Vol 91, No 8 (2017)

The possibility of obtaining analytical estimates in a diffusion approximation of the times needed by nonequilibrium small bodies to relax to their equilibrium states based on knowledge of the mass transfer coefficient is considered. This coefficient is expressed as the product of the self-diffusion coefficient and the thermodynamic factor. A set of equations for the diffusion transport of mixture components is formulated, characteristic scales of the size of microheterogeneous phases are identified, and effective mass transfer coefficients are constructed for them. Allowing for the developed interface of coexisting and immiscible phases along with the porosity of solid phases is discussed. This approach can be applied to the diffusion equalization of concentrations of solid mixture components in many physicochemical systems: the mutual diffusion of components in multicomponent systems (alloys, semiconductors, solid mixtures of inert gases) and the mass transfer of an absorbed mobile component in the voids of a matrix consisting of slow components or a mixed composition of mobile and slow components (e.g., hydrogen in metals, oxygen in oxides, and the transfer of molecules through membranes of different natures, including polymeric).

Mixing enthalpies of melts of the Ge–La system have been measured using isoperibolic calorimetry within two concentration ranges. For the first range (0 < x_La < 0.16 at 1520 K and 0.16 < x_La < 0.29 at 1570 K), agreement with the known literature data is observed within the experimental error. The second range (0.78 < x_La < 1 at 1470 K and 0.7 < x_La < 0.78 at 1580 K) has been studied for the first time. The melts are characterized by very strong exothermal effects of mixing, which have almost symmetrical concentration dependence: ΔH̅_La^∞ = ΔH̅_Ge^∞ = −245 kJ/mol at 1470 K. A thermodynamic optimization of the activities of the components and the phase diagram of the system have been conducted based on the obtained experimental data, using an ideal associated solution (IAS) model.

Models of mercury were constructed by molecular dynamics using the interparticle potential of the embedded atom model (EAM) at temperatures below 10 000 K and pressures below 2.5 GPa. The thermodynamic properties of the models were presented on the isobars of 0.5, 1.0, 1.5, 2.0, and 2.5 GPa. The compressibility factors Z = pV/(RT) were calculated; the coordinates of the inversion points of the Joule–Thomson coefficient below 5600 K were found from the positions of minima on the Z(p, T) isobars. At densities above 8–9 g/cm³, the results of simulation agreed well with experiment; at lower densities there were discrepancies associated with a loss of metal properties by real mercury. The behavior of the models was analyzed in the region of the van der Waals loop. The calculated critical temperature of mercury was found to be significantly overestimated relative to the experiment. Modeling the “meta-mercury” with the EAM potential with excluded embedded potential contribution gave better agreement with the equation of state of mercury at lower densities. The states with Z = 1 can be observed below 1.0 GPa. The calculated temperature of the inversion of the Joule–Thomson coefficient increased monotonically to 5600 K as the pressure increased to 2.5 GPa.

Pressure-induced phase transition in MgS is studied using a constant pressure ab initio molecular dynamics method, and a solid evidence of existence of its high-pressure phase is provided. As predicted by total energy calculations, MgS undergoes a structural phase transformation from the rocksalt structure to a CsCl-type structure under hydrostatic pressure. The transformation mechanism is characterized, and two intermediate phases having P4/nmm and P2₁/m symmetries for the rocksalt-to-CsCl-type phase transformation of MgS are proposed, which is different from the previously proposed mechanisms. We also study this phase transition using the total energy calculations. Our predicted transition parameters and bulk properties are in good agreement with the earlier first principle simulations.

The adsorption of substituted 1,2,3-benzotriazoles (R-BTAs) onto copper is measured via ellipsometry in a pure borate buffer (pH 7.4) and satisfactorily described by Temkin’s isotherm. The adsorption free energy (−ΔG_a⁰) values of these azoles are determined. The (−ΔG_a⁰) values are found to rise as their hydrophobicity, characterized by the logarithm of the partition coefficient of a substituted BTA in a model octanol–water system (logP), grows. The minimum concentration sufficient for the spontaneous passivation of copper (C_min) and a shift in the potential of local copper depassivation with chlorides (E_pt) after an azole is added to the solution (i.e., ΔE = E_ptⁱⁿ − E_pt^backgr characterizing the ability of its adsorption to stabilize passivation) are determined in the same solution containing a corrosion additive (0.01М NaCl) for each azole under study. Both criteria of the passivating properties of azoles (logC_min and ΔE) are shown to correlate linearly with logP, testifying to the role played by surface activity of this family of organic inhibitors in protecting copper in an aqueous solution.

A way of determining the coefficient of ozone mass transfer between the gas phase and liquid aqueous phase using a test compound (formic acid) is described. The values of ozone mass transfer coefficient (in aqueous solutions of 0.1–0.55 М HClO₄ and 0–1 М НСООН, and in 0.75 М H₂SO₄, 0.125 М KHSO₄, and 0–2 М НСООН) are determined along with the rate constants of the reaction of О₃ with undissociated НСООН molecules and formate ions at 21 ± 1°С.

The solubility data of tetranitroglycoluril in acetone, methanol, ethanol, ethyl acetate, nitromethane and chloroform at temperatures ranging from 295–318 K were measured by gravimetric method. The solubility data of tetranitroglycoluril were fitted with Apelblat semiempirical equation. The dissolution enthalpy, entropy and Gibbs energy of tetranitroglycoluril were calculated using the Van’t Hoff and Gibbs equations. The results showed that the Apelblat semiempirical equation was significantly correlated with solubility data. The dissolving process was endothermic, entropy-driven, and nonspontaneous.

The effect ionic liquid (IL) 1-ethyl-3-methylimidazolium tetrafluoroborate has on the coordination environment of Li⁺ cations in carbonate solvents is studied by means of IR spectroscopy and quantum chemical modeling using the example of propylene carbonate (PC). LiBF₄ is used as the lithium salt. This system is promising for use as an electrolyte in lithium power sources (LPSs), but the mechanism of ionic conductivity by Li⁺ ions in such systems has yet to be studied in full.

Models of the quantitative structure–property relationship (QSPR) between the structure of 19 alkylammonium cations and the basal distances (d₀₀₁) of Na⁺ montmorillonite modified with these cations are created. Seven descriptors characterizing intermolecular interaction, including new fractal descriptors, are used to describe the structure of the compounds. It is shown that equations obtained via multiple linear regression have good statistical characteristics, and the calculated d₀₀₁ values agree with the results from experimental studies. The quantitative contribution from hydrogen bonds to the formation of interplanar spacing in Na⁺ montmorillonite is found by analyzing the QSPR models.

The interactions of the lignin model, the lignin oligomer with degree of polymerization n = 2, with 1-butyl-3-methylimidazolium chloride ionic liquid were investigated through DFT calculations in detail. Computational results revealed that lignin dissolution in ionic liquids should be a result of the joint interactions of lignin with anion and cation of ionic liquid, and the formation of ion pair weakens the interactions between lignin and ionic liquid components. Unlike the dominant H-bonds within the lignin–anion interactions, the lignin–cation interactions involve a combination of hydrogen bond and π-stacking. These results would provide mechanistic insights and suggestions for lignocellulosic dissolution in ionic liquids.

Experimental data on the sol–gel synthesis of manganese oxides formed during the reduction of potassium permanganate by polyvinyl alcohol in an aqueous medium are presented. The physicochemical properties of the obtained manganese oxide systems that depend on the conditions of the synthesis are studied by means of DTA, XRD, SEM, and the low temperature adsorption–desorption of nitrogen. It is found that the obtained samples have a mesoporous structure and predominantly consist of double potassium–manganese oxide K₂Mn₄O₈ with a tunnel structure and impurities of oxides such as α-MnO₂, MnO, α-Mn₂O₃, and Mn₅O₈. It is shown that the proposed method of synthesis allows us to regulate the size and volume of mesopores and, to a lesser extent, the texture of the obtained oxides, which can be considered promising sorbents for the selective extraction of strontium and cesium ions from multicomponent aqueous solutions.

A relatively new method of regulating the size distribution function of nanoparticles—digestive ripening— was described. A hypothetical mechanism of dissolution of nanoparticles was proposed. It includes the effect of the ligand layer on the internal stability of the nanoparticle nucleus: the change in the structure of the ligand layer caused by a decrease in the nanoparticle size determines the kinetics of digestive ripening.

3D carbon linked by uniform sized nanospheres was successfully prepared by hydrothermal carbonization method. It is found that the increasing reaction temperature and extending reaction times have a similar effect on the morphology of the products, which could evolve from nanospheres to 3D carbon linked by nanospheres or layered structure. The final chemical structure of the products can be switched from a carbon rich in oxygen containing functional groups type to a carbon network of extensive aromatic domain.

The adsorption of hydrogen peroxide (H₂O₂) molecule on the outer and inner surfaces of Al₁₂N₁₂ nano-cage in terms of energetic, geometric, and electronic properties has been investigated using the density functional theory (DFT) calculations by B3LYP-D and M06-2X methods and 6-31G** basis set. It has been found that H₂O₂ molecule can be strongly chemisorbed (−3.45 eV) over the outer surface of the Al₁₂N₁₂ nanocage, where the adsorption energy depending upon its orientation with the nano-cage. Moreover, the adsorption of two H₂O₂ molecules on the outside surface of adsorbent is about −2.05 eV, while the adsorption of the molecule trapped inside adsorbent is about −1.81 eV. It was found that the H₂O₂ adsorption on the outer and inner surfaces of Al₁₂N₁₂ nano-cage leads to slightly lower energy gap and increasing the dipole moment of adsorbent.

The interaction between methanol vapors and composite film samples of polyvinyl alcohol–porous keplerate nanocluster polyoxomolybdate Mo₁₃₂ is studied by means of equilibrium interval sorption performed gravimetrically and using thermodynamic cycle calculations. Isotherms of methanol sorption by the films are obtained, and the concentration dependences of the average Gibbs energies of the interaction between methanol and films are calculated, along with the Gibbs energy and entropy of the interaction between polyoxometalate and the polymer. Micrographs of the studied composite films are presented.

It is found that the sorption recovery of copper ions from water solutions in the phase of AN-31 low basicity anion exchanger has a mixed character. It is established via diffuse reflectance spectroscopy that ions are stabilized through complexation with the participation of the functional groups of the sorbent with the formation of structures [Cu(NR₃)₂(OH)₂(H₂O)₂], [Cu(NR₃)₃(OH)(H₂O)₂], and as a result of the physical adsorption of oxide dimers and planar-squared copper clusters. It is shown that increasing the ionic strength of a solution by introducing sodium chloride into the system greatly improves the capacity of the sorbent and leads to the uniform distribution of copper ions in the resin matrix. The similarity between the ESR spectrum parameters of copper-containing samples of the ion exchanger, obtained in a wider range of pH, is determined via ESR and testifies to the homogeneity of the stabilization positions of Cu²⁺ ions. The crystalline field of tetragonal-elongated octahedron is typical of all Cu²⁺ ions. All of the complexes have Cu(NO₃)₂ coordination nodes with the covalent bonding of Cu²⁺ ions and the amine groups of the sorbent.

The brownmillerite Sr₂Fe₂O₅ is prepared by nitrate route and the physical and photo-electrochemical properties are investigated for the first time. Thermal analysis indicates the formation of the phase at 950°C. A direct optical transition at 0.94 eV, due to Fe³⁺ splitting in octahedral site, is determined from the diffuse reflectance spectra. The prepared material displays semiconducting properties, and its electrical conductivity follows an exponential type law σ = σ_oexp (–0.045/kT) with small polaron hopping. The Mott-Schottky plot at pH ~7 is characteristic of n type semiconductor with a flat band potential of 0.40 V_SCE and an electron density of 3.6 × 10¹⁸ cm^–3. The electrochemical impedance spectroscopy shows the predominance of the bulk contribution. The above data are correlated, and the energetic diagram of the junction Sr₂Fe₂O₅/KOH solution is built. The valence band of Sr₂Fe₂O₅ (1.29 V_SCE) is more anodic than the potential of the O₂/H₂O couple and oxygen is successfully evolved under visible illumination. The best performance (0.17 cm³ O₂ (g catalyst)^–1 mn^–1) occurs at pH ~ 7 with a light-to-chemical energy yield of 0.045% under a light flux of 29 mW cm^–2. No deactivation was observed during the second cycle.

New stationary phases for capillary columns in GC are synthesized and studied. The phases are prepared by depositing oligo(ethylene glycol)diacrylates on the column walls and subsequent polymerization (crosslinking) in the presence of peroxide initiators. It is shown that stationary phases based on monomers with molecular weights of 10 kDa or higher exhibit separation properties similar to those of conventional stationary phases based on polyethylene glycol (PEG); however, their thermal stability is higher because they have a higher degree of crosslinking and a more ordered structure of the crosslinked polymers than the respective parameters of phases based on native PEG.

Aspects of the formation of gels of interpolyelectrolyte complexes (IPECs) based on sodium alginate (NaAlg) and chitosan are studied. The effect the conditions of synthesis and complex composition have on the morphological structure and functional properties of these complexes is examined. It is established that complexation in this system proceeds according to a mechanism of electrostatic interaction between the oppositely charged carboxylic groups of the L-hyaluronic acid pyranose cycles of NaAlg proximal polymer chains and chitosan’s amino groups, along with a multitude of hydrogen bonds and dispersion forces. We show that the mechanism of IPEC formation is strongly influenced by the conformational state of a lyophilizing component that is present in the system in excess. The inner surfaces of cryogels based on NaAlg‒chitosan IPECs is found to be strongly influenced by the degree of conversion between the parental polyelectrolytes. The most developed mesoporous structure is obtained when a denser gel forms in the system.

The photo-kinetics of photoinduced transformation reaction of methylene green and titanium trichloride was investigated in water and different aqueous-alcoholic solvents. The reaction is pseudo-first order, dependent only on the concentration of titanium trichloride at fixed concentration of methylene green. The effect of water and aqueous-alcoholic solvents was studied in the acidic range from 4 to 7. It was observed that the quantum yield (φ) of reaction increased with increase in polarity of the solvent. The quantum yield (φ) was high in acidic condition and decreased with further increase in acidity. The quantum yield (φ) increased sharply with increase in concentration of titanium trichloride while it almost remained unaffected by change in concentration of methylene green. The addition of ions increased the quantum yield (φ) of reaction. The increase in temperature decreased the rate and quantum yield (φ) of reaction. An electron transfer mechanism for the reaction has been proposed in accordance with the kinetics of reaction. The absence of any reaction intermediate was confirmed by spectroscopic investigations. Activation energy (E_a) was calculated by Arrhenius relation. Thermodynamic parameters such as activation energy (E_a), enthalpy change (ΔH), free energy change (ΔG) and entropy change (ΔS) were also evaluated.

The self-diffusion coefficients of the molecules of hexamethylphosphoric triamide (HMPT) and ethylene glycol (EG) in ethylene glycol solutions in the concentration range 0-16 mol % HMPT and molecules of pure HMPT in the temperature range 30–60°С are measured by the spin-echo method on protons. Activation energies for the corresponding processes of self-diffusion were calculated. The obtained data are discussed in terms of solvophobic effects in the EG–HMPT system. The self-diffusion coefficient of pure HMPT was 0.344 × 10⁻⁵ cm²/s at 33.2°C, and the self-diffusion activation energy was 3.86 kcal/mol.

An automatic setup for measuring vapor pressure and its temperature dependence in a closed volume is designed. The setup can be used to investigate chemical equilibria in both condensed phase–vapor and homogeneous gas-phase systems, along with the kinetics of irreversible processes with the evolution of gas substances. The digital tensimeter offers an improved version of static tensimetry with a membrane zeromanometer. In contrast to conventional optical methods for recording the position of a zero-manometer, an approach based on the Hall effect is used. Automation of the experiment and data acquisition greatly increases the number of experimental points and reduces the errors related to measurements. With processes of irreversible hydrogen release, the method detects hydrogen with a precision of 2 × 10⁻⁶ g, remarkably exceeding the possibilities of thermogravimetric methods.