Vol 91, No 7 (2017)
- Year: 2017
- Articles: 30
- URL: https://journals.rcsi.science/0036-0244/issue/view/10334
Chemical Thermodynamics and Thermochemistry
Thermodynamic functions and the enthalpies of formation of gaseous VOX3 vanadium oxotrihalides
Abstract
A critical analysis of experimental and theoretical data on the structure and vibrational frequencies of gaseous VOX3 vanadium oxotrihalides is performed. The values of molecular constants are selected and the thermodynamic functions are calculated within a “rigid rotator–harmonic oscillator” approximation. Equations that approximate a temperature dependence of heat capacity within the temperature range of 298.15–3000 K are obtained. Analysis of the available experimental data allows the enthalpy of formation to be determined for gaseous VOCl3 molecules. The enthalpies of formation for VOF3, VOBr3, and VOI3 molecules are determined for the first time using this value and quantum-chemical calculations of energy of exchange reactions involving VOCl3. The obtained results are added to the database of the IVTANTERMO software.
Thermodynamic functions of arsenic selenides
Abstract
The solid-phase equilibria and thermodynamic properties of an As–Se system are studied using the electromotive force (EMF). The existence of compounds As2Se3, AsSe, and As4Se3 in a system with near constant composition is confirmed. The relative partial molar functions, standard Gibbs free energies, enthalpies of formation, and standard entropies of As in the alloys are calculated using EMF measurements.
Thermodynamic properties of alloys of the binary Sb–Yb system
Abstract
Mixing enthalpies of melts of the binary Sb–Yb system have been determined for the first time in the ranges 0 < xYb < 0.155 at 960–1030 K and 0.89 < xYb < 1 at 1140 K. It has been found that the melts form with great exothermic effects, and the partial enthalpies of the components at infinite dilution are: \(\Delta \bar H_{Sb}^\infty \) =–260, \(\Delta \bar H_{Sb}^\infty \) =–205 kJ/mol. An ideal associated solution model has been selected to describe the temperature and concentration dependences of thermodynamic properties of the melts, and the parameters of the model have been optimized through self-consistent analysis of the available data on the phase diagram. The model description allows to calculate the Gibbs energies and entropies of mixing of the melts, the activities of the components and the molar fractions of the associates, and the enthalpies and entropies of formation of the solid phases.
Hydrothermal synthesis, characterization, and thermal properties of alumino silicate azide sodalite, Na8[AlSiO4]6(N3)2
Abstract
First time we report the synthesis, structural characterization and thermal behavior of an unusual N3− containing alumino-silicate sodalite mineral. Azide sodalite, Na8[AlSiO4]6(N3)2 has been synthesized under hydrothermal conditions at 433 K in steel lined Teflon autoclave. The structural and microstructural properties of azide sodalite mineral was characterized by various methods including FT-IR, XRD, SEM, TGA, and MAS NMR. Crystal structure have been refined by Rietveld method in \(P\bar 43n\) space group, indicating that the N3− sodalite has cubic in lattice. High temperature study was carried out to see the effect of thermal expansion on cell dimension (ao) of azide sodalite. Thermal behavior of sodalite was also assessed by thermogravimetric method.
Chemical Kinetics and Catalysis
Effect of moisture content on the interaction between lignocellulosic materials and ozone
Abstract
The kinetics of ozonolysis for a number of plant materials (aspen and pine sawdust, wheat straw, flax chaff, and sunflower husks) is comparatively studied, and the dependences of the rate of ozone absorption on the water content in lignocellulosic samples are obtained. The kinetic curves of water absorption by different plant materials in a saturated water vapor atmosphere at room temperature are constructed, and the equilibrium values of water content are determined. It is shown that straw is characterized by a higher affinity for water than wood. The range of the moisture contents of lignocellulosic materials that ensures the maximum rate of their reaction with ozone is found. No appreciable effect of the nature of plant material on the rate of ozone absorption was detected, since the process is controlled by the diffusion of ozone in the pores of materials.
Physicochemical properties and catalytic activity of metal–carbon carrier composite materials
Abstract
Composite metal–carbon materials are created on the basis of different kinds of carbon (multiwall carbon nanotubes, carbon black, Sibunit carbon–carbon material) and metals (Ag, Ni, Co), and their physicochemical and catalytic properties are investigated. It is shown that interaction between metals and carbon carriers proceeds not only with the functional groups on the surfaces of the carriers, but also through a system of–C–C–conjugated bonds. Silver deposited on the surface of a carbon carrier has a crystalline structure (dcr = 10–15 nm), while nickel has an amorphous lamellar structure. Based on quantum-chemical calculations using the density functional theory, it is shown that cumene oxidation occurs via a homogeneous–heterogeneous mechanism.
Changes in the composition of synthesis products upon transitioning from self-ignition to combustion
Abstract
Changes in the chemical composition of condensed products upon switching from synthesis in the self-ignition mode to combustion synthesis is studied by approximate analytical and numerical means for condensed substances that react via competing reaction pathways. It is shown that these different modes of synthesis produce different compositions of the reaction products. The conditions required for transitioning from one mode of combustion initiation (thermal explosion) to another (ignition) are determined. It is found that this transition can occur upon changing the temperature of a heater by just two characteristic intervals. A scaling procedure that allows the calculation results obtained at zero dimensionless temperature of the heater to be used to determine the effect its non-zero dimensionless temperature has on the ignition mode and the composition of the obtained products is proposed. Calculations show that materials with different distributions of the chemical composition along the sample can be obtained by deliberately changing the temperature of the heater.
MOF-derived hollow NiO–ZnO composite micropolyhedra and their application in catalytic thermal decomposition of ammonium perchlorate
Abstract
Ni(II)-doped Zn-based coordination polymer particles (Ni(II)-doped Zn-CPPs) with controllable shape and size were successfully synthesized by solvothermal method, which further transformed to porous ZnO–NiO composite micropolyhedra without significant alterations in shape by calcination in air. Those products were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), infrared spectroscopy (IR) and gas adsorption measurements. The catalytic activity of ZnO–NiO composites for the thermal decomposition of ammonium perchlorate (AP) was investigated. The result shows that all ZnO–NiO composites efficiently catalyzed the thermal decomposition of AP, and NiO–ZnO composite hollow octahedrons have the highest catalytic efficiency compared with that of most materials reported to now, indicating that porous ZnO–NiO composite micropolyhedra could be a promising candidate material for application in AP-based propellant.
Physical Chemistry of Solutions
Dissociation constant of nitric acid
Abstract
The composition of nitric acid solutions is investigated by means Raman spectroscopy (RS). The results are compared to critically selected data from other authors. The value of the thermodynamic dissociation constant in an aqueous nitric acid solution at 25°C (Ka = \(\left[ {{H^ + }} \right]{\left[ {NO_3^ - } \right]_{\gamma '}}_ \pm ^2/\left[ {HN{O_3}} \right]{\gamma '_{HN{O_3}}}\) = 35.5 ± 1.5M) is determined by analyzing an extensive set of reliable and consistent literature and original data. Expressions for the dependences of the activity coefficient of undissociated HNO3 molecules (\({\gamma '_{HN{O_3}}}\) ) and the mean ionic coefficient (\({\gamma '_ \pm } = \sqrt {{{\gamma '}_H} + {{\gamma '}_{NO_3^ - }}} \) ) on the stoichiometric concentration of nitric acid in the range of 0–18 M are found.
Thermodynamics of solvation and association in solutions of fluorosiloxane rubber and polychloroprene in organic liquids
Abstract
The enthalpy of dissolution and concentration dependences of the enthalpy of dilution of solutions of fluorosiloxane rubber and polychloroprene in different organic liquids are determined by means of isothermal microcalorimetry. It is established that the processes of polychloroprene dissolution are accompanied by exothermic effects, while those of fluorosiloxane rubber are accompanied by endothermic effects. The calorimetric data are analyzed using the UNIQUAC model to calculate the model parameters associated with the local concentrations of components in the solution that characterize solvation and association. It is shown that the local distribution of the solvent molecules in the polychloroprene solution differed only slightly from the average over the volume, while the process of solvent association predominated in the solution of fluorosiloxane rubber.
Thermodynamics of the complex formation between Cu2+ and triglycine in water–ethanol solutions at 298 K
Abstract
Thermodynamic functions ΔrH, ΔrG, and TΔrS of the complex formation between Cu2+ and triglycine in water–ethanol solutions are calculated on the basis of calorimetric data. It is found that raising the concentration of EtOH results in a monotonic increase in the exothermic effect of [CuHL]2+ complex formation due to the weakening of triglycine solvation with the mutual compensation of ion solvation contributions. The enthalpy of [CuL]+ complex formation has an exothermic maximum at 0.1−0.3 molar fractions of EtOH due to competition between the solvation contributions from ions and ligands.
Determination of dextrose in peritoneal dialysis solution by localized surface plasmon resonance technique based on silver nanoparticles formation
Abstract
Determination of dextrose in peritoneal dialysis with a method based on silver nanoparticles (AgNPs) formation was investigated. In a green chemistry method, silver nanoparticles (AgNPs) were synthesized in the natural polymeric matrix of gelatin. The nanoparticles were characterized with UV–Vis spectroscopy and transmission electron microscopy (TEM). Absorbance signal of AgNPs could be applied to determine the various concentrations of dextrose solutions. Drop wise and ultrasonic methods were used and compared with each other. The dynamic range of methods with limit of detection and relative standard deviations were obtained. Results for real sample (peritoneal dialysis) were satisfied.
Calculations of phase equilibrium parameters of the quaternary systems KBr–K2SO4–K2B4O7–H2O and NaBr–Na2SO4–Na2B4O7–H2O at 298 K
Abstract
Some of the parameters and equilibrium constants of quaternary salts solutions KBr–K2SO4–K2B4O7–H2O and NaBr–Na2SO4–Na2B4O7–H2O at 298 K are calculated using the correlation equation of the Pitzer parameters. The solubilities data of the ternary subsystems were fitted by multiple linear regression method. The phase diagram was plotted. A comparison between the calculated and experimental results for the systems shows that the predicted solubilities agree well with experimental data.
Phase diagram of the NaCl–MgCl2–H2O system at 25–75°C and its application for MgCl2 · 6H2O purification
Abstract
The co-saturation line for the solid phases NaCl(s) and MgCl2 · 6H2O(s) in aqueous solution has been measured by a phase equilibrium at various temperatures. It was found that the Yb (Yb = w(NaCl)/(w(NaCl) + w(MgCl2))) value of the co-saturation line increase with increasing temperature. A new recrystallization approach has been suggested for the purification of MgCl2 · 6H2O(s) containing quite amount of impurity NaCl, i.e., dissolving the crude sample at low temperatures, followed by evaporating and phase separating at high temperatures. Applying the proposed approach a crude MgCl2 · 6H2O(s) sample can be purified to the level of Yb = 0.17% by only one crystallization process.
Molecular dynamics simulation of self-diffusion coefficients for several alkanols
Abstract
The transfer properties and microscopic structures of methanol, ethanol, 1-propanol, 2-propanol, and 1-pentanol in the temperature range from 290 to 450 K and pressure range from 0.1 to 200 MPa were studied by molecular dynamics (MD) simulation through the calculation of the self-diffusion coefficients, velocity autocorrelation functions (VACF), and radial distribution function (RDF). The calculated self-diffusion coefficients conform to the experimental values on the whole, and the temperature has greater influence, which weaken with the increase of the carbon chain, on self-diffusion coefficient than pressure. The factors affecting self-diffusion coefficients were also analyzed from micro perspective by calculation of VACF and RDF, which is helpful to understand the relationship between microscopic structures of fluid and its transfer properties. This work not only provides a reliable simulation method for transfer properties of alkanols, but also provides the prediction data for design and development of chemical processes.
Structure of Matter and Quantum Chemistry
Surface properties of sodium, potassium, and their binary alloys in the liquid state
Abstract
The results from investigating the surface characteristics of liquid sodium, potassium, and four potassium–sodium alloys are considered. The Auger spectra and profiles of metal droplets with atomically pure surfaces in the solid and liquid state are studied under the same experimental conditions. It is shown that potassium is a surfactant with respect to sodium at the temperature of an experiment in the investigated range of volume concentrations. It is noted that the obtained values of surface tension are 15% higher than the reference values.
Effect of mechanochemical modification on the surfactant and structural properties of humic and himatomelanic acids
Abstract
The structural properties of humic and himatomelanic acids are studied by means of 1Н NMR spectroscopy and differential thermal analysis after mechanochemical modification of peat. The relationship between the structural modification of humic and himatomelanic acids and their surfactant properties in aqueous solutions is established. It is shown that the critical micelle concentration of transformed himatomelanic acids is halved in comparison to the initial sample, while the adsorption equilibrium constant grows by 9 times.
Thermodynamics of the equilibrium of the reaction between (5,10,15,20-tetra(2-methoxyphenyl)porphinato)chloroindium(III) and pyridine
Abstract
The results from thermodynamic and quantum-chemical studies of the reversible reaction between (5,10,15,20-tetra(2-methoxyphenyl)porphinato)chloroindium(III) and pyridine are reported. The main physicochemical parameters of properties of its supramolecular products are obtained and analyzed. The addition of pyridine molecules to metalloporphyrin proceeds in one step to attain an equilibrium state with the formation of supramolecules with a stoichiometry of 2: 1; spectral characteristics and parameters of the stability of the latter are identified. The possibility of using substituted indium(III)porphyrin for further research in the field of hybrid solar cells is discussed.
Effect of solvent, electronic, and steric factors on the reactivity of 1,1'-diethylferrocene, 1,1'-diacetylferrocene, and 1,1'-bis(diphenylphosphino)ferrocene towards hydrogen peroxide
Abstract
The oxidation of Fc(C2H5)2, Fc(COCH3)2, and Fc(PPh2)2, where Fc is a ferrocene, with hydrogen peroxide in aprotic (dioxane and acetonitrile) and hydroxyl-containing (ethanol, acetonitrile–water, and water) solvents is studied via electron spectroscopy. The reactivity of these metal complexes relative to an oxidant is due to the electron-donor or electron-acceptor properties of substituents, their sizes, and their capability for the specific solvation by a particular solvent. Possible mechanisms of the oxidation of metal complexes are discussed. When Fc(PPh2)2 is oxidized, the formation of ferrocenyl cation Fc+(PPh2)2 is due to the redox isomerism of ferrocenylphosphonium cation Fc(PPh2)P+Ph2, which can form during the reaction between protonated complex Fc(PPh2)P(H+)Ph2 and H2O2.
FTIR spectroscopic study of Li+ solvation in the solutions of LiBF4 in propylene carbonate, dimethyl sulfoxide, and their mixtures
Abstract
Ionic solvation in solutions of lithium tetrafluoroborate (LiBF4) in propylene carbonate (PC) + dimethyl sulfoxide (DMSO) mixtures has been studied using Fourier transformed infrared (FTIR) spectroscopy. Dimerization of DMSO molecules in the solutions was taken into account. The obtained results are discussed with respect to the electrolyte concentration and properties of the cations of the electrolyte. Band changes due to solvation interaction were detected in the region of the C=O stretching vibrations and ring deformation for PC, and the S=O stretching vibrations and C–S–C skeleton stretching modes for DMSO, indicating that there is a strong interaction between lithium cations and solvent molecules. In addition, Li+ was preferentially solvated by DMSO in these binary solvents as a result of the large difference in their donor number (DN) values. The structures of PC, DMSO, Li+-PC, Li+-DMSO, and Li+-PC+DMSO were given.
Physical Chemistry of Nanoclusters and Nanomaterials
Effect of the chemical composition of silver-containing nanocomposites based on polymer, silica, and activated carbon on their adsorption and catalytic properties
Abstract
A series of silver-containing composites based on highly hydrophilic silica S-120, moderately hydrophilic activated carbon, and hydrophobic copolymer of styrene with divinylbenzene (Psb-1) is synthesized and studied using nonlinear gas chromatography, XRD, IR spectroscopy, and volumetric adsorption, and by optical means. The effect modifying an adsorbent with silver nanoparticles has on the structure, geometry, and chemistry of its surface, and the effects the concentration of metal, the nature of the matrix, the means of synthesis, and the size of nanoparticles have on its adsorption and catalytic properties, are studied. The surface plasmon resonance (SPR) effect is observed in some composites.
Synthesis and properties of Pr3+-doped ZnO nanowires
Abstract
Well-aligned Pr3+-doped ZnO nanowires (NWs) were obtained by chemical vapor deposition (CVD) method without catalysts on silicon substrates by vapor-solid process. The length and diameter of ZnO NWs were 1–2 μm and 50–100 nm, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) have been used to characterize the obtained Pr3+-doped ZnO nanowires. The concentration of dopant in the synthesized nanowires was 0.7 at %, according to EDX measurements. XPS was also used to characterize the samples and to confirm their composition. Pr3+-doped ZnO sensors were fabricated using a focused ion beam (FIB) with Au/Ti electrodes. A nanosensor is invented from an individual zinc oxide nanowire (80 nm in diameter). Response characteristics of the single nanowire towards dinitrogen monoxide (N2O), hydrogen (H2), ammonia (NH3) were examined at room temperature at different concentrations of gases.
Physical Chemistry of Surface Phenomena
Thermodynamics of acetone sorption from vapor phase by Keplerate and toroid polyoxomolybdate nanoclusters
Abstract
The sorption of acetone from the vapor phase by Keplerate polyoxomolybdate (POM) nanoclusters, Mo132 and Mo72Fe30, and Mo138, a POM with a toroid structure, is studied via equilibrium interval sorption (a modification of vapor sorption gravimetry). The highest sorption capacity is registered for Mo132, while the other two show performance an order of magnitude lower. The specific Gibbs energy of the interaction between the POMs and acetone is reported. Small-angle X-ray and neutron scattering analysis indicates a considerable difference between the natures of Mo132 and Mo138 surfaces.
Thermodynamic characteristics of the adsorption of organic molecules on modified МCM-41 adsorbents
Abstract
The adsorption of a number of organic molecules on samples of МCM-41 adsorbent modified with dichloromethylphenylsilane and subsequently treated with sulfuric acid (MDCS) and N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (MNM) is studied. Specific retention volumes equal to the Henry constant are determined by means of inverse gas chromatography at infinite dilution. The thermodynamic characteristics of adsorption, the dispersive and specific components of the Helmholtz energy of adsorption, and the increment of the methyl group to the heat of adsorption are calculated. It is shown that the grafting of aminosilane and phenylsilane groups enhances the forces of dispersion and reduces specific interactions. A greater drop in polarity is observed for MDCS than for MNM, due to the stronger polarity of amoinosilane; the enthalpy factor makes the main contribution to the adsorption of organic compounds on the investigated adsorbents. It is found that the MNM sample is capable of the irreversible adsorption of alcohols.
Features of the supercritical CO2-assisted immobilization of fluorinated tetraphenylporphyrins into tetrafluoroethylene copolymers
Abstract
The immobilization of fluorinated tetraphenylporphyrins (FTPPs) into tetrafluoroethylene copolymers (fluoroplast F-42 and MF-4SK, a perfluorinated sulfonic acid cation exchanger in H+-form) is conducted in supercritical CO2 (scCO2). The effects the conditions of immobilization (the temperature and pressure of scCO2, reaction time, and the addition of cosolvents) and the structure of the carrier polymer have on the content of porphyrin in these polymers is studied. The porphyrin-loaded polymer systems are shown to exhibit photosensitizing activity in anthracene and cholesterol oxidation in scCO2. Under conditions of photocatalysis, chemical and functional stability is a feature of only MF-4SK polymer systems; this is attributed to the formation of protonated forms of the porphyrins and their interaction with SO3−-groups of the polymer (an ion exchange process), which prevents leaching of the FTPP from the polymer matrix. The photocatalytic process actually occurs inside the matrix of the perfluorinated copolymer, with the protonated form of the porphyrin acting as a photosensitizer. The rate constant of anthracene photooxidation in the presence of FTPP-loaded MF-4SK films in scCO2 is found to pass through a maximum as a function of the porphyrin content and the polymer film thickness. The use of such catalytic systems for cholesterol photooxidation in scCO2 is shown to produce a virtual monoproduct (yield, ~10%): 6-formyl-B-norcholestane-3,5-diol, a compound with high biological activity.
Colloid Chemistry and Electrochemistry
Composition and particle size of electrolytic copper powders prepared in water-containing dimethyl sulfoxide electrolytes
Abstract
The possibility of the electroprecipitation of copper powder via the cathodic reduction of an electrolyte solution containing copper(II) nitrate trihydrate and dimethyl sulfoxide (DMSO) is shown. The effect electrolysis conditions (current density, concentration and temperature of electrolyte) have on the dimensional characteristics of copper powder is studied. The size and shape of the particles of the powders were determined by means of electron microscopy; the qualitative composition of the powders, with X-ray diffraction.
Kinetic study of photodegradation of methylene blue over P25-graphene and P25-CNT nanocomposites using Monte Carlo simulation
Abstract
Kinetic Monte Carlo simulation was applied to investigation of kinetics and photodecomposition mechanism of methylene blue over P25, P25-graphene, and P25-CNT nanocomposite catalyst under UV and visible irradiations. The reaction kinetic mechanisms of each abovementioned catalytic systems has been attained. The rate constants values for the each step of the reaction mechanisms (including recombination and charge transfer) were obtained as adjustable parameters by kinetic Monte Carlo simulation. The high value of the rate constant for electron transfer to graphene and CNT exhibits this transmission is occurred fast. The photoinduced electrons and holes can recombine with rate constant value about 0.001 min–1, but the rate constant of electron transfer is much higher than recombination. It was shown the rate constant of electron transfer to graphene is equal to CNT. There is a small difference between photocatalytic activity of P25-Gr and P25-CNT. The kinetic Monte Carlo simulation results of this research have satisfactorily agreement with the available experimental data for the methylene blue photodegradation.
Preparation of Yb, N, and F doped Er3+:Y3Al5O12/TiO2 composite films for visible-light photocatalytic degradation of organic dyes
Abstract
Several up-conversion luminescent materials (Er3+:Y3Al5O12, Yb doped Er3+:Y3Al5O12, Yb and N co-doped Er3+:Y3Al5O12, Yb and F co-doped Er3+:Y3Al5O12, and Yb, N, and F co-doped Er3+:Y3Al5O12) were synthesized using sol–gel method. The corresponding TiO2 composite films (Er3+:Y3Al5O12/TiO2, Yb doped Er3+:Y3Al5O12/TiO2, Yb and N co-doped Er3+:Y3Al5O12/TiO2, Yb and F co-doped Er3+:Y3Al5O12/TiO2, and Yb, N, and F co-doped Er3+:Y3Al5O12/TiO2) were prepared by sol–gel dip-coating method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). The UV–Vis absorption and PL spectra of Er3+:Y3Al5O12 were also determined. The visible-light photocatalytic activity of the synthesized materials was evaluated in the degradation of Azo Fuchsine (AF) dye in aqueous solution. The concentration of the dye was monitored by UV–Vis spectroscopy. Some key factors, such as layer number, heat-treatment temperature and time on the photocatalytic activity of Yb, N, and F co-doped Er3+:Y3Al5O12/TiO2 composite films were studied. The doping of Yb, N, and F into Er3+:Y3Al5O12/TiO2 significantly enhanced the visible-light photocatalytic activity of Er3+:Y3Al5O12/TiO2 composite film in the degradation of organic dyes. The experiments also indicated that the Yb, N, and F co-doped Er3+:Y3Al5O12/TiO2 composite film has a good visible-light photocatalytic activity to degrade other organic dyes under visible-light irradiation.
Short Communications
Photointeraction between substituted benzoquinones and heterocyclic compounds
Abstract
It is shown that mechanisms of photoreactions, investigated using the effects of chemically-induced dynamic nuclear polarization (CIDNP), can serve as models of primary electron transfer during photosynthesis from sensitizers (chlorophyll or porphyrin) to acceptors (membrane-associated quinone in media with different polarities).