低温催化裂解烷烃法制备碳纳米管

低温催化裂解烷烃法制备碳纳米管陈萍，王培峰，林国栋，张鸿斌，蔡启瑞（厦门大学化学系固体表面物理化学国家重点实验室，厦门，３６１００５）关键词碳纳米管，催化裂解，甲烷碳纳米管的制备与研究是国际上新材料领域的探索热点［１］．由于具有纳米级的管径，碳纳米管...     

催化裂解CH4制备不同形貌的碳纳米管

通过甲烷于较低温度(500～700℃)下在镍催化剂上催化裂解制备了各种形貌的碳纳米管.透射电镜测试结果表明,碳纳米管的外径和内径明显地受催化剂的大小和形貌的影响.本文考察了催化剂前驱体的种类、反应温度和原料气流速对镍催化剂和碳纳米管形貌的影响.     

稀土合金催化裂解乙炔合成管径可控的碳纳米管

以稀土合金MlNi5-1.35(CoAlMn)1.35为催化剂,C2H2为碳源,H2为还原气和载气,用CVD法合成了纯度较高的CNTs。通过用SEM,TEM,XRD及Raman等表征测试方法,研究了H2流量对合成的CNTs管径、产量、纯度、形态及石墨化程度的影响。结果表明:合金催化剂经还原后其粒径从μm级细化到了nm量级;在催化剂与C2H2反应过程中不通入H2时,催化剂上仍能生长出CNTs,但其长度短而管径粗(约97.8nm),管壁厚而粗糙;随着H2流量增大,CNTs管径先减小后增大,而其产量、纯度及石墨化程度则先提高后下降。当H2流量为50ml·min-1时,CNTs管径达最细(平均管径49.1nm);H2流量为75ml·min-1时,其产物纯度高,产量最大(4.05g·g-1催化剂),CNTs石墨化程度最高;H2流量为100ml·min-1时,CNTs管径最均匀(平均管径97.8nm)。     

n型金刚石薄膜催化生长碳纳米管

研究了n型金刚石薄膜作为催化剂生长碳纳米管的方法.首先采用丙酮裂解化学气相沉积(CVD)法制备均匀的n型金刚石薄膜,然后采用乙醇为碳源的CVD法,在850、900和950℃下,分别在n型金刚石薄膜上制备了碳球、竹节状碳管和多壁碳纳米管.所得产物用扫描电子显微镜、透射电子显微镜、拉曼光谱和X射线光电子能谱表征.实验结果表明产物的形貌与反应温度有关.我们还提出了与金刚石催化生长碳纳米管结果相符的实验机理.     

高硅分子筛ZSM-23催化裂解C4烷烃制乙烯丙烯的研究

采用廉价的硅溶胶作为硅源,吡咯烷为模板剂,静态水热晶化法合成出不同硅铝比的ZSM-23分子筛.采用XRD,SEM,吡啶吸附红外光谱等技术,对合成的ZSM-23分子筛的结构、形貌、表面酸性质进行了表征.并进行了所制样品对C4烷烃催化裂解制乙烯丙烯反应催化性能的研究.本文详细考察了硅铝比、反应温度、反应空速以及催化剂稳定性等各种因素对催化性能的影响.结果表明,ZSM-23分子筛的乙烯丙烯收率达到56.0%,丁烷转化率达到88.9%.     

催化裂解CH4制备碳纳米管的影响因素

以柠檬酸法制备的Fe-MgO、Co-MgO和Ni-MgO为催化剂,CH4为碳源气,H2为还原气,在873、973和1073 K制备出碳纳米管,通过TEM和拉曼光谱表征,讨论了催化剂、制备温度、反应时间等因素对碳纳米管形貌、产率和内部结构的影响.结果表明:不同的催化剂在相同的温度下制备的碳纳米管的形态和内部结构有很大的差异.其中Fe-MgO催化剂制备的碳纳米管管径粗,且大小不均匀,而Ni-MgO催化剂制备的碳纳米管管径较细、较均匀.碳纳米管的产率随着裂解温度的变化而改变.Fe-MgO催化剂制备碳纳米管的产率随制备温度的升高而提高,而Ni-MgO催化剂制备碳纳米管的产率随制备温度的升高而降低.Fe-MgO催化剂制备碳纳米管,在1073K甚至更高的制备温度才能达到其最高产率.Co-MgO催化剂制备碳纳米管的产率在973 K左右产率较高,而用Ni-MgO催化剂制备碳纳米管,则在873 K甚至更低的制备温度就能达到最高产率.反应时间与碳纳米管的产率不成正比,有一最佳反应时间,如Ni-MgO催化剂的最佳反应时间为2 h.     

催化剂制备条件对碳纳米管的影响

用柠檬酸络合法制备的Ni-La-Mg型催化剂催化裂解甲烷合成碳纳米管，并通过测定活性镍表面积研究了催化剂制备过程中柠檬酸浓度及活化温度对碳纳米管生成的影响，TEM测定结果表明，经凝胶自燃烧产生的催化剂，可通过改变柠檬酸的浓度来制得不同粒径的催化剂颗粒，从而获得一定管径的碳纳米管，另外，在500－700℃内，活化温度对催化剂活性影响不大，只有在较低或较高温度时对活性才有较大的影响。     

碳纳米管薄膜的制备及其在柔性电子器件中的应用

近年来,柔性电子器件的发展日新月异。以碳纳米管为代表的碳纳米材料,尤其是其组装成的宏观结构碳纳米管薄膜具有良好的柔性和优异的导电性,且具有化学稳定、热稳定、光学透明性等优点,在柔性电子领域展现了极大的应用潜力。本文简要综述了近年来碳纳米管薄膜在柔性电子器件领域的研究进展。首先详细介绍了碳纳米管薄膜的两类主要制备方法,分别为干法制备和湿法制备;继而介绍了碳纳米管薄膜在多种柔性电子器件的组装、性能与应用方面的最新研究进展;最后总结了碳纳米管薄膜基柔性电子领域的发展现状,并讨论了该领域所面临的挑战及其未来前景。     

C4/C5烃催化裂解制低碳烯烃的研究进展

从催化剂类型、裂解工艺、催化裂解的影响因素和裂解机理4个方面对国内外C4／C5烃催化裂解制低碳烯烃的研究进行了综述。催化裂解制低碳烯烃催化剂主要采用ZSM-5分子筛系列催化剂，在此基础上发展了酸改性或水热改性高硅ZSM系列分子筛及介孔MCM41分子筛。总结了国内外C4／C5烃的裂解工艺，认为影响催化裂解的主要因素是裂解原料、催化剂类型及工艺条件。目前，裂解机理主要是自由基与碳正离子机理相结合的机理。并简述了本课题组目前有关C4烷烃催化裂解的主要研究进展。     

催化裂解CH4或CO制碳纳米管结构性能的谱学表征

利用TEM、HRTEM、XRD、XPS和TPO等方法对CH₄或CO催化分解生成的碳纳米管结构和性能进行了表征.结果表明,所得产物是管径15～20nm的均匀碳纳米管.其XRD谱图与石墨的相近,但特征衍射峰稍宽化,表明其长程有序度较石墨的低.由CH₄制备的碳纳米管系由多层具有类石墨片状结构的同心、等径及中空圆锥形面叠合而成,类石墨层面取向与管轴倾斜;而由CO制备的碳纳米管系由多层具有类石墨片状结构的圆柱形面围叠而成,类石墨层面取向与管轴平行.碳纳米管中C_1s的电子结合能比石墨的下降约0.5eV.TPO试验结果显示所制备的两种产物中无定形碳含量都很低,其整体结构石墨化程度较高;由CH₄制得的碳纳米管与O₂反应的起燃温度比由CO制得的约高100K.     

Structural characterization and electrochemical lithium insertion properties of carbon nanotubes prepared by the catalytic decomposition of methane

Carbon nanotubes (CNTs) were synthesized by the catalytic decomposition of methane at 773, 873 and 973 K. Structures of these carbon nanotubes were characterized by TEM, HRTEM, XRD and Raman spectra, respectively. The results showed that with the increase of preparation temperature, the d ₀₀₂ value of the CNTs decreased, while the L _a values and the degree of crystallinity of the samples increased. Electrochemical lithium insertion properties of the CNTs used as positive electrodes in CNTs/Li cells were also investigated. The first charge capacities of CNTs/Li cells were 290, 254 and 202 mAh/g for samples produced at 773, 873 and 973 K, respectively. The sample from 773 K showed a larger charge capacity, which is attributed to the accommodation of lithium at microcavities, at edges of graphitic layers and at the surface of single graphitic layers. Its potential hysteresis during Li insertion and deinsertion processes may be related to the interstitial carbon atoms. Electronic Publication     

Thermal decomposition and cobalt species transformation of carbon nanotubes supported cobalt catalyst for Fischer-Tropsch synthesis

The effect of calcination condition on the cobalt species and Fischer-Tropsch synthesis (FTS) was studied. It was found that higher calcination temperature resulted in decreased FTS activities because CNTs were consumed by oxidation in air at temperature higher than 230°C. Cobalt species went through transformation from Co3O4 to metallic Co in Ar by autoreduction at temperature over 500°C. The autoreduction route might be Co3O4→CoO→Co or Co3O4→Co2C→Co. Reduction at temperature higher than 500°C also resulted in decreased FTS activities due to the methanation of CNTs in hydrogen.     

Development of multiwalled carbon nanotubes based micro-solid-phase extraction for the determination of trace levels of sixteen polycyclic aromatic hydrocarbons in environmental water samples

Micro-solid-phase extraction (μ-SPE) was developed for the determination of trace level of 16 United States Environmental Protection Agency priority polycyclic aromatic hydrocarbons (PAHs) in river water samples with gas chromatography-mass spectrometry (GC-MS). In the μ-SPE device, multiwalled carbon nanotubes was employed as sorbent and was packed inside an porous polypropylene membrane "envelope" whose edges were heat-sealed to secure the contents. The μ-SPE device was placed in a stirred sample solution to extract the analytes. The porous polypropylene membrane envelope in μ-SPE device acts as a filter to exclude potential interferences, such as eliminating or reducing the influence of particles that are bigger than the pore size. After extraction, analyte desorption was carried out with a suitable organic solvent under ultrasonication. Important extraction parameters were optimized in detail, including the selection and amount of sorbent materials, the extraction temperature and extraction time, desorption solvent and desorption time, amount of organic modifier, agitation speed and sample ionic strength. Under the developed extraction conditions, the proposed method provided good linearity in the range of 0.1-50 μg/L, low limits of detection (4.2-46.5 ng/L), and good repeatability of the extractions (relative standard deviations, <12%, n=5). The developed μ-SPE method was successfully applied to the extraction of PAHs in river water samples. The μ-SPE method was demonstrated to be a fast and efficient method for the determination of PAHs from environmental water samples.     

Multiwalled carbon nanotubes/cryogel composite, a new sorbent for determination of trace polycyclic aromatic hydrocarbons

A new cost-effective sorbent, multiwalled carbon nanotubes/poly (vinyl alcohol) cryogel composite (MWCNTs/PVA), was prepared under frozen conditions for the extraction and preconcentration of trace polycyclic aromatic hydrocarbons (PAHs) in water samples. This was followed by high performance liquid chromatography (HPLC) with fluorescence detection. The proposed method provided a high enrichment factor with an extremely high extraction efficiency (89–98%) of three spiked levels of three standard PAHs with relative standard deviations of less than 8%. The low detection limits of the method were 5, 8 and 5 ng L^{− 1} for benzo(a)anthracene, benzo(b)fluoranthene and benzo(a)pyrene, respectively. This method was successfully applied for the determination of the three PAHs in real water samples where they were found in the range of 7 to 22 ng L^{− 1}. The major advantages of MWCNTs/PVA over the commercial C₁₈ is that it can be operated at a higher loading flow rate without sorbent clogging and requires a shorter time for completion without any loss of extraction efficiency.     

Synthesis of multi-walled carbon nanotubes catalyzed by substituted ferrocenes

A range of substituted ferrocenes were used as catalysts for the synthesis of multi-walled carbon nanotubes (MWCNTs) and carbon fibers (CFs). These products were obtained in the temperature range 800-1000 °C, in a reducing atmosphere of 5% H₂ by pyrolysis of (CpR)(CpR′)Fe (R and R′ = H, Me, Et and COMe) in toluene solution. The effect of pyrolysis temperature (800-1000 °C), catalyst concentration (5 and 10 wt.% in toluene) and solution injection rate (0.2 and 0.8 ml/min) on the type and yield of carbonaceous product synthesized was investigated. Carbonaceous products formed include graphite film (mostly at high temperature; 900-1000 °C), carbon nanotubes and carbon fibers. The carbonaceous materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The ferrocene ring substituents influenced both the CNT diameter and the carbon product formed.     

Effects of negative bias on the structural,topological and tribological properties of amorphous carbon films prepared by magnetron sputtering

Amorphous carbon films were prepared in a magnetron sputtering system at different d.c. negative substrate biases (?50, ? 100, ? 150, ? 200 and ? 250 V). The surface roughness, hardness and tribological properties of as‐deposited films were investigated based on the films' structural evolution. Compared with the films deposited at the negative bias of ? 50 and ? 250 V, the microstructure and bond configuration of the films deposited at negative bias of ? 150 V favored a more graphite‐like structure, which had the maximum of graphiticclusters and ordering structures; meanwhile, the films deposited at bias of ? 150 V showed the minimum coefficient of friction (COF) in air, while the wear rate showed a decrease of two orders of magnitude. The tribotesting results were attributed to the increase of graphitic domains of amorphous carbon films which decreased the interfacial shear force and lowered the COF. The uniform and ordering structure induced steady and smooth friction curves. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermal decomposition and electron microscopy studies of single-walled carbon nanotubes

Thermoanalytical and electron microscopic methods were used as characterisation tools for the determination of the composition of single walled carbon nanotube samples. Acid purification method of single-walled carbon nanotubes (SWCN) proved to be effective, resulting in a three fold increase in the percentage of SWNTs present in the purified product as determined by thermogravimetric analysis. In this work we report the thermogravimetric analysis by conventional and high resolution methods of the raw SWNTs and purified SWNTs.     

L-酪氨酸功能化多壁碳纳米管的制备及表征

采用L-酪氨酸作为修饰剂，制备了一种新型功能化的多壁碳纳米管，并对其进行了表征。红外光谱和电化学实验均证实碳纳米管和酪氨酸是通过酰胺键共价键合的。其中，循环伏安实验中0．22V处羧基峰的消失与红外光谱中1717cm^-1处N-酰化氨基酸的-C=O峰相对应，2931和2860cm^-1处的-CH2-的伸缩振动峰的出现证明了产物的形成。     

The effect of thermal annealing on the microstructure and mechanical properties of magnetron sputtered hydrogenated amorphous carbon films

Hydrogenated amorphous carbon films were deposited by magnetron sputtering of a carbon target in a methane/argon atmosphere. A postdeposition annealing at 300 °C was performed and the microstructure, bonding structure and mechanical properties of the as‐deposited and annealed films were analyzed and compared directly by high‐resolution transmission electron microscopy, micro‐Raman spectroscopy, XPS, and nanoindentation. The results showed that the carbon films are quite stable upon annealing, since there are only minor changes in microstructure and chemical bonding in the amorphous matrix. The hardness of the films remained unaffected, but the elastic properties were somewhat deteriorated. In comparison to the outcomes of our previous work on the growth of fullerene‐like hydrogenated carbon films, we can state that the formation of fullerene‐like carbon structures requires different sputtering process conditions, such as a higher ion energy and/or different sputtering target. Copyright © 2011 John Wiley & Sons, Ltd.