MoS2 nanomaterials with varying Co or Ni substituent contents were synthesized by rapid thermolysis of mixed aerogels of ammonium tetrathiomolybdate and cobalt or nickel acetate in an inert atmosphere. Electron microscopy studies of the samples revealed microdefects in the structure of the MoS2 platelets arising from gas evolution during decomposition of the acetate moiety. X-ray photoelectron spectroscopy data showed that Co and Ni are in the 2+ oxidation state, and their introduction into MoS2 lowers the Fermi level. Extended X-ray absorption fine structure spectroscopy indicated that both Co and Ni are coordinated by four sulfur atoms, consistent with the substitution of Mo atoms at the edges of the MoS2 nanosheets. Testing of samples as anodes for sodium-ion batteries (SIBs) demonstrated optimal performance for MoS2 with 1–2% Co (Ni) substitution. The reversible specific capacity of the best samples after 55 discharge/charge cycles was ∼500 mAh·g−1 at a current density of 0.1 A·g−1. Analysis of cyclic voltammetry curves measured after more than 60 cycles revealed peaks of redox reactions corresponding to the reversible intercalation of Na+ ions between MoS2 nanosheets. SIBs with Co-MoS2 or Ni-MoS2 anodes sustained a current density of 10 A·g−1, while the Co-doped sample retained an exceptional capacity of 150 mAh·g−1 after 1000 cycles. The superior rate performance of Co-MoS2 is attributed to the higher electron density near the Fermi level provided by the Co substituents, as confirmed by density functional theory calculations.

Cu-modified zeolites provide methane conversion to methanol with high selectivity under mild conditions. The activity of different Cu-sites for methane transformation is still under discussion. Herein, ZSM-5 zeolite has been loaded with Cu2+ cations (1.4 wt % Cu) as characterized by UV-vis DRS, EPR, EXAFS, and 1H MAS NMR. It is inferred that Cu2+ cations, attached to the cation-exchange Al-O--Si sites of the zeolite framework, can exist in the form of either isolated or paired Cu2+ sites. The transformation of methane to methanol on Cu2+/H-ZSM-5 has been verified by the observation of the methoxy species formation with 13C MAS NMR and FTIR spectroscopy. The related mechanisms have been analyzed by DFT calculations. The calculations show that the paired Cu2+ sites enable heterolytic C-H bond dissociation via the "alkyl" pathway resulting in methylcopper species, which however are not detected experimentally due to further rapid transformation to surface methoxy species through methyl radical formation and recombination with Si-O-Al site. Based on the obtained data, it has been concluded that methane transformation to methanol on paired Cu2+ sites, having no extra-framework oxygen ligand, is possible in Cu-modified zeolites. The pathways of Cu2+ cations regeneration with O2 and H2O have been experimentally explored.

Nitrogen-doped carbon attracts researchers as a catalyst support due to its ability to provide high dispersion of deposited metal, which can show improved properties in various catalytic reactions as compared to the metal on nitrogen-free carbon supports. Here, we developed a procedure for modification of a porous carbon material by fluorination with bromine trifluoride vapor at room temperature followed by heating in gaseous ammonia to produce a nitrogen-doped carbon support for nickel catalyst. The obtained support has a specific surface area of 1030 m(2)/g and a total nitrogen content of 4.8 at.%, with half of it in the form of pyridinic nitrogen, which is necessary for stabilization of nickel atoms. These characteristics of the support allow a simple impregnation method to achieve a content of nickel single-atom sites up to 4.9 wt.%. Increasing the metal content to 7.4 wt.% leads to the formation of nickel particles with an average size of less than 1 nm. The catalysts were tested in the decomposition reaction of gaseous formic acid and showed high (>99 %) and stable selectivity toward hydrogen production.

Formic acid is a liquid organic hydrogen carrier from which hydrogen can be released together with CO2 by catalytic decomposition. The development of supported Ni catalysts for H-2 production is important. Here, the effects of Ni state/dispersion are considered. For this purpose, three samples were prepared with about 3 wt% Ni deposited on porous N-doped carbon. The first sample contained predominantly Ni nanoparticles (similar to 2 nm), the second contained Ni clusters (<1 nm), and the third - single-atom Ni sites. The catalysts showed close activity in the gas-phase reaction. However, a minimum apparent activation energy of 105 kJ/mol and a maximum selectivity towards H-2 production of 99% were achieved for the single-atom Ni catalyst. The nature of its singleatom sites was established to correspond to Ni-N-4 and Ni-O-4, which showed greater stability under the conditions of the catalytic reaction.

The work is devoted to the development, fabrication and analysis of broadband W / Si multilayer mirrors for a broadband monochromator, calculated for the spectral range of 7-10 keV. The possibility of using the stacking approach to obtain multilayer mirrors with a reflection coefficient of about 30% and a spectral bandwidth Delta E/E of about 20% is shown. The results of measurements of the angular and spectral reflection curves of the mirror obtained on a laboratory diffractometer and on a synchrotron in Novosibirsk are presented. Keywords: hard X-ray range, monochromator, synchrotron radiation, broadband mirrors, stack structures, multilayer X-ray mirrors.

The results of studying the morphology and crystalline, local atomic, and chemical structure of iron(III) oxide coatings on the surface of porous aluminum oxide with different morphology using methods of scanning-electron- and atomic-force microscopy, X-ray phase analysis, X-ray photoelectron spectroscopy, as well as X-ray absorption near edge structure (XANES) spectroscopy are presented. Films of porous alumina are synthesized by the two-stage anodic oxidation of aluminum in 0.3 M aqueous solutions of sulfuric and oxalic acids. To change the pore diameter, some of the films are etched in a phosphoric-acid solution. Samples of iron oxide nanocoatings are obtained by oxidation of iron films in air deposited onto porous alumina substrate matrices by magnetron sputtering at a temperature of 300°C for 3 h. It is shown that oxidation leads to a twofold increase in the coating thickness of the control sample and is associated with an increase in the density of iron oxide compared to pure iron. With a change in the nanoporous structure on the surface of the substrates, the morphological features of the coatings change: there is overgrowth of the pores with iron oxide. Controlling the processes leading to such overgrowth will make it possible to carry out a targeted change in the structure-sensitive properties of composite structures based on iron oxide.

Studying the X-ray absorption near-edge structure shows that cation substitution of a MnS matrix with lanthanide atoms does not significantly affect the character of the local environment of metal (manganese, dysprosium, thulium and ytterbium) and sulfur atoms in lanthanide-doped Ln 0.05 Mn 0.95 S ( Ln = Dy, Tm, Yb) solid solutions. Comparison of the experimental and theoretical data obtained by the finite-difference method has revealed that the main contributions of the unoccupied p- and d -states of manganese and p -states of sulfur are localized at the conduction-band bottom, both in the case of the initial MnS matrix and in the case of lanthanide-substituted Ln 0.05 Mn 0.95 S solid solutions. The main contributions of unoccupied f ‑states of ytterbium and thulium in Ln 0.05 Mn 0.95 S ( Ln = Tm, Yb) solid solutions are shifted to the high-energy region of the conduction band, while the f -states of dysprosium in dysprosium-doped Dy 0.05 Mn 0.95 S solid solutions are localized near the conduction-band bottom. According to the calculated model spectra, it is found that the contributions of the free lanthanide d -states in Ln 0.05 Mn 0.95 S ( Ln = Dy, Tm, Yb) solid solutions are shifted to the region of the conduction-band bottom with an increase of the atomic number of the lanthanide atom.

Osmium compounds with the Os5d4 electron configuration and an octahedral environment of neighboring atoms attract much attention due to the influence of the spin-orbit interaction on the appearance of magnetic properties in materials. XANES spectroscopy makes it possible to obtain information about the magnitude of the spin-orbit interaction from measuring the intensity ratio of lines near the absorption edges. The influence of the spin-orbit interaction on the XANES OsL2,3 spectra in osmium compounds having an octahedral halogen environment of osmium atoms has been studied. Two types of systems have been investigated: isolated osmium clusters in complex compounds and OsCl4 compound containing polymeric chains of Os connected by bridging Cl atoms. Magnetic susceptibility measurements show a non-magnetic ground state and Van Vleck paramagnetism in the case of isolated clusters and a non-zero magnetic moment over the entire temperature range in OsCl4. As a result of measurements of the XANES spectra, high values of the line intensity ratio near the OsL3/L2 absorption edges have been obtained, which is associated with a strong influence of the spin-orbit interaction on the electronic structure. Theoretical analysis of the XANES spectra of Os compounds with different ligands and outer-sphere cations shows that the electronic structure and magnetic properties depend on the spin-orbit interaction, the crystal field splitting, the electron pairing energy, and non-cubic distortions of the Os environment.

— The results of studying the morphology and local atomic structure of cobalt coatings deposited by magnetron sputtering on nanostructured surfaces of porous aluminum oxide with different morphology specified by the anodizing voltage in solutions of sulfuric (25 V) and oxalic (40 and 120 V) acids are presented. Using scanning electron microscopy and atomic force microscopy, it is shown that the coatings have morphological features, which are hexagonally arranged nanoparticles formed at the boundaries between pores. With an increase in the size of nanopores on the surface of the substrates, the size and shape of the morphological features of the deposited coatings change. According to X-ray absorption fine structure spectroscopy and fine structure spectroscopy of the near region of the X-ray absorption edge, changes occur in the local atomic structure of cobalt; in particular, cobalt in the sample of the coating deposited onto the surface of porous aluminum oxide obtained by anodizing at a voltage (25 V) in sulfuric acid is oxidized more strongly, which is related to greater chemical activity due to the smaller sizes of nanoparticles that make up the coating. The obtained results will allow for further directed modification in the formation of structurally sensitive properties, such as chemical and electrochemical activity, and magnetic sensitivity of the coatings obtained.

— A study of mixed systems based on zirconium oxide is carried out using X-ray absorption fine structure (XAFS: XANES, EXAFS) spectrocscopy. New reliable information concerning zirconium and yttrium on the state of Zr—Y and Zr–Y–Mg samples, parameters of the local atomic structure, interatomic distances, and coordination numbers is obtained; the possible variants of structural models are considered. An analysis of the XAFS data based on the pyrochlore and fluorite models and taking into account the abnormally low coordination numbers for zirconium and the shortening of the Zr–O bond lengths (in comparison with bulk reference points) unambiguously indicates the formation of a number of oxygen vacancies. The disordering of both sublattices (due to structural distortions of the zirconium lattice) increases in the series of samples Zr—Y and Zr–Y–Mg. With respect to yttrium, in the studied samples, the formation of both a distorted ZrY z O x fluorite nanophase (partially amorphized) with significant defects in the anion and cation sublattices, and a large amount of a distorted yttrium-oxide phase (nanophase, nanoclusters) is possible. It should also be noted that the state and local environment of yttrium is more stable than that of zirconium. The data obtained using X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy are in good agreement with each other.

The paper presents the results of studies of SrTiO 3 –TiO 2 biphase ceramics, which was previously proposed as a promising n-type thermoelectric material, carried out using synchrotron radiation techniques at the research equipment of the Shared Research Center “Siberian Synchrotron and Terahertz Radiation Center”. In particular, the in-situ heating X-ray diffraction method demonstrated that the reaction between the powder components SrCO 3 (strontianite) and TiO 2 (anatase) to produce SrTiO 3 (tausonite) was not the driving force in producing ceramics by spark plasma sintering of the reaction mixture. For two spectral methods, X‑ray luminescence and XANES spectroscopy, the spectrum of biphase ceramics was compared with the model spectrum obtained from the spectra of monophase ceramics as comparison samples. The method of X-ray luminescence revealed a shift to the high-energy region and a narrowing of the spectrum of biphase ceramics, which may indicate dimensional quantization (the presence of two-dimensional electron gas) in the system. The XANES spectrum of biphase ceramics reveals changes in the region in which its shape may significantly depend on the symmetry of the nearest Ti 4+ atoms. However, it is difficult to interpret these data without numerical simulation.

The results of a study of biphase ceramics SrTiO3–TiO2, previously proposed as a promising n-type thermoelectric material, obtained using synchrotron radiation techniques at the shared research center “Siberian Synchrotron and Terahertz Radiation Center”, are presented. In particular, it has been demonstrated by in-situ heating X-ray diffraction that the reaction between the powder components SrCO3 (strontianite) and TiO2 (anatase) to obtain SrTiO3 (tausonite) is not the driving force in the preparation of ceramics by spark plasma sintering of the reaction mixture. For two spectral methods – X-ray luminescence and XANES spectroscopy, the spectrum of biphasic ceramics was compared with a model spectrum obtained from the spectra of single-phase ceramics as reference samples. The X-ray luminescence method revealed a shift to the high-energy region and a narrowing of the spectrum of biphase ceramics, which may indicate size quantization (the presence of a two-dimensional electron gas) in the system. Changes were found in the XANES spectrum of biphase ceramics in the region in which its shape can significantly depend on the symmetry of the nearest environment of Ti4+ atoms. However, it is difficult to interpret these data without numerical simulation.

The Center for Collective Use “Siberian Center for Synchrotron and Terahertz Radiation” provides users from various organizations with the opportunity to use modern analytical techniques using synchrotron radiation beams for a wide range of research work. At present, the general direction of the development of new techniques is focused on the development of new original approaches to the use of synchrotron radiation.

Hydroxyapatite, a mineral of the apatite group, has an important and useful property. It has the propensity for various kinds of substitutions, which allows modification of its properties and expansion of the possibilities of applying the synthetic material. The properties of a synthesized substance depend on the way it is produced, as the synthesis conditions influence the structural and morphological characteristics of the particles being formed. This work shows that, in the case of mechanochemical synthesis with the introduction of iron cations as a dopant, the structure of hydroxyapatite, in which the dopant occupies the position of the calcium cation, is formed. This type of substitution is accompanied by a decrease in the lattice parameters of the hydroxyapatite. It is shown that iron cations predominantly possess a 3+ charge, which is independent of the charge of the initial reagent containing the iron cation. It is also found that in the process of mechanochemical synthesis under certain conditions, the simultaneous partial replacement of calcium cations with iron cations and phosphate groups with carbonate group can be implemented. The powders obtained by mechanochemical synthesis are characterized by powder diffraction, infrared spectroscopy, X-ray absorption near edge structure spectroscopy (XANES), and Mössbauer spectroscopy.

A comprehensive study of the local atomic structure of titanium compounds obtained by mechanical activation (Ti–Al–C, Ti2AlC) and reference samples (Ti, TiH2) using extended X-ray absorption fine structure (EXAFS) and extended electron energy loss fine structure (EXELFS) spectroscopy is carried out. An analysis of the local atomic structure of titanium hydride shows that the presence of hydrogen expands the crystal lattice and leads to a change in the parameters of the local atomic structure. This change is observed both in the EXAFS and EXELFS spectra. It is shown that after mechanical activation, the coordination numbers decrease, which may indicate the formation of a multiphase system. Further annealing leads to formation of the Ti2AlC compound, which is confirmed by the results of model calculations.

Reaction of pyridine-2,6-dicarbaldehyde with hexane-3,4-dione and ammonium acetate affords 2,6-bis(4,5-diethyl-1 H -imidazol-2-yl)pyridine (L) which was used as ligand in the synthesis of iron( ii ) chloride complex [FeL 2 ]Cl 2 •H 2 O. Conclusions about the structure of the coordination site of the complex were drawn based on the results of IR spectroscopy, EXAFS spectroscopy, static magnetic susceptibility studies, and quantum chemical calculations.

Ni supported on N-doped carbon is rarely studied in traditional catalytic reactions. To fill this gap, we compared the structure of 1 and 6 wt% Ni species on porous N-free and N-doped carbon and their efficiency in hydrogen generation from gaseous formic acid. On the N-free carbon support, Ni formed nanoparticles with a mean size of 3.2 nm. N-doped carbon support contained Ni single-atoms stabilized by four pyridinic N atoms (N4-site) and sub-nanosized Ni clusters. Density functional theory calculations confirmed the clustering of Ni when the N4-sites were fully occupied. Kinetic studies revealed the same specific Ni mass-based reaction rate for single-atoms and clusters. The N-doped catalyst with 6 wt% of Ni showed higher selectivity in hydrogen production and did not lose activity as compared to the N-free 6 wt% Ni catalyst. The presented results can be used to develop stable Ni catalysts supported on N-doped carbon for various reactions.

An Erratum to this paper has been published: https://doi.org/10.3103/S106287382301001X

The comprehensive experimental and theoretical study of the structure of the valence band and conduction band of vanadium-substituted solid solutions CuCr 1 – x V x S 2 ( x = 0–0.40) is carried out using both quantum chemistry calculations and X-ray absorption and emission spectroscopy. For a detailed analysis of the fine structure of the X-ray emission and absorption spectra, the experimental spectra are corrected for the width of the instrument-distortion function and the width of the internal level. The corrected experimental spectra are compared with the distributions of the partial atomic densities of states of metals and sulfur obtained from quantum-chemical calculations within the framework of density functional theory using the BAND and FDMNES software packages. Comparison of the experimental and theoretical data allows one to interpret changes in the fine structure of the X-ray absorption K -edges and X-ray emission lines of the valence band with an increase in the vanadium concentration. It is shown that after cationic substitution the character of the distribution of occupied and unoccupied states for copper, chromium, and sulfur is similar to that for the initial copper–chromium disulfide. The contribution of vanadium states replaces the contribution of chromium states at the valence-band top and the conduction-band bottom, which causes the metal–insulator transition. Interpretation of the nonmonotonic character of the temperature dependence of the Seebeck coefficient of CuCr 1 – x V x S 2 solid solutions, obtained for the first time, is carried out using the results of the experimental and theoretical study of the electronic structure.

Properties of a novel catalytic material, Pt/N-graphene, in gas-phase decomposition of formic acid to obtain pure hydrogen were studied. The graphene powder doped with nitrogen atoms was used as the carbon support. The following methods were used to characterize the synthesized catalysts: X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), EXAFS and CO chemisorption. It was determined that the platinum precursor substantially affects the state of the metal in the Pt/N-graphene catalysts. When Pt(NO3)(4) was used as the precursor, platinum on the catalyst surface was in the form of nanocrystals. Meanwhile, the use of H2PtCl6 led to the formation of atomically dispersed platinum stabilized on the surface of N-graphene. Carbon structures containing defects in the graphene layer surrounded by four nitrogen atoms had strong interactions with platinum atoms and acted as the sites where atomic platinum was stabilized.