Ethane Adsorption in Single Walled Carbon Nanotube by Density Functional Theory

Density functional theory (DFT) is used to calculate adsorption of ethane molecules in single walled carbon nanotubes. A compari-son of DFT calculations and grand canonical ensemble Monte Carlo (GCMC) simulations is made first and the two methods are in good agree-ment. Adsorption isotherms and structures of ethane molecules inside the tubes have been studied by DFT for the nanotubes of diameters 0.954, 2.719 and 4.077 nm at 157 K and ambient temperature, 300 K. By using the grand potential, the positions of phase transitions are exactly lo-cated, and the effect of temperature and tube diameter on phase transitions and adsorption is discussed. We found that lowering temperature and increasing the pore size of several nanometer is preferable for the ethane adsorption when temperature is in the range of 157 K—300 K and op-erating pressure reaches several MPa. Layering transitions and capillary condensations are observed at 157 K in two larger pore diameters, while these phase transitions disappear or the hysteres is loops become very narrow at 300 K.

Solvent effects on Diels-Alder reaction in ionic liquids:A reaction density functional study

Extensive experimental studies have been performed on the Diels-Alder(DA)reactions in ionic liquids(ILs),which demonstrate that the IL environment can significantly influence the reaction rates and selectivity.However,the underlying microscopic mechanism remains ambiguous.In this work,the multiscale reaction density functional theory is applied to explore the effect of 1-butyl-3-methylimidazolium hexafluorophosphate([BMIM][PF_(6)])solvent on the reaction of cyclopentadiene(CP)with acrolein,methyl acrylate,or acrylonitrile.By analyzing the free energy landscape during the reaction,it is found that the polarization effect has a relatively small influence,while the solvation effect makes both the activation free energy and reaction free energy decrease.In addition,the rearrangement of local solvent structure shows that the cation spatial distribution responds more evidently to the reaction than the anion,and this indicates that the cation plays a dominant role in the solvation effect and so as to affect the reaction rates and selectivity of the DA reactions.

Design of dual-functional protic porous ionic liquids for boosting selective extractive desulfurization

Porous ionic liquids have demonstrated excellent performance in the field of separation,attributed to their high specific surface area and efficient mass transfer.Herein,task-specific protic porous ionic liquids(PPILs)were prepared by employing a novel one-step coupling neutralization reaction strategy for extractive desulfurization.The single-extraction efficiency of PPILs reached 75.0%for dibenzothiophene.Moreover,adding aromatic hydrocarbon interferents resulted in a slight decrease in the extraction efficiency of PPILs(from 45.2%to 37.3%,37.9%,and 33.5%),indicating the excellent extraction selectivity of PPILs.The experimental measurements and density functional theory calculations reveal that the surface channels of porous structures can selectively capture dibenzothiophene by the stronger electrophilicity(Eint(HS surface channel/DBT)=-39.8 kcal mol^(-1)),and the multiple extraction sites of ion pairs can effectively enrich and transport dibenzothiophene from the oil phase into PPILs throughπ...π,C-H...πand hydrogen bonds interactions.Furthermore,this straightforward synthetic strategy can be employed in preparing porous liquids,offering new possibilities for synthesizing PPILs with tailored functionalities.

Density Functional Theory Study of MoO_3 Molecule Encapsulated inside Single-walled Carbon Nanotubes

The binding energies, geometric structures and electronic properties of molybde- num trioxide （MOO3） molecule encapsulated inside （8, 0）, （9, 0）, （10, 0） and （14, 0） single-walled carbon nanotubes （SWNTs） have been investigated using density functional theory （DFT） method. Due to curvature effect, the calculated binding energy values are different, the variation of which indicated that the stability of MoO3/SWNT systems increases with increasing the radius of SWNTs. At the same time, owing to the presence of MoO3 molecule, the band gap of MoO3/SWNTs systems decreases. The analysis of density of states （DOS） reveals hybridization between C-2p and Mo-4d and between C-2p and O-2p orbitals near the Fermi level, which results in electron transfer from SWNTs to MoO3 molecule. The present computations suggest that electronic properties of SWNTs can be modified by doping MoO3 molecule.

Synergistic effect of carbon nanotube and encapsulated carbon layer enabling high-performance SnS_2-based anode for lithium storage

Tin disulfide(SnS_(2)),due to large interlayer spacing and high theoretical capacity,is regarded as a prospective anode material for lithium-ion batteries.Nevertheless,the poor electron conductivity of SnS_(2) and huge volumetric change during the lithiation/delithiation process lead to a rapid capacity decay of the battery,hindering its commercialization.To address these issues,herein,SnS_(2) is in-situ grown on the surface of carbon nanotubes(CNT)and then encapsulated with a layer of porous amorphous carbon(CNT/SnS_(2)@C)by simple solvothermal and further carbonization treatment.The synergistic effect of CNT and porous carbon layer not only enhances the electrical co nductivity of SnS_(2) but also limits the huge volumetric change to avoid the pulverization and detachment of SnS_(2).Density functional theo ry calculations show that CNT/SnS_(2)@C has high Li^(+)adsorption and lithium storage capacity achieving high reaction kinetics.Consequently,cells with the CNT/SnS_(2)@C anode exhibit a high lithium storage capacity of 837mAh/g after 100 cycles at 0.1 A/g and retaining a capacity of 529.8 mAh/g under 1.0 A/g after 1000 cycles.This study provides a fundamental understanding of the electrochemical processes and beneficial guidance to design high-performance SnS_(2)-based anodes for LIBs.

Single‐atomic Co‐B_(2)N_(2)sites anchored on carbon nanotube arrays promote lithium polysulfide conversion in lithium-sulfur batteries

Due to low cost,high capacity,and high energy density,lithium–sulfur(Li–S)batteries have attracted much attention;however,their cycling performance was largely limited by the poor redox kinetics and low sulfur utilization.Herein,predicted by density functional theory calculations,single‐atomic Co‐B2N2 site‐imbedded boron and nitrogen co‐doped carbon nanotubes(SA‐Co/BNC)were designed to accomplish high sulfur loading,fast kinetic,and long service period Li–S batteries.Experiments proved that Co‐B2N2 atomic sites can effectively catalyze lithium polysulfide conversion.Therefore,the electrodes delivered a specific capacity of 1106 mAh g−1 at 0.2 C after 100 cycles and exhibited an outstanding cycle performance over 1000 cycles at 1 C with a decay rate of 0.032%per cycle.Our study offers a new strategy to couple the combined effect of nanocarriers and single‐atomic catalysts in novel coordination environments for high‐performance Li–S batteries.

The First Principles Study of Li, Al and Ca Doped Zigzag(7,0) Single Walled Carbon Nanotube

We use the ab initio density functional theory to calculate the band structure, density of states, charge transfer, charge density difference, binding energy and vibration frequency. We can see that the conduction band through the Fermi level include SWNT/H_2/Li, SWNT/H_2/Al and SWNT/H_2/Ca, which shows a kind of metallic character. The charge distribution and contour plots of charge difference density of ion/H_2/SWNT show charge transfer between ion and H_2 molecules rather than between H_2 and H_2. Meanwhile, the interaction between Al, Ca and H_2 is weaker than that of Li. We can also prove that the ion is the primary reason to the increase of adsorption energy of hydrogen molecule in SWNT. Finally, we calculate the vibration frequency and don＇t find any imaginary frequency, which proves that the（7,0） SWNT is more stable.

Field emission properties of capped carbon nanotubes doped by alkali metals:a theoretical investigation

The electronic structures and field emission properties of capped CNT55 systems with or without alkali metal atom adsorption were systematically investigated by density functional theory calculation.The results indicate that the adsorption of alkali metal on the center site of a CNT tip is energetically favorable.In addition,the adsorption energies increase with the introduction of the electric field.The excessive negative charges on CNT tips make electron emittance much easier and result in a decrease in work function.Furthermore,the inducing effect by positively charged alkali metal atoms can be reasonably considered as the dominant reason for the improvement in field emission properties.

Interaction of hydrogen molecules on Ni-doped single-walled carbon nanotube

Adsorption of hydrogen molecules on an Ni-doped （8,0） single-walled carbon nanotube （SWNT） is investigated by using first-principles density functional calculations. The result shows that a single Ni atom adsorbed on the bridge site of the tube could cannot dissociate the H2, however it can chemisorb three H2 at most, with the average binding energy per H2 suitable for the hydrogen storage at the room temperature. More H2 would physisorb around an Ni atom weakly. As for the SWNT with an Ni dimer adsorbed, we find that when the H2 approaches the Ni Ni bond, it dissociates without overcoming any barrier and makes bonds with Ni atom.

Structural,curvature and electronic properties of Rh adsorption on armchair single-walled carbon nanotube

This paper systematically studies the rolling effects of the （n, n） single-wall carbon nanotubes （SWCNT） with different curvatures on Rh adsorption behaviours by using density functional theory. The outside charge densities of SWCNTs are found to be higher than those inside, and the differences decrease with the increase of the tube radius. This electronic property led to the discovery that the outside adsorption energies are higher than the inside ones, and that the differences are reduced with the increase of the tube radius. Partial density of states and charge density difference indicate that these strong interactions induce electron transfer between Rh atoms and SWCNTs.

Potentials of classical force fields for interactions between Na^+ and carbon nanotubes

Carbon nanotubes （CNTs） have long been expected to be excellent nanochannels for use in desalination membranes and other bio-inspired human-made channels owing to their experimentally confirmed ultrafast water flow and theoretically predicted ion rejection. The correct classical force field potential for the interactions between cations and CNTs plays a cru- cial role in understanding the transport behaviors of ions near and inside the CNT, which is key to these expectations. Here, using density functional theory calculations, we provide classical force field potentials for the interactions of Na＋/hydrated Na＋ with （7,7）, （8,8）, （9,9）, and （10,10）-type CNTs. These potentials can be directly used in current popular classical soft- ware such as nanoscale molecular dynamics （NAMD） by employing the tclBC interface. By incorporating the potential of hydrated cation-g interactions to classical all-atom force fields, we show that the ions will move inside the CNT and accu- mulate, which will block the water flow in wide CNTs. This blockage of water flow in wide CNTs is consistent with recent experimental observations. These results will be helpful for the understanding and design of desalination membranes, new types of nanofluidic channels, nanosensors, and nanoreactors based on CNT platforms.

Phonon dispersion relations and soft modes of 4 carbon nanotubes

The phonon dispersion relations of three kinds of 4 A carbon nanotubes are calculated by using the density functional perturbation theory. It is found that the frequencies of some phonon modes are very sensitive to the smearing width used in the calculations, and eventually become negative at low electronic temperature. Moreover, two kinds of soft modes are identified for the （5,0） tube which are quite different from those reported previously. Our results suggest that the （5,0） tube remains metallic at very low temperature, instead of the metallie-semiconducting transition claimed before.

Theoretical Characterization of Chiral Carbon Nanotube Encapsulating Ellipsoidal C70

The molecular orientation of ellipsoidal C70 in carbon nanotubes is carefully studied by first principles calculations. Using （14, 7） single-wall carbon nanotube （SWCNT） as a prototype material, we explored that the weak chemical interaction between SWCNT and C70 was the crucial factor to determine the molecular orientation. However, the small energy difference makes the distinguishment of two possible molecular orientations difficult. By simulating scanning tunneling microscope images and optical properties, we found that local electronic states sensitively depended on the molecular orientation of ellipsoidal C70, which provided a practical way of using scanning tunneling microscope to recognize the molecular orientation of ellipsoidal C70.

Molecular interaction mechanism in the separation of a binary azeotropic system by extractive distillation with ionic liquid

Ionic liquids(ILs)have shown excellent performance in the separation of binary azeotropes through extractive distillation[1].But the role of the ionic liquid in azeotropic system is not well understood.In this paper,COSMO-RS model was applied to screen an appropriate IL to separate the binary azeotrope of ethyl acetate(EA)and ethanol and 1-octyl-3-methylimidazolium tetrafluoroborate([OMIM][BF4])was selected.The Quantum Mechanics(QM)calculations and molecular dynamics(MD)simulation are performed to study the interactions between the solvent molecules and[OMIM][BF4],in order to investigate the separation mechanism at the molecular level.The nature of the interactions is studied through the reduced density gradient(RDG)function and quantum theory of Atom in Molecule(QTAIM).Hydrogen bonds and van der Waals interactions are the key interactions in the complexes.The results of MD simulations indicate that the introduction of ILs has a prominent effect on the interaction between the solvent molecules,especially on reducing the number of hydrogen bonds among the solvent molecules.The radial distribution function(RDF)reveals that the interaction between the cation and solvent molecules will increase while the concentration of ILs increases.This paper provides important information for understanding the role of ILs in the separation of the azeotropic system,which is valuable to the development of new entrainers.

Theoretical Study on Ionic Liquid Based on 1-Ethyl-3-MethylImidazolium Cation and Hexafluorophosphate or Tetrafluoroborate

The Hartree-Fock and DFT/B3LYP methods have been employed to investigate the electronic structures of 1-ethyl-3-methyl-imidazolium cation （EMIM＋）, BF4^-, PF6^-, EMIM＋BF4^-, and EMIM＋-PF6^- using the Gaussian-94 soft-package at 6-31＋G（d,p） basis set level for hydrogen, carbon, nitrogen, boron, phosphorus, and fluorine atoms. Comparison of the electronic structures of the lowest energy of EMIM＋- BF4^- and EMIM＋-PF6^- pairs, and single EMIM＋, BF4^- and PF6^- showed that the optimized EMIM＋-BF4^- and EMIM＋-PF6^- pair conformers were BF4^- and PF6^- outside the 5-ring plane between the ethyl group and the methyl group. The cohesion of C H. … F hydrogen bond between cation and anion is reinforced by charge assistance. The interaction energy between EMIM＋ and PF6 is 328.8 kJ/mol at the B3LYP level and 326.6 kJ/mol at the Hartree-Fock level, whereas that between EMIM＋ and BF4 is 353.5 kJ/mol at the B3LYP level and 350.5 kJ/mol at the Hartree-Fock level. The low energy interactions caused by bulky asymmetric EMIM＋, and charge dispersion of cation and anion give rise to the low melting point of ionic liquid EMIM＋-BF4^- and EMIM＋-PF6^-. The two hydrogen bonding models of single hydrogen bond formation, and the hydrogen transfer between C2 in EMIM＋ and F in BF4^- or PF6^- were principally depicted.

DFT Studies on the Isomerization of Butene Double Bond Catalyzed by 1-Butyl-3-methyl-imidazolium in Ionic Liquid

The geometries of reactant, product and transition state of the title reaction have been optimized by using density functional theory (DFT) at the B3LYP/6-31G(d,p) and B3LYP/6- 311++G(d,p) levels. The variations of the bond parameters in the course of reaction were analyzed. The zero point energy corrections were performed by vibrational analysis. The equilibrium states and the transition state were verified according to the number of virtue frequency of geometry. The intrinsic reaction coordinates (IRC) were calculated from the transition state. The calculated results show that the double bond rearrangement of butene catalyzed by 1-butyl-3-methyl-imidazolium cation is a one-step reaction. The forward energy barrier of isomerization from 1-butene to 2- butene is about 193 kJ·mol-1 and the reverse energy barrier about 209 kJ·mol-1 at the B3LYP/6- 31G(d,p) level, which means that the reaction is easy to proceed at or above room temperature.

DFT Calculation of Room Temperature Ionic Liquid 1-Ethyl-3-Methyl-Imidazolium Chlorocuprate (Ⅰ)

The density functional theory （DFT） has been employed to investigate the electronic structures ofEMIM^＋（1-ethyl-3-methylimidazolium＋）, CuCl2^-, Cu2Cl3^- and EMIM^＋-CuCl2^-, EMIM^＋-Cu2Cl3^- pairs. Full optimization and frequency analyses of EMIM^＋, CuCl2^-, Cu2Cl3^-, eight initial EMIM^＋-CuCl2^-, and six initial EMIM^＋-Cu2Cl3^- geometries have been carried out using Gaussian-94 software-package at 6-3 I＋G （d, p） basis set level for hydrogen, carbon, nitrogen, chlorine atoms and the Hay-Wadt effective core potential for copper atoms. The electronic structures of the lowest energy of EMIM^＋-CuCl2^-, EMIM^＋-Cu2Cl3^- pairs, single EMIM^＋, CuCl2^-, and Cu2Cl3^- have been comparatively studied. The calculated results showed that the optimized EMIM^＋-CuCl2^- pair conformer of the lowest energy was five ring moiety parallel to CuCl2^- plane with a distance of around 3.5,A, while EMIM^＋-Cu2Cl3^- pair conformer of the lowest energy was five ring moiety of EMIM^＋ perpendicular to Cu2Cl3^- plane with a distance of around 3.0 ,A between terminal chlorine atoms and 5-ring plane of EMIM^＋. The cohesion between cation and anion is electrostatic interaction and C-H---Cl hydrogen bonds are reinforced by charge assistance. The frequency analyses suggested that all stationary points are minimum points because of absence of imaginary frequency. The low energy of interaction caused by bulky asymmetry of EMIM^＋, and charge dispersion of cation and anion give rise to low melting point of ionic liquids EMIM^＋-CuCl2^-, and EMIM^＋-Cu2Cl3^- . The interaction energy caused by the distance between cations and anions was investigated by single point energy scan.

Ni-Cu bimetallic alloy anchored on nitrogen-doped carbon nanotubes for CO_(2)-to-CH_(4) electrochemical conversion

Electrocatalytic CO_(2) reduction to CH_(4) remains challenging due to multi-electron transfer and intermediates adsorption.Herein,we synthesized electrocatalysts by growing Ni-Cu alloy structure on nitrogen-doped carbon nanotubes(NixCuy-NCNT)for electrocatalytic CO_(2) reduction reaction(CO_(2)RR)via hydrothermal method followed by pyrolysis.The optimized Ni_(1)Cu_(1)-NCNT demonstrated a superior CO_(2)RR performance,achieving 99.7%FECH_(4)(FE=Faradaic efficiency)and 11.54 mA·cm^(−2) current density at−1.2 V vs.reversible hydrogen electrode(RHE),which outperformed single metal counterparts.Its outstanding performance was due to the electrons transferred from Cu to Ni and Ni-Cu alloy shifted the d-band center toward the Fermi level,which was more conducive to the intermediate formation.In situ electrochemical attenuated total reflection(EC-ATR)and density functional theory(DFT)calculations revealed the appearance of *CHO intermediate and the pathway during the CO_(2)RR process.The design of the bimetallic electrocatalyst in this study provides a new perspective for the highly selective reduction of CO_(2).

Microwave-Assisted Confining Growth and Liquid Exfoliation of sp^(3)-Hybrid Carbon Nitride Nano/Micro-Crystals

As one promising carbon-based material,sp^(3)-hybrid carbon nitride has been predicted with various novel physicochemical properties.However,the synthesis of sp^(3)-hybrid carbon nitride is still limited by the nanaoscale,low crystallinity,complex source,and expensive instruments.Herein,we have presented a facile approach to the sp^(3)-hybrid carbon nitride nano/micro-crystals with microwave-assisted confining growth and liquid exfoliation.Actually,the carbon nitride nano/micro-crystals can spontaneously emerge and grow in the microwave-assisted polymerization of citric acid and urea,and the liquid exfoliation can break the bulk disorder polymer to retrieve the highly crystalline carbon nitride nano/micro-crystals.The obtained carbon nitride nano/micro-crystals present superior blue light absorption strength and surprising photoluminescence quantum yields of 57.96% in ethanol and 18.05%in solid state.The experimental characterizations and density functional theory calculations reveal that the interface-trapped localized exciton may contribute to the excellent intrinsic light emission capability of carbon nitride nano/micro-crystals and the interparticle staggered stacking will prevent the aggregation-caused-quenching partially.Finally,the carbon nitride nano/micro-crystals are demonstrated to be potentially useful as the phosphor medium in light-emitting-diode for interrupting blue light-induced eye damage.This work paves new light on the synthesis strategy of sp^(3)-hybrid carbon nitride materials and thus may push forward the development of multiple carbon nitride research.