非定向多壁碳纳米管制备过程中引入水对其生长的影响

用催化化学气相沉积法制备非定向多壁碳纳米管时,利用气体携带水进入反应区域,考察了水对碳纳米管生长的影响,并用透射电子显微镜对其形貌进行表征.结果显示,带入适量的水后,碳纳米管的产率可以得到较大提高,同时对碳纳米管形貌基本不产生影响.但水量太多或太少都会影响所得碳纳米管的产率,尤其当水过多时,还会对碳纳米管的产率产生较大影响.     

CO-Mo/MgO催化剂上甲烷化学气相沉积制备高纯度多壁碳纳米管

以甲烷为碳源,co-Mo/MgO为催化剂,通过气相化学沉积制备了直径均匀的多壁碳纳米管(MWC-NTs).采用溶胶-凝胶法所制双金属催化剂的组成为Co∶Mo∶MgO=5∶20∶75(质量比).热重分析表明多壁碳纳米管产率高达313.67%.催化剂对于多壁碳纳米管生长的选择性是91.17%(其余为无定形碳).透射电子显微镜分析显示:催化剂七生长的MWCNTs平均直径为6.2±0.5nm(平均±标准偏差).通过稀酸的简单纯化处理,纯化样品的催化剂残存率降至0.72%.     

Continuous synthesis of carbon nanotubes using a metal-free catalyst by CVD

This study demonstrates the first example of the use of a metal-free catalyst for the continuous synthesis of carbon nanotubes (CNTs) by chemical vapor deposition (CVD). In this paper silica nanoparticles produced from the thermal decomposition of PSS-(2-(trans-3,4-Cyclohexanediol)ethyl)-Heptaisobutyl substituted (POSS) were used as catalyst and ethanol was served as both the solvent and the carbon source for nanotube growth. The POSS/ethanol solution was nebulized by an ultrasonic beam. The tiny mists were continuously introduced into the CVD reactor for the growth of CNTs. The morphology and structure of the CNTs have been investigated by scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The obtained CNTs have a multi-walled structure with diameters mainly in the size range from 13 to 16 nm. Detailed investigations on the growth conditions indicate that the growth temperature and POSS concentration are important for achieving high-quality nanotubes, and that the existing of small amount of water in ethanol is effective to remove amorphous carbon species during the formation of CNTs. The mass production of CNTs without any metal contaminant will provide a chance for investing and understanding the intrinsic properties of CNTs and applications particularly in nanoelectronics and biomedicines.     

Low temperature facile synthesis of anatase TiO2 coated multiwalled carbon nanotube nanocomposites

Anatase TiO₂ coated multiwalled carbon nanotube (MWNT) nanocomposites were prepared by combining the sol-gel method with a self assembly technique at a low temperature. XRD, TEM, FTIR and XPS spectra were applied to characterize the crystal phase, microstructure, and other physicochemical properties of the sample. The results showed that MWNTs were covered with a 12-20 nm thickness layer of anatase TiO₂ or surrounded by a 30 -290 nm thickness coating of anatase TiO₂. The layer or coating is constructed of TiO₂ nanoparticles about 5.8 nm. Furthermore, as-prepared composite was rich in surface hydroxyl groups.     

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。     

Electrochemical preparation and electrochemical behavior of polypyrrole/carbon nanotube composite films

Polypyrrole/multiwalled carbon nanotube (MWNT) composite films were electrochemically deposited in the presence of an ionic surfactant, sodium dodecyl sulfate (SDS), acting as both supporting electrolyte and dispersant. The effects of the surfactant and the MWNT concentrations on the structure of the resulting composite films were investigated. The electrochemical behavior of the resulting polypyrrole/MWNT composite film was investigated as well by cyclic voltammogram. The effect of the additional alternating electric field applied during the constant direct potential electrochemical deposition on the morphology and electrochemical behavior of the resulting composite film was also investigated in this study.     

Electrochemical characterization of carbon nanotube forests grown on copper foil using transition metal catalysts

Growth of vertical, multiwalled carbon nanotubes (CNTs) on bulk copper foil substrates can be achieved by sputtering either Ni or Inconel thin films on Cu substrates followed by thermal chemical vapor deposition using a xylene and ferrocene mixture. During CVD growth, Fe nanoparticles from the ferrocene act as a vapor phase delivered catalyst in addition to the transition metal thin film, which breaks up into islands. Both the thin film and iron are needed for dense and uniform growth of CNTs on the copper substrates. The benefits of this relatively simple and cost effective method of directly integrating CNTs with highly conductive copper substrates are the resulting high density of nanotubes that do not require the use of additional binders and the potential for low contact resistance between the nanotubes and the substrate. This method is therefore of interest for charge storage applications such as double layer capacitors. Inconel thin films in conjunction with Fe from ferrocene appear to work better in comparison to Ni thin films in terms of CNT density and charge storage capability. We report here the power density and specific capacitance values of the double layer capacitors developed from the CNTs grown directly on copper substrates.     

Influence of Mo or Cu doping in Fe/MgO catalyst for synthesis of single-walled carbon nanotubes by catalytic chemical vapor deposition of methane

A series of mono-, bi- or tri-metallic Fe–Mo-Cu/MgO catalysts with the same metal loading of 6 wt% were prepared by impregnation method and used as catalysts for synthesis single-walled carbon nanotubes (SWCNTs) via methane decomposition. XRD, H₂-TPR, and nitrogen physisorption techniques were used to characterize the freshly calcined catalysts, while HRTEM, Raman spectroscopy and TGA were employed to investigate the morphology and microstructure of the SWCNTs product. The obtained results indicated that the introduction of Mo or Cu in the Fe/MgO catalyst enhanced the catalytic growth activity. TEM images showed that both bundles and isolated SWCNTs were obtained over Mo containing catalysts, whereas only SWCNTs bundles were grown over the Fe-Cu/MgO catalyst. The obtained SWCNTs having a diameter of around 0.9–2.4 nm. Raman analysis illustrated that all promoted catalysts produced high quality of SWCNTs compared to the unpromoted Fe/MgO catalyst.     

化学气相沉积法制备定向碳纳米管及其生长机理的研究

以环己烷为碳源,二茂铁作催化剂,采用浮动催化化学气相沉积法制备了定向碳纳米管,并用SEM、TEM及Raman光谱对样品进行了鉴定和表征.并从不同的角度,提出了定向碳纳米管遵循底部生长的机理.     

Synthesis of binary and triple carbon nanotubes over Ni/Cu/Al2O3 catalyst by chemical vapor deposition

Novel binary and triple carbon nanotubes (CNTs) with one common catalytic particle encapsulated have been synthesized using Ni/Cu/Al₂O₃ catalyst, which was produced by a sol-gel method. But when using Ni/Al₂O₃ as catalyst, a mass of common CNTs, that is, one CNT with one catalytic particle encapsulated, was obtained. The results showed that copper-element doping to the Ni/Al₂O₃ catalyst played a key role in the synthesis of CNTs, signifying a novel approach to modify the Ni/Al₂O₃ catalyst. Based on the transmission electron microscopy observations, a simple growth mechanism was developed to describe the growth of the binary or triple CNTs, which could be well explained by a diffusion segregation process.     

Effect of nitrogen and hydrogen on the growth of multiwall carbon nanotubes on flexible carbon cloth using thermal chemical vapor deposition

In this study, the effect of various mixture fluxes of nitrogen (N₂) and hydrogen (H₂) on carbon nanotube (CNT) synthesis grown on flexible carbon cloth using thermal chemical vapor deposition (thermal CVD) with ethylene (C₂H₄) as the carbon source and nickel (Ni) as the catalyst was investigated. Field emission scanning electron microscopy (FE-SEM) was utilized to study the morphology of CNTs on flexible carbon cloths with various N₂ and H₂ inlet flow rates. The results indicate that average diameter of MWCNTs decreases with increasing H₂ and N₂ flow rates; however, the density of CNTs increases first and then decreases with increasing H₂ and N₂ flow rates. On the other hand, in our field emission experiments, the result indicates that the field emission is strongly dependent on the density and geometry of MWCNTs. In addition, we also found that the contact electrical conductance measurement is an easy method to predict the field emission characteristics of MWCNTs.     

Effect of SF6 incorporation in the cyclic process on the low temperature deposition of carbon nanofilaments

To enhance the carbon nanofilaments (CNFs) formation density, SF₆ was incorporated in the source gases (C₂H₂/H₂) during the initial deposition stage. The source gases and SF₆ were manipulated as the cyclic on/off modulation of C₂H₂/H₂/SF₆ flow in a thermal chemical vapor deposition system. The characteristics of the CNFs formation on the substrate were investigated according to the different cyclic modulation processes and the substrate temperatures. By the incorporation of SF₆ in the cyclic process CNFs could be formed at the substrate temperature as low as 350 °C. Among the different processes, mutual alternating cyclic modulation process of C₂H₂ and SF₆ could most highly enhance the CNFs formation density. The cause for the enhancement in the characteristics of as-grown CNFs by the incorporation of SF₆ was discussed in association with the slightly enhanced etching ability by the incorporation of SF₆.     

Designing a strategy for fabrication of single-walled carbon nanotube via CH4/N2 gas by the chemical vapor deposition method

Fe/Mo catalysts supported on alumina are suggested for the growth of single-walled carbon nanotubes (SWCNTs) by chemical vapor deposition (CVD) in methane (CH₄). One obvious synergistic advantage identified by molybdenum (Mo) is that by controlling the reaction temperature, it eliminates the need to activate the catalyst in hydrogen gas (H₂). So as activation of the growth catalyst in H₂ is a costly and extra step in the CVD method, this is a significant result of the present study. Herein, the sample quality and the dependence of carbon mass yield on CVD growth conditions are disserted. The activity of the catalyst is perused in the form of oxide under CH₄ flow (160 sccm) and in the temperature range of 680 to 1000 °C. We came to the conclusion that the Fe/Mo/Al₂O₃ oxide catalyst is activated at temperatures as low as 800 °C. Under these conditions (800 °C, 160 sccm of CH₄), the temperature is not enough for the tube to grow, but by increasing it, the desired conditions can be achieved (900 –1000 °C).     

Decoration of carbon nanotubes with nearly monodisperse MFe2O4 (MFe2O4, M = Fe, Co, Ni) nanoparticles

Magnetic monodisperse ferrite MFe₂O₄ (M = Fe, Co, Ni) nanoparticles have been successfully deposited on carbon nanotubes (CNTs) by in situ high-temperature hydrolysis and inorganic polymerization of metal salts and CNTs in polyol solution. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectrometry (EDS) and vibrating sample magnetometer (VSM) investigations were used to characterize the final products. The influencing factors for formation of CoFe₂O₄ nanoparticles along CNTs have also been discussed briefly. The main advantage of this synthetic strategy is that it is beneficial for the fabrication of magnetic CNTs with a compact layer of nanoparticles and could be extended to prepare series of ferrite/CNTs nanocomposites via the substitution of metal cations.     

Optimization of synthesis condition for carbon nanotubes by chemical vapor deposition on Fe-Ni-Mo/MgO catalyst

Catalyst and reaction conditions are the main affecting factors for the yield and quality of carbon nanotubes (CNTs) produced by the chemical vapor deposition (CVD) method. In this paper a ternary component catalyst based on Fe-Ni-Mo/MgO was explored using methane as precursor. The influences of temperature and methane concentration were investigated, and the as-produced CNTs were characterized by SEM, HRTEM, XRD and TGA. The diameter of the CNTs is in the range of 20-30 nm and the maximum carbon yield can reach up to 80 times of the catalyst under the selected condition. The purity of the as-prepared CNTs is over 93%. Our results indicated that this novel tercomponent catalyst presented a good catalytic activity for manufacturing high quality and quantity of CNTs.     

Amorphous and nanocrystalline silicon growth on carbon nanotube substrates

In this study, smooth and conformal hydrogenated silicon thin films are examined and analyzed on various multi-walled carbon nanotube (MWCNT) substrates. The films are deposited using radio-frequency plasma-enhanced chemical vapor deposition with He dilution and parameters that are heavily in the γ regime. It is proposed that high-energy plasmas with limited penetration depth can induce crystallization to occur on MWCNT substrates of varying active surface areas. The samples presented exhibit properties that are promising for energy applications, including photovoltaics and lithium-ion batteries and have been studied using scanning electron microscopy, Raman spectroscopy, X-ray diffraction, UV-Vis spectrophotometry, four-point probe measurements, and Fourier transform infrared spectroscopy.     

不同催化剂作用下生长的碳纳米管和碳纳米纤维复合膜的电吸附性能

采用低压低温气相沉淀法在不同催化剂(Fe和Ni)作用下制备碳纳米管-碳纤维复合薄膜,并研究其电容去离子行为,结果表明:在Ni催化作用下石墨上生长的碳纳米复合薄膜电极的去离子能力比Fe催化作用下生长的碳纳米复合薄膜电极的强;并且碳纳米复合薄膜的电吸附遵循langmuir单层等温吸附.     

Effect of acetylene flow rate on morphology and structure of carbon nanotube thick films grown by thermal chemical vapor deposition

Carbon nanotube (CNT) films were grown on nickel foil substrates by thermal chemical vapor deposition (CVD) with acetylene and hydrogen as the precursors. The morphology and structure of CNTs depending on the acetylene flow rate were characterized by a scanning electron microscope (SEM), a transmission electron microscope (TEM) and a Raman spectrometer, respectively. The effect of acetylene flow rate on the morphology and structure of CNT films was investigated. By increasing the acetylene flow rate from 10 to 90 sccm (standard cubic centimeter per minute), the yield and the diameter of CNTs increase. Also, the defects and amorphous phase in CNT films increase with increasing acetylene flow rate. Translated from Journal of Inorganic Materials, 2006, 21(1): 75–80 [译自: 无机材料学报]     

Effect of fibre coating and geometry on the tensile properties of hybrid carbon nanotube coated carbon fibre reinforced composite

Hierarchically structured hybrid composites are ideal engineered materials to carry loads and stresses due to their high in-plane specific mechanical properties. Growing carbon nanotubes (CNTs) on the surface of high performance carbon fibres (CFs) provides a means to tailor the mechanical properties of the fibre–resin interface of a composite. The growth of CNT on CF was conducted via floating catalyst chemical vapor deposition (CVD). The mechanical properties of the resultant fibres, carbon nanotube (CNT) density and alignment morphology were shown to depend on the CNT growth temperature, growth time, carrier gas flow rate, catalyst amount, and atmospheric conditions within the CVD chamber. Carbon nanotube coated carbon fibre reinforced polypropylene (CNT-CF/PP) composites were fabricated and characterized. A combination of Halpin–Tsai equations, Voigt–Reuss model, rule of mixture and Krenchel approach were used in hierarchy to predict the mechanical properties of randomly oriented short fibre reinforced composite. A fractographic analysis was carried out in which the fibre orientation distribution has been analyzed on the composite fracture surfaces with Scanning Electron Microscope (SEM) and image processing software. Finally, the discrepancies between the predicted and experimental values are explained.     

Simple method for synthesis of carbon nanotubes over Ni-Mo/Al2O3 catalyst via pyrolysis of polyethylene waste using a two-stage process

Synthesis of valuable multi-walled carbon nanotubes (MWCNTs) by thermal pyrolysis of low-density polyethylene (LDPE) waste was investigated via a two-stage process. The first stage was the thermal pyrolysis of LDPE to gaseous hydrocarbons, and the second stage was the catalytic decomposition of the pyrolysis gases over Ni-Mo/Al₂O₃ catalysts. Two catalysts with the compositions of 5.2%Ni-10.96%Mo/Al₂O₃ and 10%Ni-9.5%Mo/Al₂O₃ were tested for carbon nanotubes (CNTs) formation. The catalyst containing 10%Ni showed better activity in terms of CNTs production. Accordingly, the impact of either pyrolysis or decomposition temperatures was investigated using the 10%Ni-9.5%Mo/Al₂O₃ catalyst. TEM, XRD, Raman spectroscopy, TGA, TPR, and BET analysis tools were used to characterize the fresh catalysts as well as the obtained carbon nanomaterials. TEM images proved that MWCNTs with various morphological structures were obtained at all pyrolysis and decomposition temperatures. Moreover, cup-stacked carbon nanotubes (CS-CNTs) were observed at the decomposition temperature of 600°C. MWCNTs with the best quality were produced at decomposition temperature of 750°C. The optimum pyrolysis and decomposition temperatures in terms of CNTs production were at 700 and 650°C, respectively.