectroscopy, simultaneous thermal analysis, and temperature-programmed reduction. The nickel-carbon nanocomposites were stable on storage in air, with only 13% of the total amount of nickel oxidized after 3.5 years of storage. In addition to nanoparticles completely covered with carbon, the composites contained partially coated metal particles, which are readily oxidized in air. Both types of particles exhibited the catalytic activity in phenylacetylene hydrogenation. At higher contents of nickel partially coated with carbon, the activity increased and the selectivity of styrene formation decreased. The minimum half-conversion temperature (75°C) was determined for a specially prepared Ni@C sample with an increased content of oxidized nickel (28%). The maximum selectivity of styrene formation (∼75% at 150°C) was recorded in the presence of the sample with the smallest amount of oxidized nickel (less than 4%).

The electronic structure of carbon shells of carbon encapsulated iron nanoparticles carbon encapsulated Fe@C has been studied by X-ray resonant emission and X-ray absorption spectroscopy. The recorded spectra have been compared to the density functional calculations of the electronic structure of graphene. It has been shown that an Fe@C carbon shell can be represented in the form of several graphene layers with Stone-Wales defects. The dispersion of energy bands of Fe@C has been examined using the measured C Ka resonant X-ray emission spectra., Comment: 8 pages, 2 figures

Based on the combination of experimental measurements and first-principles calculations we report a novel carbon-based catalytic material and describe significant acceleration of the hydrogenation of magnesium at room temperature in the presence of nickel nanoparticles wrapped in multilayer graphene. The increase in rate of magnesium hydrogenation in contrast to a mix of graphite and nickel nanoparticles evidences intrinsic catalytic properties of the nanocomposites explored. The results from simulation demonstrate that doping of the metal substrate and the presence of Stone-Wales defects turn multilayer graphene from being chemically inert to chemically active. The role of the size of the nanoparticles and temperature are also discussed.

Nickel and iron nanoparticles encapsulated in carbon were synthesized by contactless levitation melting of metal drops and their evaporation in a flow of an inert gas containing a hydrocarbon. The products were characterized by means of transmission electron microscopy, photoelectron spectroscopy, and X-ray absorption spectroscopy. It was established that carbon coating protects the metallic nanoparticles from the environmental degradation by providing a barrier against oxidation and ensures stability of the ferromagnetic core metal inside that provides their extremely high catalytic activity, biocompatibility, and nontoxicity.

IR absorption and magnetic data for the titanium dioxide nanopowders are studied. Additional absorption in IR range is revealed in nanocrystalline TiO2 and Co-doped TiO2 after reducing annealing and explained by appearance of the oxygen vacancies and delocalised charge carriers. Increasing of the absorption in IR range after annealing of Co-doped TiO2 in vacuum (or decreasing of this contribution after annealing in air) correlates with arising (or vanishing) of ferromagnetic contribution. © 2018 The Authors, published by EDP Sciences. This work was supported by the Russian Scientific Foundation, Grant No. 16-12-10004.

In order to study the effects of mechanical milling on the properties of metal hydrides, we have measured the proton nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates in two classes of nanostructured ball-milled systems: Laves-phase hydrides ZrCr 2 H 3 and MgH 2 -based hydrides with some additives (V 2 O 5 , Al). The proton NMR measurements have been performed at the resonance frequencies of 14, 23.8 and 90 MHz over the temperature range 11–420 K. Hydrogen mobility in the ball-milled ZrCr 2 H 3 is found to decrease strongly with increasing milling time. The experimental data suggest that this effect is related to the growth of the fraction of highly distorted intergrain regions where H mobility is much lower than in the crystalline grains. For the MgH 2 -based systems we have not found any effects of H jump motion at the NMR frequency scale up to 420 K. However, the measured proton spin-lattice relaxation rates for the nanostructured MgH 2 -based samples appear to be several orders of magnitude higher than for the coarse-grained MgH 2 . This relaxation rate enhancement can be attributed to the interaction between proton spins and intrinsic paramagnetic centers appearing in the process of ball milling.

The optical spectra of Cu2O and TiO2 nanopowders have been studied, which contain information about structural defects and are of interest in the search for optimum regimes providing the synthesis of ferromagnetic nanocrystals with Curie temperatures above room temperature.

The effect of grain boundaries (GB) on decomposition of solid solution was investigated in the framework generalized lattice gas model taking into account both local variation of chemical potential and the diffusion mobility near GB. It was shown that nonequilibrium GB can essentially change the phase equilibrium of alloy and surface directed spinodal decomposition (SDSD) caused by GB determines the precipitation morphology in nanograined materials. The increase of atomic mobility near GB can result in formation of lamellar structure propagating from GB to inside the grains and variation in morphology from lamellar to drop-like type structure when composition change.

Effects of preliminary magnetization on Cu–O nanoparticles (CNPs) and their electronic structures were examined in conjunction with their near-surface reactivity. CNPs were exposed to the external magnetic field, H (≤4 kOe), in a glove box of Ar atmosphere at room temperature. The absorption intensity of UV/vis diffuse reflectance spectra of CNPs at the wavelength between 500 nm and 800 nm increased with magnetization. In order to elucidate the chemical consequences from magnetization, the reaction processes of CNPs at the boundary to the cyclohexane solution of acetyl pyridine (Apy) were examined by monitoring the decrease in the UV absorption band intensity at 279.5 nm due to π–π * transition using a flow cell. The decrease in the UV absorption intensity is correlated with the increase in the extent of the reaction. We observed the two-step reaction process with a faster initial decay and a slower later one. We found the application of the magnetic field creates new active centers for the present coordination reaction. These magnetically acquired active centers are associated with the latter, more sluggish step of the two-step reaction. All these magnetic effects are consistently explained by the delocalization of the 3d electrons of Cu due to the partial change from antiferromagnetic to ferromagnetic states.

Sedimentation dynamics of magnetite (γ-Fe3O4) nanopowder (10-20 nm) in water in a gradient magnetic field Bmax=0.3 T, (dB/dz)max=0.13 T/cm was studied for different water flow speeds and starting particle concentrations (0.1 and 1.0 g/l). The aggregates formation in water was monitored under the same conditions. In cyclical water flow, the velocity of particle sedimentation increases significantly in comparison to its rate in still water, which corresponds to the intensified aggregate formation. However, at a water flow speed more than 0.1 cm/s sedimentation velocity slows down, which might be connected to aggregate destruction in a faster water flow. Correlation between sedimentation time and the nanoparticle concentration in water does not follow the trend expected for spherical superparamagnetic particles. In our case sedimentation time is shorter for c=0.1 g/l in comparison with that for c=1 g/l. We submit that such a feature is caused by particle self-organization in water into complex structures of fractal type. This effect is unexplained in the framework of existing theoretical models of colloids systems, so far. Provisional recommendations are suggested for the design of a magnetic separator on the permanent magnets base. The main device parameters are magnetic field intensity B≥0.1 T, magnetic field gradient (dB/dz)max≈(0.1-0.2) T/cm, and water flow speed V0.15 cm/s. For particle concentration c=1 g/l, purification of water from magnetite down to ecological and hygienic standards is reached in 80 min, for c=0.1 g/l the time is reduced down to 50 min.

The influence of mechanical milling of Mg-based mixtures on the structure and hydrogen sorption properties was investigated by measuring the rate of hydrogen absorption, nuclear magnetic resonance and X-ray diffraction. In order to separate different factors responsible for hydrogenation kinetics, we compare the results of milling of both pure Mg and the mixture of Mg with different metallic and oxide additives in argon at 77 K and in hydrogen atmosphere at room temperature, with the milling tools made of steel and brass. It was established that the role of grain size and different catalytic additives is considerable only for an initial formation of MgH 2 phase during mechanical activation in hydrogen. The most important effect of mechanical activation at the late stages of milling consists of the formation of a special structural state of the hydrogen-containing phase, independently on the type of the catalyst. The observed enhancement of the proton spin-lattice relaxation rate in the samples prepared by ball milling in hydrogen is attributed to the effect of paramagnetic centers which are an intrinsic feature of such a structural state.

The high-energy edge of the transparency window in nanocrystalline copper monoxide (CuO) can be shifted to 0.6 eV (against 1.45 eV in single crystals). This shift is related to a modification of the shape of the fundamental absorption edge of CuO without any change in the refractive index. The obtained nanocrystalline CuO is recommended for use as a selective solar energy absorber.

The influence of magnetic field on the rate of oxidative dehydrogenation of 2,3,5-trimetyl-1,4-hydroquinone (TMHQ) to 2,3,5-trimetyl-1,4-benzoquinone (TMBQ) with catalysts based on copper oxide nanopowders has been investigated. The initial transformation rate of TMHQ and the final product yield greatly increase after a preliminary magnetization of nanopowders. The adsorption ability of Cu-oxide-based nanopowders with respect to ammonia enhances by 1.5 after their magnetization. Physical mechanism of reactivity variation of CuO nanopowders under the influence of weak stationary external magnetic field (H≤3 kOe) has been proposed. As a result of magnetic field influence, the ferromagnetic regions with modified spin and charge state have appeared in an antiferromagnetic CuO of nonstoichiometric composition. These regions can be new catalytic or adsorption centers.

Decomposition of solid solution taking into account the grain boundaries segregations is considered in the framework of generalized Cahn-Hilliard model for finite systems. Two types—“stripe” and “drop-wise”—of the surface-directed decomposition found below spinodal depend on concentration of a wetting component. We demonstrate that grain boundaries segregations are able to drastically change the phase equilibrium inside the grain when its size becomes less than the critical value. As a result, decomposition of the solid solutions easily appears for nanograined materials.

Cu–20at.% Co was mechanically alloyed from pure elements by ball milling for 28 h. The powder was compacted into pellets at room temperature by applying a pressure of 0.5 GPa. Microstructural investigations were carried out by three-dimensional atom probing (3DAP) after annealing at 400 °C for 2 h in Ar atmosphere. The annealed Cu–20at.% Co exhibits a heterogeneous microstructure. Cu-rich and Co-rich particles with 8.7 at.% Co and 1.3 at.% Cu, respectively, and highly supersaturated regions with average Co concentrations between 25 and 35 at.% were detected. A new, sensitive statistical analysis of the 3DAP data obtained from a supersaturated region revealed concentration fluctuations of ±24 at.% Co with an average wave length of about 2 nm indicating spinodal decomposition.