Recent advances in the research of inorganic nanotubes and fullerene-like nanoparticles

This minireview outlines the main scientific directions in tile research of inorganic nanotubes （1NT） and fullerene-like （IF） nanoparticles from layered compounds, in recent years. In particular, this review describes to some detail the progress in the synthesis of new nanotubes, including those from misfit compounds; core-shell and the successful efforts to scale-up the synthesis of WS2 multiwalt nanotubes. The high-temperature catalytic growth of nanotubes, via solar ablation is discussed as well. Furthermore, the doping of the 1F-MoS2 nanoparticles and its influence on the physiochemical properties of the nanoparticles, including their interesting tribological properties are briefly discussed. Finally, the numerous applications of these nanoparticles as superior solid lubricants and for reinforcing variety of polymers are discussed in brief.     

Structural models of inorganic fullerene-like structures

In the study of fullerene-like structures, some of the more interesting systems are the inorganic cages, made of MoS₂ (usually named inorganic fullerenes), which have many important potential applications as lubricant and catalysts. In the present work, we report calculations for structural models of closed cage of inorganic fullerene-like structures for MoS₂ system. Three cage shapes were found to be the most stable: triangular pyramid, octahedron and dodecahedron. High resolution TEM images of MoS₂ cages structures were calculated to be compared with experimental data. Some examples of triangular pyramid and polyhedron in experimental MoS₂ samples are presented.     

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。     

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。     

Enhancing the hydrogen storage capacity of Pd-functionalized multi-walled carbon nanotubes

We demonstrate that the hydrogen storage capacity of multi-walled carbon nanotubes can be enhanced by polyvinylpyrrolidone functionalization. The polyvinylpyrrolidone acts as a stabilizing agent for Pd-nanoparticles, reduces their size and facilitates their uniform and enhanced loading onto multi-walled carbon nanotubes. According to sorption studies, the polyvinylpyrrolidone capping and consequent nanostructural modification enables 2.3 times more hydrogen adsorption than mere Pd-functionalization of multi-walled carbon nanotubes. Corresponding morphological changes before and after polyvinylpyrrolidone capping, characterized using Raman Spectroscopy, X-ray diffraction, TEM and thermal analysis techniques, are also presented. The results contribute towards increasing the efficiency of hydrogen based sustainable energy sources.     

Titanium-decorated carbon nanotubes as a potential high-capacity hydrogen storage medium

We report a first-principles study, which demonstrates that a single Ti atom coated on a single-walled nanotube (SWNT) binds up to four hydrogen molecules. The first H2 adsorption is dissociative with no energy barrier while the other three adsorptions are molecular with significantly elongated H-H bonds. At high Ti coverage we show that a SWNT can strongly adsorb up to 8 wt % hydrogen. These results advance our fundamental understanding of dissociative adsorption of hydrogen in nanostructures and suggest new routes to better storage and catalyst materials.     

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     

Review of theoretical calculations of hydrogen storage in carbon-based materials

In this paper we review the existing theoretical literature on hydrogen storage in single-walled nanotubes and carbon nanofibers. The reported calculations indicate a hydrogen uptake smaller than some of the more optimistic experimental results. Furthermore the calculations suggest that a variety of complex chemical processes could accompany hydrogen storage and release. Received: 24 August 2000 / Accepted: 15 November 2000 / Published online: 9 February 2001     

Li and Na Co-decorated carbon nitride nanotubes as promising new hydrogen storage media

The capacity of Li and Na co-decorated carbon nitride nanotube (CNNT) for hydrogen storage is studied using first-principles density functional theory. The results show that with two H₂ molecules attached to per Li and four H₂ molecules per Na the Li and Na co-decorated CNNT gains a gravimetric density of H₂ as high as 9.09 wt% via electrostatic interaction without the clustering of the deposited metal atoms (at T=0 K). The average adsorption energy of hydrogen molecule is in the range of 0.09-0.22 eV/H₂, which is suitable for practical hydrogen storage at ambient temperatures.     

Challenges in hydrogen storage

Hydrogen is one possible medium for energy storage and transportation in an era beyond oil. Hydrogen appears to be especially promising in connection with electricity generation in polymer electrolyte membrane (PEM) fuel cells in cars. However, before such technologies can be implemented on a larger scale, satisfactory solutions for on-board storage of hydrogen are required. This is a difficult task due to the low volumetric and gravimetric storage density on a systems level which can be achieved so far. Possibilities include cryogenic storage as liquid hydrogen, high pressure storage at 70 MPa, (cryo)adsorptive storage, or various chemical methods of binding and releasing hydrogen. This survey discusses the different options and the associated advantages and disadvantages.     

Simulation of hydrogen adsorption in carbon nanotubes

Computer simulations are reported of hydrogen adsorption in multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs). The gas-solid interaction was modelled both as pure dispersion forces and also with a hypothetical model for chemisorption introduced in a previous paper (CRACKNELL, R., F., 2001, Phys. Chem. chem. Phys., 3, 2091). A two-centre model for hydrogen was employed and the grand canonical Monte Carlo methodology was used throughout. Uptake of hydrogen in the internal space of a carbon nanotube is predicted to be lower than in the optimal graphitic nanofibre with slitlike pores (provided the gas-solid potential is consistent). Part of the difference arises from the assumption of pore surface area used in converting the raw simulation data to gravimetric adsorption; however, the majority of the differences can be attributed to the curvature of the pore. This reduces the uptake of hydrogen (on a gravimetric basis) in spite of deepening the potential minimum inside the pore associated with dispersion forces. It is concluded that for the uptake of hydrogen in SWNTs of 5–10% reported by Heben (DILLON, A. C., JONES, K. M., BEKKEDAHL, T. A., KIANG, C. H., BETHUNE, D. S., AND HEBEN, M. J., 1997, Nature, 386, 377), gas-solid forces other than dispersion forces are required and most of the adsorption must occur in the interstices between SWNTs.     

碱金属掺杂碳纳米管储氢量差异的理论分析

采用巨正则蒙特卡罗方法模拟锂掺杂单壁碳纳米管阵列（SWCNTA－Single Walled Carbon Nanotube Array）和钾掺杂SWCNTA的物理吸附储氢。重点研究了碱金属原子的种类和掺杂位置对SWCNTA储氢的影响。通过分析碱金属掺杂SWCNTA与氢分子间相互作用的差异及其变化的原因,给出了碱金属掺杂SWCNTA储氢量差异的理论解释,并对今后的研究工作提出了新的建议。     

Torsional mechanics of single walled carbon nanotubes with hydrogen for energy storage and fuel cell applications

Torsional mechanics of single walled carbon nanotubes(SWCNTs) encapsulated with hydrogen molecules was investigated in this study, using the molecular dynamics(MD) simulation approach. The torsional properties of hydrogen stored SWCNTs were crucial for determining the durability and lifetime of SWNCTs-based energy storage and proton exchange membrane fuel cell(PEMFC) applications. The influence of hydrogen storage concentration, SWCNT geometry, vacancy defects, temperature variation and varying boundaries of rotated as well as fixed groups on the torsional mechanics of SWCNT was investigated. The results and conclusions provide an insight into the torsional properties of SWCNTs with hydrogen storage that could be used for the development of SWCNTs-based hydrogen storage devices and PEMFC applications.     

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 %.     

Packing configurations for methane storage in carbon nanotubes

In this paper we investigate methane packing in single-walled carbon nanotubes. We employ classical applied mathematical modelling using the basic principles of mechanics to exploit the Lennard-Jones potential function and the continuous approximation, which assumes that intermolecular interactions can be approximated by average atomic surface densities. We consider both zigzag and spiral configurations formed by packing methane molecules into (9, 5), (8, 8) and (10, 10) carbon nanotubes, and we derive analytical expressions for the interaction potential energy of these configurations. Our findings indicate that for the zigzag configuration for a (9, 5) tube, the potential energy of the system is minimized when the methane molecules simply form a linear chain along the tube axis, but genuine zigzag patterns are found as the tube size increases such as for the (8, 8) and (10, 10) tubes. For the spiral configuration, the potential energy of the system is minimized when the angular spacing is approximately equal to π for the (9, 5) and (8, 8) tubes, and π/2 for the (10, 10) tube. Overall, our results are in good agreement with molecular dynamics simulations in the literature and show that the most energetically efficient packing configuration of the three tubes studied, occurs for a (10, 10) tube with a zigzag packing, while a (10, 10) tube with a spiral packing configuration has the largest free-cavity volume for methane adsorption at higher temperatures.     

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     

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.     

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.     

Internal investigation of saturation carbon nanotubes molecular hydrogen

The electron-energy characteristics of the saturation of the cavity of carbon nanotubes of armchair and zig-zag types with molecular hydrogen are theoretically studied. The calculations are performed based on a model of a molecular cluster with the use of the MNDO and PM3 methods, which proved to be effective in predicting the electronic structure of molecules and periodic solids. Two mechanism of saturation of the cavity of single-walled carbon tubulenes with hydrogen molecules were proposed and examined: (1) the mechanism of surface wetting and (2) the capillary mechanism of filling.