Search

The present study evaluated the interaction energy values of adsorbed gas molecules by porous nanomaterials and the effects of external magnetic and electric fields on SO2 adsorption in two Y zeolites with Si/Al ratios of ∞ and 3.0 using molecular dynamics simulation. Two types of external (electric and magnetic) fields were applied along the z-axis, and increased SO2 adsorption was observed only in silica zeolite with the electric field. The magnetic field had no significant effect on SO2 adsorption. Noticeably, the external electric field increased the SO2 adsorption by the target materials, and the adsorption capacity was observed to improve compared to the magnetic field. The results of the radial distribution function and the potential of mean force disclose that SO2-Y zeolite affinity enhanced and the adsorption energy is responsible for this observation. Since applying an electric field intensifies the structural ordering of SO2 gas, it may also be involved in the improvement of the adsorption capacity. Moreover, the comparison of the two Y zeolites indicated that the zeolite with a lower Si/Al ratio validated a higher affinity toward SO2, thereby resulting in a more significant adsorption saturation capacity.

Effect of external field on CO2 adsorption into graphene oxide framework (GOF) was studied by molecular dynamics simulation. Two regimes of electric and magnetic field in parallel or perpendicular to the linker direction of the GOF were applied. The major changes in CO2 uptake occurs when a strong electric field is applied on the GOF. Magnetization in the both parallel and perpendicular to the linker direction does not affect significantly on adsorption capacity. Results of radial distribution function and potential of mean force showed that the highest CO2-GOF affinity and adsorption energy is responsible for the highest adsorption capacity. A combined radial and angular distribution function analysis showed that a compact perpendicular ordering near the linker is responsible not only for the increase in gas capacity of the GOF by applying strong electric field in the parallel to the linker direction but also diffusion coefficient and transition time from ballistic to Fickian. Furthermore, adsorption capacity of non-treated and magnetized system is affected by temperature; however, applying a stong electric field on the system leads to an insignificant change by temperature variation. It was also observed that increasing electric field leads to increasing the adsorption capacity by an approximately linear correlation. Applying electric field increases selectivity of the CO2.

The interfacial structures and macroscopic properties of electrical double layer for 1-ethyl-3-methyl-imidazolium phenyl alanine ([EMIM][PHE]), as an amino acid ionic liquid (AAIL), have been investigated by molecular dynamics simulation and compared with conventional [EMIM][PF6] IL. Results of bulk state showed that hydrogen atoms of ring in [EMIM]+ are capable to form hydrogen bond with the nitrogen and oxygen of [PHE]−. The number of these hydrogen bonds enhances if IL is introduced to graphene sheet. Surprisingly, it was observed that anion-anion hydrogen bond is also probable for [EMIM][PHE]. Introducing the AAIL to graphene does not affect number of this anion-anion hydrogen bond. Being in touch with graphene or not, the main correlation regime between anion and cation is the tail-ring for studied systems. It was observed that phenyl ring of [PHE]− acts as an inhibitor for [EMIM]+ to form π-π stacking with graphene. This behavior leads to higher accumulation of [PHE]− than [EMIM]+ in the first layer. In the current study, a responding electrical potential for an assumed supercapacitor was also introduced. Responding potential of [EMIM][PHE] is lower than [EMIM][PF6].

Two amino acid ionic liquids (AAILs) were investigated by molecular dynamics simulation to get effect of polar group at bulk of liquid and adsorb layer of electric double layer. Hydrogen bond plays an important role in this evaluation. Polar group changed hydrogen bond site of the pure bulk. By introducing AAILs on the graphene surface, the total number of hydrogen bonds was increased and hydrogen bond site was changed in the case of common ionic liquid. It was also observed anion-anion self-hydrogen bond is probable for AAILs. Graphene surface decreases the number of this self-hydrogen bonds. Potential of mean force was also obtained to find adsorption or desorption free energy of AAILs near the surface. The interaction of anion with the surface is weakened if anion of AAIL contains polar group. Responsing with lower potential is an important factor in using an IL as an electrolyte in supercapacitors. Polar group decreases the response potential of the AAIL.

Effect of length of linker inter-space was studied on the adsorption capacity of CO2 by graphene oxide framework (GOF). Effect of linker inter-space of 14, 11, and 8 A was studied here. The linker inter-space of 11 A showed the highest CO2 adsorption capacity. A dual-site Langmuir model was observed for adsorption of CO2 and CH4 into the GOF. According to radial distribution function (RDF), facial and central atoms of linker are the dual-site predicted by Langmuir model. Two distinguishable sites of adsorption and parallel orientation of CO2 are the main reasons of high adsorption capacity in 11 A linker inter-space. Gas-adsorbent affinity obtains the orientation of CO2 near the linker. The affinity in the 11 A linker inter-space is the highest. Thus, it forces the CO2 to lay parallel and orient more localized than the other GOFs. In addition, CH4 resulted higher working capacity than CO2 in 14 A. This occurs because of the change in gas-adsorbent affinity by changing pressure. An entrance adsorption occurs out of the pore of the GOF. This adsorption is not as stable as deep adsorption.

Effect of electric or magnetic field on desalination efficiency was studied by molecular dynamics simulation. A restricted double-walled carbon nanotube (CNT) was selected, then strong and weak external field regime were applied on simulated system. Results of simulation showed that strong electric field increases water flow rate two times than untreated system. Magnetization of water decreases water flow rate because of the increase in number of hydrogen bond. In addition, it was observed that applying electric field or magnetization of water completely rejects the ions. In fact, electric field moved back Na+ ions because of the force acting on the ion opposite to the direction of reverse osmotic forces. Magnetization of water leads to a more stable hydration shell around the Na+ ion that prevents passing through the carbon nanotube. In comparison with a single-walled CNT, considering a double-walled CNT enhances the experimental agreement of simulated water flow rate.

The systems composed of metal nanoclusters in ionic liquids are relevant for applications in lubrication, electrochemical devices, catalysis, and chemical processes. The mechanism of solvation and interactions of these systems are not understood at present. In this work, we have simulated iron nanoclusters with different sizes in ionic liquid 1-butyl-1,1,1-trimethylammonium methane sulfonate [N1114][C1SO3] at two temperatures (300 and 500K) and at atmospheric pressure. We have investigated the effects of cluster size and the temperature on some of the thermodynamics, structural and dynamical properties of the systems. Our results also show that the absolute value of solvation energy increases as the nanocluster size increases. Also the absolute solvation energy increases as the temperature increases. It is also shown that the effect of the cluster size is much more than the effect of the temperature. Our structural investigations indicate at least two shells (a double layer) around the nanocluster and the anions are closer to the cluster surface than the cations. The self-diffusion coefficients of cations, anions, and iron clusters have been also presented and discussed in this work.

The role of hydrogen bond interaction on the structural orientation of pure alkanolamines, monoethanolamine (MEA), diethanolamine (DEA), and methyl diethanolamine (MDEA), was under consideration by computer simulation, molecular dynamics simulation as well as density functional theory. Molecular dynamics simulations were carried out at different pressures and temperatures to discover structural stability. A comprehensive force field validation was performed to obtain accurate density. It was also observed that independent of pressure and temperature, MEA molecules prefer head-tail parallel orientation, DEA molecules show both vertical and parallel orientation, and MDEA molecules favor parallel arrangement in liquid state. The probability of hydrogen bond as a substantial intermolecular interaction was also investigated and substantial sites were evaluated. Intermolecular and intramolecular energy, hydrogen bond strength, and transport properties, as well as cluster formation, were investigated to offer an irrefutable proof on structural orientation. Ab initio computation by analyzing frequency, stabilization energy, and electron location function confirmed similar orientation, proposed by molecular dynamics simulation.

Effect of carbon nanotube (CNT) shape on desalination efficiency was investigated by computer simulation. Three shapes of CNT including tubular, cone, and hetero-junction (a combination of two different diameter CNTs which connected by a diverged CNT) shaped were simulated at high pressure (> 50 MPa). For the first time, we placed neutral charge CNT between two inert walls to illustrate support of CNT that is an inert polymer. Cone shaped CNT conducted water ~ 4 times faster than (6,6) CNT and rejected the ions similar to (6,6) CNT. Actually, cone-shaped CNT possesses the shorter residence time and higher number of water in the tube. This is because of the higher capacity and lower energy barrier against water to pass through it. However, hetero-junction CNT showed a slower water conductance because of the formation of water cluster at the large end of CNT that implies a high-energy barrier against water. In addition, H-bond number is also responsible for energy barrier. H-bond number in bulk of water is 4 and should be decreased to 2 to penetrate in the tubular and hetero-junction shaped CNT. Nevertheless, in a cone shaped CNT H-bond number falls down to 3 only at the entrance of the tube.

The effect of methanol group on absorption of SO2 by diamine compound was investigated via density functional theory. It was observed that the presence of methanol group increases the binding energy of absorption. According to the result of binding energy, the di-methanol-diamine (D-b) structure can be the best diamine for SO2 absorption and the results of Gibbs energy verified the most thermodynamically favorable structure. According to the weak energy analysis, the absorption interactions in D-b are both vdW and HB interactions. The result of second-order perturbation energy showed that the interaction of the donor atom of diamine with antibonding orbital of S-O (BD*S) in D-b is the highest which points to the most stable structure. According to molecular frontier orbital analysis, it can be concluded that the absorption of SO2 on the diamines is not very strong and desorption of SO2 would be easier than that the strong chemical absorption.

Two relatively new amino acid ionic liquids (AAILs) were simulated in pure bulk and double layer by molecular dynamics, to investigate how carboxylic group affects thermophysical properties. In this respect, the hydrogen bond plays an important role in determining thermophysical properties of the AAILs. The carboxylic group changes the dominant hydrogen bond site in the molecule. In addition, the presence of a carboxylic group surprisingly leads to anion-anion hydrogen bond interaction. Introducing the AAIL to the graphene nanosheet is accompanied by a decrease in the number of anion-anion hydrogen bonds. Potential of mean force showed that the carboxylic group also decreases the interaction of anion-graphene. The presence of the carboxylic group decreases the response potential (voltage) of the AAIL as an electrolyte for supercapacitor application.

Molecular dynamics simulation study of carbon dioxide-monoethanolamine, CO 2 –MEA, was performed at constant pressure and temperature in a spanning range of CO 2 mole fraction. Since alkanolamine is an industrial solvent to capture gas impurity, investigating the structural analysis and interaction with gas seems substantial. Force field validation was carried out regarding the thermophysical and transport properties of pure MEA at 313 and 333 K. Structural analyses revealed that gas molecules locate among solvent particles by compacting some parts of MEA in order to achieve a position through free spaces of solvent confirmed by atomic Z -density and trajectory. Diffusion coefficient and energy contribution introduced x = 0.036 as dissolving point. The orientation of gas molecules among solvent, hydrogen bond interaction, and coordination number calculations demonstrated a stronger interaction of solute and solvent and its involvement with N–H(N) head of MEA.

In today's world, the tremendous development of science and technology has caused new problems for humans. The non-optimized consumption of fossil fuels may cause irreparable losses (environmental pollution, wide changes in the Earth's climate and The scholars and experts are looking for resources that will gradually replace fossil fuels. The distributed generation (DG) is a growing method for production of electrical energy in electric power systems. In recent years, the use of renewable energy sources in distributed generation systems has been increasing. One of these sources is solar energy. They account for a large share in distributed generation systems day by day. However, given the relatively low voltage of solar cells, there are different ways to connect these resources to load or network. In some cases, low-frequency transformer (50 or 60 Hz) is used to solve this problem. In the other cases, large photovoltaic arrays have been used for this purpose. But, Each of these methods has its own drawbacks. Therefore, considering all the above, an alternative solution to this problem is the use of power electronic transformer (PET) technologies. The power electronic transformers with high-frequency ac link are good alternative to low-frequency transformers. They may mine and transfer power with the static converters in their structure. However, this study aimed to review existing structures and provide a power electronic transformer based optimal structure. PET presented here, consists of three stages, each stage has a separate control system on the need and together can facilitate the transfer of power to the network. It also has the ability to track the maximum power point also.

The effect of temperature and complex dopant composition on oxygen ion conductivity in solid oxide electrolyte fuel cells was investigated by atomistic molecular dynamics simulation. A new electrolyte (Nd 2− x Gd x Zr 2 O 7 ) was selected to study oxygen ion conductivity using three Gd compositions ( x = 0.8, 1.0, and 1.2) in a wide range of temperature ( T = 1273 K–1873 K). MSD results of cations showed these groups of electrolyte are stable at high operating temperature. The first composition ( x = 0.8) had the highest ionic conductivity that was in good agreement with the experimental data. A simple effective model that works with configuration energy of the oxygen crossing plate was applied to explain the observed conductivity trend. The model illustrated the point as well. Increasing Gd concentration decreases existence probability of easy crossing plate. Radial distribution function analysis also confirmed results. Thermal expansion of the electrolyte has a major effect on the selecting of the electrolyte materials; thus, this important factor was also studied. Results showed the first composition had the greatest thermal expansion.

Nd2–xHoxZr2O7 is an ionic conductor for solid oxide fuel cell electrolytes. Temperature and dopant composition are two main factors that affect ionic conductivity of these groups of materials. Accordingly, Nd2–xHoxZr2O7 was studied in a wide range of temperature, 1,173–1,873 K, and dopant composition, x = 0.0–2.0, by molecular dynamics simulation. Arrhenius plots of ionic conductivity in region of low temperature declared that the maximum occurred at composition x = 0.6 (H6). Surprisingly, it was observed that complexity of dopant improved ionic conductivity of the electrolyte. Moreover, radial distribution function confirmed this result. Two types of anions were observed in the electrolyte, which were dynamic oxygen ions (DOIs) and static oxygen ions (SOIs). Mean square displacement (MSD) of DOIs was higher than SOIs and enhanced oxygen ionic conductivity. Migration barrier of Nd2–xHoxZr2O7 varied from 0.68 to 1.22 eV that was in the range of a good solid oxide electrolyte. Nd1.2Gd0.8Zr2O7 (G8) and Y0.2Zr0.9O2.1 (Y2) were simulated and their results of simulations were compared with H6. Order of ionic conductivity at low temperatures was H6 > Y2 > G8. Another important factor of electrolyte is thermal expansion. Thermal expansion of Nd2–xHoxZr2O7 was around a constant value in the studied temperature range.

Electric double layer (EDL) supercapacitors, using ionic liquid electrolytes, have been receiving a great deal of attention in response to the growing demand for energy storage systems. In the present study, the nanoscopic structure of amino acid ionic liquids (AAILs) as biodegradable electrolytes near a neutral graphene surface was studied by molecular dynamics (MD) simulation. In order to explore the influence of the anion type and structure, the effect of the alkyl side-chain length of amino acids on the EDL was investigated. The results for the AAILs, composed of 1-ethyl-3-methylimidazolium ([EMIM]) cations near alanine ([ALA]) and isoleucine ([ILE]) anions, were compared to a conventional electrolyte, [EMIM][PF6]. A lower mobility of AAIL compared to [EMIM][PF6], with diffusions as low as 10−11 m2 s−1, was observed. The structural results demonstrated a layered structure near the surface and most of the adsorbed imidazolium cation rings lay flat on the graphene surface. Both MD and quantum computations were performed to shed light on the charge behavior of AAIL electrolytes. As the current results demonstrate, an increase in the anion side-chain length leads to a decrease in both the number of adsorbed ions on the surface and the thickness of the first adsorbed layer. More impressively, it was observed that a low charge concentration in the EDL of AAILs is due to more side–side interactions. This remarkable feature could introduce AAILs as more efficient electrolyte materials than conventional [EMIM][PF6].