乙醇火焰燃烧制备螺旋碳纳米纤维及结构分析

采用乙醇火焰燃烧, 借助于基板材料上涂敷锡盐作为催化剂前驱体, 制备了螺旋结构碳纳米纤维; 借助于扫描电子显微镜、透射电子显微镜、XRD和拉曼光谱等分析了螺旋碳纤维的形貌和结构. 螺旋碳纳米纤维螺旋直径约为100nm, 纤维直径约为50nm, 螺距约80nm. 螺旋碳纤维的石墨层方向基本垂直于轴向, 近似鱼骨型结构, 相邻碳层间距为0.34nm. 借助于高分辨电子显微镜分析了螺旋碳纳米纤维的形成机理, 认为碳原子沿催化剂SnO₂各晶面析出速度不同是形成螺旋碳纳米纤维的主要原因.     

纳米洋葱碳的制备及其纯化研究

以甲烷为碳源,316号不锈钢网为催化剂,800℃下催化裂解甲烷,采用化学气相沉积法制备平均粒径为70~100nm纳米洋葱碳,通过酸洗-低温煅烧-磁选方法对洋葱碳进行纯化处理。X射线衍射、扫描电子显微镜、透射电子显微镜、红外吸收光谱、拉曼光谱和振动样品磁强计对样品的形貌结构、物相组成及磁性能进行表征分析。结果表明,酸洗-低温煅烧能有效去除初产物中裸露的催化剂颗粒及无定型碳,磁选则实现将内包有[Fe-Ni]磁性催化剂的洋葱碳与空心的洋葱碳分离,最终获得纯净的空心纳米洋葱碳。     

催化燃烧法制备碳纳米纤维球形团聚物

采用催化燃烧法制备碳纳米纤维球形团聚物，采用乙醇、丙酮分别作为碳源，采用硝酸镍、硝酸铁分别作为催化剂先体，采用铜片和铂丝分别作为基底。实验表征结果表明采用不同催化剂先体制备出的碳纳米纤维球形团聚物形貌相似，且都是由一维碳纳米纤维组成。最后对碳纳米纤维球形团聚物形成机理做了讨论。     

多方向生长碳纳米纤维的催化燃烧制备

介绍一种简单的合成具有多方向生长结构的碳纳米纤维的工艺。该工艺采用甲醇作为碳源，在铜基底上，以硝酸镍作为催化剂先体，经甲醇催化燃烧分解直接合成该结构材料，而无需任何模板。通过扫描电子显微镜的表征，不同分支结构的碳纳米纤维被合成。透射电子显微镜的结果表明，该样品具有较好的微结构。     

催化剂对乙醇催化燃烧法制备碳纳米纤维的影响

分别以硝酸铁、硝酸钴、硝酸镍以及氯化铁、氯化钴、氯化镍作为催化剂先体，利用乙醇催化燃烧法制备了碳纳米纤维。利用扫描电子显微术、透射电子显微术和X射线能量分散谱术对样品进行了表征。讨论了不同种类的催化剂先体对产物形貌和生长机制的影响。     

碳纳米团簇向碳纳米纤维相转变机理研究

为了能够快速且大面积生长碳纳米纤维,研究碳纳米纤维的形成、转变及在各种物理、化学环境下的反应机理,应用等离子化学气相沉积(PECVD)方法,以CH4为反应气体,FeCl2为催化剂在玻璃衬底上生长碳纳米薄膜.应用扫描电镜(SEM)观察了碳纳米纤维薄膜的表面形貌,拉曼(Raman)光谱分析了碳纳米纤维的结构组成.结果表明,无催化剂时薄膜主要由纳米团簇构成,而催化作用下薄膜呈纤维状生长,纳米纤维为典型的碳纳米管石墨特征峰.在温度,气压,催化剂等反应条件中,FeCl2催化剂对碳纳米薄膜的取向生长起决定性作用,通过调节催化剂的浓度与分布,可有效改变碳纳米纤维的密度与分布.     

乙醇催化燃烧法制备竹节形碳纳米管

乙醇催化燃烧法可以方便的制备出碳纳米管和碳纳米纤维。介绍采用该方法制备出一种独特的竹节形的碳纳米管，利用乙醇作为碳源和燃料，提供材料生长所需的能量；利用Cu薄片作为基底；利用FeCl3或Fe（NO3）3作为催化剂先体。通过扫描电子显微镜（SEM），透射电子显微镜（TEM），对黑色絮状的沉积产物进行表征。实验结果表明，产物中的碳纳米管具有较好的竹节形结构。实验也表明制备的竹节形碳纳米管的形貌和微结构与其独特的制备条件有关，如：火焰的抖动，催化剂先体溶液的浓度，制备时间等。并对竹节形碳纳米管的形貌和生长机制进行了详细的讨论。     

脉冲电沉积法应用于铂/垂直取向石墨烯直接甲醇燃料电池催化剂

通过恒电压以及脉冲电压在直接甲醇燃料电池(DMFCs)阳极催化剂载体(垂直取向石墨烯)表面电沉积Pt。对制得的催化剂采用扫描电子显微镜、透射电子显微镜、拉曼光谱仪、X射线衍射仪进行了表征,并采用电化学测试研究了其甲醇氧化能力。结果表明,当采用垂直取向石墨烯-碳纸(VG-CP)作为载体,且使用脉冲电压法可获得粒径更小、分布更均匀的Pt纳米颗粒,具有更优异的催化甲醇氧化性能。     

不同氩气与氢气流量比对硼掺杂纳米金刚石膜的影响

采用直流热阴极PCVD方法,以B(OCH3)3作为硼源,通过改变氩气与氢气流量比,在p型Si衬底上沉积了硼掺杂纳米金刚石膜.研究了不同氩气与氢气流最比对掺硼金刚石膜生长的影响.采用扫描电子显微镜、拉曼光谱仪、X射线衍射仪、霍尔系统等对样品的形貌、结构和导电性能进行了表征.结果表明,随着氩气与氢气流量比的增加,膜的晶粒尺寸由微米级向纳米级转变,并且膜中非晶碳成分增多,膜的导电性能变好.     

纳米碳纤维的低温制备——催化剂粒子尺寸的影响

以采用电阻加热法制备的纳米铜粒子为催化剂,在低温下催化乙炔制备了纳米碳纤维。所制备的纳米碳纤维具有螺旋型和直线型两种形貌。采用透射电子显微镜(TEM)和扫描电子显微镜(SEM)对纳米碳纤维进行了表征。纳米铜催化剂粒子在催化纤维的生长过程中,经历了一个重要的形状变化过程。催化剂粒子尺寸对所制备的纳米碳纤维的形貌有很大的影响。通常有两根螺旋纳米碳纤维以对称模式在单个粒径小于50nm的催化剂粒子上生长,它们的旋向相反,但是具有相同的螺旋直径、螺旋长度、螺旋缠绕程度和纤维直径。较大尺寸的催化剂粒子易生长直线型纳米碳纤维。     

Effects of the size of nano-copper catalysts and reaction temperature on the morphology of carbon fibers

In this study, carbon fibers with different morphologies, including coiled carbon nanofibers and straight carbon fibers, were obtained by the chemical vapor deposition using a Cu-catalytic pyrolysis of acetylene at 250 °C. The influences of nano-copper catalyst particle size and the reaction temperature on the morphology of carbon fibers were investigated. Under the same reaction condition, coiled carbon nanofibers generally were synthesized using nano-copper catalyst with smaller particles size, and bigger copper particles are apt to produce straight carbon fibers. With decreasing of reaction temperature to 200 °C, straight carbon fibers were obtained, instead of coiled carbon nanofibers at 250 °C. The product was characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray powder diffraction (XRD).     

Growth of carbon nanostructures on carbonized electrospun nanofibers with palladium nanoparticles

This paper studies the mechanism of the formation of carbon nanostructures on carbon nanofibers with Pd nanoparticles by using different carbon sources. The carbon nanofibers with Pd nanoparticles were produced by carbonizing electrospun polyacrylonitrile (PAN) nanofibers including Pd(Ac)(2). Such PAN-based carbon nanofibers were then used as substrates to grow hierarchical carbon nanostructures. Toluene, pyridine and chlorobenzine were employed as carbon sources for the carbon nanostructures. With the Pd nanoparticles embedded in the carbonized PAN nanofibers acting as catalysts, molecules of toluene, pyridine or chlorobenzine were decomposed into carbon species which were dissolved into the Pd nanoparticles and consequently grew into straight carbon nanotubes, Y-shaped carbon nanotubes or carbon nano-ribbons on the carbon nanofiber substrates. X-ray diffraction analysis and transmission electron microscopy (TEM) were utilized to capture the mechanism of formation of Pd nanoparticles, regular carbon nanotubes, Y-shaped carbon nanotubes and carbon nano-ribbons. It was observed that the Y-shaped carbon nanotubes and carbon nano-ribbons were formed on carbonized PAN nanofibers containing Pd-nanoparticle catalyst, and the carbon sources played a crucial role in the formation of different hierarchical carbon nanostructures.     

Fabrication of multi-walled carbon nanotube reinforced polyelectrolyte hollow nanofibers by electrospinning

Hybrid hollow multi-walled carbon nanotubes (MWCNTs)/polyelectrolytes (PE) nanofibers were prepared by a combination of the electrospinning method and layer-by-layer (LbL) technique. The mixed polystyrene (PS)/MWCNTs nanofibers were obtained by electrospinning method, which were employed as templates to self-assembly multilayered polyelectrolytes by LbL technique. Hollow MWCNTs/PE nanofibers were obtained by selectively removed part of the template: PS, which is confirmed by Raman spectra, transmission electron microscopy (TEM) and scanning electron microscopy (SEM).     

Growth of carbon nanofibers and related structures by combined method of plasma enhanced chemical vapor deposition and aerosol synthesis

Growth of carbon nanofibers and nanotubes by combination of aerosol synthesis and plasma-enhanced catalytic chemical vapor deposition with alcohol as carbon precursor is presented. Only a hollow cathode glow discharge (HCGD) is used as gas activation process without any specific heating of the substrate. Specially designed hollow cathode enables the evaporation of catalyst directly on the substrate for catalytic growth. Product of physical vapor deposition process was examined by energy dispersive X-ray spectrometer (EDS). Spectroscopic features of the plasma were monitored by optical emission spectroscopy (OES). Carbon deposition was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Catalytic nanofibers and multi-walled carbon nanotubes with outer diameters 20-60 nm have been observed.     

Electrocatalysts for methanol oxidation based on platinum/carbon nanofibers nanocomposite

New carbon nanomaterials, i.e., carbon nanotubes and nanofibers, with special physico-chemical properties, are recently studied as support for methanol oxidation reaction electrocatalysts replacing the most widely used carbon black. Particularly, carbon fibrous structures with high surface area and available open edges are thought to be promising. Platelet type carbon nanofibers, which have the graphene layers oriented perpendicularly to the fiber axis, exhibit a high ratio of edge to basal atoms. Different types of carbon nanofibers (tubular and platelet) were grown by plasma enhanced chemical vapour deposition on carbon paper substrates. The process was controlled and optimised in term of growth pressure and temperature. Carbon nanofibers were characterised by high resolution scanning electron microscopy and X-ray photoelectron spectroscopy to assess the morphological properties. Then carbon nanofibers of both morphologies were used as substrates for Pt electrodeposition. High resolution scanning electron microscopy images showed that the Pt nanoparticles distribution was well controlled and the particles size went down to few nanometers. Pt/carbon nanofibers nanocomposites were tested as electrocatalysts for methanol oxidation reaction. Cyclic voltammetry in H2SO4 revealed a catalyst with a high surface area. Cyclic voltammetry in presence of methanol indicated a high electrochemical activity for methanol oxidation reaction and a good long time stability compared to a carbon black supported Pt catalyst.     

Carbon helixes produced by hot filament assisted chemical vapor deposition

Carbon helix nanofibers were synthesized by a hot filament assisted chemical vapor deposition at a substrate temperature of 600 °C. It was observed that the formation of a carbon helix structure was attributed to the mixing of cobalt catalyst particles with copper. The diameter of carbon helixes varied from 20 to 500 nm. The growth mechanism and the structure of these carbon helix nanofibers are discussed based on scanning electron microscopy and Raman spectroscopy measurements.     

Controlled growth of carbon nanofibers using plasma enhanced chemical vapor deposition: Effect of catalyst thickness and gas ratio

The characteristics of carbon nanofibers (CNFs) grown, using direct current plasma enhanced chemical vapor deposition system reactor under various acetylene to ammonia gas ratios and different catalyst thicknesses were studied. Nickel/Chromium-glass (Ni/Cr-glass) thin film catalyst was employed for the growth of CNF. The grown CNFs were then characterized using Raman spectroscopy, field emission scanning electron microscopy and transmission electron microscopy (TEM). Raman spectroscopy showed that the Ni/Cr-glass with thickness of 15 nm and gas ratio acetylene to ammonia of 1:3 produced CNFs with the lowest I_D/I_G value (the relative intensity of D-band to G-band). This indicated that this catalyst thickness and gas ratio value is the optimum combination for the synthesis of CNFs under the conditions studied. TEM observation pointed out that the CNFs produced have 104 concentric walls and the residual catalyst particles were located inside the tubes of CNFs. It was also observed that structural morphology of the grown CNFs was influenced by acetylene to ammonia gas ratio and catalyst thickness.     

Hierarchical carbon nanostructure design: ultra-long carbon nanofibers decorated with carbon nanotubes

Hierarchical carbon nanostructures based on ultra-long carbon nanofibers (CNF) decorated with carbon nanotubes (CNT) have been prepared using plasma processes. The nickel/carbon composite nanofibers, used as a support for the growth of CNT, were deposited on nanopatterned silicon substrate by a hybrid plasma process, combining magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD). Transmission electron microscopy revealed the presence of spherical nanoparticles randomly dispersed within the carbon nanofibers. The nickel nanoparticles have been used as a catalyst to initiate the growth of CNT by PECVD at 600°C. After the growth of CNT onto the ultra-long CNF, SEM imaging revealed the formation of hierarchical carbon nanostructures which consist of CNF sheathed with CNTs. Furthermore, we demonstrate that reducing the growth temperature of CNT to less than 500°C leads to the formation of carbon nanowalls on the CNF instead of CNT. This simple fabrication method allows an easy preparation of hierarchical carbon nanostructures over a large surface area, as well as a simple manipulation of such material in order to integrate it into nanodevices.