86 results on '"Yang, Xin-yu"'
Search Results
2. How Do Oxygen Vacancies Influence the Catalytic Performance of Two‐Dimensional Nb 2 O 5 in Lithium‐ and Sodium‐Oxygen Batteries?
- Author
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Yang-Xin Yu and Jia-Hui Li
- Subjects
Battery (electricity) ,Reaction mechanism ,Materials science ,General Chemical Engineering ,chemistry.chemical_element ,Alkali metal ,Oxygen ,Catalysis ,General Energy ,Alkali metal oxide ,chemistry ,Chemical engineering ,Environmental Chemistry ,General Materials Science ,Lithium ,Energy source - Abstract
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.
- Published
- 2021
3. Theoretical Exploration of Electrochemical Nitrate Reduction Reaction Activities on Transition-Metal-Doped h-BP
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Jie Wu, Jia-Hui Li, and Yang-Xin Yu
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Materials science ,Inorganic chemistry ,02 engineering and technology ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,Electrochemistry ,01 natural sciences ,Redox ,0104 chemical sciences ,Ammonia production ,chemistry.chemical_compound ,chemistry ,Monolayer ,Reversible hydrogen electrode ,General Materials Science ,Physical and Theoretical Chemistry ,Boron phosphide ,0210 nano-technology - Abstract
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.
- Published
- 2021
4. Toward Large-Capacity and High-Stability Lithium Storages via Constructing Quinone–2D-MnO2-Pillared Structures
- Author
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Jia-Hui Li, Jie Wu, and Yang-Xin Yu
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Storage material ,General Energy ,Materials science ,Chemical engineering ,chemistry ,Large capacity ,chemistry.chemical_element ,Lithium ,Physical and Theoretical Chemistry ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Quinone - Abstract
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...
- Published
- 2021
5. Singlet oxygen vs. triplet oxygen: functions of 2D-MoO3 catalysts in conquering catastrophic parasitic-reactions in lithium– and sodium–oxygen batteries
- Author
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Jia-Hui Li, Yang-Xin Yu, and Jie Wu
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Battery (electricity) ,Renewable Energy, Sustainability and the Environment ,Chemistry ,Singlet oxygen ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Oxygen ,0104 chemical sciences ,Catalysis ,chemistry.chemical_compound ,Triplet oxygen ,General Materials Science ,Lithium ,0210 nano-technology ,Energy source ,Nanosheet - Abstract
Aprotic electrolyte alkali metal–oxygen batteries that possess a higher energy density than lithium-ion batteries stand out as the most promising next-generation environmentally-friendly energy source. Parasitic reactions caused by the singlet oxygen released from the superoxide disproportionation reactions, however, lead to catastrophic fading in the battery cycle life. We attempted to seek a probable catalyst surmounting this dilemma and finally discovered the 2D-MoO3 nanosheet as an electrode-catalyst to handle the side reactions. Previous studies focused mainly on the influence of solvents on side reactions and neglected the catalyst, and hence, in this research an innovative mechanism of battery reaction occurring on the 2D-MoO3 nanosheet in aprotic solvents was fully explored from both thermodynamic and kinetic prospects. It is interesting to find that the 2D-MoO3 nanosheet plays different roles in preventing the production of singlet oxygen in lithium– and sodium–oxygen batteries. The 2D-MoO3 nanosheet could also trigger the deep reduction of alkali-metal peroxides, which is considered to be an effective method to avoid parasitic reactions. This work may shed new light on future research into highly reversible and efficient alkali metal–oxygen batteries.
- Published
- 2021
6. Highly selective electroreduction of nitrate to ammonia on a Ru-doped tetragonal Co2P monolayer with low-limiting overpotential
- Author
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Jie Wu and Yang-Xin Yu
- Subjects
chemistry.chemical_compound ,Materials science ,Volcano plot ,chemistry ,Standard electrode potential ,Phosphide ,Monolayer ,Inorganic chemistry ,Overpotential ,Electrochemistry ,Catalysis ,Electrode potential - Abstract
Selective electroreduction of nitrate (NO3−) into ammonia (NH3) can not only eliminate the water pollution crisis but also provide a sustainable way for low-temperature NH3 synthesis. However, today's development of the electrochemical NO3− reduction reaction (NO3RR) is hindered by the lack of eligible electrocatalysts and clear mechanism clarification. Here, the application potentials of the tetragonal transition-metal phosphide monolayers (M2P, M = Co, Ni, Ru and Pd) as NO3RR electrocatalysts for NH3 synthesis have been comprehensively and originally studied using density functional theory. Through comparing the relative energies of various possible products along the NO3RR process, a novel alternating pathway is proposed and it is beneficial to avoid the formation of N-containing by-products. Selecting the d-band center (ed) as an effective descriptor, a volcano-type plot of the NO3RR limiting potential is established. The Ni2P monolayer stands near the top of the volcano plot with the limiting potential of −0.37 V, but its selectivity can be greatly reduced when applying the electrode potential. Then, a Ru-doped Co2P monolayer is constructed to modulate the ed close to the value at the volcano top and its limiting potential is −0.38 V, exhibiting excellent activity. In addition, the Ru-doping process is thermodynamically favorable and the competing hydrogen evolution reaction is significantly suppressed even with the application of electrode potentials. This work not only provides an atomic understanding of the NO3RR process and but also offers a reliable descriptor to help design promising electrocatalysts.
- Published
- 2021
7. Highly stable Mo-doped Fe2P and Fe3P monolayers as low-onset-potential electrocatalysts for nitrogen fixation
- Author
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Jie Wu, Jia-Hui Li, and Yang-Xin Yu
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chemistry.chemical_compound ,Materials science ,chemistry ,Phosphide ,Chemical physics ,Monolayer ,Atom ,Doping ,Molecule ,Bimetallic strip ,Redox ,Catalysis - Abstract
Ammonia (NH3) is an essential ingredient for fertilizer production and a carbon-free energy carrier for engineering applications. Searching for novel electrocatalysts with low onset potential, high selectivity and excellent stability is still one of the most attractive and challenging topics. Here, based on the conductor-like screening model and first-principles calculations, we systematically investigated nitrogen reduction reaction (NRR) pathways occurring on iron-based phosphide monolayers. It can be found that Mo-doped Fe2P and Fe3P monolayers can efficiently promote the NRR with onset potentials of −0.30 V and −0.17 V, respectively, especially for the Mo-doped Fe3P monolayer, which has the lowest onset potential to date. Electronic analysis shows that the Mo atom doping can significantly enhance the degree of matching between the d-orbitals of transition metal atoms and the p-orbitals of the N2 molecule, contributing to the activation of dinitrogen. Furthermore, Mo and Fe atoms provide bimetallic active sites, helping to avoid the linear relationship during the NRR pathway. Besides, the competing hydrogen evolution reaction (HER) is suppressed because of larger onset potentials and ab initio molecular dynamics (AIMD) simulations were performed to identify the high stabilities of the Mo-doped monolayers. This work offers useful insights into the design of high-performance electrocatalysts for the NRR and provides guidance for future experimental and theoretical investigations.
- Published
- 2021
8. Theoretical Exploration of Single-Layer Tl2O as a Catalyst in Lithium–Oxygen Battery Cathodes
- Author
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Yang-Xin Yu, Jia-Hui Li, and Jie Wu
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Battery (electricity) ,Materials science ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,Oxygen ,Cathode ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Catalysis ,General Energy ,Chemical engineering ,chemistry ,Transition metal ,law ,Lithium ,Physical and Theoretical Chemistry ,0210 nano-technology ,Single layer - Abstract
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...
- Published
- 2020
9. Stabilities of group-III phosphide (MP, M = B, Al, Ga and In) monolayers in oxygen and water environments
- Author
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Jia-Hui Li, Yang-Xin Yu, and Jie Wu
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Materials science ,Annealing (metallurgy) ,Phosphide ,Intermolecular force ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Oxygen ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Monolayer ,Photocatalysis ,Molecule ,Density functional theory ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
Group-III phosphide (MP, M = B, Al, Ga and In) monolayers have promising applications in photocatalysis, nanoelectronics and optoelectronics. Their stabilities in oxygen and water environments are crucial to their practical applications. In order to investigate the stabilities of the MP monolayers, density functional theory calculations combined with ab initio molecular dynamics (AIMD) simulations were performed to illustrate their interactions with oxygen and water molecules. It was found that an oxygen molecule spontaneously dissociates on the AlP, GaP and InP monolayers. In the meantime, the corresponding monolayer structures are severely distorted after annealing. In contrast, BP monolayer is stable in the oxygen environment due to a high dissociative barrier of 0.89 eV. We found that a water molecule dissociates on AlP monolayer with a dissociative energy barrier of 0.42 eV, but it can be stably adsorbed on the BP, GaP and InP monolayers without the breakage of O-H bonds. Nevertheless, with the increase of the number of water molecules, the formed intermolecular H-bonding can promote interactions between water molecules and the monolayers, leading to structural distortion in the GaP and InP monolayers. When putting a water molecule near the oxygen molecule, the oxidation barrier of the BP monolayer is reduced to 0.75 eV, which is still high enough to maintain its stable state. This investigation theoretically provides environmental conditions for the experimental fabrication and practical application of semiconductor monolayers.
- Published
- 2020
10. Effect of Defects and Solvents on Silicene Cathode of Nonaqueous Lithium–Oxygen Batteries: A Theoretical Investigation
- Author
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Yang-Xin Yu
- Subjects
Materials science ,Silicene ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,Oxygen ,Cathode ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,General Energy ,chemistry ,Chemical engineering ,law ,Lithium ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
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...
- Published
- 2018
11. Single Nb or W Atom-Embedded BP Monolayers as Highly Selective and Stable Electrocatalysts for Nitrogen Fixation with Low-Onset Potentials
- Author
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Jie Wu, Jia-Hui Li, and Yang-Xin Yu
- Subjects
Materials science ,02 engineering and technology ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,01 natural sciences ,Combinatorial chemistry ,0104 chemical sciences ,Catalysis ,Ammonia production ,chemistry.chemical_compound ,chemistry ,Transition metal ,Monolayer ,General Materials Science ,Boron phosphide ,0210 nano-technology ,Selectivity - Abstract
Conversion of dinitrogen (N2) molecules into ammonia through electrochemical methods is a promising alternative to the traditional Haber-Bosch process. However, searching for an eligible electrocatalyst with high stability, low-onset potential, and superior selectivity is still one of the most challenging and attractive topics for the electrochemical N2 reduction reaction (NRR). Here, by means of first-principles calculations and the conductor-like screening model, four comprehensive criteria were proposed to screen out eligible NRR electrocatalysts from 29 atomic transition metals embedded on the defective boron phosphide (BP) monolayer with B-monovacancy (M/BP single-atom catalysts, SAC, M = Sc-Zn, Y-Cd, and Hf-Hg). Consequently, the Nb/BP and W/BP SACs are identified as the promising candidates, on which the N2 molecule can only be activated through the enzymatic pathway with the onset potentials of -0.25 and -0.19 V, and selectivities of 90.5 and 100%, respectively. It is worth noting that the W/BP SAC has the lowest overpotential among the 29 systems investigated. The electronic properties were also calculated in detail to analyze the activity origin. Importantly, the Nb/BP and W/BP SACs possess high thermal stabilities due to that their structures can be retained very well up to 1000 and 700 K, respectively. This work not only provides an efficient and reliable method to screen eligible NRR electrocatalysts but also paves a new way for advancing sustainable ammonia synthesis.
- Published
- 2021
12. A Theoretical Analysis on the Oxidation and Water Dissociation Resistance on Group-IV Phosphide Monolayers
- Author
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Jie Wu, Jia-Hui Li, and Yang-Xin Yu
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Materials science ,Fabrication ,Phosphide ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Dissociation (chemistry) ,0104 chemical sciences ,chemistry.chemical_compound ,Phosphorene ,chemistry ,Chemisorption ,Monolayer ,Molecule ,Physical chemistry ,Physical and Theoretical Chemistry ,Boron phosphide ,0210 nano-technology - Abstract
Group-IV phosphide monolayers (MP, M=C, Si, Ge and Sn) provide a versatile platform for photocatalysts, as well as optoelectronic and nanoelectronic devices. Herein, comprehensive first-principles calculations and ab initio molecular dynamics (AIMD) simulations were performed to explore their stabilities in the air. We identified that the MP monolayers have excellent mechanical properties and their carrier mobilities are higher than that of phosphorene. The MP monolayers were predicted to possess superior oxidation resistance than the boron phosphide (BP) monolayer based on the proposed donation-backdonation theory. It was observed that the dissociation and chemisorption of a water molecule on the monolayers are kinetically difficult both in the water and in oxygen-water environments involving energy barriers of 1.28-3.48 eV. We also performed AIMD simulations at 300, 1000, 1200 and 1500 K. It is noteworthy that only the carbon phosphide (CP) monolayer can retain an intact structure at 1500 K, while the other three monolayers can just sustain to 1200 K. These results provide a guidance for their practical application and experimental fabrication.
- Published
- 2020
13. Adsorptive removal of Cr3+, Cu2+ and Ni2+ ions by magnetic Fe3O4@alkali-treated coal fly ash
- Author
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Yang-Xin Yu and Ya-Na Zhang
- Subjects
Chemistry ,Fly ash ,Inorganic chemistry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,0210 nano-technology ,Alkali metal ,01 natural sciences ,0104 chemical sciences ,Ion - Published
- 2018
14. Selective transformation of aqueous methanol to value-added formic acid and hydrogen on bifunctional Mo2P monolayers in fuel cells
- Author
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Jing Wen, Jie Wu, and Yang-Xin Yu
- Subjects
Chemistry ,Formic acid ,General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Photochemistry ,Dissociation (chemistry) ,Surfaces, Coatings and Films ,Catalysis ,chemistry.chemical_compound ,Direct methanol fuel cell ,Monolayer ,Dehydrogenation ,Methanol ,Bond cleavage - Abstract
Direct methanol fuel cell (DMFC) running on hydrogen is an attractive alternative power source for a wide range of applications. Importantly, the required hydrogen can be in situ released from the stable liquid, which ensures its safe transformation and storage. However, the catalyst in DMFC is usually poisoned by the generated CO species, thus it is challenging to find an efficient and durable catalyst for practical applications. Here, the mechanism of methanol oxidation reaction (MOR) on the Mo2P monolayer is first studied using density functional theory. Compared with the initial C–H and C–O bond scissions, the initial O–H bond scission is found to be the most favorable. The reason is systematically analyzed based on steric effect, activation Gibbs free energy (Gact) decomposition and the Bronsted − Evans − Polanyi (BEP) relationships. The further dehydrogenation of CH2OH via the O–H bond scission has a significantly lower Gact than that of CH3O, thus the methanol decomposition on the Mo2P monolayer may proceed via two competitive pathways, i.e., CH 3 OH → CH 3 O → CH 2 O → CHO → CO and CH 3 OH → CH 2 OH → CH 2 O → CHO → CO . Then, through overcoming a relatively low barrier, the generated CO species can be combined with hydroxyl group from water dissociation on the Mo2P monolayer to produce formic acid, which can be easily desorbed from the catalyst surface to avoid the block of active sites. This study provides a better understanding of the MOR mechanism and paves the way for further advancing the catalyst in DMFCs.
- Published
- 2021
15. Quantum capacitance, electrostatic potential, electronic and structural data for bare and functionalized niobium carbide MXenes
- Author
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Yang-Xin Yu and Yan Xin
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Supercapacitor ,Electrode material ,Multidisciplinary ,Field (physics) ,Materials Sciences ,Nanotechnology ,02 engineering and technology ,lcsh:Computer applications to medicine. Medical informatics ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,Quantum capacitance ,chemistry ,Chemical physics ,Density of states ,lcsh:R858-859.7 ,Niobium carbide ,lcsh:Science (General) ,0210 nano-technology ,MXenes ,Quantum ,lcsh:Q1-390 - Abstract
The data reported in this article are structural and physicochemical properties for bare and F, O, OH and CH3O-functionalized Nb n+1C n (n = 1, 2, 3 and 4) MXenes. The structural properties are presented as top views and side views from the X direction of the optimal structures of studied MXenes. The physicochemical properties include quantum capacitances, electrostatic potentials and electronic properties such as the projected density of states (PDOS) and band structures. Further interpretation and discussion of these data can be obtained from the article entitled "Possibility of bare and functionalized niobium carbide MXenes for electrode materials of supercapacitors and field emitters" (Xin and Yu, 2017) [1].
- Published
- 2017
16. Molecular dynamics simulations of stability at the early stages of silica materials preparation
- Author
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Yang-Xin Yu, Yujun Wang, and Reza Gholizadeh
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Chemistry ,Organic Chemistry ,Physics::Optics ,02 engineering and technology ,Dihedral angle ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Radial distribution function ,01 natural sciences ,Electric charge ,Force field (chemistry) ,0104 chemical sciences ,Analytical Chemistry ,Condensed Matter::Soft Condensed Matter ,Inorganic Chemistry ,Mean squared displacement ,Molecular dynamics ,symbols.namesake ,Chemical physics ,Computational chemistry ,symbols ,Density functional theory ,van der Waals force ,0210 nano-technology ,Spectroscopy - Abstract
The main objective of this article is the Molecular dynamics simulations of stability phenomenon at the early stages of silica production in a colloidal solution. The Dreiding force field used during the whole calculation for the search of all bonding, angle, dihedral, inversion potential sets for a given configuration. For studying the stability phenomenon, two scenarios are specified: (1) The diameter of silica nanoparticles in each simulation box is the same while initial distances of two silica nanoparticles are different (system I), (2) The initial distance between two silica nanoparticles in each simulation box is the same while silica nanoparticles diameters are different (system II). The charge of atoms in silica nanoparticles determined using density functional theory calculations (Dmol 3 ). The Born repulsion forces were predominant rather than the van der Waals attraction forces. Furthermore, trajectories, mean squared displacements, radial distribution functions, and electrical charges of silica nanoparticles are determined. The displacement of silica nanoparticles was negligible which demonstrates that atoms could not approach more close. The studied colloidal solution was stable regard to the results of molecular dynamics simulations.
- Published
- 2017
17. Determination of Solubility of Sodium Salts in Aqueous Surfactant and STPP Solutions Using an Ion Selective Electrode
- Author
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Ya-Na Zhang, Xin Wang, and Yang-Xin Yu
- Subjects
Supersaturation ,Aqueous solution ,Electromotive force ,Chemistry ,General Chemical Engineering ,Sodium ,Potentiometric titration ,Inorganic chemistry ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,Ion selective electrode ,020401 chemical engineering ,Pulmonary surfactant ,0204 chemical engineering ,Solubility ,0210 nano-technology - Abstract
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.
- Published
- 2016
18. Adsorption and substitution effects of Mg on the growth of calcium sulfate hemihydrate: An ab initio DFT study
- Author
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S.C. Hou, Lan Xiang, Yang-Xin Yu, and Yan Xin
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Chemistry ,Whiskers ,Doping ,Ab initio ,General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Ion ,symbols.namesake ,Crystallography ,Adsorption ,Atom ,symbols ,Density functional theory ,van der Waals force - Abstract
Calcium sulfate hemihydrate (CaSO 4 ·0.5H 2 O, CSH) whiskers with high aspect ratio are promising reinforce materials which have drawn much attention. In order to obtain high quality CSH materials, effect of Mg 2+ ions on properties of the (0 0 2), (2 0 0) 1 and (2 0 0) 2 planes of CSH is investigated using an ab initio density functional theory (DFT) with a van der Waals (vdW) dispersion-correction. The computed results show that strong adsorption and substitution effects take place between Mg 2+ ion and (2 0 0) 1 plane. The adsorption energies of an Mg 2+ ion on the (0 0 2), (2 0 0) 1 and (2 0 0) 2 planes are −0.066, −0.571 and −0.047 eV, respectively. An insight into the electrostatic potential of pristine CSH planes has demonstrated that the (2 0 0) 1 plane is much more negatively charged than the (0 0 2) and (2 0 0) 2 planes. The energies of the substitution of a Ca atom with an Mg atom on the CSH (0 0 2), (2 0 0) 1 and (2 0 0) 2 planes are 1.572, 0.063 and 1.349 eV, respectively. It is found that Ca atoms on the (2 0 0) 1 plane are relatively easy to be substituted by Mg atoms. The calculation results of a Ca 2+ ion adsorption on the Mg-doped (2 0 0) 1 plane indicate that the adsorption energies increase apparently as the doping ratio varies from 0 to 1.0. Compared with K + , Na + and Al 3+ ions, Mg 2+ ion is the most promising additive to promote the growth of CSH along c axis.
- Published
- 2015
19. N2O + CO reaction over Si- and Se-doped graphenes: An ab initio DFT study
- Author
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Yang-Xin Yu and Reza Gholizadeh
- Subjects
Graphene ,Ab initio ,General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Activation energy ,Condensed Matter Physics ,Chemical reaction ,Surfaces, Coatings and Films ,law.invention ,Catalysis ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,Computational chemistry ,law ,Physics::Atomic and Molecular Clusters ,symbols ,Physical chemistry ,Density functional theory ,Physics::Chemical Physics ,van der Waals force ,Carbon monoxide - Abstract
Catalytic conversion of non-CO2 green house gases and other harmful gases is a promising way to protect the atmospheric environment. Non-metal atom-doped graphene is attractive for use as a catalyst in the conversion due to its unique electronic properties, relatively low price and leaving no burden to the environment. To make an attempt on the development of green catalysts for the conversion, ab initio density functional theory is used to investigate the mechanisms of N2O reduction by CO on Si- and Se-doped graphenes. We have calculated the geometries and adsorption energies of reaction species (N2O, CO, N2 and CO2) as well as energy profiles along the reaction pathways. The activation energies of N2O decomposition and CO oxidation on both Si- and Se-doped graphenes have been obtained. Our calculated results indicate that the catalytic activity of Si-doped graphene is better than the Fe+ in gas phase and comparable to the single Fe atom embedded on graphene. In the calculations, we found that van der Waals interactions and zero-point energy are two non-negligible factors for the predictions of the activation energies. Further discussion shows that Si-doped graphene can be one of efficient green catalysts for conversion of the airborne pollutants and Se-doped graphene can be a candidate for oxidizing CO by atomic oxygen.
- Published
- 2015
20. Density functional theory study on ion adsorption and electroosmotic flow in a membrane with charged cylindrical pores
- Author
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Yuan-Xiang Zheng, Yan Xin, and Yang-Xin Yu
- Subjects
Valence (chemistry) ,Chemistry ,Monte Carlo method ,Biophysics ,Analytical chemistry ,02 engineering and technology ,Electrolyte ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Ion ,Adsorption ,Chemical physics ,Electric field ,Density functional theory ,Surface charge ,Physical and Theoretical Chemistry ,0210 nano-technology ,Molecular Biology - Abstract
Ion adsorption and electroosmotic flow induced by an external electric field have a variety of practical applications, especially for membrane technology. In this work, a partially perturbative density functional theory (DFT) based on the modified fundamental measure theory was applied to investigate the ion density distributions and partitions in a charged cylindrical pore. Different types of electrolyte solutions, including both charge symmetric and asymmetric, were examined using the proposed theory with various pore diameters, bulk densities, ion valencies and surface charge densities. The ion concentration profiles calculated with the theory exhibit good agreements with the results of the Monte Carlo simulations, while the results of the Poisson–Boltzmann equation deviate greatly especially for the high valence electrolytes in narrow cylindrical pores. Some interesting phenomena discovered in both experiments and simulations, such as the reverse distribution of the ions and charge inversion, ...
- Published
- 2015
21. Work Functions of Pristine and Heteroatom-Doped Graphenes under Different External Electric Fields: An ab Initio DFT Study
- Author
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Reza Gholizadeh and Yang-Xin Yu
- Subjects
Condensed matter physics ,Graphene ,Chemistry ,Doping ,Ab initio ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Dipole ,General Energy ,law ,Electric field ,Physics::Atomic and Molecular Clusters ,Density of states ,Density functional theory ,Work function ,Physical and Theoretical Chemistry - Abstract
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...
- Published
- 2014
22. Efficient and Reversible Electron Doping of Semiconductor-Enriched Single-Walled Carbon Nanotubes by Using Decamethylcobaltocene
- Author
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Dan Xie, Yilin Sun, Xian Li, Yan Xin, Jianlong Xu, Ruixuan Dai, Tian-Ling Ren, Lan Xiang, Yang-Xin Yu, and Sui-Dong Wang
- Subjects
Materials science ,Science ,Electron donor ,02 engineering and technology ,Carbon nanotube ,010402 general chemistry ,01 natural sciences ,Article ,law.invention ,chemistry.chemical_compound ,law ,Surface charge ,Multidisciplinary ,Dopant ,business.industry ,Doping ,021001 nanoscience & nanotechnology ,Acceptor ,0104 chemical sciences ,Threshold voltage ,Semiconductor ,chemistry ,Medicine ,Optoelectronics ,0210 nano-technology ,business - Abstract
Single-walled carbon nanotubes (SWCNTs) offer great potential for field-effect transistors and integrated circuit applications due to their extraordinary electrical properties. To date, as-made SWCNT transistors are usually p-type in air, and it still remains challenging for realizing n-type devices. Herein, we present efficient and reversible electron doping of semiconductor-enriched single-walled carbon nanotubes (s-SWCNTs) by firstly utilizing decamethylcobaltocene (DMC) deposited by a simple spin-coating process at room temperature as an electron donor. A n-type transistor behavior with high on current, large I on /I off ratio and excellent uniformity is obtained by surface charge transfer from the electron donor DMC to acceptor s-SWCNTs, which is further corroborated by the Raman spectra and the ab initio simulation results. The DMC dopant molecules could be reversibly removed by immersion in N, N-Dimethylformamide solvent, indicating its reversibility and providing another way to control the carrier concentration effectively as well as selective removal of surface dopants on demand. Furthermore, the n-type behaviors including threshold voltage, on current, field-effect mobility, contact resistances, etc. are well controllable by adjusting the surface doping concentration. This work paves the way to explore and obtain high-performance n-type nanotubes for future complementary CMOS circuit and system applications.
- Published
- 2017
23. A dispersion-corrected DFT study on adsorption of battery active materials anthraquinone and its derivatives on monolayer graphene and h-BN
- Author
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Yang-Xin Yu
- Subjects
Renewable Energy, Sustainability and the Environment ,Graphene ,Chemistry ,Inorganic chemistry ,Binding energy ,General Chemistry ,Electrolyte ,law.invention ,symbols.namesake ,Adsorption ,Physisorption ,law ,Monolayer ,symbols ,General Materials Science ,van der Waals force ,Nanosheet - Abstract
9,10-Anthraquinone (AQ) and its derivatives, i.e., benzofuro[5,6-b]furan-4,8-dione (BFFD), benzo[1,2-b:4,5-b′]dithiophene-4,8-dione (BDTD) and pyrido[3,4-g]isoquinoline-5,10-dione (PID), are environmentally friendly and cheap electrode materials. However, their significant solubility in electrolyte solutions limits the cycle performance of lithium-ion batteries. In this work a comparative investigation of these four organic molecules adsorbed on monolayer graphene and hexagonal boron nitride (h-BN) has been carried out using van der Waals (vdW) dispersion-corrected density-functional theory (DFT). The calculated results indicate that the vdW dispersion contributes to more than 80% of the total attractive interaction for all the complexes studied. The binding energies range from 1.06 to 1.31 eV, showing strong physisorption. The calculated binding energies of the four organic molecules are in the order: BFFD < BDTD < AQ < PID on monolayer graphene and BFFD < BDTD < PID < AQ on monolayer h-BN. The physisorption causes a work function shift relative to the isolated graphene or h-BN nanosheet in the order: AQ < BDTD < BFFD < PID on both the graphene and h-BN nanosheets. This sequence is dominated by the work functions of the four organic molecules. The strong physisorption suggests that the solubility of the four organic compounds in the electrolyte solutions can be reduced by binding them to a graphene or h-BN nanosheet, making the organic compound–graphene or organic compound–h-BN composite a promising electrode material for lithium-ion batteries.
- Published
- 2014
24. An important atomic process in the CVD growth of graphene: Sinking and up-floating of carbon atom on copper surface
- Author
-
Yue Yu, Mwenya Trevor, Yingfeng Li, Fan Bai, Yang-Xin Yu, Meicheng Li, and Gu Tiansheng
- Subjects
Materials science ,Dimer ,General Physics and Astronomy ,chemistry.chemical_element ,Nanotechnology ,law.invention ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Adsorption ,law ,Physics::Atomic and Molecular Clusters ,Physics::Atomic Physics ,Physics::Chemical Physics ,Condensed Matter::Quantum Gases ,Graphene ,Relaxation (NMR) ,Tetravalence ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Copper ,Surfaces, Coatings and Films ,chemistry ,Chemical physics ,Density functional theory ,Carbon - Abstract
By density functional theory (DFT) calculations, the early stages of the growth of graphene on copper (1 1 1) surface are investigated. At the very first time of graphene growth, the carbon atom sinks into subsurface. As more carbon atoms are adsorbed nearby the site, the sunken carbon atom will spontaneously form a dimer with one of the newly adsorbed carbon atoms, and the formed dimer will up-float on the top of the surface. We emphasize the role of the co-operative relaxation of the co-adsorbed carbon atoms in facilitating the sinking and up-floating of carbon atoms. In detail: when two carbon atoms are co-adsorbed, their co-operative relaxation will result in different carbon–copper interactions for the co-adsorbed carbon atoms. This difference facilitates the sinking of a single carbon atom into the subsurface. As a third carbon atom is co-adsorbed nearby, it draws the sunken carbon atom on top of the surface, forming a dimer. Co-operative relaxations of the surface involving all adsorbed carbon atoms and their copper neighbors facilitate these sinking and up-floating processes. This investigation is helpful for the deeper understanding of graphene synthesis and the choosing of optimal carbon sources or process.
- Published
- 2013
25. Simulation study on dynamics of A- to B-form transition in aqueous DNA solution: Effect of alkali metal counterions
- Author
-
Shintaro Fujimoto and Yang-Xin Yu
- Subjects
chemistry.chemical_classification ,Molecular dynamics ,Aqueous solution ,chemistry ,Inorganic chemistry ,Molecule ,Concentration effect ,Physical chemistry ,A-DNA ,General Chemistry ,Counterion ,Alkali metal ,Ion - Abstract
DNA and its conformational transition can be used to design nanometer-scale structures, nano-tweezers and nanomechanical devices. Experiments and molecular simulations have been used to study the concentration effect on the A-DNA→B-DNA conformational transition, but a systematical investigation on counterion effect on the dynamics of this transition has not been reported up to now. In present work, restrained and unrestrained molecular dynamics (MD) simulations have been performed to characterize the stability of DNA conformations and the dynamics of A-DNA→B-DNA transitions in aqueous solutions with different alkali metal counterions. The DNA duplex d(CGCGAATTCGCG)2, coion Cl− and counterions Li+, Na+, K+, Rb+ and Cs+ as well as water molecule were considered using the PARM99 force field in the AMBER8 package. It was found that B-form DNA is more stable than A-form DNA in aqueous electrolyte solutions with different alkali metal counterions. Increasing KCl concentration in solution hinders the A-DNA→B-DNA transition and the transition times for different alkali metal counterions conform to neither the simple sequence related to naked ion size nor to hydrated diameter, but an apparently abnormal sequence of K+ < Rb+ < Cs+ < Na+ < Li+. This abnormal sequence can be well understood in terms of an electrostatic model based on the effective cation diameters and the modified mean-spherical approximation (MMSA). The present results provide valuable information for the design of DNA-based nanomaterials and nanodevices.
- Published
- 2013
26. Molecular dynamics simulation of the A-DNA to B-DNA transition in aqueous RbCl solution
- Author
-
Shintaro Fujimoto and Yang-Xin Yu
- Subjects
chemistry.chemical_classification ,Aqueous solution ,chemistry.chemical_element ,General Chemistry ,Electrolyte ,Rubidium ,Ion ,Molecular dynamics ,chemistry.chemical_compound ,Crystallography ,chemistry ,A-DNA ,Counterion ,DNA - Abstract
Unrestrained molecular dynamics (MD) simulations have been carried out to characterize the stability of DNA conformations and the dynamics of A-DNA→B-DNA conformational transitions in aqueous RbCl solutions. The PARM99 force field in the AMBER8 package was used to investigate the effect of RbCl concentration on the dynamics of the A→B conformational transition in the DNA duplex d(CGCGAATTCGCG)2. Canonical A- and B-form DNA were assumed for the initial conformation and the final conformation had a length per complete turn that matched the canonical B-DNA. The DNA structure was monitored for 3.0 ns and the distances between the C5′ atoms were obtained from the simulations. It was found that all of the double stranded DNA strands of A-DNA converged to the structure of B-form DNA within 1.0 ns during the unrestrained MD simulations. In addition, increasing the RbCl concentration in aqueous solution hindered the A→B conformational transition and the transition in aqueous RbCl solution was faster than that in aqueous NaCl solution for the same electrolyte strength. The effects of the types and concentrations of counterions on the dynamics of the A→B conformational transition can be understood in terms of the variation in water activity and the number of accumulated counterions in the major grooves of A-DNA. The rubidium ion distributions around both fixed A-DNA and B-DNA were obtained using the restrained MD simulations to help explain the effect of RbCl concentration on the dynamics of the A→B conformational transition.
- Published
- 2013
27. Adsorption of carbon monoxide on Ag(I)-ZSM-5 zeolite: An ab initio density functional theory study
- Author
-
Jianguo Mi, Zhen-Zhen Qiu, and Yang-Xin Yu
- Subjects
Coordination number ,Inorganic chemistry ,Ab initio ,General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Bond length ,chemistry.chemical_compound ,Adsorption ,chemistry ,Atom ,Physical chemistry ,Density functional theory ,Zeolite ,Carbon monoxide - Abstract
Adsorption of carbon monoxide on different Ag + -exchange sites of Ag–ZSM-5 zeolite has been investigated using density functional theory. The coordination and local geometry of the Ag + ion in Ag–ZSM-5 as well as adsorption structures and energies of CO adsorbed on these sites are explored extensively. The structure of Ag + -exchange sites, location of the Al atom on the T site, and number of the Al atoms contained in the sites are considered in the theoretical calculations. The calculated results show that the Ag O coordination number of two is strongly preferred before and after CO adsorption. The Ag O bond lengths are in a broad range of 2.2–2.9 A, and the Ag C bond lengths for CO adsorbed on Ag–ZSM-5 zeolite are calculated to be 2.0–2.2 A. Both Ag O and Ag C bond lengths for CO–Ag–ZSM-5 complex are longer than those for CO–Cu–ZSM-5 complex. The calculated adsorption energy of CO adsorbed on the I2 sites is between 28.5 and 29.6 kcal/mol, and that on the Z5, Z6, M5 and M6 sites containing one Al atom on the T position is between 11.3 and 18.9 kcal/mol whereas the calculated adsorption energy of CO adsorbed on the M7 site containing one Al atom is 19.9 kcal/mol. The introduction of the two Al atoms to the Ag + -exchange site results in a reduction of CO adsorption energy. In general, the adsorption energy of CO on Ag–ZSM-5 is lower than that on Cu–ZSM-5. The predicted coordination of the Ag + ion, bond lengths of Ag O and Ag C as well as adsorption energy are in accord with available experimental results.
- Published
- 2012
28. Vapor-liquid equilibrium properties for confined binary mixtures involving CO2, CH4, and N2 from Gibbs ensemble Monte Carlo simulations
- Author
-
Yuan-Xiang Zheng, Jiding Li, Yingfeng Li, and Yang-Xin Yu
- Subjects
Canonical ensemble ,Relative volatility ,Chemistry ,Monte Carlo method ,Vaporization ,Vapor–liquid equilibrium ,Thermodynamics ,General Chemistry ,Enthalpy of vaporization ,Entropy of vaporization ,Phase diagram - Abstract
The effects of solid-fluid interactions on the vapor-liquid phase diagram, coexistence density, relative volatility and vaporization enthalpy have been investigated for confined binary systems of CO2-CH4, CO2-N2 and CH4-N2. The Gibbs ensemble Monte Carlo (GEMC) simulation results indicate that the confinement and the solid-fluid interaction have significant influences on the vapor-liquid equilibrium properties. The confinement and the strength of the solid-fluid interaction make the p-x i phase diagram move to higher pressure regions. They also make the two-phase region become narrower for each binary mixture. The strength of the solid-fluid interactions can cause increases in the coexistence liquid and vapor densities, and cause the decrease of the relative volatility and the vaporization enthalpy for the systems studied. As the pore width is decreased, the two-phase region of the binary mixture becomes narrower.
- Published
- 2012
29. An Equation of State for the Isotropic–Nematic Phase Transition of Semiflexible Polymers
- Author
-
Yingfeng Li, Yang-Xin Yu, and Yuan-Xiang Zheng
- Subjects
chemistry.chemical_classification ,Phase transition ,Range (particle radiation) ,Equation of state ,Materials science ,General Chemical Engineering ,Isotropy ,Thermodynamics ,General Chemistry ,Polymer ,Industrial and Manufacturing Engineering ,chemistry ,Liquid crystal ,Perturbation theory (quantum mechanics) - Abstract
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...
- Published
- 2011
30. A viscosity equation for polyatomic fluids under normal and high pressures
- Author
-
Xu-Guang Zhang and Yang-Xin Yu
- Subjects
Alkane ,chemistry.chemical_classification ,Chemistry ,General Chemical Engineering ,Intrinsic viscosity ,Polyatomic ion ,General Physics and Astronomy ,Tangent ,Thermodynamics ,Molecule ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Viscosity solution ,Scaling ,Residual entropy - Abstract
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.
- Published
- 2010
31. Shift of the azeotropic point of binary Lennard–Jones mixtures confined in a slit-like pore
- Author
-
Yang-Xin Yu, Yingfeng Li, Yuan-Xiang Zheng, and Jiding Li
- Subjects
Canonical ensemble ,Relative volatility ,Chemistry ,Component (thermodynamics) ,General Chemical Engineering ,General Physics and Astronomy ,Thermodynamics ,Interaction energy ,Quantitative Biology::Subcellular Processes ,Reduced properties ,Phase (matter) ,Azeotrope ,Physical and Theoretical Chemistry ,Phase diagram - Abstract
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.
- Published
- 2010
32. Structural and Kinetic Properties of α-Tocopherol in Phospholipid Bilayers, a Molecular Dynamics Simulation Study
- Author
-
Shan-Shan Qin, Yang-Xin Yu, and Zhi-Wu Yu
- Subjects
Phosphatidylethanolamine ,Stereochemistry ,Hydrogen bond ,Lipid Bilayers ,alpha-Tocopherol ,Temperature ,Phospholipid ,Hydrogen Bonding ,Molecular Dynamics Simulation ,Surfaces, Coatings and Films ,Kinetics ,chemistry.chemical_compound ,Molecular dynamics ,chemistry ,Phosphatidylcholine ,Phosphatidylcholines ,Materials Chemistry ,Molecule ,lipids (amino acids, peptides, and proteins) ,Lipid bilayer phase behavior ,Physical and Theoretical Chemistry ,Lipid bilayer - Abstract
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.
- Published
- 2009
33. Structural Characterization on the Gel to Liquid-Crystal Phase Transition of Fully Hydrated DSPC and DSPE Bilayers
- Author
-
Zhi-Wu Yu, Shan-Shan Qin, and Yang-Xin Yu
- Subjects
Quantitative Biology::Biomolecules ,Physics::Biological Physics ,Phase transition ,Molecular Structure ,Chemistry ,Phosphatidylethanolamines ,Transition temperature ,Bilayer ,Lipid Bilayers ,Nucleation ,Water ,Surfaces, Coatings and Films ,Quantitative Biology::Subcellular Processes ,Condensed Matter::Soft Condensed Matter ,Crystallography ,Liquid crystal ,Phase (matter) ,Phosphatidylcholines ,Materials Chemistry ,lipids (amino acids, peptides, and proteins) ,Lipid bilayer phase behavior ,Physical and Theoretical Chemistry ,Lipid bilayer - Abstract
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.
- Published
- 2009
34. Mutual diffusion coefficients of concentrated 1:1 electrolyte from the modified mean spherical approximation
- Author
-
Yang-Xin Yu, Hong-Bing Shi, and Guang-Hua Gao
- Subjects
Aqueous solution ,Molar concentration ,Smoluchowski coagulation equation ,Chemistry ,General Chemical Engineering ,General Physics and Astronomy ,Thermodynamics ,Electrolyte ,Function (mathematics) ,Radial distribution function ,symbols.namesake ,Ionic strength ,symbols ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Diffusion (business) - Abstract
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.
- Published
- 2007
35. Density functional study on the osmotic coefficient for the DNA–electrolyte solutions
- Author
-
Yang-Xin Yu, Ke Wang, and Guang-Hua Gao
- Subjects
Chemistry ,General Chemical Engineering ,Monte Carlo method ,General Physics and Astronomy ,Thermodynamics ,Hard spheres ,Electrolyte ,Time-dependent density functional theory ,Ion ,symbols.namesake ,Helmholtz free energy ,symbols ,Osmotic coefficient ,Density functional theory ,Physical and Theoretical Chemistry - Abstract
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.
- Published
- 2007
36. Measurement of Activity Coefficient at Infinite Dilution of Hydrocarbons in Sulfolane Using Gas−Liquid Chromatography
- Author
-
Qiang Gong, Yang-Xin Yu, and Li-Li Huang
- Subjects
Activity coefficient ,Heptane ,Chromatography ,General Chemical Engineering ,Analytical chemistry ,General Chemistry ,Toluene ,Dilution ,chemistry.chemical_compound ,chemistry ,Extractive distillation ,Sulfolane ,Nonane ,Benzene - Abstract
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.
- Published
- 2007
37. A molecular-thermodynamic model for the interactions between globular proteins in aqueous solutions: Applications to bovine serum albumin (BSA), lysozyme, α-chymotrypsin, and immuno-gamma-globulins (IgG) solutions
- Author
-
Yang-Xin Yu, Lin Jin, and Guang-Hua Gao
- Subjects
Models, Molecular ,Surface Properties ,Globular protein ,Serum albumin ,Thermodynamics ,Models, Biological ,Quantitative Biology::Subcellular Processes ,Biomaterials ,Electrolytes ,chemistry.chemical_compound ,symbols.namesake ,Colloid and Surface Chemistry ,Osmotic Pressure ,Chymotrypsin ,Bovine serum albumin ,Potential of mean force ,chemistry.chemical_classification ,Physics::Biological Physics ,Quantitative Biology::Biomolecules ,Binding Sites ,Chromatography ,biology ,Osmolar Concentration ,Water ,Serum Albumin, Bovine ,Hard spheres ,Hydrogen-Ion Concentration ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Solutions ,Condensed Matter::Soft Condensed Matter ,chemistry ,Ionic strength ,Immunoglobulin G ,biology.protein ,symbols ,Muramidase ,Salts ,Lysozyme ,van der Waals force ,Hydrophobic and Hydrophilic Interactions ,Protein Binding - Abstract
To investigate globular protein-protein and protein-salt interactions in electrolyte solutions, a potential of mean force including hard-core repulsion, van der Waals attraction and electric double layer repulsion is proposed in this work. Both van der Waals attraction and double-layer repulsion are represented using hard spheres with two-Yukawa tails. The explicit analytical solution of osmotic pressure is derived from the first-order mean spherical approximation. From the comparison between the calculated and experimental values of osmotic pressures for aqueous bovine serum albumin (BSA), lysozyme, alpha-chymotrypsin, and immuno-gamma-globulins (IgG) solutions, we found that the proposed model is adequate for the description of the interactions between proteins at low ionic strength and small self-association of protein molecules. At high ionic strength, the charge inversions of protein molecules should be taken into account.
- Published
- 2006
38. Theoretical calculation on the membrane potential of charged porous membranes in 1-1, 1-2, 2-1 and 2-2 electrolyte solutions
- Author
-
Wei-Juan Shang, Xiaolin Wang, and Yang-Xin Yu
- Subjects
chemistry.chemical_classification ,Membrane potential ,Diffusion ,Analytical chemistry ,Charge density ,Filtration and Separation ,Electrolyte ,Biochemistry ,symbols.namesake ,Membrane ,chemistry ,symbols ,General Materials Science ,Nernst equation ,Physical and Theoretical Chemistry ,Counterion ,Dimensionless quantity - Abstract
The space-charge (SC) model and the Teorell–Meyer–Sievers (TMS) model are widely employed to calculate the membrane potential of charged porous membranes in 1-1 electrolyte solutions, but few works with the other kinds of electrolyte solutions have been reported. In this article, membrane potentials for 1-1, 1-2, 2-1 and 2-2 electrolyte solutions have been calculated numerically based on the two models using parameters of concentration, pore radius and surface charge density. The results suggest that equivalent electrolyte concentration is more suitable to characterize the membrane potential in different kinds of electrolyte solutions than electrolyte concentration. Membrane potential approaches to the Nernst potential in the low concentration region, which indicates membrane potential in monovalent cation electrolyte solution is twice as large as that in divalent cation electrolyte solution. In the high concentration region, membrane potential is close to the diffusion potential, which implies membrane potential would be reversed if the diffusion coefficient ratio of coion and counterion is larger than 1.0. While in the intermediate concentration region, membrane potential as a function of electrolyte concentration is almost linear. In the comparison of the SC and TMS models, theoretical predictions by the two models for 1-2, 2-1 and 2-2 electrolyte solutions appear to be similar to those for 1-1 electrolyte solutions reported earlier by Westermann-Clark and Christoforou [3]. The two models coincide with each other when the radius, rp, is less than 5.0 nm and the dimensionless charge density in the pore wall, q0 is less than 1.0. Otherwise, the TMS model would overestimate the membrane potential. Furthermore, the membrane potential shows dependence on the ratio of the volume charge density to equivalent electrolyte concentration, ξf, q0 and rp by the SC model, but only varies with ξf irrespective of q0 and rp by the TMS model. These findings have a significant influence on the establishment of an appropriate theory to evaluate membrane potentials in different electrolyte solutions.
- Published
- 2006
39. Density Functional Theory Study on the Structure and Capillary Phase Transition of a Polymer Melt in a Slitlike Pore: Effect of Attraction
- Author
-
Xiaolin Wang, Guang-Hua Gao, and Yang-Xin Yu
- Subjects
chemistry.chemical_classification ,Quantitative Biology::Biomolecules ,Phase transition ,Capillary action ,Thermodynamics ,Polymer ,Radial distribution function ,Surfaces, Coatings and Films ,Condensed Matter::Soft Condensed Matter ,Correlation function (statistical mechanics) ,symbols.namesake ,chemistry ,Computational chemistry ,Helmholtz free energy ,Materials Chemistry ,symbols ,Density functional theory ,Perturbation theory (quantum mechanics) ,Physical and Theoretical Chemistry - Abstract
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.
- Published
- 2006
40. Grand canonical Monte Carlo and non-equilibrium molecular dynamics simulation study on the selective adsorption and fluxes of oxygen/nitrogen gas mixtures through carbon membranes
- Author
-
Yang-Xin Yu, Guang-Hua Gao, and Shu-Mei Wang
- Subjects
chemistry.chemical_element ,Thermodynamics ,Filtration and Separation ,Permeation ,Biochemistry ,Oxygen ,Nitrogen ,Quantitative Biology::Subcellular Processes ,Molecular dynamics ,Membrane ,chemistry ,Selective adsorption ,Physical chemistry ,General Materials Science ,Graphite ,Physical and Theoretical Chemistry ,Carbon - Abstract
The equilibrium selective adsorption and fluxes of oxygen/nitrogen binary gas mixtures through carbon membranes are investigated at 303 K, respectively, using a grand canonical Monte Carlo simulation and a dual control volume grand canonical molecular dynamics method. The carbon membrane pores are modeled as slit-like pores with a two-dimensional structure where carbon atoms are placed according to the structure of graphite layers. The effect of the membrane thickness, bulk pressure, and pore width on the equilibrium selective adsorption and dynamic separation factor is discussed. Meanwhile a new iteration approach to calculate the flux and dynamic separation factor of binary gas mixtures through membranes is proposed, by which we can simulate the permeation and fluxes of gases through the membranes in the presence of pressure gradient and consider the effect of pressure and composition of low-pressure side in the meantime. The simulated results show that bulk pressure and membrane thickness have no effect on the equilibrium selectivity, but they have a great effect on the fluxes and dynamic separation factors of gases. The pore width impacts the equilibrium selectivity and dynamic separation factors strongly, especially when the pore width is very small. Molecular sieving dominates the separation of oxygen/nitrogen in non-equilibrium simulations. But due to the comparable molecular size of oxygen and nitrogen, we have to modify the carbon membranes in order to improve dynamic separation of atmosphere.
- Published
- 2006
41. Structure and Adsorption of A Hard-Core Multi-Yukawa Fluid Confined in A Slitlike Pore: Grand Canonical Monte Carlo Simulation and Density Functional Study
- Author
-
Fengqi You, Yiping Tang, Yang-Xin Yu, Guang-Hua Gao, and Yi Gui Li
- Subjects
Surface (mathematics) ,Chemistry ,Monte Carlo method ,Yukawa potential ,Thermodynamics ,Surfaces, Coatings and Films ,symbols.namesake ,Grand canonical ensemble ,Correlation function (statistical mechanics) ,Adsorption ,Helmholtz free energy ,Materials Chemistry ,symbols ,Density functional theory ,Physical and Theoretical Chemistry - Abstract
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.
- Published
- 2005
42. Structural and hydrogen bond analysis for supercritical ethanol: A molecular simulation study
- Author
-
Yi-Gui Li, Jichu Yang, Yang-Xin Yu, and Yang Zhang
- Subjects
Ethanol ,Hydrogen bond ,General Chemical Engineering ,Monte Carlo method ,Molecular simulation ,Condensed Matter Physics ,Supercritical fluid ,chemistry.chemical_compound ,Distribution function ,chemistry ,Phase (matter) ,Physical chemistry ,Methanol ,Physics::Chemical Physics ,Physical and Theoretical Chemistry - Abstract
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.
- Published
- 2005
43. Density functional for structures of colloids confined in a slit-like pore
- Author
-
Sheng Fu, Fengqi You, Guang-Hua Gao, and Yang-Xin Yu
- Subjects
Chemistry ,digestive, oral, and skin physiology ,Monte Carlo method ,Yukawa potential ,Radial distribution ,Condensed Matter Physics ,Molecular physics ,Condensed Matter::Soft Condensed Matter ,Colloid ,symbols.namesake ,Colloidal particle ,Quantum mechanics ,Desorption ,Helmholtz free energy ,symbols ,General Materials Science ,Density functional theory - Abstract
A density functional theory is applied to calculating the local density profiles of colloids confined in a slit-like pore as well as the radial distribution functions of bulk colloids. The interaction between the colloidal particles is described using a hard-core Yukawa model. The excess Helmholtz energy functional is a combination of the modified fundamental measure theory of Yu and Wu (2002) for the hard-core contribution and a corrected mean-field theory for the attractive contribution. Comparison with the results from the Monte Carlo simulations shows that the corrected theory improves the density profiles of colloids in the vicinity of contact over the original mean-field theory. Both the present corrected theory and simulations suggest that there are depletion and desorption for the colloid with strong attraction between particles at low temperature.
- Published
- 2005
44. Self-diffusion coefficients of ions in primitive model electrolyte solutions by smart Brownian dynamics simulation
- Author
-
Hong-Bing Shi, Guang-Hua Gao, and Yang-Xin Yu
- Subjects
chemistry.chemical_classification ,Self-diffusion ,Molecular model ,General Chemical Engineering ,General Physics and Astronomy ,Salt (chemistry) ,Thermodynamics ,Radius ,Electrolyte ,Radial distribution function ,Ion ,chemistry ,Brownian dynamics ,Physics::Chemical Physics ,Physical and Theoretical Chemistry - Abstract
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.
- Published
- 2005
45. Density-functional theory of spherical electric double layers and ζ potentials of colloidal particles in restricted-primitive-model electrolyte solutions
- Author
-
Jianzhong Wu, Yang-Xin Yu, and Guang-Hua Gao
- Subjects
Classical mechanics ,Chemical physics ,Chemistry ,General Physics and Astronomy ,Charge density ,Ionic bonding ,Density functional theory ,Electrolyte ,Physical and Theoretical Chemistry ,Poisson's equation ,Electrostatics ,Boltzmann equation ,Ion - Abstract
A density-functional theory is proposed to describe the density profiles of small ions around an isolated colloidal particle in the framework of the restricted primitive model where the small ions have uniform size and the solvent is represented by a dielectric continuum. The excess Helmholtz energy functional is derived from a modified fundamental measure theory for the hard-sphere repulsion and a quadratic functional Taylor expansion for the electrostatic interactions. The theoretical predictions are in good agreement with the results from Monte Carlo simulations and from previous investigations using integral-equation theory for the ionic density profiles and the zeta potentials of spherical particles at a variety of solution conditions. Like the integral-equation approaches, the density-functional theory is able to capture the oscillatory density profiles of small ions and the charge inversion (overcharging) phenomena for particles with elevated charge density. In particular, our density-functional theory predicts the formation of a second counterion layer near the surface of highly charged spherical particle. Conversely, the nonlinear Poisson-Boltzmann theory and its variations are unable to represent the oscillatory behavior of small ion distributions and charge inversion. Finally, our density-functional theory predicts charge inversion even in a 1:1 electrolyte solution as long as the salt concentration is sufficiently high.
- Published
- 2004
46. Density functional study of the adsorption and separation of hydrogen in single-walled carbon nanotube
- Author
-
Guang-Hua Gao, Chong Gu, and Yang-Xin Yu
- Subjects
Nanotube ,Hydrogen ,Renewable Energy, Sustainability and the Environment ,Chemistry ,Energy Engineering and Power Technology ,Thermodynamics ,chemistry.chemical_element ,Monoxide ,Carbon nanotube ,Condensed Matter Physics ,Separation process ,law.invention ,Hydrogen storage ,Fuel Technology ,Adsorption ,law ,Density functional theory ,Physics::Chemical Physics - Abstract
In this work, we report an investigation by means of density functional theory (DFT) of the adsorption of hydrogen and the separation of hydrogen–carbon monoxide mixture in an isolated single-walled carbon nanotube. The theory is based on a perturbative construction of free energy functional for inhomogeneous pure fluid and binary fluid mixture. The reformulated Rosenfeld's fundamental-measure theory using the excess Helmholtz energy density from the Boublik–Mansoori–Carnahan–Starling–Leland equation of state proposed by Yu and Wu (J. Chem. Phys. 117 (2002) 10156) is applied to represent the pure and binary hard-sphere repulsive interaction, and Weeks–Chandler–Andersen perturbation theory is used to build the attractive contribution. The density profiles in three sizes of tubes at 300 K and reduced bulk density from 0.2 to 0.7 for pure hydrogen and hydrogen–carbon monoxide mixture are obtained. The theoretical calculations are in good agreement with the simulation results in this work and other data available in literature. The adsorption of hydrogen and the selectivity of hydrogen–carbon monoxide mixture are predicted from DFT and the adsorption characteristics of the isolated cylindrical wall is discussed.
- Published
- 2004
47. Density functional study of hydrogen adsorption at low temperatures
- Author
-
Guang-Hua Gao, Yang-Xin Yu, and Chong Gu
- Subjects
Quantum fluid ,Hydrogen ,Monte Carlo method ,General Physics and Astronomy ,chemistry.chemical_element ,Thermodynamics ,symbols.namesake ,Adsorption ,chemistry ,Mean field theory ,Helmholtz free energy ,Quantum mechanics ,Path integral formulation ,symbols ,Density functional theory ,Physical and Theoretical Chemistry - Abstract
In substitution of path integral isomorphism of the quantum particle, an effective polymer ring model is proposed in the density functional calculation for hydrogen adsorption in single-walled carbon nanotubes. The excess intrinsic Helmholtz energy for quantum particles includes contributions from hard-sphere repulsion, interatomic bonding and soft attraction. The first two contributions are considered through the method developed by Yu and Wu [J. Chem. Phys. 117, 2368 (2002)], and the last contribution is obtained from mean field approximation using Weeks–Chandler–Anderson potential. The theoretical predictions are in good agreement with Monte Carlo simulation data for the density distributions of the hydrogen molecule inside the tube. In addition, the proposed model is applied to the calculation of the adsorption isotherms of hydrogen at 100 and 150 K. The present model is simpler than the current existing theories for quantum fluids.
- Published
- 2003
48. Prediction of solid–liquid equilibria in mixed electrolyte aqueous solution by the modified mean spherical approximation
- Author
-
Yang-Xin Yu, Guang-Hua Gao, Jean-Luc Daridon, and Bernard Lagourette
- Subjects
Activity coefficient ,Aqueous solution ,Chemistry ,General Chemical Engineering ,General Physics and Astronomy ,Ionic bonding ,Thermodynamics ,Aqueous electrolyte ,Electrolyte ,Spherical approximation ,Condensed Matter::Soft Condensed Matter ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Saturation (chemistry) ,Solid liquid - Abstract
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.
- Published
- 2003
49. Extended test-particle method for predicting the inter- and intramolecular correlation functions of polymeric fluids
- Author
-
Jianzhong Wu and Yang-Xin Yu
- Subjects
Correlation ,Distribution function ,Classical mechanics ,Chemistry ,Present method ,Intramolecular force ,Monte Carlo method ,General Physics and Astronomy ,Density functional theory ,Statistical physics ,Physical and Theoretical Chemistry ,Test particle ,Integral equation - Abstract
The Percus’ test-particle method is extended to predict the inter- and intramolecular correlation functions of polymeric fluids using a density functional theory developed earlier [J. Chem. Phys. 117, 2368 (2002)]. The calculated inter- and intramolecular distribution functions as well as the site–site correlation functions agree well with the results from Monte Carlo simulation for freely jointed hard-sphere chains. Compared with the integral-equation approaches and alternative density functional theories, the present method is free of molecular simulations as input and has the advantage of self-consistency among inter- and intramolecular correlation functions and thermodynamic properties.
- Published
- 2003
50. Density functional theory for inhomogeneous mixtures of polymeric fluids
- Author
-
Jianzhong Wu and Yang-Xin Yu
- Subjects
Adsorption ,Chain (algebraic topology) ,Solid-state physics ,Chemistry ,Monte Carlo method ,Excluded volume ,General Physics and Astronomy ,Thermodynamics ,Density functional theory ,Monotonic function ,Physical and Theoretical Chemistry ,Perturbation theory - Abstract
A new density functional theory is developed for inhomogeneous mixtures of polymeric fluids by combining Rosenfeld’s fundamental-measure theory for excluded volume effects with Wertheim’s first-order thermodynamic perturbation theory for chain connectivity. With no adjustable parameters, theoretical predictions are in excellent agreement with Monte Carlo simulation data for the density distributions and for the adsorption isotherms of hard-sphere chains near hard walls or in slit-like pores. This theory is applied to calculate the force between two parallel hard walls separated by hard-sphere chains at different densities. Calculated results indicate that the chain-mediated force is attractive and decays monotonically with separation at low chain densities, it oscillates at high chain densities and in between, it is attractive at small separation and repulsive at large separation. This new density functional theory is simpler than similar theories in the literature and is directly applicable to mixtures.
- Published
- 2002
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