JOURNAL OF PHYSICAL AND THEORETICAL CHEMISTRY
Year:2013 | Volume:10 | Issue:2|Papers Count:8

Separation and capture of carbon dioxide from the flue gas of power plants in order to reduce environmental damages has always been of interest to researchers. In this study, aqueous solution of methylamine was used as an absorbent for CO2 capture. In order to study this reaction, Density Functional Theory (DFT) was employed at the level of B3LYP/6-311++G (d, p) by using the conductor-like polarizable continuum model (CPCM). Two possible reaction products were studied: carbamate ion and bicarbonate ion. The estimation of the thermodynamic parameters indicated that the reaction of bicarbonate ion forming is not thermodynamically feasible at room temperature. However, the reaction of carbamate ion formation is exothermic (DH= -12.4 kcal mol-1) and exergonic (DG=-1.48 kcal mol-1). Also, various atomic radii were employed to build up the solute cavity within CPCM model and the effects of the solute cavity on the thermodynamic properties of the reaction were studied.

In the present work, impact of Lewis acid (LA) catalysts BF3, BCl3, and BBr3 on the kinetics and regioselectivity of 1, 3-dipolar cycloaddition (1, 3-DC) reaction between azidobenzene and acrolein was theoretically studied using B3LYP/6-31G* level. Our results indicate while the uncatalyzed 1, 3-DC reaction under investigation takes place via a non-polar, non-regioselective, and low asynchronous process, the LA catalyzed 1, 3-DC reaction takes place via a polar, regioselective, and high asynchronous process. In addition, the barrier height of the studied 1, 3-DC reaction is considerably reduced in the presence of LA catalysts, and the catalytic activity of LAs in order to increase the electrophilicity character of acrolein and, consequently, to reduce barrier height of reaction, is increased with the increase of halogen atom size; BBr3> BCl3> BF3. Regioselectivity in these LA catalyzed 1, 3-DC reactions appears to be controlled by steric repulsion effects between the LA catalyst and the azide phenyl substituent instead of the electronic effects.

In the present work, the regioselectivity for a series of Diels–Alder reactions (4 reactions) has been studied using hardness, electrophilicity and polarizability of products. Furthermore, thermodynamic and kinetic calculations have been done. In all results predicted pararegioisomer is more favorable regioisomerinthese investigated reactions. All calculations have been done at the DFT-B3LYP/6-31G (d) level of theory.

Using the Gaussian 2003 software and MP2/ 6–311++G** method for He: He, Ne: Ne and MP2/6-31G method for Ar: Ar, Kr: Kr and HF/STO-3G method for Xe: Xe, the optimized interaction energies between two like atoms of rare gases (He, Ne, Ar, Kr and Xe) as a function of the distances between the centers of two considered atoms were evaluated and the results were interpreted according to the Lennard-Jones equation. In addition, the second virial coefficient of each rare gas was calculated upon the appropriate equations of statistical thermodynamics. The resultent coefficients were comparable with those are available in the literature.

Methyl orange is one dye resulted from the textile industry. The aim of this study is to test the adsorption capacity of nickel oxide nanoparticles for removing the methyl orange from aqueous solution. The parameters studied were the effect of temperature, contact time and initial pH of solution. Results indicate that the removal efficiency of nickel oxide nanoparticles increases with increasing concentration of methyl orange and temperature. Adsorption isotherms were investigated to complete understanding the adsorption processes. The adsorption behavior was analyzed by Langmuir, Freundlich and Tempkin isotherms. The values of correlation coefficients (R2) showed that the Langmuir isotherm model has a better fitting than Freundlich and Tempkin isotherms. Sorption kinetic data were fitted to the pseudo second-order model.

Hydroxyapatite nanocrystals were synthesized by sol-gel combustion method for the sorption of Hg (II) ions from aqueous solutions. The effects of varying parameters such as pH, temperature, initial metal concentration, and contact time on the adsorption process were examined. Adsorption equilibrium was established in 360 minutes and the maximum adsorption of Hg (II) on the hydroxyapatite was observed to occur at pH 7.0. The adsorption data correlated with Freundlich and Langmuir isotherms. The Langmuir isotherm showed a better fit to the equilibrium data. The adsorption thermodynamic parameters (DG 0, D H 0, and D S 0) were calculated which showed an endothermic adsorption process. The equilibrium parameter (RL) indicated that hydroxyapatite nanocrystals are useful for Hg (II) removal from aqueous solutions.

Metal oxides play a very important role in many areas of chemistry, physics and materials science. The metal elements are able to form a large diversity of oxide compounds. In this investigation, we synthesis SnO2 and C, N, S-tridoped SnO2 nanoparticles by precipitation method. The synthesized SnO2 and C, N, S-tridoped SnO2 nanoparticles were characterized by instrumental analysis methods, such as X-ray diffraction (XRD), Fourier transform infrared  spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The observed results showed particle size 30 nm.

In this paper we studied the thermal negativity in a two-qubit XX spin 1/2 chain model and XXX spin 1/2 chain model(isotropic Heisenberg model)spin-1/2 chain subjected to an external magnetic field in z direction. We calculate analytical relation for the thermal negativity for two qubit XX and XXX spin chain models in the external magnetic field. Effects of the magnetic field and temperature on the negativity are shown. We have also plotted two kind of behavior in the thermal negativity which scales by magnetic field and temperature. It is shown that when the magnetic field along in axis z is considerable, thermal negativity can be decrease for higher temperature. We found the critical temperature of negativity for XX spin chain model and XXX spin chain model with added external magnetic field where there are independent from magnetic field. We also have shown in both of two models after T=TC the negativity is zero. We find the critical temperature for this models and show that the critical temperature is independent of magnetic field. We found that the negativity with increasing the temperature T, at first the quantum correlations in the system increase, smoothly reaches the maximum, and then after the critical temperature turn into zero.