Physical Chemistry Research
Volume:7 Issue: 2, Spring 2019

Consecutive adsorption of ethylene molecules on different nanoclusters as representatives of the active sites of NiMCM-41 catalyst was investigated with respect to structural, topological, and energetic properties at the B3LYP/6-311+G* and M06/Def2-TZVP levels of theory. The dimeric adsorption of the ethylene molecules was found to be exothermic on all sites (adsorption enthalpies ranging from –54.7 to –13.1 kcal/mol at M06/Def2-TZVP) with the most favorable adsorption on 2T while being non-spontaneous on 5T sites. The π complexation led to positive total charges on the adsorptive molecules, a lengthening of the Ni–O and C=C distances, and reduced O–Ni–O angles, with the smallest changes on 2T and the largest alterations on 4T and 5T. The QTAIM analysis revealed closed-shell interactions between the nickel ion and the olefinic bond. The calculated HOMO–LUMO gaps attributed the highest and lowest reactivities to the adsorption complexes formed on 2T and 5T (4.22 and 3.11 eV at B3LYP/6-311+G*), respectively. The presented results underscored the importance of a systematic study of the adsorption steps on different active sites of transition metal catalysts.

Captopril is one of the most significant angiotensin-converting enzyme inhibitors. In spite of numerous experimental and computational studies on its properties, not enough geometrical and thermodynamic data is available on this compound. So, this study aimed to investigate the structural properties and assignment of possible conformers of captopril in the gas-phase. To this end, 1152 unique trial structures were generated by allowing for all the combinations of internal single-bond rotamers and pyrrolidine ring-inversion. A total of 119 conformers were found at the B3LYP/6-311++G** level after three sequential steps of optimization and their relative energies, dipole moments, and rotational constants were obtained. The ionization energies, electron affinities, topical proton affinities, and gas-phase basicities of the first six low-energy conformers of captopril were also calculated via the abovementioned method. As we know, it is widely known that protonation is of great importance in the formation of new structures. Hence, the protonated forms of the favorable captopril conformers were structurally examined.

In order to study the variation of electronic properties, a set of bithiophene derivatives has been ‎developed. Here, the effect of substitution on the aromaticity properties of some cyclic ‎bithiophene derivative compounds was investigated using theoretical calculations. Calculations ‎were performed at B3LYP/6-31+G (d,p) level; and calculated properties included energy, dipole ‎moment, total charge on sulfur atom, energy gap, hardness and dipole polarizability. ‎Experimental polarizability values were comparable with the theoretical values. Theoretical ‎refractive indices were obtained using average polarizability in Lorentz-Lorentz equation. The ‎results of comparison between theoretical and experimental refractive indices demonstrated that ‎the scaling factors for refractive index and polarizability were 0.99-1.14 and 0.98-1.28, ‎respectively. ‎

In this study the intermolecular potential energies of some environment-friendly industrial HFC refrigerants were obtained through the inversion method which is based on the corresponding states principle. These potentials were later employed in calculation of transport properties (viscosity, diffusion, thermal conductivity and thermal diffusion factor) of some binary and ternary refrigerant mixtures, in the low density region. Predicted transport properties were compared with the available literature data and gave rise to the acceptable agreement. On the other hand, the interaction potential was fitted to an analytical form, and the calculated low density transport properties were also fitted to the fairly exact equations. In the case of R410A and R421B mixtures, high density viscosity values were also calculated through the Vesovic-Wakeham method. Due to lack of experimental values on high density viscosities of these two mixtures, we could only compare calculated high density viscosities for other available molar compositions of R124-R134a and R125-R32 binary mixtures, with literature data, while again acceptable accordance was observed.

Graphene oxide proficient adsorption of metals are often affected by preparation method. Graphene oxide was prepared using atypical modified hummers method for adsorptive removal of Zn2+ from aqueous solution. The experimental data fitted into the Langmuir isotherm. The reaction was irreversible, but had a small energy of adsorption which was indicated by Freundlich isotherm model. Tempkin model and Dubinin Radushkevich revealed a physical adsorption process driven by a slow adsorptive process. The Pseudo 2nd order had the best correlation coefficient at 0.9958 while Langmuir was 0.9545. Elovich function indicated a non-spontaneous reaction, while the intra-particle diffusion was not the rate-determining step. The slow adsorption rate in pseudo 1st order correlated with the small energy of adsorption shown by Freundlich isotherm, and correlated the small boundary layer thickness shown by intra particle diffusion. All adsorptive functions showed that some other competing mechanisms were existing. XRD showed an increased number of graphene layers, d-spacing and improved crystallite size. FTIR data showed the oxygen containing groups on the graphene oxide surface. Hence, the study showed that the prepared graphene oxide proficiently adsorbed Zn2+ and affected by method of synthesis.

Here, we report a significant enhancement in photo-activity of Titanium dioxide by combination of CoFe2O4 intoTiO2 structure. First, CoFe2O4, TiO2 and TiO2@CoFe2O4 nanofibers were prepared via a combination of electrospinning method and in-situ polymerization. The morphology and crystalline structure of composite nanofibers were investigated using scanning electron microscopy (SEM) and X-ray diffraction, comprehensively. The advantage of combining CoFe2O4 with TiO2 has been accepted which it’s due to the magnetic activity of CoFe2O4 ferrites. By the way easier/faster separation of the photocatalysts after photo-oxidative process is occurred. The photocatalytic activities of the nanofibers were conducted by photo-oxidative decomposition of Direct Red 80 (DR80). Furthermore, the influence of some parameters that affect on dye removal including, nanofiber dosage, initial dye concentration and solution pH were studied to gain a maximum degradation. The results confirmed that initial dye concentration has the highest impact on the photo-degradation of DR80. Among the synthesized samples, TiO2@CoFe2O4 composite demonstrated much higher photocatalytic activity as well as initial degradation rate.

This study demonstrates removal of phenol from aqueous solution using the carbons prepared from the natural sources, i.e. olive-pit, date-pit, and pomegranate-kernel in a batch system. For comparison purpose, the adsorption tests were also carried out on a commercial activated carbon. Influences of effective parameters such as pH, adsorbent dosage, contact time, phenol initial concentration and temperature on the removal of phenol from water were investigated. The optimum conditions for maximum adsorption were determined. In this work, the Langmuir and Freundlich models were chosen to evaluate the adsorption isotherms of phenol. The experimental isotherms showed that Freundlich isotherm fit adequately the experimental data for all adsorbents used. The adsorption data followed closely the pseudo-second-order. In addition, thermodynamic analysis was carried out for phenol adsorption. In this work, the two conventional analysis techniques, Fourier transform infrared (FTIR), and scanning electron microscopy (SEM), were used to investigate the structural and morphological properties of the adsorbents surface.

Density, viscosity and refractive index measurements were performed for ternary mixture of trichloroethene + ethanoic acid + N,N-dimethylformamide and their binary mixtures in the whole composition range. Density data were obtained within the temperature range (293.15 to 303.15) K and viscosity and refractive index data were measured at 298.15 K. Excess molar volumes, viscosity deviations and refractive index deviations were calculated from the experimental data. The values for the ternary mixture and also for the two binary mixtures of trichloroethene (1) + N,N-dimethylformamide (3) and ethanoic acid (2) + N,N-dimethylformamide (3) were negative and became more negative by increasing temperature. For the trichloroethene (1) + ethanoic acid (2) mixture, the values were positive and become more positive with rising temperature. An inverse trend was observed for viscosity deviations of the mixtures. The refractive index deviations were positive for all the mixtures. The experimental data for the binary and ternary mixtures were correlated with Redlich–Kister, and Cibulka equations respectively.

The density and viscosity of three binary mixtures composed of methyl tert-butyl ether (MTBE) with 2-propanol, 2-butanol, and 2-pentanol over the whole composition range at 293.15 to 323.15 K were measured. The excess molar volume and deviation in viscosity , were calculated and interpreted in terms of intermolecular interactions among the species in the mixtures. For all binary mixtures, negative values of and were fitted to the Redlich-Kister polynomial function. By increasing temperature, and were reduced and increased, respectively. The density of the binary systems was modeled in terms of the perturbed chain statistical associating fluid theory (PC-SAFT) and compared with the corresponding experimental data. Maximum of deviation between the experimental data and calculated values by this theory is 1.4% and belongs to the MTBE + 2-butanol system

In this work, the properties of 2,4-dioxo-4-phenylbutanoic acid (DPBA) and some of its derivatives have been investigated using quantum mechanical calculations in the gas phase and solution media. The electron delocalization and intramolecular H-bonds substantially affect the potential energy surface. At all levels of calculations and phases (gas and three solutions) selected in this work, enolic tautomers are more stable than diketo, and the repulsive H∙∙∙H interaction and the orientation of double bonds affect the relative stability of enolic tautomers. The trend does not change in the presence of substituents located on the phenyl group. The acidity of most stable enolic tautomer is lower than that of the other two tautomers. The effect of solvent on the acidities of tautomers was investigated by explicitly introducing the molecules, and implicitly introducing them as a uniform environment. Although the acidity of enolic group is higher than that of carboxylic group in the gas phase, the order is reversed in the aqueous solution using both methods. The order of acidities of tautomers depends on the phase and substituents; increases in the acidity and the trend of acidities of tautomers change after complexation with Mg2+.

The pure and 2% Fe doped TiO2 nanoparticles were synthesized using simple sol-gel method involving an ethanol solvent in the presence of ethylene glycol (EG) as the stabilizer. The physicochemical properties were investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), electron dispersive spectroscopy (EDS), diffuse reflectance spectrum (DRS) and photolumincense (PL) analyses. XRD analysis showed the tetragonal anatase structure in presence of Fe doping. The size of the nanoparticles (NPs) decreased to 29 nm by adding Fe content with less agglomeration. PL analysis showed that the intensity of photoluminescence decreases for doped sample, suggest decrease in recombination of the electron–holes pair. The UV-DRS analysis indicated that the band gape energy decreases to 3 eV for Fe doped TiO2 nanoparticles.

There is a great technical interest in solid-liquid equilibrium (SLE) of binary fatty acids. Mainly, these substances are used for the design, development, and operation of many industrial processes because of the application in many manufacturing fields such as the cosmetic, pharmaceutical and biotechnology industries. In this study, an approach is presented for binary fatty acid mixtures to estimate the melting temperatures as a function of mole fraction in the solid-liquid phase equilibrium. Derivation of the Wilson model was developed to predict the melting temperatures and latent heat to achieve eutectic points of capric acid, undecylic acid, pentadecylic acid, and margaric acid binary mixtures. The results showed that in the all binary mixtures, the eutectic point is near to a lighter compound except capric+undecylic acid because of lower melting temperature of undecylic acid than capric acid. Comparison of experimental and thermodynamic studies revealed the low deviations between measured and calculated values obtained in this study.

Biodiesel is one of the sources of renewable fuel. Due to increasing environmental pollution, global warming caused by fossil fuels and limited fossil fuel resources, its production has been increased. Nowadays, low prices renewable sources are used to produce biodiesel. In this study, biodiesel is produced from edible oil wastes, such as goat fat, chicken fat and palm kernel-derived oil using the transesterification process. The produced biodiesel is mixed with different ratios of petroleum diesel to improve the physical properties of the produced biodiesel, such as flash point, kinematic viscosity, density, cloud point and pour point. The physical properties are measured according to the ASTM D6751 standard. The results show that some of the properties, such as density, viscosity and flash point are improved with the addition of biodiesel to diesel fuel. The other properties, such as pour point and cloud point are increased with the higher proportion of the biodiesel in the mixture. This causes a bad effect on the consumption of fuel and cannot be used in cold weather. Generally, adding biodiesel to diesel enhance the fuel properties.

Experimental solubility curve and tie-line data were obtained for the ternary system (water + phosphoric acid + 1-undecanol) at T = 303.2 K and ambient pressure. The cloud point method was employed to determine the binodal curve data. The mass fraction compositions of each layer were explored by acid-base and the Karl Fisher titration methods accompanied by mass balance calculations. For above mentioned ternary system, a type-1 LLE behavior was observed. The reliability of the experimental compositions was proved by using the Othmer–Tobias and Hand plots. The UNIQUAC and NRTL thermodynamic models were applied to correlate the equilibrium tie-line points. The experimental points were adequately regressed using the thermodynamic models. Distribution coefficients and separation factors were computed over the non-miscible region. For the separation process, separation factor should be greater than one and for the investigated system, this factor was suitable to apply separation treatment in all concentrations of phosphoric acid at the studied temperature. The Katritzky parameters were utilized for LSER modeling of distribution coefficients of the studied mixtures. The ternary system showed good fittings with the LSER model.

The adsorption properties of black phosphorus monolayer (BPML) nanostructure toward methanol and ethanol were investigated using periodic density functional theory calculations. Despite the subtle in-plane distortions, the integrity of the BPML nanostructure was preserved. All complexes revealed interactions of pure electrostatic nature as evinced by the LOL and QTAIM data. The band gap was slightly enlarged, and both valence and conduction bands moved upward upon the detection of both alcohols. These observations implied that the perfect surface of the semiconductor could be considered a work function sensor for the alcohol molecules. The adsorption energy ranged from –0.13 to –0.36 eV, with ethanol presenting relatively stronger physisorption.