Opening of single-walled carbon nanotubes: evidence given by krypton and xenon adsorption

Adsorption isotherms of krypton between 77 and 93 K and xenon between 110 and 120 K on mechanically-opened single-walled carbon nanotubes (SWNTs) have been measured. The comparison of the results with those obtained under the same conditions on closed nanotubes is discussed. Evidence of adsorption inside the tubes is given through the appearance of an additional adsorbed amount at very low relative pressure on the isotherms. Different orderings are predicted for xenon and krypton, based on their respective adsorbed amounts inside the nanotubes, and on geometrical considerations. Finally, the fraction of opened nanotubes accessible to xenon and krypton was estimated, as well as the impurity content originating from the cutting process.     

Halloysite nanotubes template-induced fabrication of carbon/manganese dioxide hybrid nanotubes for supercapacitors

Ionics - Carbon/manganese dioxide (C/MnO2) hybrid nanotubes were prepared by the successive deposition of carbon and manganese dioxide using natural halloysite nanotubes as template. The...     

碳纳米管吸附去除工业废水中亚甲基蓝的研究

研究了碳纳米管作为一种新型吸附剂去除水中亚甲基蓝。考察了溶液pH值、振荡时间、温度等对亚甲基蓝吸附的影响。溶液pH对亚甲基蓝吸附影响较大,动力学数据显示吸附在8h达到平衡。通过对吸附数据拟合,发现在温度为298—338K和浓度为2.5—12.5mg/L的范围内,碳纳米管对亚甲基蓝的吸附等温线均符合弗仑德里希（Feundlich）兰缪儿（Langmuir）吸附等温式。     

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。     

Routes to the synthesis of carbon nanotube–polyacetylene composites by Ziegler–Natta polymerization of acetylene inside carbon nanotubes

We present a route to synthesize polyacetylene filled multi-walled carbon nanotubes (MCNT) by in situ polymerization. We use supercritical carbon dioxide to fill the nanotubes with toluene and then add the Ziegler–Natta catalyst. In order to assure controlled polymerization inside the nanotube, the catalyst outside is removed before the reaction. The resulting polyacetylene filled nanotubes are characterized by ¹H NMR and scanning electron microscope.     

Monolayer aspects of high-resolution αs-plots

The problem of the estimation of high resolution comparative plots (α_s method) is revised. Adsorption isotherms of Ar (T = 87 K) are simulated (GCMC) on the bundles of closed and opened multiwalled carbon nanotubes. Those materials are chosen in order to observe the influence of porosity on Ar adsorption, and consequently, on the comparative plots. The introduction of the structural heterogeneity (defects in the external and internal walls of osculating and separated nanotubes) is also studied. The monolayer and multilayer parts of adsorption are extracted from the total amount adsorbed for all studied adsorbents and the reference one (the bundle of the ideal 3-layered carbon tubes with very wide diameters). The significant influence of the distance between carbon nanotubes and defects (in the external and internal walls) is observed on the monolayer α_s-plots. In the case of comparative plots calculated for the multilayer adsorption the differences are also visible; however, the expected linear dependence of the amount adsorbed on a porous solid plotted against the amount adsorbed on a reference nonporous solid (the layer-by-layer adsorption occurs on both solid surfaces) in a wide range of relative pressures is not observed. The obtained results demonstrate the complexity of α_s method when both microporosity and surface heterogeneity are present. A comparison of isotherms shows that for the studied adsorbents Ar is sensitive to the appearance of the geometrical and structural defects, even at low coverage.     

Effect of carbon nanotubes addition on thermoelectric properties of Ca3Co4O9 ceramics

Increasing the phonon scattering center by adding nanoparticles to thermoelectric materials is an effective method of regulating the thermal conductivity. In this study, a series of Ca$_{3}$Co$_{4}$O$_{9}/x$ wt.% CNTs ($x=0$, 3, 5, 7, 10) polycrystalline ceramic thermoelectric materials by adding carbon nanotubes (CNTs) were prepared with sol-gel method and cold-pressing sintering technology. The results of x-ray diffraction and field emission scanning electron microscopy show that the materials have a single-phase structure with high orientation and sheet like microstructure. The effect of adding carbon nanotubes to the thermoelectric properties of Ca$_{3}$Co$_{4}$O$_{9}$ was systematically measured. The test results of thermoelectric properties show that the addition of carbon nanotubes reduces the electrical conductivity and Seebeck coefficient of the material. Nevertheless, the thermal conductivity of the samples with carbon nanotubes addition is lower than that of the samples without carbon nanotubes. At 625 K, the thermal conductivity of Ca$_{3}$Co$_{4}$O$_{9}$/10 wt.% CNTs sample is reduced to 0.408 W$\cdot$m$^{-1}\cdot$K$^{-1}$, which is about 73% lower than that of the original sample. When the three parameters are coupled, the figure of merit of Ca$_{3}$Co$_{4}$O$_{9}$/3 wt.% CNTs sample reaches 0.052, which is 29% higher than that of the original sample. This shows that an appropriate amount of carbon nanotubes addition can reduce the thermal conductivity of Ca$_{3}$Co$_{4}$O$_{9}$ ceramic samples and improve their thermoelectric properties.     

CO2活化温度对碳气凝胶结构及氢吸附性能影响

 以间苯二酚(R)和甲醛(F)为前驱体制备出RF碳气凝胶,并利用CO₂气体对其进行活化,通过热重分析(TG)、X射线衍射(XRD)、氢吸附等表征手段研究了活化过程中温度对碳气凝胶微结构及氢吸附性能的影响。结果表明：CO₂活化可使碳气凝胶比表面积大幅提高,且不会影响其微孔网络结构。随着活化温度的升高,碳气凝胶非晶性变得更加明显,失重率显著增加,微孔体积、比表面积及氢吸附量先增后减,有望通过改变CO₂活化温度增加碳气凝胶微孔数量来提高其氢吸附性能。     

Determination of the texture of arrays of aligned carbon nanotubes from the angular dependence of the X-ray emission and X-ray absorption spectra

The properties of materials containing carbon nanotubes depend on the degree of alignment and the internal structure of nanotubes. It is shown that the degree of misorientation of carbon nanotubes in samples can be evaluated from the measurements of the angular dependences of the carbon X-ray emission and carbon X-ray absorption spectra. The CK _α emission and CK X-ray absorption spectra of the array of multiwalled carbon nanotubes synthesized by catalytic thermolysis of a mixture of fullerene and ferrocene are measured. A comparison of the calculated model dependences of the relative intensities of the π and σ bands in the spectra with the experimental results makes it possible to evaluate the degree of misorientation of nanotubes in the sample and their internal texture.     

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.     

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。     

Raman spectroscopy of graphene and carbon nanotubes

This paper reviews progress that has been made in the use of Raman spectroscopy to study graphene and carbon nanotubes. These are two nanostructured forms of sp² carbon materials that are of major current interest. These nanostructured materials have attracted particular attention because of their simplicity, small physical size and the exciting new science they have introduced. This review focuses on each of these materials systems individually and comparatively as prototype examples of nanostructured materials. In particular, this paper discusses the power of Raman spectroscopy as a probe and a characterization tool for sp² carbon materials, with particular emphasis given to the field of photophysics. Some coverage is also given to the close relatives of these sp² carbon materials, namely graphite, a three-dimensional (3D) material based on the AB stacking of individual graphene layers, and carbon nanoribbons, which are one-dimensional (1D) planar structures, where the width of the ribbon is on the nanometer length scale. Carbon nanoribbons differ from carbon nanotubes is that nanoribbons have edges, whereas nanotubes have terminations only at their two ends.     

Hybrid MnO2/CNT nanocomposite sheet with enhanced electrochemical performance via surfactant-free wet chemical route

Ionics - In this work, manganese dioxide (MnO2) were grown onto the surface of multi-walled carbon nanotubes (CNT) forming nanocomposite binder-free sheet, employing wet chemical synthesis method....     

A novel carbon nanotubes/Fe3O4 inorganic hybrid material: Synthesis, characterization and microwave electromagnetic properties

Magnetite particles with nanoscale sizes were self-assembled along multiwalled carbon nanotubes through a simple, effective and reproducible solvothermal method. The morphology, composition and phase structure of as-prepared hybrid materials were characterized by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results showed that denseness, size and crystallinity of magnetite can be altered by controlling the reaction parameters. Magnetization measurement indicated that both coercivity and saturation magnetization increased linearly with increasing magnetite concentration in the hybrid materials. Electromagnetic properties of the carbon nanotubes/magnetite inorganic hybrid materials were measured at 1∼18 GHz. The magnetic loss was caused mainly by ferromagnetic natural resonance, which is in agreement with the Kittel equation. The as-prepared inorganic hybrid materials are believed to have potential applications in the microwave absorbing area.     

On the limiting physical adsorption of hydrogen in carbon materials

The specific features of hydrogen adsorption (and adsorption of other gases) at supercritical temperatures (specifically, the absence of capillary condensation and polymolecular adsorption and the appearance of a maximum in the adsorption isotherm in the pressure range 1–10 MPa) are discussed. Hydrogen adsorption decreases by an order of magnitude as the temperature increases from the critical temperature to the room value. The experimental adsorption isotherms in the supercritical range found in the literature are used to deduce a criterion of limiting hydrogen adsorption at various temperatures. Carbon adsorbents of different types (individual single-wall nanotubes, bundles of such nanotubes, multiwall nanotubes, and carbon fibers) are considered. A model of single graphite plane shows that the limiting hydrogen adsorption is 5 wt % at 77 K and 1 wt % at 293 K. These values can only be approached by adsorption in a material made of individual single-wall nanotubes. Methods to increase the adsorption are proposed.     

Nanotube nanoscience: A molecular-dynamics study

Carbon nanotubes, fullerenes, and other nanostructured carbon materials are now the most important material phases in the field of nanoscience and nanotechnology. We study the structural stabilities and the interconversion of carbon nanotubes and various other carbon nanostructured phases at elevated temperatures as well as under high pressure using the molecular dynamics method combined with a newly parametrized transferable tight-binding model. The model can deal with not only sp² and sp³ covalent bonds but also the interaction between sp² layers, which plays an important role in the structural and electronic properties of carbon nanostructured materials. It is found that, during a thermal transformation process of carbon nanotubes with C₆₀ fullerenes trapped inside into double-walled carbon nanotubes, the outer carbon-nanotube wall is chemically active and forms covalent bonds with inner carbon atoms, and that most vacancies on the initially imperfect outer tube wall are eventually filled with atoms migrated from inner fullerenes. It is also found that external pressure of about 20 GPa induces a variety of structural transformations in carbon nanostructures. On the other hand, pressure of 30 GPa or higher usually results in sp³-rich amorphous carbon materials. Finally, the rotational interlayer friction force in double-walled carbon nanotubes is studied for the system of (4,4)@(9,9), and the torque of the friction force per unit area acting on each nanotube of the system is found to be as small as . This small value indicates the importance of carbon nanostuctured materials not only for nanoelectronics but also for nanometer-scale machines in the future.     

Preparation of carbon nanosheets deposited on carbon nanotubes by microwave plasma-enhanced chemical vapor deposition method

Carbon nanosheets were synthesized by microwave plasma-enhanced chemical vapor deposition method on carbon nanotubes substrate which was treated by hydrogen plasma. The results showed that the diameters of carbon nanotubes first got thick and then “petal-like” carbon nanosheets were grown on the outer wall of carbon nanotubes. The diameters of carbon nanotubes without and with carbon nanosheets were 100-150 and 300-500 nm, respectively. Raman spectrum indicated the graphite structure of carbon nanotubes/carbon nanosheets. The hydrogen plasma treatment and reaction time greatly affected the growth and density of carbon nanosheets. Based on above results, carbon nanosheets/carbon nanotubes probably have important applications as cold cathode materials and electrode materials.     

碳纳米管--一种新的巨电致变形纳米智能材料

纳米机电系统的发展要求智能材料具有大的应变和功率密度，以获得优良的能量转换能力．文章介绍了作者的最新发现：在电场的作用下，碳纳米管能产生巨大电致变形；而且与传统智能材料如铁电体等相比，其体积功率密度和质量功率密度预计可分别提高3个和4个量级，是一种极具潜力的新型智能材料．     

Comparison of different types of polypyrimidine/CNTs/Pt hybrids in fuel cell catalysis

In this paper, we mainly studied the preparation of platinum-containing composite materials with carbon nanotubes wrapped by polypyrimidine-conjugated polymers and the performance of the composites. The polymer-based carbon nanotubes/Pt catalysts were prepared successfully and confirmed by infrared spectroscopy, XPS, XRD, and TEM images. The performance of polypyrimidine/multi-walled carbon nanotubes (MWCNTs)/Pt and polypyrimidine/double-walled carbon nanotubes (DWCNTs)/Pt was compared with the polypyrimidine/single-walled carbon nanotubes (SWCNTs)/Pt. The amount of the loaded Pt on the polypyrimidine/MWCNTs and polypyrimidine/DWCNTs was calculated to be 50.5 wt% and 52.7 wt% respectively. The effective specific surface area of the polypyrimidine/MWCNTs/Pt (45.7 m²/g) and polypyrimidine/DWCNTs/Pt (42.47 m²/g) was observed by electrochemical cyclic voltammetry. These studies strongly imply that the MWCNTs were better candidates than DWCNTs and SWCNTs in the application of polypyrimidine/CNT materials as catalyst for fuel cells.