Russian Journal of Physical Chemistry A最新文献

A comparative study of composites based on imidazolium phosphomolybdates of the SILP type of catalysts for peroxide oxidative desulfurization was performed by mass spectrometry and other physicochemical methods, in particular, XPS (X-ray photoelectron spectroscopy). An analysis of the data obtained revealed partial destruction of heteropolyanions during the synthesis of heterogeneous samples. The results of mass spectrometric measurements are well correlated with the XPS data, indicating the possibility of using mass spectrometry (MS) in the surface-activated laser desorption/ionization (SALDI) technique for characterization of these composites. The results of the analysis of the desulfurization rate showed the important role of the products of partial destruction of heteropolyacid anions in the catalysis of the process.

Lipid nanoparticles such as nanoemulsions, nanostructured and solid lipid particles made of stearic acid and paraffin oil and stabilized with a mixture of nonionic surfactants Tween 60 and Span 60 are studied. The effect of incorporated yttrium stearate (YSt) as an additive in the modelling of radiopharmaceuticals and radiotherapy on the physicochemical properties of lipid nanoparticles is considered. The resultes indicate that the size of the oil droplets changes slightly when YSt is included in the nanoemulsions. The incorporation of YSt into lipid nanoparticles with stearic acid reduces their size, due apparently to the incorporation of YSt into the adsorption layer together with stearic acid. The studied lipid nanoparticles are resistant to radioactive irradiation with a dose of 5 kGy. No changes in the molecular structure of the components are observed after irradiation, and the aggregative stability of the lipid nanoparticles is not changed.

Spatial distributions of the electron temperature and intensity of luminescence of molecular complex C₂ are measured in the plasma jet of an optical discharge in a mixture of argon with molecular additives, supported by continuous CO₂ laser radiation. Diamond coatings are obtained on cutting inserts of a turning tool made of WC-Co8 hard alloy by scanning a plasma jet along the surfaces of the inserts, and diagnostics of the coatings are performed.

Nonwoven materials are fashioned from polyimide (PI) and its copolymer derivative (urethane–imide) (CPUI) through the formation of electrical fibers, referred to as electrospinning (ES). Diaminobiphenyl ether (DABPE) and pyromellitic anhydride (PMA) are chosen as monomers in the synthesis of polyimide. Diamine dianhydride and toluene di-isocyanate (TDI) are used in the synthesis of copoly(urethaneimide), as is polycaprolactone (M_n = 2000). A nonwoven polyimide material is obtained from an aqueous–ethanolic solution of the triethylammonium salt of polyamide acid (SPAA) with subsequent thermal imidization of the nonwoven prepolymer at 250°C. A nonwoven material based on SPAA is obtained from a solution of copoly(urethaneamidoacid) in dimethyformamide (DMF) using a catalytic mixture consisting of triethylamine and acetic anhydride. Optimum conditions are selected for the formation of nonwoven fibers in electrospinning. The chemical structure of nonwovens is confirmed via IR spectroscopy. The morphology of the microstructure of nonwovens is studied by means of scanning electron microscopy (SEM). The thermal and mechanical properties of the obtained nonwovens are determined using TGA, DSC, and DMA, and their deformation and strength characteristics are determined. Membrane filtration properties of the obtained nonwovens are studied. It is concluded that nonwovens can be used as membranes that operate in nonaqueous organic media.

The results of a study of the activity of catalysts for the reaction of catalytic isotope exchange between carbon dioxide and water vapor are presented. The samples were synthesized on the basis of iron, cobalt and nickel oxides, applied to a carrier—γ-aluminum oxide. The results of structural studies of the obtained samples were analyzed using scanning electron microscopy, X-ray fluorescence analysis, and low-temperature nitrogen adsorption to determine the specific surface area and porosity. It was concluded that nickel oxide supported on aluminum oxide has the highest catalytic activity (observed rate constant k = 5.49 ± 0.36 s^–1).

Polydecylmethylsiloxane–polyperfluorooctyl methylsiloxane (PDec-PFOMS) copolymers are synthesized for the first time. NMR data are used to determine the quantitative substitution of the Si–H bond in the PDec-PFOMS. It is shown that raising the content of PFO expands the wetting angle for n-butanol. It is established that injecting the polymer with 2 mol % of PFO increases the sorption of n-butanol by a factor of 1.5. The performance of the obtained composite membranes during the separation of the ABE fermentation mixture is studied for 70 h in the vacuum pervaporation mode. It is established that introducing 2 mol % of PFO substituents raises the total membrane flow from 0.29 kg/(m² h) to 0.55 kg/(m² h). After 70 h of separation, the reduction of the total flow through the 2PFO/MFFK membrane is found to be 10% less than that of PDecMS/MFFK. The improved stability of the transport characteristics of 2PFO/MFFK testifies to the advantage of modifying PDecMS by introducing PFO to create a material resistant to clogging when separating alcohols from an ABE-fermentation mixture.

The electronic structure of AnO₂ (An = Th‒Lr) and the structure of X-ray photoelectron spectra of their valence electrons were calculated by the relativistic discrete variation method in the MO LCAO cluster approximation (molecular orbitals as linear combinations of atomic orbitals). This structure is in satisfactory agreement with the available experimental spectra. The effective charges Q_An of the An ions in AnO₂ were determined as the difference between the number of electrons in the neutral An atom and the number of electrons in the actinide ion in the AnO₈ cluster. The dependence of the effective charges Q_An in AnO₂ on the atomic number Z was obtained. The estimated values in the range 0.42 e < Q_An < 1.04 e differ significantly from Q_An(IV) = 4 e, found in the ionic approximation. This is attributed to the significant covalence effects in AnO₂, associated with the overlap of not only An6d, but also of An6p and An5f AOs with the oxygen orbitals. There is qualitative agreement between the obtained Q_An values and the values of the chemical shifts (several electron-volts) of the lines of the actinide 4f core electrons in the XP spectra of dioxides relative to the metals.

The Fe/MgAl₂O₄ catalysts modified with In were prepared by joint impregnation of aluminum–magnesium spinel with solutions of metal nitrate salts. Data on the adsorptive and reductive properties of the catalysts obtained by the in situ magnetic method, XPS, thermolysis, and IR spectroscopy of adsorbed CO are compared. It was established that the presence of indium in the catalyst inhibits the reduction of iron oxides to magnetite, as well as the stage of water removal from the catalysts and the decomposition of metal nitrates. It was shown by IR spectroscopy that the main adsorption sites are the structures that include Fe²⁺ cations.

The confinement effect of carbon nanotubes plays a significant role in the field of catalysis. A bamboo-structured N-doped carbon nanotubes (NCNT) encapsulated PdCo nanoparticles (PdCo@NCNT) was prepared by pyrolysis method with melamine as carbon and nitrogen source. The preparation conditions of PdCo@NCNT and the growth mechanism of NCNT were studied. TEM test showed that the PdCo nanoparticles are fully encapsulated by the graphitic shell on the top of carbon nanotubes. There exists electron transfer between Pd and Co, and a bimetallic PdCo active center with electron-rich Pd and electron-deficient Co formed. PdCo@NCNT exhibited higher catalytic activity for furfural hydrogenation than Co@NCNT. PdCo@NCNT with PdCo encapsulated within NCNT showed better furfural hydrogenation activity and reusability property compared with PdCo/NCNT with NCNT external loading method.

The adsorption, electronic, and thermodynamic properties of the 2 × 2 × 1 and 3 × 3 × 1 supercells of the binary compounds (({{{text{A}}}_{n}}{{{text{B}}}_{m}} = 4{text{H}}- {text{SiC}},) ({{alpha }}{kern 1pt} {text{ - }}{kern 1pt} {text{L}}{{{text{i}}}_{2}}{{{text{C}}}_{2}},) ({text{L}}{{{text{i}}}_{n}}{text{S}}{{{text{i}}}_{m}})) of the Si–C–Li system were studied using the density functional theory (DFT). The theoretical capacity of the 4H–SiC hexagonal polytype was found to exceed that of graphite (370 mA h/g) used as an anode material for lithium-ion batteries. The crystalline compounds ({{{text{A}}}_{n}}{{{text{B}}}_{m}}) have electronic conductivity. The DFT calculations used the exchange-correlation functional within the framework of the generalized gradient approximation (GGA PBE). The parameters of the crystal structure, the adsorption energy of the ({text{L}}{{{text{i}}}_{{{text{ads}}}}}) adatom on the 4H–SiC substrate, the electronic band structure, and the thermodynamic properties of the supercells of ({{{text{A}}}_{n}}{{{text{B}}}_{m}}) compounds were calculated. The thermodynamically favorable position of ({text{L}}{{{text{i}}}_{{{text{ads}}}}}) and the stable configuration of the 4H–SiC〈Li_ads〉 supercells were determined. The DFT calculations of the enthalpy of formation of ({{{text{A}}}_{n}}{{{text{B}}}_{m}}) compounds in the Si–C–Li ternary system were performed. The calculated characteristics of ({{{text{A}}}_{n}}{{{text{B}}}_{m}}) agree with the experimental data. The equilibrium connodes in the concentration triangle of Si–C–Li were established using the standard thermodynamic potentials of ({{{text{A}}}_{n}}{{{text{B}}}_{m}}) compounds and the changes in energy in solid-phase exchange reactions between these compounds. An isothermal section of the phase diagram of Si–C–Li at 298 K was constructed.