Growth of metal-free carbon nanotubes on glass substrate with an amorphous carbon catalyst layer

We have investigated the direct growth of metal-free carbon nanotubes (CNTs) on glass substrates with microwave-plasma enhanced chemical vapor deposition (MPECVD). Amorphous carbon (a-C) films were used as a catalyst layer to grow metal-free CNTs. The a-C films were deposited on Corning glass substrates using RF magnetron sputtering with the use of a carbon target (99.99%) at room temperature. They were pretreated with hydrogen plasma using a microwave PECVD at 600 degrees C. Then, CNTs were prepared using microwave PECVD with a mixture of methane (CH4) and hydrogen (H2) gases. The CNTs were grown at different substrate temperatures (400 degrees C, 500 degrees C, and 600 degrees C) for 30 minutes. Other conditions were fixed. The growth trends of CNTs against substrate temperature were observed by field emission scanning electron microscopy (FE-SEM). The structure of a-C catalyst layer and grown CNTs were measured by Raman spectroscopy. High-resolution transmission electron microscopy (HR-TEM) images showed that the CNTs had bamboo-like multi-walled structures. Energy dispersive spectroscopy (EDS) measurements confirmed that the CNTs consisted of only carbon.     

The production of high purity carbon nanotubes with high yield using cobalt formate catalyst on carbon black

Carbon nanotubes (CNTs) were synthesized by catalytic chemical vapour deposition of acetylene diluted with nitrogen. Cobalt formate supported on carbon black was used as the catalyst. The synthesis was carried out at 700 °C in a quartz reactor for 30 min. Thermal analysis was used to determine the CNT yield. The purity of the nanotubes in the deposit was 96% and the yield was 1940% of the weight of the catalyst. Transmission electron microscopic images of as synthesized and oxidized nanotubes supported the thermogravimetric observations regarding the oxidation of CNT. The purity and the yield obtained are one of the highest reported.     

Controlled transformation of carbon coating on silicon nanochains into nanotubes of carbon by Joule heating

A method of carbon coating of silicon nanochains is developed for the controlled transformation of silicon nanochains into nanotubes of carbon: the surface of silicon nanochains is coated with hexadecanoic acid by annealing after plasma cleaning. Individual silicon nanochains are heated by applying an electric current using a micro-manipulator for the transformation. The transformation is observed in situ by means of transmission electron microscopy.     

催化剂对爆炸法合成碳纳米管的影响

通过热引发方式使炸药-催化剂前驱体-碳氢化合物体系在密闭反应管中发生爆炸合成碳纳米管。采用TEM,HRTEM,XRD和TG等方法研究了以二茂铁、甲酸镍和乙酸钴作为催化剂前驱体对所合成碳纳米管产物的形貌、微观结构和纯度的影响。以乙酸钴为前驱体可以得到纯度较高(约80%～90%)、微观结构较好的管腔中空的碳纳米管。以二茂铁为前驱体,只有约10%～20%的碳管生成且多呈竹节状形貌。以甲酸镍为前驱体,得到的碳管纯度也不高(约10%～20%),碳管管壁富含结构缺陷,相当多的碳管端口膨胀成直径约为160nm的纳米泡。XRD分析表明这些催化剂前驱体在爆炸反应后均被分解、还原为金属单质。通过对生成的碳纳米管的质量和纯度进行比较,得出本方法中催化剂的催化活性依次为:钴>铁>镍,并对本方法中高碳源浓度环境下不同催化剂的活性差异作了简要分析。     

添加炭黑和碳纳米管对酚醛树脂热解炭的结构及抗氧化性的影响(英文)

采用酚醛树脂为原料,分别以炭黑和碳纳米管作为改性添加剂制备酚醛树脂热解炭。利用差热分析(DSC)、X射线衍射分析(XRD)和压汞法孔径分析对酚醛树脂热解炭进行表征,探讨添加剂和热处理温度对树脂热解炭的结构和抗氧化性的影响。结果表明,碳纳米管和炭黑均可提高热解炭的石墨化度和抗氧化性;碳纳米管改性树脂热解炭的石墨化度高于炭黑改性树脂热解炭,但由于前者热解炭的显微结构中较高的气孔率,所以使其抗氧化性劣于后者。升高热处理温度同样可改善热解炭的抗氧化性和提高石墨化度。     

Preparation of Pt-Ru bimetallic catalyst supported on carbon nanotubes

The template carbonization of polyphenyl acetylene yields hollow, uniform cylindrical carbon nanotubes with outer diameter almost equal to pore diameter of the template used. High resolution transmission electron microscopic investigation reveals that Pt-Ru nanoparticles are highly dispersed inside the tube with an average particle size of 1.7 nm.     

Growth of carbon nanotubes on glass substrate by MPECVD

We have grown carbon nanotubes (CNTs) with a microwave plasma-enhanced chemical vapor deposition (MPECVD) method, which has been regarded as one of the most promising candidates for the synthesis of CNTs due to the vertical alignment, the low temperature and the large area growth. We had used methane (CH₄) and hydrogen (H₂) gas for the growth of CNTs. 10-nm-thick Ni catalytic layer were deposited on the Ti-coated glass substrate by RF magnetron sputtering method. In this work, we report the low-temperature growing properties of the CNTs on glass substrate with a MPECVD. We have pretreated the Ni/Ti/glass catalytic layer in different microwave power (600, 700, 800, and 900 W) and grown the CNTs in the same microwave power (800 W). SEM (Scanning electron microscopy) images of the Ni catalytic layer shows the diameter and density variation to be dependent with the pretreatment conditions. Raman spectroscopy of CNTs shows that the synthesized CNTs were multi-wall CNTs.     

Field emission of carbon nanotubes grown on nickel substrate

Carbon nanotubes (CNTs) have been synthesized directly on the electrically conducting nickel substrate without additional catalyst. Field emission properties of the as-prepared sample were characterized using parallel plate diode configurations. It was observed that the field emission qualitatively follows the conventional Fowler–Nordheim (F–N) theory from the straight line of ln(I/V²) versus 1/V plot at the high applied field region. The uniformity and stability of the electron emission have also been examined. The low electron turn-on field (E_to) and high emission current density indicates the potential applications of this new CNT-based emitter.     

Studies on transformation of titanate nanotubes into nanoribbons

High aspect ratio titanate nanostructures were synthesized by simple hydrothermal treatment and the nature of two distinct morphologies, hollow nanotubes and titanate nanoribbons was explored as a function of hydrothermal processing conditions. The samples were characterized by means of SEM, XRD and TEM. The specific surface area of the final products was determined by Brunauer-Emmett-Teller (BET) method. It has been found that hydrothermal temperature and the treatment duration have a strong effect on the morphological control of the resulting products. Transformation of nanotubes into nanoribbons was observed with increase in the treatment temperature from 180 °C to 200 °C which became more dense with further increase in the temperature from 200 °C to 220 °C and treatment duration from 12 h to 24 h.     

Influence of catalyst particles on multi-walled carbon nanotubes morphology and structure

Multi-walled carbon nanotubes (MWCNTs) have been successfully grown by Chemical Vapor Deposition (CVD) method. Elucidating the key characteristics of catalyst sources that affect carbon nanotubes growth is of great importance for improving and control MWCNTs morphology and structure. In this work we present a systematically study of CVD parameters, such as catalyst source, substrate morphology and temperature and how it affects carbon nanotubes synthesis. The novelty of this work lies on the catalyst composition. Two specific catalyst sources were analyzed: (i) Fe₂Co and (ii) Fe₂Co with ferrocene. Cyclic Voltammetry results confirmed the presence of Fe²⁺ in the Fe₂Co with ferrocene solution. X-Ray Diffraction analysis confirmed the presence of iron particles on the substrate surface after its submission to growth conditions. Raman results suggested an improvement in carbon nanotubes crystalline quality catalyzed by Fe₂Co with ferrocene. For tridimensional substrates such as fibers, the Fe₂Co with ferrocene provided aligned CNTs with lower defects density noticed in Raman spectra and SEM micrographs. Finally, we corroborated the Fe²⁺ encapsulation relation with the growth mechanism and MWCNTs formation.     

Effect of catalyst thickness and plasma pretreatment on the growth of carbon nanotubes and their field emission properties

We demonstrated that the diameter and the density of carbon nanotubes (CNTs) which had a close relation to electric-field-screening effect could be easily changed by the control of catalytic Ni thickness combined with NH3 plasma pretreatment. Since the diameter and the density of CNTs had a tremendous impact on the field-emission characteristics, optimized thickness of catalyst and application of plasma pretreatment greatly improved the emission efficiency of CNTs. In the field emission test using diode-type configuration, well-dispersed thinner CNTs exhibited lower turn-on voltage and higher field enhancement factor than the densely-packed CNTs. A CNT film grown using a plasma-pretreated 25 angstroms-thick Ni catalyst showed excellent field emission characteristics with a very low turn-on field of 1.1 V/microm @ 10 microA/cm2 and a high emission current density of 1.9 mA/cm2 @ 4.0 V/microm, respectively.     

催化剂结构与形态对碳纳米管生长的影响

采用溶胶-凝胶超临界流体干燥技术制备了含铁、钴的纳米SiO2复合气凝胶催化剂,用于碳纳米管和纳米碳包覆磁性纳米粒子的合成。利用N2物理吸附、XRD、TEM、HRTEM、EDS、SAED等手段对催化剂在不同温度下处理后晶型的转变、形态的变化进行了分析,并考察了催化剂对碳纳米管形貌、结构和碳增重率的变化。结果表明:随着处理温度从600℃升高到1000℃,催化剂比表面积从312.4m2 g降低到79.6m2 g,催化剂粒子从非晶态向晶态转变,粒径从5nm增大至60nm左右,碳的增重率从254.8%下降41.5%。采用低温处理的催化剂,碳产物中以碳纳米管为主,而采用较高温度处理后的催化剂,碳产物中则以碳包覆粒子为主,且随处理温度的升高碳包覆粒子的含量逐渐增加。     

The growth of carbon nanotubes on large areas of silicon substrate using commercial iron oxide nanoparticles as a catalyst

A new approach to chemical vapour deposition (CVD) growth of carbon nanotubes (CNTs) using commercial magnetite nanoparticles, avoiding its in situ synthesis, is reported. Commercial magnetite nanoparticles were used as catalyst material to growth multiwalled carbon nanotubes by chemical vapour deposition onto a silicon substrate of several square centimeters in area. It is shown that the application of an alternating electric field during the deposition of catalytical nanoparticles is an effective technique to avoid their agglomeration allowing nanotube growth. Scanning electron microscopy showed that the nanotubes grow perpendicularly to the substrate and formed an aligned nanotubes array. The array density can be controlled by modifying the deposited nanoparticle concentration.     

Role of the catalyst in the growth of single-wall carbon nanotubes

Classical molecular dynamics simulations are carried out to analyze the physical state of the catalyst, and the growth of single-wall carbon nanotubes under typical temperature and pressure conditions of their experimental synthesis, emphasizing the role of the catalyst/substrate interactions. It is found that a strong cluster/substrate interaction increases the cluster melting point, modifying the initial stages of carbon dissolution and precipitation on the cluster surface. Experiments performed on model Co-Mo catalysts clearly illustrate the existence of an initial period where the catalyst is formed and no nanotube growth is observed. To quantify the nature of the Co-Mo2C interaction, quantum density functional theory is applied to characterize structural and energetic features of small Co clusters deposited on a (001) Mo2C surface, revealing a strong attachment of Co-clusters to the Mo2C surface, which may increase the melting point of the cluster and prevent cluster sintering.     

Application of aromatization catalyst in synthesis of carbon nanotubes

In a typical chemical vapour deposition (CVD) process for synthesizing carbon nanotubes (CNTs), it was found that the aromatization catalysts could promote effectively the formation of CNT. The essence of this phenomenon was attributed to the fact that the aromatization catalyst can accelerate the dehydrogenation–cyclization and condensation reaction of carbon source, which belongs to a necessary step in the formation of CNTs. In this work, aromatization catalysts, H-beta zeolite, HZSM-5 zeolite and organically modified montmorillonite (OMMT) were chosen to investigate their effects on the formation of multi-walled carbon nanotubes (MWCNTs) via pyrolysis method when polypropylene and 1-hexene as carbon source and Ni₂O₃ as the charring catalyst. The results demonstrated that the combination of those aromatization catalysts with nickel catalyst can effectively improve the formation of MWCNTs.     

浮动催化体系中碳纳米管的生长机理

提出了气相形核生长（VPN）机理解释浮动催化体系中碳纳米管的生长过程。浮动催化系统中生长碳纳米管的活性碳原子是由苯热解产生的,被硫原子部分覆盖的液态铁颗粒是单壁碳纳米管的形核中心,生成的单壁碳纳米管继续径向生长、逐渐石墨化后,得到多壁碳纳米管。气相形核生长机理能够解释浮动催化系统生长碳纳米管的结构特征。     

Insight into the nucleating and reinforcing efficiencies of carbon nanofillers in poly(vinylidene fluoride): a comparison between carbon nanotubes and carbon black

Poly(vinylidene fluoride) (PVDF) nanocomposites containing homogeneously dispersed multi-walled carbon nanotubes (MWCNTs) and carbon black (CB) were fabricated by a small melt mixer. The uniform dispersion of the nanofillers in PVDF was confirmed by both scanning electron microscopy and transmission electron microscopy. Both the heterogeneous nucleation efficiency and crystallization half-time show that MWCNTs exhibit higher nucleation efficiency than CB for the crystallization of PVDF. Meanwhile, MWCNTs show greater contribution to the reinforcement of the storage modulus of PVDF as revealed by dynamic mechanical analysis, especially at low temperatures. However, the enhancement of the storage modulus in the melt state is reversed due to the network formed by serious agglomeration of CB. This study provides some insights into the nucleating and reinforcing efficiency of MWCNTs and CB in polymers.     

Growth of double-walled carbon nanotubes using a conditioning catalyst

Here we describe the effect of different synthetic conditions on the quality and purity of double-walled carbon nanotubes (DWNTs) with the aid of a conditioning catalyst. By lowering the reaction temperature down to 875 degrees C and utilizing a conditioning catalyst, increased purity and a decreased inner diameter of the DWNTs was achieved, while adverse results were observed with increasing reaction temperature. Based on detailed high-resolution transmission electron microscopy studies on the diameter distribution of the tubes, preferential growth conditions for DWNTs over single-wall carbon nanotubes are identified solely from increased carbon solubility considerations (caused by an increased portion of active carbon species by use of Mo) for the same distribution of metal particles.     

碳纳米管和炭黑在橡胶体系增强的协同效应

分别以碳纳米管、炭黑以及碳纳米管和炭黑复合体作为橡胶补强剂,在开炼机上进行混炼加工制得橡胶复合材料.实验结果表明:与炭黑补强橡胶体系相比,碳纳米管能够提高橡胶复合材料弹性模量、定伸应力、耐磨和导电性能,但复合材料的拉伸强度、撕裂强度、伸长率,黏度以及加工性能都较差;而以碳纳米管和炭黑混合物作为复合补强剂,通过二者的协同补强效应,形成真正意义的"葡萄串"结构,整体地提高了橡胶复合材料的性能.当碳纳米管和炭黑的质量比为1:4时,制备的橡胶复合材料抗撕裂强度(78.4kN/m)、硬度(68)以及磨耗(0.122cm3/km)性能都优于相同含量炭黑橡胶体系;与相同含量的碳纳米管橡胶体系相比,伸长率(470%)和黏度(65 Pa·s)均大大改进.碳纳米管的加入使橡胶复合材料具有优良的动态力学性能,在低滚动滞后性和抗疲劳损失的轮胎胎面胶方面将有潜在的实用价值.