Hydrogen storage in BC3 composite single-walled nanotube:a combined density functional theory and Monte Carlo investigation

This paper applies a density functional theory(DFT) and grand canonical Monte Carlo simulations(GCMC) to investigate the physisorptions of molecular hydrogen in single-walled BC 3 nanotubes and carbon nanotubes.The DFT calculations may provide useful information about the nature of hydrogen adsorption and physisorption energies in selected adsorption sites of these two nanotubes.Furthermore,the GCMC simulations can reproduce their storage capacity by calculating the weight percentage of the adsorbed molecular hydrogen under different conditions.The present results have shown that with both computational methods,the hydrogen storage capacity of BC 3 nanotubes is superior to that of carbon nanotubes.The reasons causing different behaviour of hydrogen storage in these two nanotubes are explained by using their contour plots of electron density and charge-density difference.     

Study of titanium adsorption on perfect and defected BC3 nanotubes using density functional theory

Density functional theory calculations were used to study the titanium (Ti) adsorption on perfect and defected (4, 0) BC₃ nanotubes, considering Stone–Wales and vacancy defects. The binding energy values for these nanotubes were larger than the corresponding values for carbon nanotubes. The charge transfer from the Ti atom to nanotube was observed for all systems studied. The most exothermic binding process occurred for the Ti adsorption on a native V_B defect, which showed minimum structural deformation with respect to a perfect BC₃ tube. In the case of a nanotube with a reconstructed carbon vacancy, the adsorption of Ti generated a half-metallic anti-ferromagnet. The results obtained in this paper are relevant for spintronics and hydrogen adsorption applications.     

BC3复合纳米管的储氢性能研究

采用巨正则蒙特卡罗方法（GCMC）研究了BC3复合纳米管的物理吸附储氢性能,获得了该纳米管在不同温度和压强下的吸附等温线,及其在不同条件下的物理储氢吸附量,并和相应的碳纳米管进行了对比研究。结果表明,BC3纳米管在所有条件下的储氢性能均优于相应的碳纳米管,因而它是一种比碳纳米管更强的氢存储介质,并从纳米管和H2分子以及H2分子和H2分子之间的平均总相互作用能的分布情况等因素出发解释了这两种纳米管有不同储氢行为的原因。     

Interaction of Methane with Single-Walled Carbon Nanotubes： Role of Defects,Curvature and Nanotubes Type

We investigate the interaction of single-walled carbon nanotubes （SWCNTs） and methane molecule from the first principles. Adsorption energies are calculated, and methane affinities for the typical semiconducting and metallic nanotubes are compared. We also discuss role of the structural defects and nanotube curvature on the adsorption capability of the SWCNTs. We could observe larger adsorption energies for the metallic CNTs in comparison with the semiconducting CNTs. The obtained results for the zig zag nanotubes with various diameters reveal that the adsorption energy is higher for nanotubes with larger diameters. For defected tubes the adsorption energies are calculated for various configurations such as methane molecule approaching to the defect sites pentagon, hexagon, and heptagon in the tube surface. The results show that the introduce defects have an important contribution to the adsorption mechanism of the methane on SWNTs.     

Entropy-driven adsorption of carbon nanotubes on (0 0 1) and (1 1 1) surfaces of CeO2 islands grown on sapphire substrate

According to the aim to compose combinatorial material by adsorption of carbon nanotubes onto the structured CeO₂ surface the interaction of the armchair (5,5) and zigzag (8,0) nanotubes with the (0 0 1) and (1 1 1) surfaces of CeO₂ islands have been investigated by theoretical methods. The thermodynamics of the adsorption were studied at the low surface coverage region. The interaction energy between the nanotube and the different CeO₂ surfaces shows significant increase when the size of the interface reaches 7–8 unit cells of CeO₂ and it remains unchanged in the larger interface region. However, the entropy term of the adsorption is significantly high when the distances of CeO₂ islands are equal to 27 nm (adsorption of armchair (5,5) nanotube) or 32 nm (adsorption of zigzag (8,0) nanotube). This property supports adsorption of nanotubes onto CeO₂ surfaces which possesses a very specific surface morphology. A long-wave vibration of nanotubes was identified as background of this unexpected phenomenon. This observation could be applicable in the development of such procedures where the nanotube adsorption parallel to the surface is aimed to perform.     

单壁BN纳米管和碳纳米管物理吸附储氢性能的理论对比研究

采用巨正则蒙特卡罗方法(GCMC)研究了单壁氮化硼纳米管(SWBNNTs)和单壁碳纳米管(SWCNTs)的物理吸附储氢性能,主要对比研究了纳米管的管径、温度和手性对二者物理吸附储氢量的影响. 研究结果表明：在低温下,SWBNNTs的物理吸附储氢性能优于相应的SWCNTs;但是随着温度的升高,二者的物理吸附储氢性能差别越来越小,在常温下,SWBNNTs不具备有比SWCNTs更强的物理吸附储氢性能,而是和相同条件下的SWCNTs相差不大,只是在高压下的物理吸附储氢量稍稍大于SWCNTs,并给出了合理的理论解释 关键词： 巨正则蒙特卡罗方法(GCMC) 单壁氮化硼纳米管(SWBNNTs) 单壁碳纳米管(SWCNTs) 储氢     

Adsorption of hydrogen on normal and pentaheptite single wall carbon nanotubes

Density functional calculations of the physisorption of molecular hydrogen and the dissociative atomic chemisorption on the external surface of hexagonal and pentaheptite carbon nanotubes, have been carried out. Physisorption binding energies are near 100 meV/molecule and are similar on metallic and semiconducting nanotubes. Full coverage of the nanotube with one molecule per graphitic hexagon decreases the binding energy per molecule. Chemisorption binding energies per H atom are larger on pentaheptites than on hexagonal carbon nanotubes. The molecular physisorption and dissociative chemisorption states on pentaheptites have very similar total energies (some chemisorbed states are even slightly more stable than the physisorbed states), while on hexagonal carbon nanotubes molecular physisorption is more stable than dissociative chemisorption. However, a substantial energy barrier has to be overcome to go from physisorption to dissociative chemisorption in both types of nanotubes.     

A Theoretical Study of a Single-Walled ZnO Nanotube as a Sensor for H2O Molecules

We have studied the property of single-walled ZnO nanotubes with adsorbed water molecules, and theoretically designed a new sensor for detecting water molecules using single-walled ZnO nanotubes using a combination of density functional theory and the non-equilibrium Green's function method. Details of the geometric structures and adsorption energies of the H₂O molecules on the ZnO nanotube surface have been investigated. Our computational results demonstrate that the formation of hydrogen bonding between the H₂O molecules and the ZnO nanotube, and adsorption energies of the H₂O molecules on the ZnO nanotube are larger than the adsorption energies of other gas molecules present in the atmospheric environment. Moreover, the current-voltage curves of the ZnO nanotube with and without H₂O molecules adsorbed on its surface are calculated, the results of which showed that the H₂O molecules form stable adsorption configurations that could lead to the decrease in current. These results suggest that the single-walled ZnO nanotubes are able to detect and monitor the presence of H₂O molecules by applying bias voltages.     

A Theoretical Study of a Single-Walled ZnO Nanotube as a Sensor for H_2 O Molecules

We have studied the property of single-walled ZnO nanotubes with adsorbed water molecules, and theoretically designed a new sensor for detecting water molecules using single-walled ZnO nanotubes using a combination of density functional theory and the non-equilibrium Green's function method. Details of the geometric structures and adsorption energies of the H 2 O molecules on the ZnO nanotube surface have been investigated. Our computational results demonstrate that the formation of hydrogen bonding between the H 2 O molecules and the ZnO nanotube, and adsorption energies of the H 2 O molecules on the ZnO nanotube are larger than the adsorption energies of other gas molecules present in the atmospheric environment. Moreover, the current-voltage curves of the ZnO nanotube with and without H 2 O molecules adsorbed on its surface are calculated, the results of which showed that the H 2 O molecules form stable adsorption configurations that could lead to the decrease in current. These results suggest that the single-walled ZnO nanotubes are able to detect and monitor the presence of H 2 O molecules by applying bias voltages.     

Role of Stone–Wales defects on the functionalization of (8,0) single wall carbon nanotubes by the amine group: Ab initio study

Using first-principle calculations, we have investigated the chemical functionalization of (8,0) zigzag single wall carbon nanotubes (SWNTs) by the amine group on Stone–Wales (SW) defects. The binding of NH₂ with the defective (8,0) nanotube was explored and the preferential grafting sites have been identified. On the other hand, the modifications induced by SW defect and functional groups in the structural and electronic properties of (8,0) SWNT have also been investigated. The role of SW defects in the chemical reactivity of carbon nanotubes was well identified.     

Strange non-chaotic attractors in a state controlled-cellular neural network-based quasiperiodically forced MLC circuit

The adsorption energies, bond order, atomic charge, optical properties, and electrostatic potential of nitrogen molecules of armchair single-walled carbon nanotubes (SWCNTs) and nitrogen-doped single-walled carbon nanotubes (N-SWCNTs) were investigated using density functional theory (DFT). Our results show that adsorption of the \(\hbox {N}_{2}\) molecules on the external wall of a nanotube is more effective than on the internal wall in SWCNTs. The results show that \(\hbox {N}_{2}\) molecule(s) are weakly bonded to SWCNTs and N-SWCNTs through van der Waals-type interactions. The interaction of \(\hbox {N}_{2}\) molecules with SWCNTs and N-SWCNTs is physisorption as the adsorption energy and charge transfer are small, and adsorption distance is large. The electronic transitions from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) (\(\hbox {H}\rightarrow \hbox {L}\)) have the maximum wavelength and the lowest oscillator strength. The potential sensor on the surface of pristine SWCNTs and N-SWCNTs for the adsorption of \(\hbox {N}_{2}\) molecule(s) is investigated. The N-loaded single-walled carbon nanotube is introduced as a better \(\hbox {N}_{2}\) molecule(s) detector when compared with SWCNTs.     

Interaction of alkanethiols with single-walled carbon nanotubes: First-principles calculations

We report the results of our first-principles study based on density functional theory on the interaction of alkanethiols with both defected and defect-free single-walled carbon nanotube (SWCNT). The adsorption energies are calculated for various configurations such as alkanethiol molecule approaching to defect sites heptagon, hexagon, and pentagon in defective tube, and another case where the alkanethiol approaching to hexagon in defect-free nanotube. The calculated results showed that alkanethiols are rather strongly bound to the outer surface of both the defected and defect-free carbon nanotubes with the binding energy of about −50.58 kcal/mol, consistent with the experimental result. We also find that alkanethiols prefer to be adsorbed on the hexagon ring site of defect-free nanotube. Furthermore, the effect of alkanethiols chain length on the adsorption of alkanethiols on carbon nanotubes has been investigated, and the obtained results reveal that the longer alkanethiols bind rather more strongly to the nanotube surface.     

B（N）掺杂单壁碳纳米管的Al原子吸附性能的第一性原理研究

采用基于密度泛函理论的平面波赝势方法和广义梯度近似,对未掺杂、掺B、掺N的碳纳米管(CNT)不同位置上Al原子的吸附进行了几何优化,计算了吸附Al、掺杂前后CNT的能带结构、态密度、差分电荷密度、电荷布居数和吸附能.计算结果表明,掺B使CNT形成缺电子状态,利于具有自由电子的Al原子的吸附结合,可显著提高Al在金属性的(5,5)CNT和半导性的(8,0)CNT外壁的吸附能;掺杂N形成多电子状态,在费米能级附近半满的施主能级也利于填充Al的价电子,改善Al在(5,5)CNT和(8,0)CNT外壁的吸附结合性 关键词： 密度泛函理论 单壁碳纳米管 B(N)掺杂 Al原子吸附     

Molecular dynamics simulations of hydrogen adsorption/desorption by palladium decorated single-walled carbon nanotube bundle

Utilising molecular dynamics simulations, the hydrogen molecules adsorption isotherms of the (8,?0) palladium decorated single-walled carbon nanotube (SWNT) were obtained. The hydrogen adsorption was studied on the external, interstial and internal surfaces of the SWNT bundle at several temperatures ranging from 77 to 400?K. The results were compared with the bare single-walled carbon nanotube bundle under the same conditions. The decorated carbon nanotube bundle hydrogen adsorption was significantly higher than that of the bare one. The hydrogen desorption and readsorption were studied using temperature as the readsorption/desorption variable. The rate constants were calculated for the hydrogen desorption at different temperatures. The calculated decorated SWNT bundle hydrogen desorption activation energy was higher than that for the bare SWNT bundle. The calculated activation energies for the hydrogen desorption in both nanotube bundles specified the temperature dependency of hydrogen desorption.     

Hydrogen adsorption and desorption in carbon nanotube systems and its mechanisms

The hydrogen physisorption properties in single-walled carbon nanotube (SWNT) based materials were characterized. The SWNTs were highly purified and three useful pores for hydrogen physisorption were activated. Hydrogen was physisorbed in intra-tube pores at room temperature and the capacity was estimated to be about 0.3–0.4 wt.% at room temperature. The adsorption capacity can be explained by the Langmuir model. The intra-tube pores have large adsorption potential and this induces hydrogen physisorption at comparatively higher temperatures. This fact indicates the importance of fabricating sub-nanometer ordered pores for this phenomena. PACS 51.30.+i; 51.90.+r; 81.05.Tp; 81.07.De     

单壁碳纳米管低温及常温下储氢行为的模拟计算研究

采用巨正则系综蒙特卡罗方法, 通过含有此方法模块的GULP软件, 系统地研究了扶手椅式单壁碳纳米管在低温和常温下的储氢性能, 给出了5种半径的扶手椅管在液氮温度(77 K)和常温(280 K)下的吸附等温线, 同一管径在不同温度不同压强下氢分子在碳纳米管中的分布构型图等. 对77 K和280 K下不同压强不同管径的碳纳米管储氢能力做了较为全面的对比分析, 最后根据模拟计算的结果, 对碳纳米管储氢能力的强化提出了一些建设性意见.     

Passively Q-switched laser operation in a composite Nd:YVO<Subscript>4</Subscript>/Nd:YVO<Subscript>4</Subscript>/Nd:YVO<Subscript>4</Subscript> crystal with a single-walled carbon nanotube saturable absorber

By using a piece of single-walled carbon nanotube saturable absorber, the performance of the passively Q-switched composite Nd:YVO₄ laser has been demonstrated for the first time. The maximum average output power and the shortest pulse width are 1220 mW and 103 ns at the incident pump power of 5.04 W for a 10% transmission of the output coupler. The highest pulse repetition rate of 415.6 kHz and the largest single-pulse energy of 2.94 μJ are also obtained. The composite Nd:YVO₄ crystal has more excellent laser performance than the normal Nd:YVO₄ crystal at 1064 nm.     

Simulation of chemical adsorption of hydrogen by carbon nanotubes

The hydrogen chemical adsorption on a single-walled carbon nanotube (6, 6) has been studied by quantum-chemical computer simulation. Different variants of hydrogen coverage of the nanotube have been considered, and the dependences of the adsorption energy and the nanotube strain energy on the coverage density have been found. In addition, the adsorption has been considered on both the outer and inner surfaces of the nanotube wall. It has been established that some adsorption conformations are unstable, which leads to fracture of the nanotubes.     

Theoretical study of the adsorption of CO2 on tungsten carbide nanotubes

The adsorption of CO₂ on the single-walled tungsten carbide nanotubes has been investigated employing density functional theory method. The center of a hexagon of tungsten and carbon atoms in sites on tungsten carbide nanotube surfaces is the most stable adsorption site for CO₂ molecule, with a binding energy of −1.68 eV (−38.72 kcal/mol) and a WO binding distance of 1.95 Å. Furthermore, the adsorption of CO₂ on the single-walled carbon nanotubes has been investigated. Our first-principles calculations predict that the CO₂ adsorptive capacity of tungsten carbide nanotubes is about quadruple that of carbon nanotubes. This might have potential for greenhouse gas detection and bioremediation.     

Effect of passivating Al<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films on MnO<Subscript>2</Subscript>/carbon nanotube composite lithium-ion battery anodes

MnO₂/carbon nanotube composite electrodes for Li-ion battery application were directly coated with ultrathin thicknesses of aluminum oxide film by atomic layer deposition (ALD). The non-reactive Al₂O₃ layer not only provides a stable film to protect the manganese oxide and carbon nanotubes from undesirable reaction with the electrolyte but also restrains the volume change strain of manganese oxide during cycling. The first cycle Coulombic efficiency of coated samples was increased to different extents depending on the coating thickness. In the following cycles, the coated electrodes denote high specific capacity, good capacity retention ability, and perfect rate charge/discharge performance.