Vol 91, No 9 (2017)

The effect the nature of metal oxide components, quantitative and qualitative composition, structure of binary metal oxide nanocomposites, and temperature have on the physicochemical processes that occur during the detection of reducing gases and are responsible for the efficiency and selectivity of sensors based on these composites is considered. The relationship between the mechanisms of the conductivity and sensor effect in composites is determined. The crucial role of electron transfer between metal oxide components with different work functions leading to the mutual charging of these components is noted. The mechanisms of electronic and chemical sensitization of the sensor effect in composite materials consisting of metal oxides with various electronic and chemical properties are discussed. The important role of the way composite materials are obtained is noted. The effect of small clusters of one oxide on the surfaces of nanoparticles of other components, formed during the synthesis of composites via impregnation, is studied. Systems consisting of composite nanofibers of the core–shell type based on metal oxides of different natures are considered. It is shown that by changing the nature of the components and their relative location in the nanofibers, the sensitivity and selectivity of a sensor system can be adjusted for different chemical compounds.

A phenomenological mathematical model of the formation and growth of phases in a binary multiphase system with allowance for factors influencing the process of diffusion in a binary system is presented. It is shown that phases can grow for a certain time at different ratios between diffusion parameters according to a parabolic law that depends on the duration of isothermic annealing. They then slow their growth after successor phases appear at their interface with one component and can completely disappear from a diffusion layer or begin to grow again, but only at a rate slower than during their initial formation. The dependence of the thickness of each phase layer in a multiphase diffusion zone on the duration of isothermic annealing and the ratio between the diffusion parameters in neighboring phases is obtained. It is established that a certain ratio between the phase growth and rates of dissolution with allowance for the coefficients of diffusion in each phase and the periods of incubation can result in the complete disappearance of one phase as early as the onset of the growth of phase nuclei and be interpreted as a process of reaction diffusion.

The heat capacities and thermal diffusivities of ethyl esters of liquid n-alkane acids C_nH_2n–1O₂C₂H₅ with the number of carbon atoms in the parent acid n = 10, 11, 12, 14, and 16 are measured. The heat capacities are measured using a DSC 204 F1 Phoenix heat flux differential scanning calorimeter (Netzsch, Germany) in the temperature range of 305–375 K. Thermal diffusivities are measured by means of laser flash method on an LFA-457 instrument (Netzsch, Germany) at temperatures of 305–400 K. An equation is derived for the dependence of the molar heat capacities of the investigated esters on temperature. It is shown that the dependence of molar heat capacity C_p,m(298.15 K) on n (n = 1–6) is close to linear. The dependence of thermal diffusivity on temperature in the investigated temperature range is described by a first-degree polynomial, but thermal diffusivity a (298.15 K) as a function of n has a minimum at n = 5.

In present paper, the insertion and H₂ elimination reactions of H₂GeFMgF germylenoid with RH (R = Cl, SH, PH₂) were investigated by means of B3LYP and QCISD calculation methods. One transition state and one intermediate were found along the potential energy surface in each insertion reaction, while for the H₂ elimination reactions, only one transition state was found between the reactants and products in each reaction process. Both for the insertion and H₂ elimination reactions, RH reactivity increases in the following order: H–Cl > H–SH > H–PH₂. The insertion and H₂ elimination reactions were compared, and the results demonstrated that the H₂ elimination should be more favorable than the corresponding insertion. The solvent effects on these two types of reactions were considered. The calculated results indicated that the solvents could accelerate the reactions by reducing their barrier heights.

A series of HM/MCM-48 samples with different SiO₂/Al₂O₃ molar ratio were prepared by sol-gel method. The prepared catalysts were characterized by XRD, N₂ adsorption-desorption, NH₃-TPD, FT-IR, SEM, and TEM techniques, and their catalytic performance was investigated in alkylation of toluene with tert-butanol. The adsorption capacity and the acid sites amount of HM/MCM-48-4 sample prepared by growing MCM-48 on the surface of HM zeolite are much higher than that of their mechanical mixture (HM/MCM-48(4) sample) due to its biporous structure; it shows higher catalytic performance than other HM/MCM-48 samples. The influence of reaction conditions on the catalytic performance of HM/MCM-48-4 zeolite was discussed. Toluene conversion of 41.4% and p-tert-butyltoluene selectivity of 73.5% were obtained at the weight ratio of toluene to HM/MCM-48-4 of 5, reaction temperature of 453 K, reaction time of 5 h and the molar ratio of toluene to tert-butanol of 0.5.

the enthalpies of dissolution of glycine (Gly), glycylglycine (GlyGly), and glycylglycylglycine (GlyGlyGly) are measured in aqueous solutions of sodium dodecyl sulfate (SDS) at SDS concentrations m = 0–0.7 mol kg⁻¹ and Т = 298.15 K by means of calorimetry. The obtained data are used to calculate the standard values of enthalpies of dissolution (Δ_solH^m) and enthalpies of transfer (Δ_trH^m) of glycine and its oligomers from water to SDS aqueous solutions. The dependences of Δ_solH^m and Δ_trH^m on SDS concentration in an aqueous solution at a constant concentration of glycine and its oligomers are determined. A comparative analysis of the thermodynamic characteristics of Gly, GlyGly, and GlyGlyGly transfer within the studied range of SDS concentrations is performed. The results are interpreted in terms of ion–ion, ion–polar, and hydrophobic interactions between SDS and molecules of glycine and its oligomers.

Acid–base and coordination properties of alkyl and aryl meso-substituted porphyrins are studied spectrophotometrically in nonaqueous solutions. It is found that the nature of the substituent greatly affects the basicity of ligands for porphyrins characterized by a flat structure of macrocycle. The electronic effects of substituents have a much weaker influence on the kinetics of complexing. These effects could be due to the opposite orientation of some factors: an increase in the basicity and stability of the N–H bonds of porphyrin reaction centers. Dissociation constants pK_b of the cationic forms of meso-substituted derivatives of porphyrin are measured. The values of pK_b are in good agreement with classic concepts of the nature of substituents, particularly those indirectly included in the macrocycle through phenyl buffer rings.

The refraction, dielectric, viscosity, density, data of the binary mixtures of N,N-dimethylacetamide (DMA) with n-butanol at 308.15 and 313.15 K. The measured parameters used to obtain derived properties like Bruggeman factor, molar refraction and excess static dielectric constant, excess inverse relaxation time, excess molar volume and excess viscosity, excess molar refraction. The variation in magnitude with composition and temperature of these quantities has been used to discuss the type, strength and nature of binary interactions. Results confirm that there are strong hydrogen-bond interactions between unlike molecules of DMA+ n-butanol mixtures and that 1: 1 complexes are formed and strength of intermolecular interaction increases with temperature.

Structural changes that occur in lignin surface-modified with nickel nanoparticles during microwave- assisted dry reforming (DR) are studied via vibrational spectroscopy. IR spectroscopy reveals that the nickel deposition has a considerable effect on the structural characteristics of lignin. It is found that nickel deposition from an acetate salt substantially reduces the intensity of absorption bands at 1700 cm⁻¹. This finding suggests that Ni(2+) interacts mostly with formate groups, which are subsequently oxidized to carboxylate groups. It is shown that with the deposition of metallic nickel particles from a colloidal nickel solution in toluene prepared via metal vapor synthesis, the nickel particles do not interact with the surface functional groups of the lignin. Deep conversion of an organic mass of lignin by DR to form synthesis gas reduces the intensity of the absorption bands of the identified functional groups and raises the intensity of the absorption bands of the aromatic rings. Raman spectroscopy shows that during lignin conversion, the aromatic rings condense partially to form amorphized graphite. In operando studies reveal that the DR of nickel-modified lignin heated to 200–400°C results in the isolation of vanillic oxygenates that are probably intermediate products of reforming.

The coefficients of scattering and the depolarization of scattered light are measured in liquid benzene, chlorobenzene, o-dichlorobenzene, o-chlorotoluene, toluene, and o-xylene in the temperature range of 293‒368 K at a wavelength of 546 nm. Isothermic compressibility, internal pressure, and the functions of radial and orientational correlation are calculated for these liquids in the indicated temperature range, using the classical theory of molecular light scattering. We show that the local structure of these liquids is determined by orthogonal contacts between benzene rings (the T-configuration) and stacked (S-type) configurations. T-configurations predominate in benzene, chlorobenzene, and o-chlorotoluene, while toluene, o-xylene, and o-dichlorobenzene are characterized by S-configurations. It is also shown that the local structures of these liquids are reorganized in a certain temperature range.

The binding energy of Cu²⁺(H₂O) is computed to be 98.4 kcal/mol and thus one-photon photodissociation is not possible in the 3400–3800 cm^–1 (9.7–10.9 kcal/mol) region. To study whether the infrared photodissociation processes of Cu²⁺(H₂O) can occur by multiple argon atoms tagging technique, density functional and CCSD(T) methods are used to investigate the geometries, OH stretching frequencies and the argon atom binding energies of Cu²⁺(H₂O)Ar_n (n = 1–4) complexes. Various isomers are found resulting from the different coordination sites of argon atoms. The OH stretches in these complexes are shifted to lower frequencies than those of the free water molecule, and the corresponding vibrational red shifts are progressively smaller as more argon atom is added to Cu²⁺ while binding an argon atom to an OH site should lead to additional sizable red shift to the OH stretching vibrations.

The effect the solvent and transfer pressure of graphene oxide (SLGO) Langmuir–Blodgett films on the physicochemical properties of monolayers, and on their structural and optical properties, is studied. Examination of the physicochemical properties of SLGO monolayers on subphase surfaces that are formed from SLGO dispersions in different organic solvents reveals that monolayer behavior is virtually independent of the solvent. Electron microscope and optical studies show that the monolayers formed from SLGO dispersions in DMF and acetone have the highest transfer coefficients. It is concluded that the structural heterogeneity of the surfaces of graphene oxide films results from simultaneous effect of electrostatic interactions between graphene oxide particles and Van der Waals interactions with the solvation shell of the particles. Studies focusing on the effect the pressure of transferring a graphene oxide monolayer onto the surface of a solid substrate has on structural features of LB films show that films produced at low surface pressures have more homogeneous structures.

We use a facile pyrolysis method to prepare reduced graphene oxide and copper nanocomposite (RGO/Cu) based on it. The product shows an outstanding wave absorption properties. The maximum reflection loss is up to–50.7 dB at 3.8 GHz. The reflection loss of–10 dB (90% power absorption) corresponds to a bandwidth of 11.2 GHz (3.4–14.6 GHz range) for the layer thickness of 2–5 mm. Therefore, it is suggested that the RGO/Cu nanocomposite is also a new kind of lightweight and high-performance EM wave absorbing material.

Understanding the interaction properties of biological materials with ZnO NPs is fundamental interest in the field of biotechnological applications as well as in the formation of optoelectronic devices. In this research, the binding of ZnO NPs and chlorogenic acid (CGA) were investigated using fluorescence quenching, UV–Vis absorption spectroscopy, Fourier transform infrared (FTIR), Raman spectroscopy, scanning electron microscopy (TEM), and dynamic light scattering (DLS) techniques. The study results indicated the fluorescence quenching between ZnO NPs and CGA rationalized in terms of static quenching mechanism or the formation of nonfluorescent CGA–ZnO. From fluorescence quenching spectral analysis the binding constant (K_a), number of binding sites (n), and thermodynamic properties, were determined. The quenching constants (K_sv) and binding constant (K_a), decrease with increasing the temperature and their binding sites n are 2. The thermodynamic parameters determined using Van’t Hoff equation indicated binding occurs spontaneously involving the hydrogen bond and van der Walls forces played the major role in the reaction of ZnO NPs with CGA. The Raman, SEM, DLS, and Zeta potential measurements were also indicated the differences in the structure, morphology and sizes of CGA, ZnO NPs, and their corresponding CGA–ZnO due to adsorption of CGA on the surface of ZnO NPs

Gas chromatography sorbents based on Silokhrom C80 and modified by 1-phenylazo-2-naphtholic complexes of 3d metals (Co(II), Ni(II), Cu(II)) are obtained. Their structural, chromatographic, and sorption characteristics are investigated. It is found that modifying them with 1-phenylazo-2-naphthols of transition metals has a considerable effect on the chromatographic polarity and selectivity of sorption materials. The prospects for the practical application of the obtained sorbents are demonstrated by experiments on the gas chromatographic separation of mixtures of different classes of organic compounds.

A way of preparing separation layers by the pyrolysis of fluorinated polyimide obtained from 2,4,6-trimethyl-m-phenylenediamine (2,4,6-TMmPDA) and 2,2-bis(3′,4′-dicarboxyphenyl)hexafluoropropane (6FDA) applied onto a diatomite carrier is described. Thermogravimetry, elemental analysis, low-temperature nitrogen adsorption, high-resolution electron microscopy, and gas chromatography are used to study changes in the texture and chromatographic characteristics of these layers. It is found that changes in the structure and the effectivity of separation characteristic of the layers depend on the temperature of pyrolysis, which ranges from 250 to 1100°C. It is established that a layer of separation is formed at 250–350°C, and the order of elution of hydrocarbons is similar to their chromatographic behavior on such stationary phases as OV-101. Layers of amorphous carbon formed on the surfaces of individual particles on a diatomite surface at 500–700°C. These layers ensure highly stable and selective separation of permanent gases and hydrocarbons when they are present together.

Properties of the surfaces, morphologies, and voltammetric characteristics of glass-carbon materials with developed porosity are investigated. The sizes of micro-, meso-, and macropores are determined, along with specific surface areas. The voltammetric curves of samples in sulfuric acid solution are analyzed.

A mathematical model of multistep photoinduced electron transfer (PET) in a polar medium with a single relaxation time (Debye solvent) is developed. The model includes the polarization nonequilibrity formed in the vicinity of the donor–acceptor molecular system at the initial steps of photoreaction and its influence on the subsequent steps of PET. It is established that the results from numerical simulation of transient luminescence spectra of photoexcited donor–acceptor complexes (DAC) conform to calculated data obtained on the basis of the familiar experimental technique used to measure the relaxation function of solvent polarization in the vicinity of DAC in the picosecond and subpicosecond ranges.

A fluorescent biosensor is synthesized and described. The biosensor consists of polyelectrolyte microcapsules with glucose oxidase (GOx) entrapped in the cavities and an oxygen-sensitive fluorescent indicator Ru(dpp) immobilized in shells, where Ru(dpp) is tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) dichloride. The theoretical activity of the encapsulated GOx and the effect storage time and medium composition have on the stability of sensor microcapsules are determined from polarographic measurements. No change in the activity of the encapsulated enzyme and or its loss to the storage medium are detected over the test period. The dispersion medium (water or a phosphate buffer) are shown to have no effect on the activity of microcapsules with immobilized GOx. The described optical sensor could be used as an alternative to electrochemical sensors for in vitro determination of glucose in the clinically important range of concentrations (up to 10 mmol/L).