利用电沉积Ni纳米晶制备无缠绕阵列碳纳米管

以金属Cu基板上脉冲电沉积Ni纳米晶薄膜作为催化剂,在乙醇火焰中制备了直立、无缠绕阵列碳纳米管.利用原子力显微镜(AFM)、扫描电子显微镜(SEM)、透射电镜(TEM)和激光拉曼谱仪(Raman)对不同工艺制备的Ni纳米晶薄膜和阵列碳纳米管的形貌进行了表征.结果表明:通过综合控制脉冲电沉积参数、电沉积时间和火焰中的合成时间,可以获得大面积、密集、均匀、直立、无缠绕、形态良好、重复性高的阵列碳纳米管.脉冲电沉积Ni纳米晶和合成无缠绕阵列碳纳米管的最佳工艺条件是:脉冲电沉积正、负脉冲的工作频率为154Hz、占空比为38.5%、电沉积时间为1min、基板预热至600℃、火焰中停留1min.通过对生长机理的研究发现:当电沉积时间较短时,获得的Ni纳米晶薄膜较薄,具有较高的局域粗糙程度和催化活性,有利于碳纳米管的同时大面积"拥挤生长"形成阵列结构;另外,通过调整脉冲电沉积参数,可以控制Ni纳米晶的大小,从而控制碳纳米管的长径比,当长径比较小时即可获得无缠绕的阵列碳纳米管.     

Synthesis of uniform double-walled carbon nanotubes using iron disilicide as catalyst

The preparation of carbon nanotube (CNT) materials with high purity is critical for many potential applications. These materials not only need to be free of carbonaceous impurities but also have uniform diameters. Within the CNT family, double-walled carbon nanotubes (DWNTs), as the simplest member of multiwalled carbon nanotubes, have demonstrated good potential in many bulk applications. However, the synthesis of DWNTs with uniform diameter and high purity is still a challenge. Here, a method to prepare high-purity DWNTs using iron disilicide (FeSi2) as catalyst is demonstrated. Over 90% of CNTs in the sample were DWNTs with a narrow diameter distribution in the range of 4-5 nm. An additional advantage of using FeSi2 as catalyst is to simplify the process to prepare suitable catalyst because commercially available FeSi2 can be used directly without any further treatment.     

以LaNi5合金为催化剂制备碳纳米管的研究

在800℃下,以LaNi5合金粉末为催化剂,乙炔为原料,采用化学气相沉积法(CVD)分别在氢气氛和氮气氛下合成了多壁碳纳米管.研究了以LaNi5合金粉末为催化剂的条件下,反应气氛对生成碳纳米管的影响,探讨了CVD法生长碳纳米管的反应机理及LaNi5合金的催化机理.实验结果表明,反应过程中LaNi5分解为La3Ni7和Ni;在碳纳米管的生成过程中,La3Ni7进一步分解为La和Ni.氢的参与能显著改变生成的碳纳米管的质量.     

CVD growth of carbon nanotubes on thin-film Ni20Ti35N45 alloy catalyst

The possibility of forming carbon nanotube (CNT) arrays on a Ni–Ti–N catalytic alloy with low nickel content by chemical vapor deposition (CVD) is demonstrated. Adding nitrogen to the Ni–Ti alloy composition favors the formation of TiN compound and segregation of Ni on the surface, where it produces a catalytic effect on the CNT growth. It is found that, using CVD from acetylene gas phase at a substrate temperature of 650°C, a CNT array of 9-µm height can be grown for 2 min.     

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.     

The effect of temperature on the growth of carbon nanotubes on copper foil using a nickel thin film as catalyst

Growth of carbon nanotubes (CNTs) on bulk copper foil substrates has been achieved by sputtering a nickel thin film on Cu substrates followed by thermal chemical vapor deposition. The characteristics of the nanotubes are strongly dependent on the Ni film thickness and reaction temperature. Specifically, a correlation between the thin film nickel catalyst thickness and the CNT diameter was found. Two hydrocarbon sources investigated were methane and acetylene to determine the best conditions for growth of CNTs on copper. These results demonstrate the effectiveness of this simple method of directly integrating CNTs with highly conductive substrates for use in applications where a conductive CNT network is desirable.     

以氯化铁为前驱态催化剂制备碳纳米管

利用氯化铁为催化剂前驱体,结合悬浮催化剂法和基体法的优点,采用一种我们称之为悬浮-基体的新方法在700℃生长出了管壁清洁、直径均匀的碳纳米管,同时实验结果和分析证明,对所沉积的催化剂铁颗粒用氢气进行预处理具有细化碳纳米管和减少碳纳米管缺陷的作用。实验显示这种以氯化铁为催化剂前驱体的悬浮-基体法是一种很有前途实现碳纳米管廉价、大批量生产的方法。     

Synthesis and characterization of Ni-Si mixed oxide nanocomposite as a catalyst for carbon nanotubes formation

Ni-Si mixed oxide nanocomposite was prepared by co-precipitation method with Ni(NO₃)₂ · 6H₂O and tetraethylorthosilicate (TEOS) at pH = 10.5 under reflux condition for 6 days. It was then used as a catalyst for the formation of carbon nanotubes (CNTs) by CVD procedure. Characterization of the catalyst and the CNTs was carried out using X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results showed that Ni-Si mixed oxides nanorods with the average diameter of 3 to 4 nm play a key role in CNTs formation.     

Synthesis of carbon nanotubes and nanospheres with controlled morphology using different catalyst precursors

Carbon nanotubes and carbon nanospheres have been selectively synthesized in a polypropylene matrix by simply altering the catalyst precursor. When a mixture of ferrocene and cobalt (II) acetate was added to the polypropylene, well-dispersed carbon nanotubes were produced. When only cobalt (II) acetate was added, however, carbon nanospheres were obtained. In a third case, when the added catalyst precursor was ferrocene, no graphitic carbon was formed.     

调变Ni／Mo／MgO催化剂中Ni／Mo比例可控合成薄壁碳纳米管

采用摩尔分数1%Ni及负载少量Mo的Ni/MO/MgO催化剂裂解甲烷合成薄壁碳纳米管.通过SEM、TEM、XRD和Raman光谱表征方法研究了碳纳米管直径和催化剂中Ni/Mo比例关系.实验发现:通过控制Ni/Mo比例可以调变催化剂颗粒大小以及活性相.TEM及XRD表征发现,随着Ni/Mo比例的降低,金属Mo相逐渐从NiMo合金相中析出.NiMo合金相对应的活性组分颗粒很小,容易催化裂解甲烷形成薄壁碳纳米管;而后析出的Mo相则主要形成了大管径厚壁的碳纳米管.当Ni/Mo比例为6时可以高选择性地获得窄分布,内径为1.3nm,外径为3.0nm的溥壁碳纳米管.Raman光谱进一步验证了碳纳米管含有较少的缺陷.薄壁碳纳米管形成的关键因素主要体现为碳在其表而的快速扩散以及小颗粒的碳纳米管催化剂活性相控制.     

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.     

Synthesis of vertically aligned carbon nanotubes using natural palm oil as carbon precursor

Vertically aligned carbon nanotubes (VACNTs) have been synthesized on silicon substrates in a thermal catalytic chemical vapor reactor using natural palm oil as the carbon source. Field Emission Scanning Electron Microscopy (FESEM) and microraman analysis revealed dense bundles of mixed multi-walled and single-walled carbon nanotubes (CNTs). The diameters of the single-walled carbon nanotubes (SWCNTs) were estimated to be between 0.6 nm and 1.2 nm. Thermogravimetric analysis (TGA) results showed that 90% purity was achieved at the expense of 4% weight catalyst material.     

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。     

Growth of carbon nanotubes on cobalt catalyst film using electron cyclotron resonance chemical vapour deposition without thermal heating

This paper demonstrates that carbon nanotubes (CNTs) can be synthesized on a cobalt coated silicon substrate using electron cyclotron chemical vapour deposition and without intentionally heating the substrate. With the mixed gases of C(3)H(8)/N(2), CNTs with a multi-walled structure and a diameter up to 70?nm have been observed. Results show that the diameter of the CNTs increases with the thickness of the cobalt catalyst film and the amount of nitrogen incorporated in the CNT films considerably influences the structures of the CNTs. Vertically aligned CNTs can be fabricated with a microwave power as low as 300?W and the flow rate ratio of C(3)H(8)/N(2) = 20/20?sccm. The CNTs exhibit a turn-on field of 0.2?V?μm(-1) determined at the emission current density of 10?μA?cm(-2).     

Synthesis of carbon nanotubes using SBA-15 as a template by the reaction of methane and carbon dioxide

Multiwalled carbon nanotubes (CNTs) were synthesized using Ni loaded mesoporous SBA-15 as a template by reaction of methane and carbon dioxide. The influences of nickel content on the selectivity and crystallinity of CNTs were investigated. It can be seen that the crooked CNTs with a diameter varied from 9.9, 12.5 to 36.5 nm with creasing content of Ni from 5, 15, and 30 wt%/SBA-15. A uniform diameter and good quality CNTs were obtained in our system.     

The preparation of carbon nanotubes by dc arc discharge using a carbon cathode coated with catalyst

Carbon nanotubes (CNTs) were grown using a dc arc discharge process and relevant process parameters were investigated. Unlike the usual process in which a carbon anode is filled with metal catalyst powder, CNTs were prepared using a carbon cathode on which the metal catalyst had been deposited using an electroplating system. Various transition metals were investigated. The results show that multi walled carbon nanotubes (MWNTs) and single walled carbon nanotubes (SWNTs) can both be synthesized using this technique. SWNTs are detected in the soot sample collected around the cathode, whereas the MWNTs are detected mainly in the deposit sample collected from the central area of the cathode. The CNT yield varies depending on the catalyst used and the properties of a good catalyst are discussed.     

Large-scale synthesis of BN nanotubes using carbon nanotubes as template

Boron nitride nanotubes (BN-NTs) were synthesized in large scale by the reaction of NaBH₄ and NH₄Cl in the temperature range of 500-600 °C for 10-18 h, where carbon nanotubes (CNTs) were mixed together with the reactants to serve as template. Pure BN-NTs were obtained by oxidizing the product at about 800 °C in air atmosphere. The structure and morphology of the product with a surface area of 106.635 m²/g were characterized by X-ray diffraction, transmission electron microscopy, Fourier transformation infrared spectroscopy, and thermogravimetric analysis. Large scale preparation of BN-NTs could be realized by this simple and effective route.     

The influence of Ni catalyst on the growth of carbon nanotubes on Si substrates

This article treats the influence of the treatment of a Ni catalyst upon the growth of carbon nanotubes in alcohol catalytic chemical vapour deposition (AC CVD) equipment. Prior to the growth of diamond, a thin film of Ni was deposited on a silicon substrate by magnetron sputtering. We observed that a combination of annealing of the Ni catalyst in vacuum and NH₃ had a positive effect upon the growth of carbon nanotubes (CNTs). The prepared CNTs were analysed by scanning electron microscopy and Raman spectroscopy.     

Selective growth of carbon nanotubes using catalyst poisoning and geometric trench

This work suggests catalyst poisoning and geometric patterned approaches to selectively grow multiwall carbon nanotubes. Ferromagnetic particles as a catalyst for CNTs growth vanish when they are deposited over an aluminum thin film. Additionally, geometric features, such as trenches or cavities, are revealed to be capable of selectively ceasing the growth of CNTs even though catalytic thin films were covered on entire samples by an atmospheric thermal chemical vapor deposition technique.