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Electrocatalytic conversion of nitrate (NO3-) into ammonia can not only eliminate harmful pollutant but also provide a green method for a low-temperature ammonia synthesis. The electrochemical NO3- reduction reactions (NO3RRs) of a series of transition-metal-doped hexagonal boron phosphide (h-BP) monolayers were comprehensively evaluated using density functional theory. The V-doped h-BP monolayer was found to stand near the top of the volcano plot with the limiting potential of -0.22 V versus a reversible hydrogen electrode, exhibiting the lowest overpotential among the investigated systems in this work. Besides, the competing hydrogen evolution reaction is significantly suppressed due to the weak adsorption of the H atom. Importantly, the structure of the V-doped h-BP monolayer can be retained very well until 900 K, illustrating the initial indication of high thermal stability and great promise for synthesis. This study not only offers an eligible NO3RR electrocatalyst but also provides an atomic understanding of the behind mechanisms of the NO3RR process.

Due to wide applications of lithium-ion batteries (LIBs), scientists have never stopped pursuing larger-capacity and higher-stability lithium storage materials. To obtain better LIBs, three distinc...

Two-dimensional transition metal oxides have been widely explored as a catalyst in the high capacity non-aqueous lithium-oxygen batteries due to their excellent electrochemical performance in the o...

Silicene has recently shown high electrochemical performance with discharging product Li2O(s) and high stability, avoiding discharging byproducts for nonaqueous lithium–oxygen batteries. At the fun...

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.

Sodium storage capacity, mobility, and volume change during sodiation on the surfaces of interlayer-expanded Ti3C2 MXenes are investigated using ab initio density functional theory. The theoretical results reveal that the interlayer-expanded bare, F-, O-, and OH-functionalized Ti3C2 MXenes exhibit low barriers for sodium diffusion and small changes of lattice constant during sodiation. In addition, enlarged interlayer distance enables the stable multilayer adsorption on the bare and O-functionalized Ti3C2 MXenes and therefore significantly enhances their theoretical capacities. Both bare and O-functionalized Ti3C2 MXenes are predicted to be prospective anode materials for sodium-ion batteries with high theoretical capacities, fast discharge/charge rates, and good cycling performances. The present results provide a new route to improve the battery performances of anode materials based on MXene intercalation hosts.

Low contact barrier electrodes and various field-emitting devices require a tunable work function, and graphene is a dream material for these applications. In this work, the theoretical investigations on the variation of the work function for monolayer graphene doped with different kinds of atoms from groups IIA–VIA of the Periodic Table are reported. The geometry, density of states, dipole moment, and work function of each heteroatom-doped graphene are calculated using ab initio density functional theory with a dispersion correction. The obtained formation energy of the heteroatom-doped graphenes is in the order: N < B < P < O < S < Si < As < Se < Ge < Al < Ga. The work functions without an electric field abide by a periodic law in terms of doping atoms except for O-doped graphene. The calculated results demonstrate that the work functions of all heteroatom-doped graphenes are a linear function of the applied external electric field intensity, and the slopes of the lines deviate from the ideal value to a...

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...

Structural and kinetic properties of vitamin E in biomembranes provide the key to understanding the biological functions of this lipophilic vitamin. We report a series of molecular dynamics simulations of two alpha-tocopherol/phosphatidylcholine systems and two alpha-tocopherol/phosphatidylethanolamine systems in water at 280, 310, and 350 K. The preferential position, hydrogen bonding, orientation, and dynamic properties of the alpha-tocopherol molecule in the bilayers have been examined. In all the four systems simulated, the vitamin remains in one leaflet of lipid bilayer at 280 and 310 K but flips over from one side to the other at 350 K within 200 ns of the simulation. The hydroxyl oxygen in the headgroup of alpha-tocopherol preferred a location between the third and the fifth carbon atom in the sn-2 acyl chains of the lipids. Hydrogen bonding analysis shows that the hydrogen bonds are mainly with the oxygens of the fatty acid esters rather than with the phosphate oxygens of the lipid molecule, and those with the amino groups are trivial in the case of phosphatidylethanolamines, at all three temperatures. The hydrogen bonds with phosphatidylethanolamines are more stable than those with phosphatidylcholines at low temperatures. The orientation of alpha-tocopherol in the bilayers is relatively flexible: the chromanol ring takes various tilt angles with respect to the bilayer normal, and the isoprenyl chain is mobile and able to adopt many different conformers. Calculation of lateral diffusion coefficients of alpha-tocopherol and phospholipid molecules shows that alpha-tocopherol has a comparable diffusion rate with phospholipid molecules at the gel phase but diffuses more rapidly than lipid molecules at the liquid-crystal phase.

The structural properties of fully hydrated distearoylphosphatidylcholine (DSPC) and distearoylphosphatidylethanolamine (DSPE) bilayers near the main phase transition were investigated using molecular dynamics simulations on the basis of a united-atom model. Although largely similar in their molecular structures, the two lipids were found with different molecular packing modes at temperatures below the phase transition. For DSPC, three packing modes, namely, cross-tilt, partially interdigitated, and "mixed" gel phases, were observed, while, for DSPE, the lipid tails were almost perpendicular to the lipid surface. Above the main transition temperature, both lipid bilayers transformed into a disordered liquid-crystal phase with marked greater area per lipid and gauche % of the acyl chains and smaller bilayer thickness and order parameter, in comparison with the gel phase. The transformation process of liquid-crystal to gel phase was proved to experience the nucleation and growth stages in a hexagonal manner. The electron density profiles of some major components of both lipid bilayers at various temperatures have been calculated, and the results reveal that both lipid bilayers have less interdigitation around the main transition temperature.

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.

A density functional theory is proposed to investigate the effects of polymer monomer-monomer and monomer-wall attractions on the density profile, chain configuration, and equilibrium capillary phase transition of a freely jointed multi-Yukawa fluid confined in a slitlike pore. The excess Helmholtz energy functional is constructed by using the modified fundamental measure theory, Wertheim's first-order thermodynamic perturbation theory, and Rosenfeld's perturbative method, in which the bulk radial distribution function and direct correlation function of hard-core multi-Yukawa monomers are obtained from the first-order mean spherical approximation. Comparisons of density profiles and bond orientation correlation functions of inhomogeneous chain fluids predicted from the present theory with the simulation data show that the present theory is very accurate, superior to the previous theory. The present theory predicts that the polymer monomer-monomer attraction lowers the strength of oscillations for density profiles and bond orientation correlation functions and makes the excess adsorption more negative. It is interesting to find that the equilibrium capillary phase transition of the polymeric fluid in the hard slitlike pore occurs at a higher chemical potential than in bulk condition, but as the attraction of the pore wall is increased sufficiently, the chemical potential for equilibrium capillary phase transition becomes lower than that for bulk vapor-liquid equilibrium.

Because of the increasing interest in studying the phenomenon exhibited by charge-stabilized colloidal suspensions in confining geometry, we present a density functional theory (DFT) for a hard-core multi-Yukawa fluid. The excess Helmholtz free-energy functional is constructed by using the modified fundamental measure theory and Rosenfeld's perturbative method, in which the bulk direct correlation function is obtained from the first-order mean spherical approximation. To validate the established theory, grand canonical ensemble Monte Carlo (GCMC) simulations are carried out to determine the density profiles and surface excesses of multi-Yukawa fluid in a slitlike pore. Comparisons of the theoretical results with the GCMC data suggest that the present DFT gives very accurate density profiles and surface excesses of multi-Yukawa fluid in the slitlike pore as well as the radial distribution functions of the bulk fluid. Both the DFT and the GCMC simulations predict the depletion of the multi-Yukawa fluid near a nonattractive wall, while the mean-field theory fails to describe this depletion in some cases. Because the simple form of the direct correlation function is used, the present DFT is computationally as efficient as the mean-field theory, but reproduces the simulation data much better than the mean-field theory.

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...

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.