催化剂焙烧温度对热解火焰法合成碳纳米管的影响

为了探讨在制备Fe/Mo/Al2O3载体载入式催化剂过程中的焙烧温度对实验产物的影响,在热解火焰法中,以CO为碳源,设计了6组实验工况,对不同焙烧温度的合成产物碳纳米管进行对比分析,实验产物的形貌与特征用扫描电镜和拉曼光谱表征.分析表明,在本组实验条件下,催化剂焙烧温度为800～1000℃时,可以使催化剂颗粒尺寸更小,分散性更好,催化活性更高,实验合成的碳纳米管以多壁碳纳米管为主,产量较多,质量较佳,焙烧温度为900 ℃附近时,合成了高质量的单壁碳纳米管.     

Electron microscopy of carbon nanotubes

High-resolution electron microscopy was used to study multiwall carbon nanotubes obtained by the arc-discharge technique and double-and single-wall nanotubes produced by the arc-discharge catalytic synthesis. The structure of conical layer nanotubes obtained by the CVD technique is characterized in detail. It is established that heat treatment of nanotubes gives rise to their structural changes. The structure of nanotubes obtained by carbon evaporation in the N₂-Ar atmosphere under high pressure is determined. A new type of nano-and microtubes with surface-modulated walls is revealed. Possible applications of carbon nanotubes are reviewed.     

热解火焰法合成碳纳米管:催化剂与合成环境的影响

以CO为碳源,通过氧炔焰形成热解火焰合成了碳纳米管.为了详细研究催化剂与合成环境对合成产物的影响,实验分别应用不同催化剂在不同合成环境中进行取样分析.结果表明:催化剂颗粒尺寸直接决定合成产物的种类,不同产物对合成温度也有不同要求,过高温火焰环境会遏制碳纳米管的合成.最终得出,Fe/Mo/Al2O3载体催化剂适合在热解腔内部830℃无氧的环境下催化合成小直径的单壁、双壁和三壁碳纳米管,而由Fe(CO)5热解-附着-聚合产生的Fe催化剂颗粒适合在600℃的V型体火焰中催化合成大直径多壁碳纳米管.     

Inclusion of carbon nanotubes in a TiO2 sol-gel matrix

We report here the successful inclusion of carbon nanotubes (CNs) into a TiO₂ matrix prepared by a sol-gel method. The presence of CNs in the sol-gel matrix and the structure of the film were analyzed principally by transmission electron microscopy. Complementary information about the behavior of embedded carbon nanotubes versus heat treatment and ion irradiation were obtained by X-ray photoelectron spectroscopy. The elaboration of an inorganic matrix containing embedded carbon nanotubes leads to a new nanocomposite. The possible applications of this nanocomposite are discussed.     

V型热解火焰合成碳纳米管的影响因素研究与分析

介绍了用V型热解火焰燃烧器制备碳纳米管的实验条件,利用扫描电子显微镜和透射电子显微镜对碳纳米管进行表征,详细研究和分析了温度、反应物成分、催化剂、燃氧比等影响因素对碳纳米管形态的影响.结果表明:温度在800～1000 ℃之间,采用CO/H_2/He作为反应气体,用Fe(CO)_5作为催化剂时,可以得到的形态较好、杂质较少的碳纳米管.     

Preparation of amorphous carbon nanotubes using attapulgite as template and furfuryl alcohol as carbon source

Amorphous carbon nanotubes were synthesized by vapor deposition polymerization (VDP) method using attapulgite as template and furfuryl alcohol as carbon source. The morphology and microstructure analysis of the as-prepared samples showed that highly pure amorphous carbon nanotubes were obtained, and determined by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SEAD) and energy dispersive X-ray (EDX) spectrum. The Brunauer–Emmett–Teller (BET) surface area analysis indicated that the specific surface area of the as-prepared amorphous carbon nanotubes reaches up to 503.1 m²/g. A hypothesis about the formation mechanism of the amorphous carbon nanotubes was also proposed accordingly.     

Vertically aligned N-doped carbon nanotubes by spray pyrolysis of turpentine oil and pyridine derivative with dissolved ferrocene

Vertically aligned nitrogen-doped carbon nanotubes were synthesized from the pyrolysis of a mixture of turpentine oil, 4-tert-butylpyridine (C₉H₁₃N) and ferrocene on silicon and quartz substrate in nitrogen atmosphere at 700 °C by simple spray pyrolysis technique. SEM, TEM, TGA/DTA, Raman spectroscopy, XPS and electron probe micro analysis (EPMA) techniques were used to characterize the structural analysis and composition of the as-grown N-doped carbon nanotubes. Morphology of the films was greatly affected by the nature of the substrate. From the XPS and EPMA data, it was found that nitrogen content of the nanotubes were 1.6 at.% and 2 at.% on silicon and quartz substrate, respectively. Our studies show that two different types of N atoms can be present in these materials. These are ‘pyridinic’ and ‘graphitic’ nitrogen with binding energies of 398.2 eV and 400.4 eV, respectively. Raman spectroscopy reveals that graphitization of carbon nanotubes grown on silicon is better than nanotubes grown on quartz substrate. Thermogravimetric analysis showed that the thermal stability of as-prepared nanotubes grown on silicon substrate is higher than the nanotubes deposited on quartz substrate.     

衬底对沉积碳纳米管薄膜的影响

利用微波等离子体化学气相沉积(MPCVD)方法,分别在不锈钢衬底上和刻线的镍膜上直接沉积了碳纳米管膜。通过SEM、拉曼光谱和XRD表征,讨论了不同衬底对碳纳米管膜生长的影响。结果表明:在一定条件下,可在镍膜上沉积垂直于衬底的高度取向的碳纳米管,但在不锈钢衬底上却长出取向无序的碳纳米管膜,这说明衬底对碳纳米管的取向生长起着关键作用。     

以尿素为氮源合成AlN粉体过程中非晶碳的石墨化

针对有机合成过程中碳及碳化物的残余,传统方法中普遍使用除碳的工艺,而很少有文章针对非晶碳的结构和形貌进行表征。为此,本文采用高尿素含量的前驱盐体系,通过在氮气保护气氛中煅烧获得AlN粉体。采用X射线衍射分析、红外和拉曼光谱分析、扫描电子显微镜和透射电子显微镜对850~1 500 ℃温度范围内煅烧获得产物的结构和形貌进行表征,对AlN合成过程中含碳产物结构形貌的变化,以及AlN和含碳产物之间相互的依存生长关系进行分析。结果表明,AlN生长的过程中伴随着无定形碳的石墨化转变,AlN颗粒的形貌也受含碳残余产物形貌的影响而出现有规律的变化。     

利用基板法在V型热解火焰中合成碳纳米管的实验研究

利用V型热解火焰合成碳纳米管是一项新的技术和方法,实验中采用304不锈钢片作为取样基板,将硝酸镍溶液均匀涂敷在取样基板上作为催化剂,利用扫描电镜和透射电镜对碳纳米管进行形态和结构表征。实验中得到了典型形态及特殊形态的碳纳米管,催化剂颗粒的直径在为5~8 nm之间。实验结果表明,取样时间为10 min,温度约为1150 K时最有利于产生碳纳米管。最后分析讨论了特殊形态的碳纳米管的结构及可能的形成机理。     

Ru@Pt/CNTs纳米粒子的制备及催化乙醇氧化电化学活性的研究

通过乙醇还原方法制备了不同比例的碳纳米管负载钌铂核壳结构的纳米粒子(Ru@Pt/CNTs),并用作直接乙醇燃料电池的阳极催化剂。利用透射电镜(TEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)等手段表征该催化剂的结构。结果表明Ru@Pt/CNTs纳米颗粒具有核壳结构(以钌为核),Ru@Pt/CNTs在乙醇电氧化反应(EOR)中表现出优良的电化学催化活性,其中,当铂∶钌摩尔比为0.75时,催化性能达到最优,电流密度值达到1 767.77 mA/mg Pt,是商业Pt/C的3.25倍。另外,耐久性的实验发现当铂∶钌摩尔比为1.00时, CV测试循环了250圈后衰减了19.7%。因此,具有核壳结构的Ru@Pt/CNTs纳米粒子对乙醇氧化反应有优良的催化活性。     

Deposition of iron nanoparticles onto multiwalled carbon nanotubes by helicon plasma-enhanced,chemical vapor deposition

We report helicon plasma-enhanced, chemical vapor deposition (helicon-PECVD) of iron (Fe) nanoparticles onto multiwalled carbon nanotubes (MWCNTs) with ferrocene as an iron source. Ferrocene was evaporated from the bubbler by heating, and the helicon plasma treatment was performed with the evaporated ferrocene and hydrogen gas at (−)DC bias voltage. The resulting MWCNT/Fe nanoparticle hybrids were characterized by X-ray fluorescence spectroscopy, X-ray diffraction spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and superconducting quantum interference device magnetometry.     

Observation of the growth of carbon nanotubes prepared at low temperature

Lack of information during the growth of carbon nanotubes has hindered efforts to understand the growth mechanism of these unique nanoscale structures. Here, we report that Multi‐walled carbon nanotubes with bamboo‐shaped structure may be synthesized by solvothermal method at 300°C using benzene as carbon source and Zn as catalyst. We have obtained direct experimental information on the growth under Transmission electron microscopy. It has been shown that all the compartments of bamboo‐like tube successively joined leading to the formation of regularly segmented nanobamboos. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of the influence of electron irradiation on the properties of cobalt nanotubes

Cobalt nanotubes have been synthesized by electrochemical deposition in pores of ion track membranes. The structures obtained have been studied by scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction analysis, and gas permeability method. The influence of electron irradiation on the cobalt nanotube structure has been investigated. It is shown that an increase in the irradiation dose leads to the transformation of the sample crystal structure. This fact can be explained by the simultaneous reduction of the β-Co metastable phase and relaxation of the microstress formed by the fcc phase in the lattice. The degree of sample texturing along the [100] direction increases under electron irradiation. The dependences of the resistive and magnetic properties of cobalt nanotubes on the irradiation dose have been analyzed.     

Fenton试剂对碳纳米管表面改性研究

利用Fenton试剂对碳纳米管进行表面改性,研究了Fenton, Fenton/超声波(US)以及Fenton/紫外线(UV)对碳纳米管表面的影响,并探讨了Fenton试剂与碳纳米管的作用机理.用热重分析(TGA)来观察纯化前后碳纳米管的纯度,用红外光谱(FTIR)分析碳纳米管表面官能团的变化,用透射电镜(TEM)对碳纳米管微观结构进行分析.结果表明:Fenton/UV反应能够在碳纳米管表面引入大量羟基以及少量的羧基,且不会较大程度地损坏碳纳米管的结构;机理分析表明, Fenton试剂主要是利用Fenton反应产生的羟基自由基(HO·)对碳纳米管的不饱和键进行羟基化加成.     

辉光放电对负偏压增强热丝化学气相沉积碳纳米管的准直生长作用研究

利用负偏压增强热丝化学气相沉积在不同的负偏压和压强下,在沉积有不同厚度NiFe膜的Si衬底上制备了碳纳米管,并用扫描电子显微镜研究了它们的生长.发现在无辉光放电的情况下,碳纳米管弯曲生长,而在辉光放电时,碳纳米管准直生长,表明辉光放电对碳纳米管的准直生长起到了重要的作用.由于辉光放电的产生,在衬底表面附近形成很强的电场.相对无辉光放电时的电场,场强提高了两个数量级.本工作详细地研究了辉光放电对碳纳米管的准直生长作用.     

Growth of SiC nanorods prepared by carbon nanotubes-confined reaction

SiC nanorods have been synthesized by means of the carbon nanotubes-confined reaction between SiO gas and carbon nanotubes. The diameters of SiC nanorods can be controlled by the local partial pressure of the CO gas produced during reaction. The morphology of SiC nanorods depends on the shape of the carbon nanotubes at high reaction temperatures. The growth mechanism of SiC nanorods is basically a shape memory synthesis.     

Studies of hydrogen interaction with carbon deposit containing carbon nanotubes

Nanocarbon materials were obtained by catalytic decomposition of ethylene on nanocrystalline iron at 500 and 550 °C. The increase in the carbon mass was controlled using the thermogravimetric method. After synthesis the samples were analyzed using the HRTEM and X-ray diffraction methods and contained iron carbide (cementite) and nanocarbon materials (carbon nanofibers, carbon nanotubes and amorphous carbon). Cementite crystallites were observed at the end of filamentous structures. In order to remove amorphous carbon and thick carbon nanofibers the samples were reduced under hydrogen atmosphere. As a result of the hydrogenation treatment, the cementite was decomposed into iron and carbon. The samples contained mainly multi-walled carbon nanotubes with open ends and had diameters in the range of approx. 10–30 nm.     

火焰热解法与电加热热解法合成碳纳米管的对比分析

应用Fe/Mo/Al2O3载体载入式催化剂,以CO为碳源,分别通过火焰热解法和电加热热解法合成了碳纳米管.为了探究导致两种方法合成产物异同的原因,分别对两种方法中对应的实验操作和参数进行了对比分析.分析表明:(1)由于热解形式不同-火焰热解形式的剧烈性和电加热热解形式的缓和性,导致两种方法热解区气流扰动强度存在巨大差别,极大影响了产物的产量和质量;(2)由于合成温度不同,火焰热解法合成温度为830℃,可以合成单壁碳纳米管,而电加热热解法合成温度为790℃,仅能合成双壁、三壁碳纳米管.     

氯化亚铁催化制备硼碳氮纳米管

采用固相反应法,以无定型硼粉为原料,氯化亚铁为催化剂,在无水乙醇和氨气气氛中高温热处理3 h成功制得大量竹节状的三元硼碳氮(BCN)纳米管.利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)以及X射线光电子能谱仪(XPS)等手段对所得纳米管进行了表征.结果显示,纳米管的直径在60~90 nm之间,纳米管由B、C、N三种元素组成,其原子比为9.77∶1∶8.65.纳米管的生长机理属于气-液-固(VLS)机制.同时初步探讨了反应温度对纳米管的影响.