A. V. Naumkin

Reduced graphene oxide

This paper describes a novel approach to the preparation of reduced graphene oxide and its dispersions in organic solvents. Graphite oxide, graphene oxide, and reduced graphene oxide have been prepared and characterized by a variety of physicochemical techniques.

X-ray photoelectron spectra and structure of composites prepared via deposition of Au, Ni, and Au + Ni nanoparticles on SiO2 from colloidal solutions in triethylamine

Monometallic (Au and Ni) and bimetallic (Au + Ni) nanoparticles deposited on SiO2 from colloidal solutions in triethylamine have been studied by x-ray photoelectron spectroscopy (XPS). The solutions were prepared through vapor-phase metal synthesis. We have determined the basic parameters of the core-level and valence-band XPS spectra of the Au/SiO2, Ni/SiO2, and Au-Ni/SiO2 systems. The results indicate that the Au in these systems is in the Au(0) state, while Ni is oxidized to Ni(II). The Au/SiO2 and Au-Ni/SiO2 samples differ little in the shape of the Au 4f peak. In the Au-Ni/SiO2 system, the Ni 2p3/2-Au 4f7/2 binding energy difference is 0.3 eV larger and the Ni 2p3/2 peak is narrower than those in the monometallic samples. The effects characteristic of the bimetallic system may be due to the interaction between Ni and Au or may be interpreted as evidence that the Au particles level off the potential relief on the SiO2 surface.

Composite materials for medical purposes based on polyvinylpyrrolidone modified with ketoprofen and silver nanoparticles

A method for obtaining composite medical materials based on polyvinylpyrrolidone (PVP K15) modified with ketoprofen in a medium of supercritical carbon dioxide and with Ag nanoparticles prepared by metal vapor synthesis is developed. A system in which ketoprofen and Ag nanoparticles with an average size of ∼16 nm are uniformly distributed over the bulk of PVP is obtained. It is found that the yield of ketoprofen from the composite in the physiological solution is higher than that for an analogous system obtained by mechanical mixing of the components.

Categorization system of nanofillers to polymer composites

The paper deals with a systematic categorization of nanofillers in terms of their effect arising upon introduction into polymer composites of tribological applications. The authors study the nature of this effect and the tribological behavior of different types of nanofillers acting in composites and exhibiting either a tribochemical effect or a discrete surface one. Nanofillers having an indirect influence on friction and intercalation compounds are also studied.

Effect of particle size and composition of powdered nanocrystalline molybdenum disulfide on its tribological behavior

The tribological behavior of two types of nanocrystalline molybdenum disulfide produced from natural molybdenum disulfide by monolayer dispersion in the presence of water (nano-MoS2(H2O)) and acetonitrile (nano-MoS2(CH3CN)) is studied. The study of the friction of these materials against polished and ground steels, as well as XPS examinations, show the advantage of the more thermally stable nano-MoS2(CH3CN), which is primarily due to the origin of low-molecular products adsorbed on the surfaces of nanoparticles.

The influence of plasma chemical treatment of a platinum catalyst on its activity in the dehydrogenation of cyclohexane

The influence of plasma chemical treatments on the catalytic activity of 0.64 wt % Pt/SiO2 and 1.0 wt % Pt/SiO2 platinum catalysts in the dehydrogenation of cyclohexane was studied. The state of the surface of the catalysts was examined using X-ray photoelectron spectroscopy. Temperature hysteresis caused by the formation of active carbon was observed in flow experiments. It was shown that the reaction on the initial catalysts occurred on neutral and positively charged Pt particles, and that the active centers contained carbon. After catalyst treatment with a high-frequency plasma in H2, its activity increased by many times because of the formation of a large number of low-activity centers on positively charged platinum particles also containing carbon. Glow discharge plasma in Ar sharply decreased catalytic activity, and the reaction then predominantly occurred on centers localized on neutral Pt particles, whereas centers on positive Pt particles were blocked. The state of the substrate (silica gel) did not change under the action of plasmas of both kinds.

Dehydrogenation of isopropanol on a cerium-nickel catalyst

The effect of a cerium additive on the catalytic activity of a 2 wt % Ni/SiO2 catalyst is studied. It found that under both flow and static conditions the activity of (2 wt % Ni + 0.2 wt % Ce)/SiO2 catalyst is higher than that of the original sample; the increase in activity results from a sharp increase in the number of active sites. A change in the composition of the surface layer of the catalysts is analyzed by X-ray photoelectron spectroscopy. It was found that the fraction of nickel decreases and the fraction of carbon increases in cerium-containing catalyst. An explanation of the change in the elemental composition of the catalytic active sites of a nickel catalyst in the presence of cerium is proposed on the basis of XPS data and previous quantum chemical calculations.

Cyclohexane Dehydrogenation on a Copper-Platinum Catalyst

The reaction of the dehydrogenation of cyclohexane on a copper-platinum catalyst supported by silica gel (1 wt % Pt + 0.15 wt % Cu)/SiO2 was studied. The state of the catalyst surface was investigated using X-ray photoelectron spectroscopy. It was established that under both flow and static conditions, the activity of the copper-platinum catalyst is higher than the activity of a catalyst containing 1 wt % Pt/SiO2. The rise in activity as a result of the introduction of copper, due to a decrease in the activation energy, is explained by an increase in the fraction of carbon in the composition of active centers localized on particles of neutral (Ptm0) and positively charged (Ptn+δ) platinum, and by the formation of centers with increased activity as a result of the adsorption of Cu+δ on particles of Ptm0. It was demonstrated that treating the copper-platinum catalyst with the plasma of a glow discharge in argon and oxygen increases its activity, while treatment in high-frequency H2 plasma reduces it. The indicated changes in the activity are associated with the alteration of the activation energies and the number of active centers, revealed by X-ray photoelectron spectroscopy, that depend on changes in the catalyst surface composition.

X-ray photoelectron spectra of polynuclear manganese complexes

Manganese trimethylacetate complexes with different ligand environments were studied by X-ray photoelectron spectroscopy (XPS). Changes in the Mn 2p, C 1s, O 1s, and N 1s X-ray photoelectron spectra caused by the substitution of Mn → N coordination bonds for Mn → O coordination bonds were examined. In the spectra of manganese trimethylacetate complexes, the satellite component was identified, which is evidence of the high-spin state of manganese atoms. An increase in the magnetic moment of the manganese complexes, both with the oxygen and mixed oxygen-nitrogen environment, is accompanied by an increase in the spin-orbit splitting, the difference in Eb between the satellite and the Mn 2p3/2 line, and the ratio between the integrated intensities of the satellite and the Mn 2p3/2 line (I sat3/2/I Mn 2p3/2). The XPS data made it possible to determine the measure of covalence of the metal-ligand bond. The XPS results are consistent with X-ray crystallography data.

Fibroporous polytetrafluoroethylene modified with iron nanoparticles: Structure and electronic and magnetic properties

A method for synthesizing iron-containing nanocomposite based on fibroporous polytetrafluoroethylene (PTFE) is described. Fibroporous PTFE obtained under the radiation of a CO2 laser on block PTFE is modified in supercritical carbon dioxide (sc CO2) to form micro- and nanoporous structures. Porous fluoropolymer is treated with a solution of bis(toluene)iron(0) obtained by metal-vapor synthesis (MVS). The composition and structure of iron-containing fluoropolymer is studied by transmission electron microscopy and X-ray photoelectron and Mössbauer spectroscopy. Fe nanoparticles with an average size of 9 nm, consisting of ∼30% FeO and ∼70% Fe3+, are registered in the sample. Fe0 nanoparticles are stabilized in fluoropolymer pores and are coated with nanoparticles of nonstoichiometric iron oxides that have superparamagnetic properties.