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Alkali metal-oxygen batteries possess a higher specific capacity than alkali-ion batteries and stand out as the most competitive next-generation energy source. The core reaction mechanism of the battery is mainly the formation of alkali metal oxide during the discharge process and the decomposition of these oxides during the charge process. A large number of researchers have devoted themselves to seeking promising catalysts for the reaction. Two-dimensional Nb2 O5 was discovered to be a highly potential catalyst that can promote the reaction of alkali-metal-oxygen batteries, but few studies focus on it. In this study, the catalytic performance of both pristine Nb2 O5 and oxygen-deficiency modified Nb2 O5 was investigated. Furthermore, the effect of oxygen defects on catalytic performance was analyzed from multiple angles, namely, the reaction mechanism, d-band center theory, and the diffusion behavior of alkali metals. The exploration revealed the microscopic mechanism of oxygen deficiency affecting the alkali-metal battery reaction and provided a theoretical basis for quantitatively changing the d-band center of the catalyst through oxygen deficiency to ultimately change the performance of the catalyst.

Solubility of inorganic salts in the mixed systems containing surfactants and sodium tripolyphosphate (STPP) is very important for the production of laundry detergents. In this work we explored the solubility of NaCl, Na2SO4, and Na2CO3 in aqueous surfactant and STPP solutions using an ion selective electrode at 298.15 K. In the experiments, electromotive forces (EMF) for the ternary systems were measured using an ion-meter with a sodium ion-selective composite electrode and the relationship between the solubility and EMF was analyzed by a potentiometric analysis. The proposed method has advantages in avoiding the solid–liquid separation operation and solution supersaturation. The experimental results indicated that the salting-out effect caused by surfactant and STPP can decrease the solubility of sodium salts in the aqueous systems.

Based on the thermodynamic perturbation theory for polymer, a new equation is proposed by incorporating a wide range of molecular flexibility and perturbative interactions to describe the isotropic...

In this work, we relate the self-diffusion coefficient to the residual entropy of the system according to the free volume theory and scaling principle. The viscosity equation for a freely jointed Lennard-Jones chain fluid is then obtained from the expression of self-diffusion coefficient by applying the Stokes–Einstein equation. The real polyatomic compounds are modeled as chains of tangent Lennard-Jones segments. The segment size and energy parameter as well as chain length (expressed by the number of segments) are obtained from the experimental viscosity data. The proposed viscosity equation reproduces the experimental viscosity data with an average absolute deviation of 5.12% for 18 polyatomic compounds (1600 data points) over wide ranges of temperature and pressure. For engineering applications, the generalized model parameters for normal alkanes with the number of carbon atoms n > 3 are proposed. The segment energy parameter is suggested to be evaluated from the critical temperature, and the segment size parameter and chain length are correlated with the number of carbon atoms in an alkane molecule.

The Gibbs ensemble Monte Carlo simulation is used to investigate the vapor–liquid phase behavior of a binary Lennard–Jones mixture confined in a slit-like pore at reduced temperature T* = 1.0. Our simulation program is tested by comparing the simulated phase diagram with the previous simulation results from various methods. Then phase diagrams of a binary asymmetric Lennard–Jones mixture confined in the slit-like pores are investigated by varying the pore width and fluid–pore wall interaction. The asymmetric system studied exhibits azeotropic behavior. The pore walls are symmetric but selective to the two components. The simulated results indicate that both the pore width and interactions between fluid and the pore wall have significant influence on the vapor–liquid phase diagram for the binary Lennard–Jones mixture. When the interaction energy parameter between component 1 and the pore wall is fixed, the azeotropic point is shifted from the bulk azeotropic composition to component 2-rich side of the phase diagram as the interaction strength between component 2 and the pore wall is increased. In the meantime, both the azeotropic pressure and the relative volatility increase significantly. As the pore becomes narrower, it is found that the azeotropic pressure increases significantly while the azeotropic composition remains almost unchanged. The phase selectivity decreases as the pore becomes narrower in the whole range of composition. All the simulated results suggest that the azeotropic point of a binary mixture can be shifted or even be removed by the confinement and the relative volatility for vapor–liquid equilibria can be changed greatly by changing the pore width or fluid–pore wall interactions.

Mutual diffusion coefficients of concentrated 1:1 electrolyte solutions are investigated using a modified mean spherical approximation (MSA), in which the effective cationic diameter is a function of total ionic strength. We apply this improved MSA to calculate the equilibrium pair correlation function, and the Smoluchowski equation is used for the dynamics. We compare the calculated mutual diffusion coefficients of 18 uni-valence electrolyte solutions for molar concentrations up to 4.0 mol/L known experimental data. Good agreement between theoretical results and the experimental mutual diffusion coefficients are found for all the cases studied.

The ion density profiles and mean electrostatic potentials around DNA from the Monte Carlo simulations are compared with the predictions of the Poisson–Boltzmann equation and the density functional theory. The DNA molecules are modeled as a charged cylinder while the ions are represented as charged hard spheres with different diameter. In the density functional theory, the Helmholtz free energy functional due to hard-sphere repulsion and electrostatic interaction are obtained from the modified fundamental measure theory and a quadratic functional Taylor expansion, respectively. The results show that due to the inclusion of the ion–ion correlation, the density functional theory is more accurate than the Poisson–Boltzmann equation. The density functional theory gives accurate ion structures and mean electrostatic potentials near the surface of DNA. When the established density functional theory is combined with the cell model, the osmotic coefficients of aqueous DNA–electrolyte solutions can be predicted. The results show that the DFT-cell model captures the essential features of the experimental osmotic coefficient, but fails to give a quantitative description. Possible reasons for this discrepancy are discussed.

Activity coefficients at infinite dilution are reported for ten solutes (heptane, octane, nonane, decane, benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene) in sulfolane at temperatures T = (333.15 to 373.15) K. These data were measured with the help of gas−liquid chromatography (GC) in which sulfolane was used as the stationary phase. The results show good agreement with the activity coefficients at infinite dilution obtained from various methods in the literature. The temperature dependence of the activity coefficients found in the GC experiments could be confirmed using the excess enthalpy data. The present data can be used to determine and compare the selective effect caused by the addition of sulfolane to a given binary mixture in the separation processes such as extractive distillation and solvent extraction. The calculated selectivity suggests that both sulfolane and ionic liquid [HMIM+][BF4-] can act as a good solvent in separating aromatic and aliphatic compounds.

Monte Carlo simulations have been carried out to investigate supercritical ethanol using the OPLS–UA [W.L. Jorgensen, Optimized intermolecular potential functions for liquid alcohols, J. Phys. Chem. 90 (1986) 1276–1284] and TraPPE–UA [B. Chen, J.J. Potoff, J.I. Siepmann, Monte Carlo calculations for alcohols and their mixtures with alkanes. Transferable potentials for phase equilibria. Part 5: united-atom description of primary, secondary, and tertiary alcohols, J. Phys. Chem. B 105 (2001) 3093–3104] force fields. Two potentials were compared and TraPPE potential performed better in reproducing densities as a function of pressure, so, it was selected in further structural analysis. The pair distribution functions were obtained and their pressure and temperature dependence were analyzed. In addition, a serial two dimensional distribution functions were plotted to depict the detailed structure of liquid and supercritical ethanol. Based on a widely used geometric criterion, hydrogen bonding statistical results showed that the hydrogen bonds become weaker but still exist under supercritical condition, which are in good agreement with recent experimental measurements. The hydrogen bonds of water, methanol and ethanol were compared and ethanol has nearly the same behavior as methanol under supercritical conditions.

The structural properties and transport properties of electrolyte solutions are investigated by smart Brownian dynamics simulation based on the primitive model. To test the simulation program, the radial distribution functions of ions g +- (r) and g ++ (r) for KCl solution are calculated and compared with the results of previous simulations. And then, the effects of ions diameter and concentration on the structural properties and transport properties of electrolyte solution at 298 K are extensively simulated. The results indicate that both the radial distribution function and the self-diffusion coefficient are more sensitive to the ion size than salt concentration. As the radius ratio of cation to anion increases, self-diffusion coefficients of both cation and anion become larger.

Solid–liquid equilibria in mixed electrolyte aqueous solution have been investigated using available thermodynamic data for solids and for aqueous electrolyte solutions. The mean spherical approximation (MSA) modified by Lu et al. [Fluid Phase Equilib. 85 (1993) 81] is used to calculate the mean ionic activity coefficients in mixed electrolyte solutions at saturation conditions. Solid–liquid equilibria of seven mixed electrolyte systems at 298.15 K are successfully predicted using the modified MSA method with the parameters obtained from activity coefficient data of corresponding single electrolyte solutions. The total average absolute deviation between predicted and experimental values is 5.58%. Furthermore, the predicted results of solid–liquid equilibria for four mixed electrolyte solutions over a range of temperature indicate that the modified MSA method can fairly be used to predict solid–liquid equilibria for mixed electrolyte aqueous solutions at various temperatures.

In this paper, the separation of binary gas mixture carbon monoxide and hydrogen using single-walled carbon nanotubes (SWNTs) is studied by grand canonical Monte Carlo (GCMC) simulation. All of the particle–particle interactions between hydrogen, carbon monoxide and carbon are modeled with Lennard–Jones potential. Widom test particle method in NVT ensemble is used in determining chemical potentials of the two components of the fluid. It can be concluded from the adsorption isotherms at 293.15 K that the selectivity of carbon monoxide decreases with the increase of the bulk pressure. In the adsorption isostatics at 0.157 MPa, the selectivity has a maximum along with the increase of temperature. However, to given pressure and temperature, the selectivity fluctuates violently with different van der Waals (VDW) distances or diameters of carbon nanotubes. For example, at 0.157 MPa, 293.15 K, diameter of 0.892 nm and VDW distance of 1 nm, with the feed containing hydrogen and carbon monoxide both 50 mol%, carbon monoxide could be enriched up to 98 mol% in the adsorbate, so that the selectivity comes to 60. It can be indicated that carbon nanotube, as a novel material developed in the past 10 years, can make a very effective separation tool of certain gas mixtures.

Boiling points have been determined at 101.33 kPa for the binary mixtures of sulfolane+o-xylene, sulfolane+m-xylene, sulfolane+p-xylene, sulfolane+ethylbenzene and sulfolane+1,2,4-trimethylbenzene. Calculations of the non-ideality of the vapor phase were made with the second virial coefficients evaluated from the Hayden–O’Connell method. The binary parameters for five activity coefficient models (Margules, van Laar, Wilson, NRTL and UNIQUAC) have been fitted with the experimental boiling points measured in this work. A comparison of model performances has been carried out using the criterion of the average absolute deviations in boiling point. The activity coefficient of the component in the liquid phase is discussed based on the UNIFAC model with the consideration of the dipole–dipole interactions.

The solubilities of oxygen in 0.2, 0.5, 0.7 and 1.0 M Na 2 CO 3 solution have been measured at 300.15 K and under pressures up to 10 MPa using a magnetically stirred autoclave and a direct sampling technique. The accuracy of apparatus was verified by duplicating the solubility of oxygen in pure water in literature. The experimental data of the solubility of oxygen in aqueous sodium carbonate solution were shown that the solubility of oxygen increases with increasing pressure and decreases with increasing salt concentration due to salting-out effect. The experimentally measured data were satisfactorily compared with the predicted values by our model based on non-primitive mean spherical approximation (MSA) and perturbation theory.

An attempt is made in this work to combine the Lennard‐Jones chain model (LJC) of self-diffusion coefficient with the statistical associating fluid theory (SAFT). The real non-spherical associating molecules are modeled as chains of tangent Lennard‐Jones segments with association sites. An equation for the self-diffusion coefficient in a polyatomic associating fluid is presented as a product of a non-hydrogen-bond contribution and a hydrogen-bond contribution. The SAFT equation provides the density and temperature dependence of an average number of hydrogen bonds in a molecule, and the LJC equation is used to calculate the self-diffusion coefficient for a non-associating fluid. The segment‐segment interaction energy " is obtained from the critical temperature for alcohols and hydrogen fluoride, and, the segment diameter , the chain length N (the number of segments), association energy " HB and volume HB are determined from the experimental diffusion data. The equation reproduces the experimental self-diffusion coefficient with total average absolute deviation of 6.69% for water, 6% alcohols and hydrogen fluoride over wide ranges of temperature and pressure, including the super-critical water. © 2001 Elsevier Science B.V. All rights reserved.

The concentration dependence of the surface tension of single and mixed electrolyte aqueous solutions is studied, based on the assumption that the surface layer can be treated as a separate phase located between vapor and bulk liquid phases. The mean spherical approximation modified by Lu et al. [J.-F. Lu, Y.-X. Yu, Y.-G. Li, Fluid Phase Equilibria 85 (1993) 81–100] is used to calculate the activity coefficients of water in the surface and bulk liquid phases. The relation between the electrolyte concentration in the surface and bulk liquid phases is established and only one parameter needs to be determined. The surface tensions for 31 single electrolyte aqueous solutions are correlated and the overall average absolute deviation is 0.70%. The surface tensions at different temperatures are predicted with the parameters obtained at one fixed temperature. By introducing the proper mixing rules, the surface tensions for 14 mixed electrolyte aqueous solutions are predicted without any mixing parameters, and the total average absolute deviation is 0.63%. All the calculated results are compared with that of the surface tension model for aqueous electrolyte solutions proposed by Li et al. [Z.-B. Li, Y.-G. Li, J.-F. Lu, Ind. Eng. Chem. Res. 38 (1999) 1133–1139].

Isobaric vapor−liquid equilibrium data were determined at 101.33 kPa for the binary mixtures of water + sulfolane and water + tetraethylene glycol. Calculations of the nonideality of the vapor phase were made with the second virial coefficients obtained from the Hayden−O'Connell method. The boiling points and vapor-phase compositions reported were well correlated by the Wilson, NRTL, and UNIQUAC models. In addition, the densities of binary mixtures of water + sulfolane, water + tetraethylene glycol, and benzene + tetraethylene glycol were determined over the entire concentration range at 298.15 K and atmospheric pressure by using an oscillating tube densimeter. Excess volumes were calculated for each data point. All mixtures exhibit negative excess volumes with a minimum which occurs at x ≅ 0.5 for the benzene + tetraethylene glycol system; it is shifted toward the water-rich region for the water + sulfolane and water + tetraethylene glycol systems. The experimental excess volumes were correlated using th...

An equation for the self-diffusion coefficient in a polyatomic fluid is presented as a sum of three friction coefficient terms: the temperature-dependent hard-sphere contribution, the chain contribution and the soft contribution. This equation has been developed by using the molecular dynamics simulation data for the HS chain fluid and the expression for the Lennard–Jones (LJ) fluid proposed by Ruckenstein and Liu. The real nonspherical compounds are modeled as chains of tangent LJ segments. The segment diameter σ LJ , segment–segment interaction energy e LJ and chain length N (the number of segments) are obtained from the experimental diffusion data. The equation reproduces the experimental self-diffusion coefficients with an average absolute deviation (AAD) of 3.72% for 22 polyatomic compounds (1081 data points) over wide ranges of temperature and pressure. The results have been compared with that of the rough LJ (RLJ) equation. To minimize the number of the fitting parameters, the energy parameter e LJ is estimated using a correlation obtained from viscosity data. The equation with two parameters gives an AAD of 4.72%.

A new model for calculating high-pressure solubility of gas in aqueous electrolyte solution is proposed based . on non-primitive mean spherical approximation MSA equation and perturbation theory. The non-primitive MSA is used to describe the interactions of ion-ion, ion-dipole and dipole-dipole. The Lennard-Jones potential energy as a perturbation term is introduced to represent the dispersion effects among particles including both ion and molecule species. The water molecule parameters are derived from the experimental saturated vapor pressure data of pure water and the ion parameters of cations and anions are obtained by fitting experimental mean ionic activity coefficients. The parameters of gas solved in aqueous salt solution are only derived from the experimental solubility data of gas in pure water. The equation of state derived from the previous procedures have been used successively to predict gas solubility in aqueous salt solution using the pure-component parameters. q 1999 Elsevier Science B.V. All rights reserved.

Isobaric vapor–liquid equilibrium data have been determined at 101.33 kPa for the binary mixtures of benzene-tetraethylene glycol (TeEG), toluene-TeEG and o-xylene-TeEG. The vapor-phase fugacity coefficients were calculated from the virial equation. The thermodynamic consistency of the data has been tested via Herington analysis. The binary parameters for four activity coefficient models (van Laar, Wilson, NRTL and UNIQUAC) have been fitted with the experimental data. A comparison of model performances has been made by using the criterion of root mean square deviations in boiling point and vapor-phase composition.

Excess molar volume data on mixing for binary mixtures of sulfolane with toluene, o-xylene, m-xylene, p-xylene, ethylbenzene and 1,2,4-trimethyl benzene have been measured over the entire composition range at 298.15 K and atmospheric pressure in order to investigate interactions between molecules. A vibrating tube density meter was used. All mixtures exhibit negative excess volumes with a minimum which occurs approximately at x=0.5. The experimental results have been correlated using the Redlich–Kister equation and have been qualitatively discussed.

An apparatus for measuring high pressure liquid–liquid equilibria was established. In order to diminish disturbance for the equilibration, the capillaries of stainless steel with 0.7 mm in inside diameter were used to take samples. The taken samples were totally evaporated into gas chromatography. The accuracy of the apparatus was verified by duplicating the literature data. Liquid–liquid equilibrium data for pseudo-ternary mixture of water–2-butanol–C4-hydrocarbon (the mixture of n-butane+trans-2-butene+cis-2-butene) were experimentally determined under pressure 8 MPa and at temperatures from 403.2 to 443.2 K. The measured liquid–liquid equilibrium data could be correlated by modified Redlich–Kwong (R–K) equation of state.

An equation of state for homonuclear chain molecules is formulated on the basis of thermodynamic perturbation theory of Wertheim. It yields a very accurate prediction of the compressibility factor of different chain molecules including hard spheres and hard dumbbells as well as flexible chains with up to 200 bonds in a molecule. In addition, a large number of molecular simulation results are used to test the thermodynamic first-order perturbation theory (TPT1), the thermodynamic second-order perturbation theory (TPT2), the scaled particle theory (SPT), the Percus-Yevick and Carnahan-Starling (PY-CS) equation, the generalized Flory-Dimer equation (GF-D) and our equation. For short chain molecules ( m ≥ 4), good agreement between the calculated and computer simulation data can be obtained from all of the above equations, but for long chain molecules the equation proposed in this work is better than the other equations.

Lu, J.-F., Yu, Y.-X. and Li, Y.-G., 1993. Modification and application of the mean spherical approximation method. Fluid Phase Equilibria, 85: 81-100. The mean spherical approximation (MSA) method is improved by the introduction of the effective diameter of the cation. The dependence of the ionic strength on the effective diameters is mainly attributed to the solvation effect. This modified model has been used to correlate the mean ionic activity coefficients for 85 single-electrolyte solutions. The results show that the modified MSA gives smaller deviations than the original MSA and Pitzer models. The modified MSA was also applied to calculate 32 mixed-electrolyte solutions without any mixing parameters. The calculated results indicate that the modified MSA can be used to calculate the mixture properties in terms of the parameters of single-electrolyte solutions. Furthermore, the mean ionic activity coefficients of some single-electrolyte solutions can be calculated for other temperatures by using the parameters obtained at 298.15 K.

The solubility of sodium dimethyl isophthalate-5-sulfonate in water and in a mixed solvent (water + methanol) containing sodium sulfate was determined from 292.7 K to 360.0 K. Sodium sulfate has a salting out effect on the solubility of sodium dimethyl isophthalate-5-sulfonate in water. The results were correlated by a polynomial equation.