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.     

氢在多壁碳纳米管中的吸附储存

利用巨正则系综蒙特卡罗(GCMC)的方法模拟了氢在多壁碳纳米管中的吸附,氢气分子之间、氢气分子和碳原子之间的相互作用势能采用Lennard-Jones势能模型。模拟了不同结构参数(管内径、管壁数、管壁间距)的多壁碳纳米管在77K和298K下的吸附等温线,分析了多壁碳纳米管的管内径、管壁数以及管壁间距对吸附性能的影响。模拟结果表明:多壁碳纳米管的管壁数和管壁间距对吸附性能的影响较明显;管壁数越少,管壁间距越大,其吸附性能越好;多壁碳纳米管的管内径对其吸附性能的影响甚微。     

微孔对单壁纳米碳管储氢性能的影响

用巨正则蒙特卡罗分子模拟方法研究了单壁纳米碳管中的微孔即单壁纳米碳管基本孔-内管腔和管间孔对单壁纳米碳管储氢性能的影响.与低温下氮气吸附实验结果的比较发现单壁纳米碳管的内管腔是吸附的主要位置.分析单壁纳米碳管内管腔中吸附势的叠加和利用效率，发现管径为2nm左右时单壁纳米碳管内管腔的储氢容量最高.当单壁纳米碳管阵列的管间距增加时，单壁纳米碳管的管间孔也会成为有效的氢吸附位. 关键词： Monte Carlo方法 单壁纳米碳管 储氢 微孔     

Tunable adsorption on carbon nanotubes

We investigated the adsorption of a single atom, hydrogen and aluminum, on single-wall carbon nanotubes from first principles. The adsorption is exothermic, and the associated binding energy varies inversely as the radius of the zigzag tube. We found that the adsorption of a single atom and related properties can be modified continuously and reversibly by the external radial deformation. The binding energy on the high curvature site of the deformed tube increases with increasing radial deformation. The effects of curvature and radial deformation depend on the chirality of the tube.     

Effect of atomic hydrogen adsorption on the transport characteristics of semiconducting carbon nanotubes

The effect of atomic hydrogen adsorption on the conduction and diffusion properties of carbon nanotubes of zigzag type in an external electric field is considered. The model of adsorption of atomic hydrogen on the surface of single-walled carbon nanotubes of zigzag type is based on the single-impurity periodic Anderson model. The theoretical calculation of the diffusion coefficient and electrical conductivity of carbon nanotubes of zigzag type doped with hydrogen atoms is carried out in the relaxation time approximation. It has been revealed that the electrical conductivity and electron diffusion coefficient decrease with increasing concentration of adsorbed hydrogen atoms. It has been shown that the dependence of the electrical conductivity and the diffusion coefficient on the amplitude of the constant electric field at the constant concentration of hydrogen adatoms is nonlinear.     

单壁碳纳米管储氢的第一原理分子动力学模拟

本文用第一性原理平面波赝势方法模拟研究了手性单壁碳纳米管与氢分子的相互作用,考察了碳纳米管直径对储氢性能的影响。对单壁碳纳米管储氢的模拟结果表明: (1)物理吸附时,H2可以吸附在空腔内,也可以吸附在管与管之间的空隙中,纳米管内部的氢吸附力均高于管外,而“完好无损”的H2分子不能够穿过管壁而进入管内。(2)化学吸附时,碳纳米管对氢的吸附首先出现在管的边缘附近,碳纳米管局部会发生形变,SWCNTs的张力会随C-H键的增加而增大,系统不稳定。（3）随着直径的增加,纳米管内、外的氢吸附力差异减小。     

单壁碳纳米管储氢的第一原理分子动力学模拟

本文用第一性原理平面波赝势方法模拟研究了手性单壁碳纳米管与氢分子的相互作用,考察了碳纳米管直径对储氢性能的影响.对单壁碳纳米管储氢的模拟结果表明:(1)物理吸附时,H2可以吸附在空腔内,也可以吸附在管与管之间的空隙中,纳米管内部的氢吸附力均高于管外,而“完好无损”的H2分子不能够穿过管壁而进入管内.(2)化学吸附时,碳纳米管对氢的吸附首先出现在管的边缘附近,碳纳米管局部会发生形变,SWCNTs的张力会随C-H键的增加而增大,系统不稳定.(3)随着直径的增加,纳米管内、外的氢吸附力差异减小.     

NMR spectroscopy of hydrogen adsorption on single-walled carbon nanotubes after exposure to high pressure

Hydrogen storage properties of single-walled carbon nanotubes (CNTs) after exposure to a pressure of 14.3 MPa are studied by (1)H nuclear magnetic resonance spectroscopy. The nanotubes were carefully pre-characterized using inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy (TEM), and Raman spectroscopy. We have shown previously that at ambient temperature in the pressure range from 0 to 1.5 MPa, hydrogen adsorption is fast and reversible and must be described as physisorption. However, exposure to a much higher pressure (14.3 MPa) of hydrogen leads to slower desorption kinetics where longer exposure causes greater hydrogen uptake. Our data suggest that interstitial sites and the tube interior may be identified as these strong adsorption sites.     

Chemisorption of hydrogen by carbon nanotubes

Chemisorption of hydrogen by carbon nanotubes (CNTs) is studied by thermodynamics and kinetics methods. Expressions are derived for the adsorption isotherm and desorption kinetics. Methods for determining chemisorption parameters are developed. The partial free energy of binding of hydrogen with a CNT (3.6 eV) is determined. It is shown that residual products of synthesis are removed from CNTs as a result of prolonged annealing at high temperatures. The capacity of a CNT relative to chemisorbed hydrogen is esti mated at 4 mass %.     

Concentration dependent magnetism induced by hydrogen adsorption on graphene and single walled carbon nanotubes

We performed first principles calculations to study magnetic properties of hydrogenated graphene and single-walled carbon nanotubes (SWNTs) with different hydrogen concentrations. The hydrogen adsorptions on graphene and SWNTs generate localized states and accordingly flat bands near the Fermi level, opening substantial gaps. The magnetic properties of the compounds depend on hydrogen concentration. At high hydrogen concentration, the flat band splits into spin-up and spin-down branches located above and below the Fermi level, respectively, making the systems to have spontaneous magnetization. However, the spin-up and spin-down branches of the flat band are energetically degenerated at low hydrogen concentration and the systems are therefore nonmagnetic. This result is understandable from the point of view of direct interaction between unpaired π electrons of adjacent hydrogen-adsorption sites.     

A model of the multiple adsorption of hydrogen atoms on the surface of carbon nanotubes

A model of the multiple adsorption of atomic hydrogen on the surface of single-walled carbon nanotubes of the zigzag and arm-chair types was constructed. The adsorption model is based on the Anderson periodic model. An analytic equation for the band structure of carbon nanotubes with adsorbed hydrogen atoms was obtained, and the special features of this structure were studied. The dependence of the band structure of carbon nanotubes on the concentration of adsorbed hydrogen atoms was analyzed. The model constructed can be used to study adsorption of other univalent atoms on the surface of carbon particles.     

Amino acid adsorption on single-walled carbon nanotubes

We investigate and discuss the adsorption of a few amino acids on (3,3) carbon nanotubes and on graphite sheets through calculations within density functional theory. Results show weak binding of the biomolecules on both substrates, but through generally favourable adsorption pathways. Zwitterion adsorption through the charged amine and carboxylate groups are bound stronger to the nanotube surface in comparison to their nonionic counterparts, as well as on histidine, phenylalanine, and cysteine side chain groups fixed in specific orientations. Binding strengths on graphite suggest dissimilar trends for amino acid interactions with increasing nanotube diameter.     

氢气分子在沸石中的吸附模拟研究

采用巨正则蒙特卡罗方法模拟了氢气在沸石中的吸附行为,并采用Dubinin-Astakhov微孔分析方法,分析了沸石结构对储氢量大小的影响,总结了影响储氢量大小的物理因素,该工作有利于指导合理的设计与合成储存材料,为改善材料储氢能力提供了有力的理论支撑. 关键词： 储氢 吸附等温线 巨正则蒙特卡罗     

Brightening of triplet dark excitons by atomic hydrogen adsorption in single-walled carbon nanotubes observed by photoluminescence spectroscopy

Adsorption and desorption of atomic hydrogen on single-walled carbon nanotubes were observed by photoluminescence spectroscopy. A satellite peak appeared at the lower energy side of the E11 photoluminescence emission peak after exposure to atomic hydrogen and then disappeared after annealing at 300?°C in vacuum. The energy difference between the satellite peak and E11 peak was 40-80 meV, depending on the tube diameter. The satellite peak was attributed to the triplet dark exciton that became optically active because of the effectively enhanced spin-orbit interaction induced by adsorbed hydrogen atoms.     

Quasi-one-dimensional liquid hydrogen confined in single-walled carbon nanotubes

H₂ molecules confined in single-walled carbon nanotubes were studied using molecular dynamics simulations and ab initio calculations. It was found that at zero-temperature, H₂ molecules with low density tended to condense. Increasing the linear density of the H₂ molecules confined in the tube, various quasi-one-dimensional solid lattices were observed at low temperature. Heating the lattices above room temperature, molecular H₂ liquids with varying densities were observed. The quenching behavior of the H₂ fluids was examined. PACS 61.46.+w; 78.67.Bf     

Electrochemically decorated carbon nanotubes for hydrogen sensing

Low-density networks of single-wall carbon nanotubes have been modified by palladium nanoparticles using an electrochemical method. A major advantage of this approach is that it allows for selective metal deposition on the electrically contacted nanotubes, whereas the remaining substrate surface and the non-contacted tubes remain essentially unaffected. The Pd-decorated networks function as effective hydrogen sensors enabling the detection of hydrogen concentrations as low as 10 ppm at room temperature. The electrochemical metal deposition scheme is promising for the development of sensor arrays suitable for analysing gas mixtures.     

Study on the electronic structure and hydrogen adsorption by transition metal decorated single wall carbon nanotubes

The ground state geometry and electronic structure of various 4d transition metal (TM) atom (Y, Zr, Nb and Mo) decorated single wall carbon nanotubes (SWCNTs) are obtained using density functional theory and the projector augmented wave (PAW) method. We found a systematic change in the adsorption site of the transition metal atom with increasing number of d electrons. We also predicted that Y and Zr decorated SWCNTs are metallic whereas Nb and Mo decorated SWCNTs are semiconducting. From detailed electronic structure and Bader charge analysis we found that the systematic variation of the adsorption site with the number of d electrons is related to the decreasing amount of charge transfer from the TM atom to the SWCNT along the 4d series. We have also studied the hydrogen adsorption capabilities of these decorated SWCNTs to understand the role of transition metal d electrons in binding the hydrogen molecules to the system. We found that metallic SWCNT + TM systems are better hydrogen adsorbers. We showed that the hydrogen adsorption by a TM decorated SWCNT will be maximum when all the adsorptions are physisorption and that the retention of magnetism by the system is crucial for physisorption.     

Chemisorption of atomic hydrogen in graphite and carbon nanotubes

An orthogonal tight-binding model of the carbon-hydrogen interaction was modified to deal with the different hybridization states of atomic hydrogen on carbon surfaces, without explicitly including charge self-consistency. The resulting model has great flexibility and computational efficiency, generally with a good quantitative accuracy. The non-self-consistent C-H model was tested by calculating structural properties of small hydrocarbons and simple polymers, and against ab initio results of H binding to both perfect and defective graphite. The model was employed to study the chemisorption properties and dynamics of atomic hydrogen on perfect and defective surfaces of graphite and carbon nanotubes.     

Hydrogen adsorption on N-decorated single wall carbon nanotubes

Using density functional theory and molecular dynamics we found that N-decorated single walled (8,0) carbon nanotubes are potential high capacity hydrogen storage media. This system could store up to 6.0 wt% hydrogen at 300 K and ambient pressure, with average adsorption energy of −80 meV/(H₂). Nitrogen coverage was C₈N.     

碳纳米管在储氢上的应用

氢能是一种理想的能源载体,而经济有效的储氢手段是氢能实现规模应用急需解决的关键问题之一。碳纳米管在存储氢气上表现出来的独特性质,使其最有希望成为一种新的高效的储氢材料。从实验、理论研究两个方面总结了前人在碳纳米管储氢上的研究成果,并对碳纳米管储氢吸附方式,吸附量影响因素等方面做出分析。最后指出为实现碳纳米管储氢大规模应用仍需做的一些基础性研究工作。