Russian Journal of Physical Chemistry A

Electron paramagnetic resonance (EPR) is a widely used instrumental research method in chemistry, physics, biology, and materials science that can be successfully applied to characterize the electronic structure of carbon nanomaterials. This work presents a brief review of studies of various types of carbon nanostructures (CNS) by EPR, including measurement techniques, principles of spectral data processing and interpretation, and experimental results. The relationship between the properties of CNS and the nearest environment of paramagnetic centers, oxidation, and degradation of materials with time is analyzed.

The heat capacity of lutetium titanate was measured in the temperature range 2–1869 K and the smoothed temperature dependences of heat capacity entropy enthalpy changes and reduced Gibbs energy were calculated. The presence of a gentle anomaly in the heat capacity of Lu₂Ti₂O₇ in the low temperature range was confirmed and its parameters were determined. Based on the calculated values of Gibbs energy thermodynamic stability in the studied temperature range was estimated.

Corrosion of low-carbon steel in solutions of HCl, HCl + H₃PO₄, and H₃PO₄ containing Fe(III) salts is studied. In the systems involved, the corrosion of steel results from its reaction with the acid solution and Fe(III) salt. In the discussed media, partial reactions of anodic ionization of iron, cathodic reduction of H⁺ and Fe(III) cations are realized on steel. The first two reactions are characterized by kinetic control, and the latter is characterized by diffusion control. The accelerating effect of Fe(III) cations on steel corrosion in the media studied is predominantly due to Fe(III) reduction. Binding of Fe(III) cations into complex compounds with anions of the corrosive medium reduces the value of their diffusion coefficient (D_Fe(III)). The value of DFe(III) is maximum in the HCl solution and minimum in the H₃PO₄ solution. The rate of partial cathodic reduction reaction of Fe(III) is determined by the value of D_Fe(III). As a result, the accelerating effect of Fe(III) on the cathodic reaction and, hence, the general corrosion of steel in the flow of aggressive medium is most significant in the HCl solution and least significant in the H₃PO₄ solution.

Interaction of tetra-4(4-methoxyphenoxy)phthalocyanine with pyridine, 2-methylpyridine, morpholine, piperidine, n-butylamine, tert-butylamine, diethylamine, and triethylamine in benzene and the benzene-dimethylsulfoxide system is studied. The acid-base interaction reaction belongs to the number of unusually slow processes and leads to the formation of time-stable complexes with proton transfer. Their structure is proposed. The change of reactivity of tetra-4(4-methoxyphenoxy)phthalocyanine depending on the polarity of the medium, proton acceptor ability, and spatial structure of the nitrogen-containing base is considered.

The available experimental data on the solution densities of two binary subsystems, viz. water — choline chloride and urea — choline chloride, and the ternary water — urea — choline chloride system are analyzed. The parameters of the Pitzer-Simonson-Clegg bulk model describing the experimental values of molar volumes of solutions of both binary subsystems and ternary system one function V_m = f(T, p, x₁, x₂) in the temperature range from 278.15 to 363.15 K and the pressure range from 0.1 to 50 MPa are determined. In the course of thermodynamic modeling, the dependence of the molar volume of choline chloride melt on the state parameters (p, T) is proposed. The obtained model parameters describing binary interactions in the water — choline chloride and urea — choline chloride subsystems can be used to model bulk properties of solvents with deep eutectic of different component composition.

A structural rheological model is used to describe the thixotropic dispersed system of silicon dioxide in oil. The model includes a kinetic equation of the processes of formation and destruction of particle aggregates and a rheological equation containing a structural parameter (the number of aggregated particles in a unit volume). The case of an equilibrium plastic flow, which corresponds to experimental flow curves, is considered. The coefficients of the rheological equation are calculated. For a stepwise increase in the shear rate from ${\dot{\gamma }}_1$ to ${\dot{\gamma }}_2$, the transient process is considered as a transition from one equilibrium state of the flow to another equilibrium state through a certain nonequilibrium state of the flow. The coefficient of deviation from equilibrium is introduced, and its dependence ζ(t) is calculated using exponential functions; the limiting value ζ₀ is determined. The transient dependences τ^1/2(t) are approximated.

Adsorption and reaction of nitrogen oxide (NO) molecules on the surface of a model metal-oxide system formed by controlled deposition of nickel clusters under ultrahigh vacuum conditions on the surface of α-Al₂O₃(0001) aluminum oxide thin film grown on the Mo(110) substrate is studied in-situ by experimental surface analysis methods. According to X-ray photoelectron and electron Auger spectroscopy, infrared Fourier spectroscopy, and temperature-programmed desorption data, there is a conditional Ni cluster size of 2 nm that separates the nature of the electronic state of NO molecules adsorbed on their surface and their reactivity. It is found that the peculiarity of Ni clusters with a characteristic size not exceeding 2 nm is that NO molecules are adsorbed on their surface in the form of dimers (NO)₂ while for clusters of larger size adsorption occurs in the form of monomers (NO). It is concluded that this difference is the reason for the different reaction behavior of the molecules. The key difference between clusters smaller and larger than 2 nm in size is that in the former case N₂O molecules are formed upon heating the system and desorbed into the gas phase while this does not occur in the latter case. The formation of N₂O is due to the mutual influence of NO molecules forming the (NO)₂ dimer under the action of the metal/oxide interface. The results indicate that it is possible to tune the catalytic efficiency of the metal-oxide system by varying the size of the applied metal cluster.

Sorption properties of mechanically activated graphite towards molybdenum and rhenium are studied for the first time. The optimal conditions are found such that the metals can be separated, and adsorption of molybdenum up to 95 % with adsorption of rhenium 3 % is achieved: nitric acid solution, pH 3 in the presence of 50 vol.% ethanol, stirring for 60 min. The maximum sorption capacity of the sorbent towards Mo(VI) according to the Langmuir model is 115 mg/g. The adsorption followed a pseudo-second order kinetics model. The sample after molybdenum adsorption is characterized by X-ray photoemission spectroscopy, X-ray diffraction, and X-ray-structural analysis, and scanning electron microscopy. The mechanical activation resulted in a decrease in the average size of graphite crystallites, an increase in the distance between layers, and a change in the surface state of carbon.

Thermodynamic characteristics of sorption (retention factors, heat and entropy factors of sorption) of various chlorine, bromine, and iodine derivatives of adamantanes from water-methanol eluent on the graphite-like material Hypercarb and octyl silica gel (SiO₂–C8) are determined experimentally under HPLC conditions. Hypercarb is shown be characterized by the highest structural selectivity in HPLC with respect to stereoisomers of halogen adamantanes. It is established that the order of elution of isomeric chlorine, bromine, and iodine derivatives of adamantanes from the polar eluent medium on Hypercarb under HPLC fully coincides with the retention patterns of these compounds on columns with graphitized thermal soot in gas chromatography. The retention of the considered halogen adamantanes and halogenoarenes on Hypercarb is described by the adsorption mechanism of sorption, with the principal contribution to the retention being made by dispersive interactions of sorbate molecules with the adsorbent surface. The dependence of the heat and entropy factors of sorption on the composition and structure of halogen adamantanes on Hypercarb is noted to be described by the molecular polarizability and molecular site values of the sorbates and by the lipophilicity of the compounds in the case of sorption on SiO₂–C8. It is concluded that the found regularities of halogen adamantane sorption under HPLC conditions allow referring Hypercarb and SiO₂–C8 to sorbents with 2D- and 3D-types of structural selectivity, respectively.

A low-temperature technique for preparation of highly dispersed powders of lithium-cobalt double phosphates with a highly ordered crystal lattice and a given morphology is proposed. The electrochemical performance and cyclic life of the obtained compounds are shown to exceed the respective characteristics of the known analogs. The proposed method can be extended to obtain a wide range of electrode materials for lithium-ion batteries with olivine structure.

The experimental setup for obtaining fluorescence excitation spectra of molecules cooled in a supersonic inert gas jet is described. Fluorescence excitation spectra of substituted aldehyde molecules cooled in a supersonic jet are recorded using this setup. The spectra obtained using the setup is concluded to have a better signal-to-noise ratio as compared to the spectra known from publications. Further ways to modify the setup for registration of excitation spectra of sensibilized phosphorescence and phosphorescence of semivolatile molecules of polyaromatic hydrocarbons are considered.