CVD synthesis and purification of single-walled carbon nanotubes on aerogel-supported catalyst

Single-walled carbon nanotubes (SWNTs) were synthesized by disproportionation of carbon monoxide on an aerogel-supported Fe/Mo catalyst. A simple acidic treatment followed by an oxidation process produced a high purity (>99%) of SWNTs. The nanotubes obtained are bundled SWNTs and free of amorphous-carbon coating. Several factors that affect the yield and the quality of the SWNTs were also studied. This method shows great promise for large-scale production of SWNTs. Received: 30 August 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002     

Gas-dynamic consideration of the laser evaporation synthesis of single-wall carbon nanotubes

The abundance of carbon single-wall nanotubes (SWNTs) in soot synthesized by pulsed laser evaporation of graphite is studied over a wide range of synthesis conditions. The derived SWNT growth time-scale appears to be much longer than any characteristic time-scale in a simplified model of the relaxation of a high-pressure hot condensing gas bubble in a background atmosphere. It is concluded that SWNT nucleation and growth take place in relaxed, condensed, thermalized evaporation products at an optimal temperature between 850-1250 °C at a rate of few 7m length per second, which is consistent with a condensed state "precipitation" mechanism for the SWNT formation.     

碳纳米管晶格振动模及拉曼光谱的研究进展

本文介绍了碳纳米管的结构特征和晶格振动模的理论研究 ,综述了不同方法生长的多壁碳纳米管和单壁碳纳米管拉曼光谱的研究进展。另外 ,还简单描述了单壁碳纳米管的应用前景     

Single-walled carbon nanotube fibers, films and balls

Well-defined fibers and films of single-walled carbon nanotubes (SWNTs) with high purity and narrow diameter distributions were obtained from the strand-like raw soot produced by a dc arc-discharge method. These architectures made up of SWNTs have very uniform smooth surfaces. When the strand-like product was placed on a silicon substrate, dipped into water, treated ultrasonically, and then dried in air, another interesting architecture, an SWNT ball, was obtained. This ball-like structure could also be found on the surface of purified SWNTs. We propose that the surface tension of water and the interaction between SWNTs and silica sphere played the key role in the ball (SWNTs outside and silica sphere inside) formation process.     

Comparative analysis of various methods of purification of single-walled carbon nanotubes

A comparative analysis of the purification methods for single-walled carbon nanotubes (SWNTs) obtained by electric-arc-discharge synthesis is carried out. The purification methods include air oxidation of the initial material at various temperatures, treatment and/or oxidation in solutions of inorganic acids, microfiltration of the suspension of the initial and/or oxidized materials, and various combinations of these methods. The purity of the SWNTs obtained is determined with the help of Raman spectroscopy. It is shown that the best results can be obtained using a purification method including the following consecutive stages: treatment and oxidation of the initial material in nitric acid, microfiltration of the suspension of the oxidized material in aqueous solutions of surface-active substances through track membranes, drying, air oxidation, and vacuum annealing at various temperatures. The purity of the SWNTs obtained attains 70–80%.     

Synthesis of single-walled carbon nanotubes in oxy-fuel inverse diffusion flames with online diagnostics

A novel technique for synthesis of single-walled carbon nanotubes (SWNTs) in diffusion flames is presented, as is a diagnostic tool that can provide online information about nanotube size, number density, and purity. An inverse diffusion flame with a high stoichiometric mixture fraction (Z_st) is used to produce SWNTs with an average length of 1 μm. The high Z_st flame allows nanotubes to be produced in a fuel-rich region that is void of soot and polycyclic aromatic hydrocarbons (PAH). In addition, by operating as an inverse diffusion flame the carbon nanotubes (CNTs) are not exposed to oxygen and thus, can be collected downstream. Consequently, this flame provides a potential approach to large-scale synthesis of pure SWNTs. In addition, a differential mobility analyzer (DMA) is employed as an online diagnostic tool. The DMA can distinguish between excess catalyst particles and CNTs due to the differences in their electrical mobilities. Thus, the presence of CNTs as well as their size, number density, and purity relative to excess catalyst particles can be identified from the size distribution of the aerosol sampled downstream of the flame. This tool allows for rapid identification of the effect of changing process variables on nanotube growth and thus, the production process can be quickly optimized.     

Microwave-induced electrophilic addition of single-walled carbon nanotubes with alkylhalides

We report the microwave-induced electrophilic addition of single-walled carbon nanotubes (SWNTs) with alkylhalides using Lewis acid as a catalyst followed by hydrolysis. The reaction results in the attachment of alkyl and hydroxyl groups to the surface of the nanotubes. This rapid and high-energy microwave radiation is found to be highly efficient for this reaction, which only needs as low as several minutes. The resulting nanotubes were characterized with FTIR, UV-vis-NIR, Raman, TGA, TEM and AFM. It demonstrates that iodo-alkanes show higher reaction activity with SWNTs than chloro- and bromo-alkanes.     

催化剂比例对单壁碳纳米管制备的影响

采用电弧放电法以Y/Ni为催化剂制备了单壁碳纳米管 ,研究了不同催化剂比例对制备产物的影响。获得了不同激发波长下 (476 5～ 1 0 6 4nm)单壁碳纳米管的拉曼光谱 ,采用图表法对径向呼吸模的谱峰进行了认定。结果表明 :样品中碳管的直径分布在 1 2～ 1 6nm之间 ,直径在 1 43nm附近的碳管居多。催化剂的比例只是影响碳管的产额 ,对其直径分布的影响很小     

Donor doping of single-walled carbon nanotubes by filling of channels with silver

The channels of single-walled carbon nanotubes (SWNTs) are filled with metallic silver. The synthesized nanocomposites are studied by Raman spectroscopy and optical absorption spectroscopy, and these data indicate a substantial modification of the electronic structure of the nanotubes upon their filling. Moreover, X-ray photoelectron spectroscopy shows that the incorporation of the metal leads to a change in the work function of SWNTs due to the Fermi level upshift and to the transfer of an electron density from inserted nanoparticles to the nanotube walls. Thus, the filling of the channels with silver results in donor doping of the nanotubes.     

Multi-functionalized single-walled carbon nanotubes as tumor cell targeting biological transporters

Multi-functionalized single walled carbon nanotubes (SWNTs) were prepared and applied as tumor cell targeting biological transporters. A positive charge was introduced on SWNTs to get high loading efficiency of fluorescein (FAM) labeled short double strands DNA (20 base pairs). The SWNTs were encapsulated with the folic acid modified phospholipids for active targeting into tumor cell. The tumor cell-targeting properties of these multi-functionalized SWNTs were investigated by active targeting into mouse ovarian surface epithelial cells. The experimental results show that these multi-functionalized SWNTs have good tumor cell targeting property.     

Standing or lying C70s encapsulated in carbon nanotubes with different diameters

Single-walled carbon nanotubes (SWNTs) encapsulating C₇₀s, so-called C₇₀ peapods, were synthesized in high yield by a vapor-phase doping method. Raman spectra, high resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) measurement indicate that the tube diameter is one of the important factors to determine the orientation of C₇₀ molecules inside the SWNTs. SWNTs with different diameters give different alignment of C₇₀ molecules. The lying orientation is favorable over the standing orientation in thin nanotube, i.e. 1.36 nm nanotubes, whereas the standing orientation is favorable in thick nanotubes, i.e. 1.49 and 1.61 nm nanotubes.     

Exciton localization of single-walled carbon nanotubes revealed by femtosecond excitation correlation spectroscopy

Photoluminescence (PL) dynamics in single-walled carbon nanotubes (SWNTs) has been studied by the femtosecond excitation correlation method with a 150 fs time resolution. The SWNT samples were synthesized by different methods and suspended in gelatin films or D2O solutions. The PL dynamics of SWNTs depends on the local environment surrounding the SWNTs rather than the synthesis methods. The very weak temperature dependence of tauPL and the environment-dependent tauPL reveal that the PL relaxation process is dominated by the interplay between free excitons and weakly localized excitons.     

具有优异储氢性能的高质量单壁纳米碳管的合成

高纯度单壁纳米碳管的合成是应用研究和实际应用的基础和关键,提出了一种氢等离子电弧方法,在适当的生长促进剂的作用下,能大量制备出高纯度的单壁纳米碳管。选用宏观数量的单壁纳米碳管,进行适当预处理,在室温及约１００ａｔｍ下进行储氢实验,发现该材料的储氢容量可达（４．２－４．７）ｗｔ％,经过５次循环实验,其储氢容量先略有下降,随后便稳定不变,这些初步实验结果表明,单壁纳米碳管是一种很有前途的储氢材料。     

Raman spectroscopy of carbon nanotubes

The use of Raman spectroscopy to reveal the remarkable structure and the unusual electronic and phonon properties of single wall carbon nanotubes (SWNTs) is reviewed comprehensively. The various types of Raman scattering processes relevant to carbon nanotubes are reviewed, and the theoretical foundations for these topics are presented. The most common experimental techniques used to probe carbon nanotubes are summarized, followed by a review of the novel experimental findings for each of the features in the first order and second order Raman spectra for single wall carbon nanotubes. These results are presented and discussed in connection with theoretical considerations. Raman spectra for bundles of SWNTs, for SWNTs surrounded by various common wrapping agents, and for isolated SWNTs at the single nanotube level are reviewed. Some of the current research challenges facing the field are briefly summarized.     

A facile and efficient gas phase process for purifying single-walled carbon nanotubes

Reproducible, low loss and high-yield purification process for single-walled carbon nanotubes (SWNTs) was developed by coupling of oxidation in wet air and treatment with gas phase nitric acid. Oxidation in wet air can burn out the carbonaceous particles and gas phase nitric acid treatment can etch away the catalytic metals. The as-synthesized SWNTs and the purified SWNTs were characterized by field emission scanning electron microscopy, high resolution transmission electron microscopy, Raman spectrophotometer and thermal gravimetric analysis. It was shown that such a facile and controllable gas phase process for purifying SWNTs can lead to the minimal losses and minimal destruction of SWNTs, thus highly purified SWNTs without amorphous carbon and with very low metal content were obtained.     

以Y/Ni为催化剂制备的单壁碳纳米管的拉曼光谱研究

采用电弧放电法以Y/Ni为催化制备了单壁碳纳米管（SWNTs），对样品进行了扫描电镜、透射电镜和拉曼光谱的研究。所制备的样品中单壁碳纳米管的含量较高。对单壁碳纳米管的共振拉曼散射增强效应进行了观察，随激光波长的不同，单壁碳纳米管的拉曼光谱也随之变化，尤其是低频区径向呼吸模的变化比较明显。利用布里渊区折叠法计算了单壁碳纳米管的电子态密度曲线，根据SWNTs电子态密度尖峰之间的能量差、管子的直径和呼吸模频率建立了一个图表，并对SWNTs的呼吸模进行了归属。分析结果表明：样品中单壁碳纳米管的直径分布在0.79-1.76nm范围，金属管和半导体管均存在，并且直径在1.45nm附近的碳管居多。     

Synthesis, integration, and electrical properties of individual single-walled carbon nanotubes

High-quality single-walled carbon nanotubes (SWNTs) are synthesized by chemical vapor deposition (CVD) of methane on silicon-dioxide substrates at controlled locations using patterned catalytic islands. With the synthesized nanotube chips, microfabrication techniques are used to reliably contact individual SWNTs and obtain low contact resistance. The combined chemical synthesis and microfabrication approaches enable systematic characterization of electron transport properties of a large number of individual SWNTs. Results of electrical properties of representative semiconducting and metallic SWNTs are presented. The lowest two-terminal resistance for individual metallic SWNTs (≈5 μm long) is ≈16.5 kΩ measured at 4.2 K. Received: 17 May 1999 / Accepted: 18 May 1999 / Published online: 14 July 1999     

Effect of PVA functionalization on hydrophilicity of Y-junction single wall carbon nanotubes

Hydrophilic surface of carbon nanotubes (CNTs) are of great interest for various applications including chemical and biological sensing. Surface functionalization of single wall carbon nanotubes (SWNTs) mats with a biocompatible polymer polyvinyl alcohol (PVA) was studied. PVA modification induced a drastic change in water wettability of the SWNT surface transforming it from hydrophobic to highly hydrophilic. These PVA modified SWNTs mats have also demonstrated increasing impedance variation in relative humidity compared to the pristine nanotubes. An appreciable change in conductivity of Y-junction SWNT mats as a function of relative humidity indicates its potential application as humidity sensor. This higher sensitivity for humidity variation shown in Y-junction SWNT mats could be attributed to the greater portion of semiconducting nanotubes in these mats revealed by Raman analysis. A possible conductance changing mechanism of surface modified SWNTs mats is discussed.     

Synthesis,characterization, and electrochemical properties of imidazole derivatives functionalized single‐walled carbon nanotubes

The imidazole derivatives functionalized single‐walled carbon nanotubes (SWNTs) were synthesized by a diazonium‐based reaction. We have designed and synthesized two imidazole derivatives to modify SWNTs. The resulting products were characterized by Fourier transform infrared (FT‐IR) spectroscopy, Raman spectroscopy, ultraviolet visible (UV/Vis) spectroscopy, thermo gravimetric analysis (TGA), energy dispersive X‐ray spectroscopy (EDX), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Electrochemical measurements via a cyclic voltammetry method revealed that the weak intramolecular electronic interactions presented between the attached imidazole derivatives groups and the nanotubes. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface growth of single-walled carbon nanotubes from ruthenium nanoparticles

In this paper, we report that ruthenium is an active and efficient catalyst for growth of single-walled carbon nanotubes (SWNTs) by a chemical vapor deposition (CVD) process for the first time. High density random and horizontally superlong well-oriented SWNTs on substrate can be fabricated via CH₄ or EtOH as carbon source under suitable conditions. Scanning and transition electron microscopy investigations, Raman spectroscopy and atomic force microscopy measurements show the tubular structure, the high crystallinity, and the properties of the grown nanotubes. The results show that the SWNTs from ruthenium have better structural uniformity with less defects and provides an alternative catalyst for SWNTs growth. The successful growth of SWNTs by Ru catalyst provides new experimental information for understanding the growth mechanism of SWNTs, which may be helpful for their controllable synthesis.