Selection of single-walled carbon nanotubes according to both their diameter and chirality via nanotweezers

Diameter- and chirality-dependent interactions between aromatic molecule-based nanotweezers and single-walled carbon nanotubes (SWNTs) are revealed by density functional theory calculations. We found that the threshold diameter of selected SWNTs is determined by the end-to-end distance of the nanotweezer. Large-diameter SWNTs are preferred by a nanotweezer with an obtuse folding angle, whereas small-diameter SWNTs are favored by a nanotweezer with an acute folding angle. The adsorption can be further stabilized by the orientational alignment of the hexagonal rings of the nanotweezer and the SWNT sidewall. Therefore, by taking advantage of the supramolecular recognition ability of the aromatic molecule-based nanotweezer, SWNTs can be enriched with both controllable diameter and chirality.      

Soluble carbon nanotubes and their applications

Carbon nanotubes (CNTs) have been the forefront of nanoscience and nanotechnology due to their unique electrical and mechanical properties and specific functions. However, due to their poor solubility in solvents, the applications using the materials have been limited. Therefore, strategic approaches toward the solubilization of CNTs are important in wide fields including chemistry, physics, biochemistry, biology, pharmaceuticals, and medical sciences. In this article, we summarize: (i) the strategic approaches toward the solubilization of CNTs using chemical and physical modifications, (ii) nanocomposites of CNTs and biological molecules including DNA, (iii) formation of CNTs with topological structures, (iv) separation of metallic and semiconducting nanotubes, (v) the preparations of films and fibers of CNTs and hybrid materials of CNTs and organic and inorganic molecules.     

Electrochemically functionalized carbon nanotubes and their application to rechargeable lithium batteries

Electrochemical polymerization of N-vinyl carbazole (VC) on carbon nanotube (CNT) films was studied by cyclic voltammetry (CV) in LiClO4/acetonitrile solutions. Comparing the cyclic voltammograms recorded on a blank Pt electrode with those obtained when single- or multi-walled carbon nanotube (SWNT or MWNT) films were previously deposited onto the Pt electrode, a downshift of the VC reduction peak potential is observed in the latter case. The influences of monomer concentration, type of solvent, and supporting electrolyte on the polymerization conditions and electrochemical properties of these composite materials are also investigated. The morphological aspects of poly(N-vinyl carbazole) (PVC)-functionalized CNTs are revealed by transmission electron microscopy (TEM) studies. A covalent functionalization of carbon nanotubes with PVC is invoked as a result of attenuated total reflection infrared (ATR-IR) spectroscopic studies. Using PVC-functionalized CNTs as a positive electrode and an electrolytic solution containing LiPF6, the charge-discharge characteristics of the rechargeable lithium cells are determined. High specific discharge capacity (approximately 45 and 115 mA h g(-1)) is reported for PVC-functionalized single- and multi-walled carbon nanotubes, respectively.     

Carbene-functionalized single-walled carbon nanotubes and their electrical properties

Pure metallic single-walled carbon nanotubes (m-SWCNTs) are very desirable for many electrode and interconnecting applications. However, the lack of reliable processing techniques to sort m-SWCNTs from the as-synthesized SWCNT samples is an obstacle to these applications. The effects of carbene-based covalent functionalization on the electrical properties of an isolated m-SWCNT, a semiconducting (s)-SWCNT, and a mixture network of both m- and s-SWCNTs are reported. For the first time, a semiconducting-to-metallic SWCNT transition upon dichlorocarbene functionalization is observed. Interestingly, the transition is reversible upon thermal annealing under ambient conditions. The electrical properties of m-SWCNTs remain largely unaffected whereas the on-state conductivity of s-SWCNTs is greatly reduced by this process, in agreement with the relevant theoretical predictions. These findings could pave the way for fabricating large-scale SWCNT-based interconnects and electrodes in full-carbon integrated circuits.     

Mechanical properties of carbon nanotubes and their polymer nanocomposites

More than 10 years have passed since carbon nanotubes (CNT) have been found during observations by transmission electron microscopy (TEM). Since then, one of the major applications of the CNT is the reinforcements of plastics in processing composite materials, because it was found by experiments that CNT possessed splendid mechanical properties. Various experimental methods are conducted in order to understand the mechanical properties of varieties of CNT and CNT-based composite materials. The systematized data of the past research results of CNT and their nanocomposites are extremely useful to improve processing and design criteria for new nanocomposites in further studies. Before the CNT observations, vapor grown carbon fibers (VGCF) were already utilized for composite applications, although there have been only few experimental data about the mechanical properties of VGCF. The structure of VGCF is similar to that of multi-wall carbon nanotubes (MWCNT), and the major benefit of VGCF is less commercial price. Therefore, this review article overviews the experimental results regarding the various mechanical properties of CNT, VGCF, and their polymer nanocomposites. The experimental methods and results to measure the elastic modulus and strength of CNT and VGCF are first discussed in this article. Secondly, the different surface chemical modifications for CNT and VGCF are reviewed, because the surface chemical modifications play an important role for polymer nanocomposite processing and properties. Thirdly, fracture and fatigue properties of CNT/polymer nanocomposites are reviewed, since these properties are important, especially when these new nanocomposite materials are applied for structural applications.     

A facile method to fabricate silica-coated carbon nanotubes and silica nanotubes from carbon nanotubes templates

Silica-coated multiwalled carbon nanotubes (MWCNTs) have been prepared by the sol–gel polymerization of tetraethoxysilane (TEOS) in the presence of the acid-oxidized MWCNTs at room temperature, followed by oxidizing the MWCNTs templates at high temperature in air to produce hollow silica nanotubes. The thickness and architectures of silica shell were well controlled by rationally adjusting the concentration of TEOS, and by adding cationic surfactant as a structure-directing agent. These results also give a clear answer to prove the fact that the structures of spherical silica particles can be fully “copied” to the coating shell and the wall of silica nanotubes when prepared by the same method as the synthesis of silica particles in the presence of templates.     

Dispersion of functionalized multi-walled carbon nanotubes in multi-walled carbon nanotubes/liquid crystal nanocomposites and their thermal properties

A novel liquid crystal functionalized multi-walled carbon nanotubes (LC-MWNTs)/2-methyl-N,N′-bis(4′-methoxy benzoyloxy)-terephthalamide liquid crystal (LC) nanocomposite (LC-MWNTs/LC) was prepared via solution blend. The dispersion and thermal property of the nanocomposites with different loadings of LC-MWNTs (0.1-1 wt.%) were investigated using SEM, TGA and DSC. The results show that the dispersion of LC-MWNTs in LC matrix is more homogeneous than purified MWNTs. The decomposition temperature of nanocomposites exhibits obvious decrease at first and then increase with increasing concentration of LC-MWNTs, which is lower than that of LC for 0.1-0.4 wt.% LC-MWNT loadings and higher than that of LC for 0.5-1 wt.% LC-MWNT loadings. The addition of LC-MWNTs has little effects on the texture of smectic mesophase. These results illustrate the LC-MWNTs/LC nanocomposites, which have lower melting point and higher decomposition temperature than those of LC by adding adequate amount of LC-MWNTs, show a wide temperature range of mesophase and high thermostability. The increased mesophase temperature region of LC materials will be beneficial to their practical applications.     

Preparation of CdS doped carbon nanotubes and their electrochemical properties

A CdS doped carbon nanotube sol was synthesised by the sol-gel technique and applied to a titanium plate to synthesise a composite electrode. Energy dispersion X-ray spectroscopy and X-ray diffraction analysis confirmed that the electrodes contain CdS. Scanning electron microscopy revealed that the carbon nanotubes were uniformly dispersed on the surface of the plate. A two-chamber microbial fuel cell was constructed using the electrode as the anode, flexible graphite as the cathode and glucose solution as the substrate in the anode chamber. The effects of CdS dose, glucose concentration and temperature on the cell efficiency and organic degradation have been analysed. At 313 K, the two-chambered fuel cell possessed the optimum output voltage of 906 mV, with a power of 19·6 mW m^?2 and a removal rate of 81% for chemical oxygen demand in treatment of wastewater. The composite electrode was found to be stable and to perform reproducibly.     

An attempt to prepare carbon nanotubes by carbonizing polyphosphazene nanotubes with high carbon content

Polyphosphazene nanotubes with about 20 nm in inner diameter and 100-200 nm in outer diameter were fabricated easily and then carbonized at 800 °C in a nitrogen atmosphere. Scanning electron microscopy and transmission electron microscope results showed that the bulk morphology of polyphosphazene nanotubes was retained after carbonization. The carbon content of the carbonized samples reached 93.28%. X-ray diffraction and Raman spectrum showed that the carbonized samples had low graphitization state. The present method can be used for a mass production of carbon nanotubes.     

Nano-silver modified carbon nanotubes to reinforce the copper matrix composites and their mechanical properties

In ensuring the effective load transfer of carbon nanotubes (CNTs) reinforced copper (Cu)-based composites, good and stable interface contact is a key factor. Powder electrodeposition technology is used in the present study to coat silver (Ag) nanoparticles on CNTs for the first time. Subsequently, by ball milling and spark plasma sintering, uniform distribution of CNTs in the Cu matrix and tight Cu/C interface bonding are successfully achieved. It is found that Ag nanoparticles with a size of 5 nm are evenly embedded in the surface of CNTs. The results reveal that the agglomeration of CNTs is prevented by the addition of Ag nanoparticles and the adhesion between CNTs and Cu matrix is enhanced by the formation of coherent interface. Further, the load transfer of composite materials is effectively realized by the pinning effect of Ag particles on CNTs. The tensile strength, elongation, and conductivity of the 0.75 CNT-Ag/Cu samples were 314 MPa, 24.8%, and 93.6% IACS, respectively, which are 40.1%, 818%, and 3.3% higher than those of the CNT/Cu samples, respectively. The present method provides a new direction for the uniform coating powder materials and the synergistic strengthening of metal matrix composites.     

Field-emission characteristics of carbon nanotubes and their applications in photonic devices

Based upon the field-emission investigation of carbon nanotubes, several prototype devices have been suggested that operate with low swing voltages with sufficiently high current densities. Characteristics that allow improved current stability and long operating lifetime as electrical and opto-electronic devices are presented. The aim of this paper is to illustrate the useful characteristics of carbon nanotubes and their possible applications.     

PEGylation of double-walled carbon nanotubes for increasing their solubility in water

Polyethylene glycol (PEG) functionalized double-walled carbon nanotubes (DWNTs) have been synthesized by a [2 + 1] cycloaddition reaction and characterized by transmission electron microscopy, atomic force microscopy, Raman spectroscopy, thermal gravimetric analysis, and UV-visible spectroscopy. Functionalization affords a large increase in the aqueous solubility of DWNTs. The saturated concentrations of DWNTs functionalized with diazido-terminated PEG₈₀₀ (with a molecular weight of 800) and azido-terminated PEG₇₅₀ monomethylether (with a molecular weight of 750) are very similar—0.36 and 0.37 mg/mL (DWNTs equivalent concentration), respectively.     

氨基化多壁碳纳米管的制备及其在复合材料中的应用

采用不同链长的乙二胺(EDA)、己二胺(HMDA)和癸二胺(DMDA)对多壁碳纳米管(MWCNTs)进行了修饰.利用红外光谱、拉曼光谱、透射电镜及X射线光电子能谱对二元胺修饰的MWCNTs的化学结构进行了表征.结果表明:二元胺可以有效地修饰MWCNTs.经胺化修饰后,MWCNTs-EDA、MWCNTs-HMDA、MWCNTsDMDA表面的N元素含量可分别达到3.52%、4.18%和2.88%,表明在相同的氨化条件下,己二胺的接枝率最高.进一步采用紫外-可见吸收光谱及全能稳定性分析仪对不同链长的二元胺修饰的氨基化MWCNTs在有机溶剂中的分散性进行了半定量的表征.结果显示:氨基化修饰有效改善了碳纳米管在极性溶剂中的分散稳定性,其中己二胺修饰的MWCNTs在乙醇中的分散稳定性最好.将MWCNTs-HMDA引入到传统的炭纤维/环氧树脂复合材料体系中,复合材料的冲击性能及弯曲性能均有较大提高.     

脂肪酸修饰多壁碳纳米管及其摩擦性能研究

采用硫酸和硝酸混合酸对催化裂解法(CVD法)制备的多壁碳纳米管(MWNTs)进行纯化,然后运用硬脂酸对碳纳米管表面进行修饰,并研究了硬脂酸修饰后的碳纳米管的表面状况以及作为润滑油添加剂的摩擦学行为.实验结果表明,在硫酸催化剂作用下,通过化学反应碳纳米管能够被硬脂酸包覆,而且硬脂酸修饰的碳纳米管作为润滑油添加剂能够显著提高成品油的减摩抗磨性能.在1000N载荷下硬脂酸在成品油中的质量百分比为0.4%和多壁碳纳米管质量百分比为0.15%～0.2%时,成品油的摩擦学性能最佳.     

多壁碳纳米管的表面修饰及其在溶剂中的分散性

利用高温催化裂解生长多壁碳纳米管,用硝酸氧化使其表面羧酸化,并经酰氯化后与十二烷基胺反应形成表面酰胺化,通过红外、核磁、微量热天平等方法进行表征.结果表明:硝酸氧化后的碳纳米管在水等强极性溶剂中有良好的分散性;酰胺化后,十二烷基脂肪链使碳纳米管表面极性大为降低,因此在氟仿等弱极性溶剂中有良好的分散性.     

碳纳米管的等离子体功能化及其聚苯胺复合材料的制备

采用等离子体技术对碳纳米管(CNTs)功能化,而后与苯胺原位聚合制备CNTs/聚苯胺(PANI)复合材料。电导测试结果表明:相对于CNTs的强酸氧化法(0.936S/cm),等离子体处理更易获得高电导率的复合材料(2.86S/cm)。相应的最佳等离子体工艺参数为:处理功率50W、时间5min、压力0.08Torr、温度110℃、磁场线圈电流0.08A及电极距离5cm。SEM观察发现:聚合后,CNTs的光滑表面转变成粗糙结构,同时管径增加了80nm。XRD、FTIR及Raman结果均证实:PANI被均匀包覆于CNTs的表面。