Volume 92, Nº 10 (2018)

The behavior of the autocorrelation functions of shear stress and the kinematic viscosity coefficient during glass transition processes is studied by means of molecular dynamics using the example of liquid aluminum. A film of liquid metal cooled at a rate of 2 × 10¹² K/s is simulated. The dependence of the kinematic viscosity coefficient on temperature is obtained using the Green–Kubo formula. Over long periods of time, the behavior of the autocorrelation functions is approximated by a power-law dependence throughout the range of temperatures. The dependence of the exponent on temperature, which enables us to estimate the temperature of the transition from the liquid to the amorphous state (it agrees with the temperature from the calorimetric criterion), is given. The temperature of the transition to glass is determined. When it is lower than that of the glass transition, features of a solid body appear: shear stress is maintained and transverse oscillations arise.

The behavior of the entropy on the isotherm depends on the sign of the coefficient of thermal expansion (CTE). The boundaries of positive and negative CTEs are considered for water in the normal and supercooled state as a model for the behavior of other substances in structural transformations that ultimately ensure non-negative entropy values of matter.

The mechanisms of the cyclization reaction of 3-(ethynylamino)-1,3-diphenyl-2-en-1-one catalyzed by AuCl and AuCl₃ catalysts were studied using the density functional theory based on the M06 and B3LYP functionals combined with the 6-31G(d,p), 6-311++G(d,p), LANL2TZ) basis sets. The results show that the reaction can occur through one pathway containing four processes to yield the final product both with AuCl and AuCl₃ catalysts. The energy barrier of the rate-determining step of the reaction with AuCl, hydrogen transferring process, is 18.22 kJ mol^–1 lower than that of the reaction with AuCl₃. And the energy barrier of the catalysts depriving from the product with AuCl is 58.11 kJ mol^–1 lower than that with AuCl₃. These results indicate that the catalytic activity of AuCl is better than that of AuCl₃ for this type of reactions. The results of this study can be a theoretical reference in selecting a suitable catalyst for this type of reactions.

UV–Vis spectra of neutral and acidic solutions of C-methyl derivatives of dimethylaminoazobenzene are compared to the analogous spectra of dimethylaminoazobenzene (DAB), the main state of which is Rydberg dimers (rydimers) DAB₂. The identical nature of the spectra of DAB and its 2-, 2′-, 3′-, 4′-methyl derivatives in neutral ethanol is established, testifying to the rydimer structure of these azo dyes and the identical nature of their chromogens, which have intense Vis bands at 400–430 nm. Uniform spectral changes are observed for solutions of 2-, 3′-, 4-methyl-substituted DAB and DAB₂ during protonation at low acidities, demonstrating the stability of the respective rydimers and the identical protonation mechanism of their dimethylamino groups. UV bands at 320 nm and Vis bands at 500–530 nm are observed in the spectra of the resulting rydimers with ammonia groups. It is concluded that as acidity rises, these rydimers first attach a proton to the azo group, change into a triprotonated form, and then decompose with the formation of diprotonated monomers. At low acidity, rydimers with methyl groups at positions 2′ and 3 on phenylene rings are also protonated on amino groups but dissociate with the formation of the corresponding monomeric ammonium cations, the spectra of which copy the UV–Vis spectrum of azobenzene. Based on an analogy between the observed spectral characteristics and those known from the literature on a large number of azo dyes, it is concluded that the rydimer structure is a common property of azo dyes.

Chemical shift measurements were performed for several percentages of H₂O added to D₂O, in several H₂O/D₂O mixtures without and with a single concentration of albumin, and also in a mixture of 0.1H₂O/0.9D₂O containing increasing concentrations of albumin. The chemical shifts of pure mixtures decreases with increasing fraction of pure water. This is closely related to isotope effects. The chemical shift corrected for isotope effects increases with percentage of H₂O. The chemical shift obtained for the mixture of 0.1H₂O/0.9D₂O increases with increasing concentration of albumin. These increments are consistent with fast chemical exchange in H₂O/D₂O mixture. In conclusion, present study reveals the presence of isotope effect on albumin in H₂O/D₂O solutions, and demonstrates fast chemical exchange in D₂O solutions with albumin in a different way.

The elastic properties of some aluminum-based metal-organic framework compounds with rod atomic packings were studied. The tensors of elastic constants were calculated by the ab initio quantum-mechanical methods. The dependences of elasticity moduli on the direction were studied. They were correlated with the configurations of organic linkers and metal centers. The dependence of elastic properties on the nature of the functional group in the isoreticular series CAU-10-X was studied.

The structural morphological characteristics of 1,1,9-trihydroperfluoro-1-nonanol and layered aluminosilicate montmorillonite are studied via X-ray diffraction, electron microscopy, EPR spectroscopy, and FTIR spectroscopy. Estimates of these characteristics allow the subsequent construction of polymer materials containing these nanofillers and characterized by an improved set of properties. It is shown that the formation of hydrophobic polyfluoroalkyl layers stable with respect to desorption is observed both on the surface and in the interlayer space of clay. The elemental composition of samples is studied by means of X-ray fluorescence analysis and micro–X-ray spectral analysis.

The equilibrium structure of the 4-cyanopyridine molecule was determined from experimental data for the first time. The computations performed at the CCSD(T) level agree well with the results of the combined electron diffraction and microwave data analysis. The effect of the para-cyano substituent on the geometry of the pyridine ring is observed in comparison with the literature data for the pyridine molecule.

Cation-π and anion-π interactions were studied in the Na⁺-substituted-COT and F-substituted-COT complexes (where substituted-COT is planar cyclooctatetraene with four X‒C≡C-substituents (X = OH, CH₃, H, F, and CN) using computational quantum chemistry methods. There are no direct electrostatic interactions of substituents with cations and anions in these complexes. The electron-donating and electron-withdrawing substituents lead to increase of the strength of cation-π and anion-π interactions, respectively. There are meaningful correlations between the Hammett constants and binding energies. The AIM analysis shows that the electron-donating and electron-withdrawing substituents lead to increase in electronic charge density values at ring critical points (RCPs) of the Na⁺-substituted-COT and F^–-substituted-COT complexes, respectively (compared to complexes with X = H). NMR calculations demonstrate that the cation-π interactions are consistent with more antiaromatic rings and the anion-π ones are in accord with less antiaromatic rings.

We have modeled multifunctional compounds from 4,6-di(2-furyl)pyrimidine, because 4,6-di(2-furyl)pyrimidine has alternate π-rich and π-poor units. The π-backbone has been elongated along with push–pull strategy to reduce the HOMO–LUMO energy gap and to enhance the intra-molecular charge transfer. All the molecular geometries in ground state have been optimized by using density functional theory (DFT). The time dependent density functional theory (TDDFT) was used to compute the absorption spectra. The frontier molecular orbital (HOMO and LUMO) has been conferred and the charge transfer properties have been discussed on the basis of electron affinities, ionization potentials and reorganization energies. We tuned the optical and electronic properties of 4,6-di(2-furyl)pyrimidine derivatives and it is anticipated that the proposed derivatives might be comparable to the widely used hole and electron transfer materials such as pentacene and (tris(8-hydroxyquinolinato)aluminum). The relationship between structure and property has been thoroughly discussed.

In this paper, pure ZnO, Ag, and Mg mono-doped and co-doped ZnO nanoparticles were synthesized via sol-gel method. The synthesized nanoparticles were characterized using XRD, DRS, BET, TEM, SEM-EDX, and PL techniques. The photocatalytic activity of the prepared photocatalysts was evaluated in degradation Rhodamine B (RhB) dye. Response surface methodology (RSM) was used as a statistical technique for optimizing the effect of synthesis variables on the removal efficiency of RhB. The results predicted from RSM were found to be in good agreement with the experimental results as indicated by correlation coefficient (R²) of 0.9624. Furthermore, statistical tests such as ANOVA table and lack of fit indicated that the model was adequate for representing the experimental data. Ag and Mg co-doped ZnO nanoparticles demonstrated the highest photocatalytic activity in comparison with pure and mono-doped ZnO. Maximum photocatalytic activity of co-doped ZnO nanoparticles was observed for a sample with 3 wt % Ag, 4 wt % Mg calcined at 530°C.

The possibility of deriving a model of the kinetics of batch sorption processes is considered by transforming a nonlinear difference kinetic equation with a nonconstant equilibrium parameter for the interface into approximate pseudo first- and second-order equations with fixed parameters, depending on the characteristic of equilibrium isotherms in a certain way. The calculated and experimental equilibrium and kinetic parameters are compared for a large number of processes, including the sorption and electrosorption of metal ions on activated coals, the sorption of lead on nanostructured carbon materials, and phosphatidylcholine sorption on ordered mesoporous nanostructured silica materials. Good coincidence is observed between the calculated equilibrium data and the respective experimental results obtained in kinetic experiments. At the same time, there is no correspondence between calculated and experimental dimensionless parameters based on the relationships of kinetic coefficients for different order equations (due apparently to great errors in determining these coefficients when processing the experimental data using the pseudo second-order model of kinetics). The obtained results confirm earlier conclusions that it is impossible to characterize the mechanisms of kinetic processes based only on good descriptions of experimental results using pseudo first- or second-order kinetic equations.

Magnetic composite sorbent consisting of a synthetic magnetite and ground coffee waste is produced and characterized. The point of zero charge is determined. The presence of carbonyl and carboxyl groups on the sorbent surface is established. The sorbent’s sorption capacity toward methylene blue dye is determined. The adsorption kinetic curves are analyzed using models of diffusion and chemical kinetics. It is shown that adsorption proceeds in the mixed diffusion regime and can be described by pseudo second-order kinetics. The correlation between the adsorption isotherms and the Langmuir and Freundlich models is evaluated. The possibility of sorbent regeneration is demonstrated. It is concluded that the proposed composite magnetic sorbent has high efficiency and can be used to purify water of organic dyes.

The possibility of extracting vanadium, molybdenum, and tungsten compounds from acidic media via adsorption is demonstrated. Highly dispersed layered aluminosilicates, modified with a cationic surfactant (didecyldimethylammonium chloride), are used as sorbents. Interactions between the cationic surfactant and the sorbent’s surface are confirmed by means of spectroscopy. It is established that the sorbent is modified through immobilization of the didecyldimethylammonium chloride molecules in the interlayer space of the sorbent. It is observed that the sorbent’s surface acquires a positive charge as a result of modification, allowing adsorption of polyoxoanions of vanadium, tungsten, and molybdenum from solutions. Spectroscopic and thermodynamic investigations show that the interaction between the vanadium and the active centers of the sorbent was due to the formation of ionic associates and corresponded to physical adsorption. Because of the similarities between the chemical properties of vanadate, molybdate, and tungstate ions, their adsorption on a surface of modified montmorillonite is governed by a similar mechanism. Experimentally determined limiting adsorption values of vanadium, molybdenum, and tungsten are 1.65, 1.96, and 1.21 mmol/g, respectively, which corresponds to a 94–95% degree of extraction. It is established that the optimum conditions of isolation are found at рН 3.4 for vanadium, pH 4.0 for molybdenum, and pH 4.5 for tungsten, due to the different forms of their polyoxoanions in solutions.

In this work, Bi(OH)SO₄ · H₂O, a novel photocatalyst was prepared by a facile method. The sample was characterized by XRD, XPS, SEM, Mott-Schottky curve and ESR. The band gap of Bi(OH)SO₄ · H₂O is about 4.64 eV, and its CB and VB are estimated at –0.5 and 4.14 eV, respectively. Degradation of RhB and PhOH under UV light irradiation illustrates that the sample has good UV activity. The results of ESR spectra and tapping experiments indicate that the main active species in the photocatalytic reaction process are hydroxyl radicals, superoxide radicals and holes. A possible mechanism of catalytic degradation of organic pollutants was proposed. This semiconductor has a positive valence band and high oxidation capacity theoretically and it may have broad application in synthesizing highly efficient photocatalysts through doping other elements or creating heterojunctions.

The copper zinc tin sulfide (CZTS) thin films are prepared by a promising non vacuum compacting process based on ball milling and coating technique. The results reveal that a well-formed crystalline structure of kesterite CZTS are observed after sintering at 450°C. The optical band gap is 1.49, 1.59, 1.33, and 1.21 eV for the films with Cu/Zn/Sn atomic radio of 1.00 : 0.50 : 0.52, 1.00 : 0.44 : 0.41, 1.00 : 0.60 : 0.49, and 1.00 : 0.49 : 0.58, respectively. The compacting process can further improve the performances of CZTS film. For the CZTS thin film with Cu/Zn/Sn atomic radio of 1.00 : 0.60 : 0.49, the surface morphology of the film is significantly improved by a compacting process applied to the coating films before sintering, and the resistivity decreased from 23.67 to 1.18 Ω cm with the compacting pressure increasing from 0 to 200 MPa at room temperature, which showing a promising application of the compacting process method in fabricating CZTS film for solar cells.

The enthalpies of solvation of piperidine (Ppd) in methanol (MeOH), ethanol (EtOH), N,N‑dimethylformamide (DMF), and dimethylsulfoxide (DMSO) are calculated by means of quantum-chemical modeling. The enthalpies of solvation of Ppd in EtOH and DMF are determined calorimetrically. The energies of Ppd solvation in aprotic solvents is found to be generally governed by universal types of interactions between amine and solvent molecules. The energy contributions from both universal and specific types of interactions to the overall enthalpy of Ppd solvation are determined in amphoteric MeOH and EtOH.