载体焙烧及螯合剂种类对火焰法制备碳纳米管质量的影响

为了实现V型火焰法可控批量生产碳纳米管,以铁钼为活性中心,纳米Al_2O_3为载体,采用二次浸渍法合成Fe/Mo-Al_2O_3催化剂,研究载体焙烧及螯合剂对碳纳米管形态的影响。通过对不同催化剂合成的碳纳米管进行扫描电镜、透射电镜和拉曼光谱表征分析。结果表明:焙烧载体能够提高碳纳米管产量,促使小直径碳管的生成。柠檬酸作螯合剂能有效改善产品质量,形成长而细的碳纳米管。载体经过预处理并以柠檬酸为螯合剂制备的催化剂得到的碳纳米管产量高、缺陷少、平均直径小且管径分布窄。研究发现,载体焙烧及螯合剂种类影响碳纳米管的平均直径、直径分布及结晶度,可为调整碳纳米管性质提供简单且有效的途径。     

催化剂制备方法对碳纳米管质量和形态的影响研究

改变催化剂性质是提高碳纳米管质量的一个重要的途径。在火焰法制备碳纳米管实验中,主要对比了溶胶-凝胶法和浸渍法2种催化剂制备方法。通过扫描电子显微镜、拉曼光谱仪和透射电子显微镜3种手段对合成的碳纳米管进行系统性表征。结果表明:浸渍法制备的催化剂粘性更大,更易于粘在探针或基板上,有利于碳纳米管的大型化生产;与溶胶-凝胶法相比,用浸渍法催化剂合成的碳纳米管拉曼光谱中D峰与G峰的比值下降了12.5%,碳纳米管直径缩小了18.1%且碳管更平直,石墨化程度更高。在催化剂制备工艺相近的条件下,选择浸渍法可以改善碳纳米管的质量。     

甲烷在Ni/Al2O3催化剂上积碳与失活行为研究

采用浸渍法制备Ni/Al2O3催化剂,研究反应条件对甲烷裂解生成碳产物形貌的影响和催化剂的失活机制.结果表明:在40Ni/Al2O3催化剂上碳生成物的沉积形式均呈纤维状结构,反应温度越高、空速越大,碳纤维的直径越小;碳在金属颗粒体相中的扩散是碳纳米纤维生长过程的速率控制步骤,当碳的生成速率低于碳在Ni中的体相扩散和迁移速率,生成的炭以纤维状结构生长.     

单壁碳纳米管在基底表面的离散生长

通过旋涂硝酸铁异丙醇溶液于P型硅表面以获得均匀分布的催化剂颗粒,以CH4为反应气体采用CVD方法即可在P型硅表面均匀生长单壁碳纳米管,并且部分碳纳米管呈直立状.研究了催化剂浓度、生长基底、反应温度对单壁碳纳米管表面生长情况的影响.研究表明,催化剂浓度升高或采用二氧化硅替代P型硅为生长基底时,都会导致单壁碳纳米管生长的密度加大,而碳纳米管长度变短且更易贴附基底表面生长;随反应温度的提高碳纳米管的生长效率降低,并使得碳纳米管更易贴附基底表面生长.采用此方法制备的生长有直立碳纳米管的硅片作为扫描基底,在原子力显微镜敲击模式下利用拾取法成功制备了碳纳米管原子力显微镜针尖.     

辅助气体对RF-PECVD制备碳纳米管薄膜形貌的影响

采用射频等离子体增强化学气相沉积(RF-PECVD)技术,以Ni为催化剂,经600℃裂解C2H2在Si基底上制备出定向碳纳米管薄膜。采用扫描电子显微镜(SEM)表征了刻蚀后Ni颗粒与沉积的碳纳米管薄膜的形貌。研究了辅助气体对等离子体预处理催化剂与碳纳米管生长的影响。结果表明:辅助气体(H2与N2)流量比对催化剂颗粒尺寸、分布以及碳纳米管生长有显著影响;合适的气体流量比有利于减少碳纳米管薄膜的杂质颗粒,促进其定向生长。预处理过程中气体流量比H2:N2=20:5时,预处理后催化剂Ni颗粒分布密度大、粒径小且分布范围窄,适合碳纳米管均匀着床;沉积生长碳纳米管薄膜时,H2:N2=20:15可得到纯度高、定向性好的碳纳米管。     

定向碳纳米管薄膜的制备

以二茂铁为催化剂前驱体,氢气为载气,乙炔为碳源,硅片作衬底,用化学气相沉积法,采用不同的催化剂引入方式,在700℃下分别制备出定向碳纳米管薄膜及非定向碳纳米管薄膜.并基于实验结果对影响生长定向碳纳米管的因素进行分析,表明催化剂颗粒的诱导作用是导致生长定向碳纳米管的重要原因.     

高分散度非晶态NiB／CNTs催化剂制备及其催化加氢性能

利用苯胺、曲拉通分别对氨气热处理的碳纳米管进一步功能化，修饰碳纳米管表面，促进碳纳米管分散。采用超声波辅助的浸渍-化学还原法制备非晶态NiB／CNTs合金催化剂，平均粒径为14nm、10nm的非晶态NiB颗粒均匀分布在苯胺、曲拉通处理的碳纳米管表面。苯胺、曲拉通功能化处理使催化剂的Ni负载量分别提高了10．4％、14．6％，同时提高了催化剂的乙炔加氢活性和乙烯选择性。将苯胺和曲拉通的处理效果比较，发现无论是NiB颗粒的分散度还是催化剂的加氢性能，曲拉通处理的效果明显优于苯胺。     

用ECR-CVD方法制备定向碳纳米管

以FeaO4纳米粒子为催化剂,CH4和H2为气源,采用电子回旋共振微波等离子体化学气相沉积技术(ECR-CVD)在多孔硅基底上制备出定向生长的碳纳米管.研究了气氛组成、气压、温度和反应时间对碳纳米管生长特性的影响.使用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和拉曼光谱(Raman spectrum)表征了样品的形貌和结构.结果表明:气氛组成和气压影响了反应腔内离解碳的浓度,从而影响碳纳米管的成核、生长速度及定向生长;温度的变化改变催化剂的尺寸从而改变碳纳米管的直径,在过低的温度下碳纳米管不能实现定向生长;碳纳米管随着反应时间的延长而不断增长,但超过一定时间后催化剂颗粒被碳包覆而失去催化作用,生长停止.     

碳纤维表面生长碳纳米管及其增强复合材料性能的研究

通过电化学阳极氧化法改性碳纤维表面,利用浸渍法在连续的碳纤维表面加载了均匀的催化剂前驱体涂层,并通过化学气相沉积法(CVD)在碳纤维表面催化生长了均匀、规整的碳纳米管。利用场发射扫描电镜(FESEM)研究了电化学氧化电流强度对碳纤维表面加载催化剂颗粒的形貌与碳纤维表面催化生长碳纳米管形貌的影响,发现最佳的电化学氧化电流强度为0.4 A;Co作为催化剂时,500℃气相沉积10min后制备的复合材料层间剪切强度与未做任何处理的碳纤维及脱浆后的碳纤维作为增强体时相比,分别提高了11.0%与26.5%。     

碳纤维上原位生长碳纳米管对C/C复合材料弯曲性能的影响

以碳毡为基底原位生长了碳纳米管（CNTs）,借助化学气相渗透制备了CNTs-C/C复合材料。研究了催化剂含量对碳纳米管生长的影响以及不同含量碳纳米管对C/C复合材料弯曲性能的影响。结果表明：催化剂对CNTs产量影响较大,且含量越多,生成的CNTs量越大;原位生长CNTs引入的催化剂会导致CNTs-C/C复合材料弯曲性能变差;CNTs的加入改变了热解碳的沉积行为,诱导了球状和锥状小尺寸热解碳的形成,减少了微裂纹的出现。适量CNTs能提高C/C复合材料的弯曲强度和模量,并改善材料的断裂行为。     

Nanocarbon-induced rapid transformation of polymer surfaces into superhydrophobic surfaces

We present a facile method for fabricating superhydrophobic polymer surfaces by solubility modulation and nanocarbon (NC)-induced crystallization of polycarbonate (PC). The method consists of dipping polymer sheets in a solvent in which the polymer is partially soluble and then inducing solution crystallization by dipping the sheet in a poor solvent for several seconds. A solvent mixture of methyl ethyl ketone and isopropyl alcohol (IPA) was optimized to shorten the crystallization time in a poor solvent. Single-walled carbon nanotubes, multiwalled carbon nanotubes (MWNTs), and graphene sheets were used to nucleate PC crystallization. In particular, monolayer graphene sheets were prepared by reducing graphene oxide with hydrazine. Crystalline micro- and nanostructures rapidly formed upon dipping of the PC sheets in the solution containing NCs, followed by immersion in IPA. The structures depended on the dimensions of the NCs. Especially, in the MWNT solution, dipping for 10 s was sufficient to create a superhydrophobic surface. Crystallization of PC and the incorporation of NCs during crystallization were characterized by Raman spectroscopy.     

Effects of hydrogen on the formation of aligned carbon nanotubes by chemical vapor deposition

Well-aligned carbon nanotubes with controllable properties were grown on porous silicon substrates by thermal chemical vapor deposition. The morphologies of the carbon nanotubes were varied with the introduction of H2 during the catalyst activation and/or carbon nanotube growth processes. It was found that H2 promotes the growth of carbon nanotubes while preventing the formation of spherical amorphous carbon particles. Without the introduction of H2 during the C2H2 thermal decomposition, aligned carbon nanotubes mixed with spherical carbon particles were formed on the substrate. However, with the introduction of H2, pure carbon nanotubes were synthesized. These nanotubes also had uniform diameters of 10-20 nm, which is much smaller than nanotubes synthesized without H2. The average growth rate of nanotubes was also affected by the introduction of hydrogen into the reaction chamber during nanotube growth. With the addition of hydrogen, the average growth rate changed from 78 nm/s to 145 nm/s. A possible growth mechanism, including the effect of a high ratio of H2 to C2H2, is suggested for the growth of these well-aligned carbon nanotubes with uniform diameters.     

Pretreatment of stainless steel substrate surface for the growth of carbon nanotubes by PECVD

Multiwalled carbon nanotubes were grown from acetylene and hydrogen gas mixture directly on stainless steel plates by rf powered PECVD and then electric double layer capacitors were fabricated from them without any further treatment. It was found that suitable pretreatment of stainless steel substrates was required for the satisfactory growth of carbon nanotubes on them. In this study substrates were polished, etched in HF solution and then treated with hydrogen plasma before the growth of carbon nanotubes. SEM shows that the surface of the substrate became smooth after polishing. It was severely etched to reveal grains of stainless steel after dipping in HF solution. With hydrogen plasma treatment the grains become more rounded in shape and grew in size. When the grains size was tens of nanometers, carbon nanotubes were grown. Exposing substrates to the hydrogen plasma for 10 min or longer caused the grains to grow larger and the growth of carbon nanotubes became poorer. Carbon nanotubes grown in this study were mutiwalled and curly in shape. Capacitors made from the carbon nanotubes showed initial specific capacitance in the range of 80–100 F/g.     

In situ nucleation of carbon nanotubes by the injection of carbon atoms into metal particles

The synthesis of carbon nanotubes (CNTs) of desired chiralities and diameters is one of the most important challenges in nanotube science and achieving such selectivity may require a detailed understanding of their growth mechanism. We report the formation of CNTs in an entirely condensed phase process that allows us, for the first time, to monitor the nucleation of a nanotube on the spherical surface of a metal particle. When multiwalled CNTs containing metal particle cores are irradiated with an electron beam, carbon from graphitic shells surrounding the metal particles is ingested into the body of the particle and subsequently emerges as single-walled nanotubes (SWNTs) or multiwalled nanotubes (MWNTs) inside the host nanotubes. These observations, at atomic resolution in an electron microscope, show that there is direct bonding between the tubes and the metal surface from which the tubes sprout and can be readily explained by bulk diffusion of carbon through the body of catalytic particles, with no evidence of surface diffusion.     

选择冲洗法在碳纳米管内部填充金属粒子

报道一种直接合成纳米碳管衍生材料的方法.利用纳米碳管的表面张力和毛细管作用,经过注入和选择冲洗法的两步法,制备填充铁、钴和镍的纳米碳管.通过选择合适的注入和洗脱溶液,金属粒子只会填充在纳米管内部.使用扫描电镜和扫描透射电镜研究证实金属粒子仅存在于纳米碳管内部.     

Multicomponent and multidimensional carbon nanotube micropatterns by dry contact transfer

One of the critical aspects of nanotechnology is to assemble different nanoscale components into a single system. In such a multicomponent system, the overall functionality depends strongly on the precise location and structural characteristics of each of the constituent components. In this context, we have prepared multicomponent micropatterns of silica particles interposed within the discrete areas of aligned multiwall carbon nanotubes. The patterns were fabricated by dry contact transferring aligned carbon nanotubes onto a tape pre-patterned with a thin layer of gold structure, followed by region-specific adsorption of thiol-modified silica particles onto the gold surface from solution. The dry contact transfer technique has further enabled us to develop micropatterns of aligned single-wall carbon nanotubes with interdispersed non-aligned multiwall carbon nanotubes and microsized carbon fibers sheathed with micropatterned aligned carbon nanotubes.     

Formation of an adherent polyacrylonitrile/carbon nanotubes composite film onto a polyacrylonitrile brush electrografted on copper

An adherent polymer film based on a composite of polyacrylonitrile/multiwall carbon nanotubes (PAN/MWNTs) have been elaborated on a copper substrate. The first layer is an electrografted PAN brush on which of a subsequent layer of PAN/carbon nanotubes composite has been deposited by simple dipping from solution in dimethylformamide (DMF). MWNTs have been previously chemically functionalized with 3-cyanopropyltrichlorosilane to promote de-bundling and homogeneous dispersion of the carbon nanotubes in the composite.     

窄直径分布竹节状纳米碳管膜的制备和表征

采用短时间一次阳极氧化法制备了纳米级孔氧化铝(AAO)模板,有效地缩短了模板的制备时间,获得的AAO模板孔洞排列有序程度虽有所下降,但分布依然均匀.该模板有效地增加了表面积,为金属沉积提供了均匀的纳米孔洞.采用电沉积法在AAO模板上沉积了颗粒尺寸一致且分布均匀的钴催化剂层后,用CVD法在该模板上生长纳米碳管.经SEM和TEM观察,所制得的纳米碳管密度高直径分布均匀,具有单一的竹节状结构,而且直径远小于孔径.试用了生长动力学来解释这种竹节状纳米碳管的形成原因.     

DNA-assisted dispersion and separation of carbon nanotubes

Carbon nanotubes are man-made one-dimensional carbon crystals with different diameters and chiralities. Owing to their superb mechanical and electrical properties, many potential applications have been proposed for them. However, polydispersity and poor solubility in both aqueous and non-aqueous solution impose a considerable challenge for their separation and assembly, which is required for many applications. Here we report our finding of DNA-assisted dispersion and separation of carbon nanotubes. Bundled single-walled carbon nanotubes are effectively dispersed in water by their sonication in the presence of single-stranded DNA (ssDNA). Optical absorption and fluorescence spectroscopy and atomic force microscopy measurements provide evidence for individually dispersed carbon nanotubes. Molecular modelling suggests that ssDNA can bind to carbon nanotubes through pi-stacking, resulting in helical wrapping to the surface. The binding free energy of ssDNA to carbon nanotubes rivals that of two nanotubes for each other. We also demonstrate that DNA-coated carbon nanotubes can be separated into fractions with different electronic structures by ion-exchange chromatography. This finding links one of the central molecules in biology to a technologically very important nanomaterial, and opens the door to carbon-nanotube-based applications in biotechnology.     

等离子体射流辅助双催化剂原位催化法合成碳纳米管

以甲烷为碳源，Fe2O3／Ni为固定相催化剂，在常压条件下利用等离子体射流的高温将甲烷裂解生成碳自由基和氢气。同时联合原位催化法将碳自由基在Fe2O3／Ni双催化剂的共同作用下生长出碳纳米管。运用TEM和元素分析等测试手段对所得碳纳米管进行形貌、含量、结构的表征分析。结果表明，在一定反应条件下，可获得外径为10nm-30nm，管长约数百纳米、产率为75％左右的碳纳米管。与单催化剂相比，双催化剂的联合催化作用更有利于碳管的生长。