纳米碳管的电化学贮锂性能

用透射电镜、高分辩透射电镜、X射线衍射和拉曼光谱表征了用催化热解法制备的纳米碳管的结构,研究了纳米碳管的电化学嵌脱锂性能.以纳米级铁粉为催化剂热解乙炔气得到的纳米碳管石墨化程度较低,结构中存在褶皱的石墨层、乱层石墨和微孔等缺陷,具有较高的贮锂容量,初始容量为640mAh/g,但循环稳定性较差.而以纳米级氧化铁粉为催化剂热解乙烯得到的纳米碳管结构比较规则,循环稳定性较好,但贮锂容量较低,初始容量为282 mAh/g.讨论了纳米碳管的结构对其温度特性和不同电流密度下的充放电容量的影响.     

Ni-Mo双金属氧化物催化剂CVD法大量制备成束多壁纳米碳管

采用溶胶凝胶法合成的Ni-Mo双金属氧化物催化剂,用CVD法催化裂解甲烷从而大量制备高质量高纯度的成束多壁纳米碳管.实验结果表明,该催化剂具有很高的活性和催化效率.反应2 h后,制备的多壁纳米碳管的量可达到初始催化剂量的80倍以上.碳管的直径较均匀,在10～20 nm之间.随着反应时间的延长,制备的纳米碳管石墨化程度增加,反应1 h后,粗产品中纳米碳管的含量就超过了97％. 简单放大后,单炉每克催化剂可以在0.5 h内制得40 g以上多壁纳米碳管.     

Fe—Co双金属催化剂对纳米碳管规模化生产的影响

在C2H2和N2的氛围下,以Fe－Co双金属氧化物为催化剂,利用催化裂解法大量制备了多壁纳米碳管,实验结果表明,以Fe－Co双金属氧化物为催化剂制备纳米碳管的产量明显高于Fe或Co单独存在时所得的纳米碳管的产量,且Fe摩尔分数为0.2时效果最佳;同时发现,在制备的产品中存在很多螺旋形的纳米碳管,此方法工艺简单,有利于纳米碳管的规模化、大批量生产,为纳米碳管的深入研究及广泛应用打下了基础。     

以介孔分子筛为金属催化剂载体制备纳米碳管

 以不同的介孔分子筛作为金属催化剂载体,对催化合成纳米碳管进行了系统的研究,讨论了反应条件对纳米碳管纯度和产量的影响. 结果表明,不同的介孔分子筛对金属活性中心的形成、碳组分的扩散、纳米碳管的管径及形态均有明显的影响. 此外,金属的种类、状态和含量也影响纳米碳管的合成. 探索了合成高产量纳米碳管的条件,并对介孔分子筛上生长纳米碳管的特点进行了讨论.     

纳米碳管负载金属镍催化叶绿素加氢反应

用等体积浸渍法制备了纳米碳管负载金属镍催化剂，采用电镜(TEM）、红外光谱（IR）对催化剂的形貌、结构进行了表征.并考察了常温常压下不同Ni负载量的催化剂对叶绿素加氢反应的性能.结果表明，纳米碳管负载镍催化剂在催化反应过程中保持高分散态，不会发生团聚.而经过硝酸氧化后的纳米碳管负载镍催化剂在催化反应中表现出高的活性.当Ni负载量为7％时，催化活性最好，叶绿素分子开环生成各种小分子.     

过渡金属氧化物和金属负载型沸石催化剂上合成 纳米碳管及其表征

采用气相催化沉积法催化合成纳米碳管,比较了不同金属氧化物和金属负载型沸石催化剂以及不同分子筛载体对合成纳米碳管的影响,并用TEM,XRD表征其形貌和结晶度,用DTA-TG考察了纳米碳管的热和稳定性。实验结果表明纳米碳管的形成除了与金属种类有关外,还直接与催化剂的颗粒大小和分散状态有关。粒径在20nm左右的不规则形状的纳米粒子是形成纳米碳管的活性组分,非负载和负载型的催化剂均表明活性组分的粒径与纳米碳管的管径有一定的对应关系。化学提纯后能得到高纯度的纳米碳管;其管壁具有较好的石墨化结构,在空气中的热稳定性大于400℃,而在氮气中能维持到1200℃以上。     

Ni基催化剂上CH4裂解制备纳米碳管的研究

本文研究了负载型Ni催化剂上, 以CH4为原料制备纳米碳管的方法。考察了载体、温度、CH4浓度及在反应气中添加O2或CO2等因素对纳米碳管的生长的影响。实验发现, 采用稀释的CH4在较低的温度下反应或在反应气中添加O2或CO2均有利于纳米碳管的生长。     

La~2NiO~4催化制备纳米碳管

制备了四方结构复合氧化物La~2NiO~4,并以其为催化剂前体,甲烷和一氧化碳为碳,合成出大量高纯度的纳米碳管。XRD结果表明La~2NiO~4经还原后,在La~2O~3的隔离作用下Ni晶粒实现纳米级均匀分散。利用TEM,HRTEM,SEM,XRD,Raman等手段对所制备的纳米碳管进行了观察和表征。所制备的纳米碳管管径均匀、石墨化程度较高,该法制备纳米碳管工艺简单、产量较高,产品易于纯化。     

纳米碳管负载金属镍催化叶绿素加氯反应

用等体积浸渍法制备了纳米碳管负载金属镍催化剂，采用电镜（TEM）、红外光谱（IR）对催化剂的形貌、结构进行了表征，并考察了常温常压下不同Ni负载量的催化剂对叶绿素加氢反应的性能。结果表明，纳米碳管负载镍催化剂在催化反应过程中保持高分散态，不会发生团聚，而经过硝酸氧化后的纳米碳管负载镍催化剂在催化反应中表现出高的活性，当Ni负载量为7％时，催化活性最好，叶绿素分子开环生成各种小分子。     

高Co含量的Co-Mo系列催化剂甲烷裂解制备单壁纳米碳管

制备了高Co含量的Co-Mo／γ-A12O3系列催化剂，发现此类催化剂可以在温和的反应温度下制备高质量的单壁纳米碳管．讨论了Mo组分的作用．认为Mo分散、稳定金属颗粒，促进了SWNTs的生长．同时，Mo组分的升华决定了单壁纳米碳管的生长和管径分布．这为可控地制备单壁纳米碳管提供了依据．     

Formation and growth mechanism of dissimilar coiled carbon nanotubes by reduced-pressure catalytic chemical vapor deposition

Dissimilar coiled carbon nanotubes were prepared by catalytic chemical vapor deposition (CCVD) on finely divided Co nanoparticles supported on silica gel under reduced pressure and at lower gas flow rates. The morphology of the regular coiled carbon nanotubes were examined by TEM, while the polygonization characteristics of the helix were examined by SAED. Observations were made on other forms of irregular coils with various shapes by TEM. On the basis of the heptagon-pentagon construction theory, we proposed a helix formation mechanism, which involves a carbon core formation centering on a catalytic particle followed by carbon helices growth controlled by kinetics.     

Production of single-walled carbon nanotubes from methane over Co-Mo/MgO nanocatalyst:A comparative study of fixed and fluidized bed reactors

In this study,the performances of fixed and fluidized bed reactors in the production of single-walled carbon nanotubes(SWNTs)have been investigated.In both reactors,single-walled carbon nanotubes were grown by catalytic chemical vapor decomposition(CCVD)of methane over Co-Mo/MgO nanocatalyst under two different operating conditions.The synthesized samples were characterized by TEM,TGA and Raman spectroscopy.It is found that the performance of a fluidized bed in the synthesis of carbon nanotubes is much better than that of a fixed bed.The quality of carbon nanotubes obtained from the fluidized bed was significantly higher than that from the fixed bed and the former one with the ID/IG ratio of 0.11 while the latter one with the ID/IG ratio of 0.71.Also,the yield of SWNTs in the fluidized bed was 92 wt%,while it was 78 wt%in the fixed bed.These advantages of fluidized bed reactors for the synthesis of carbon nanotubes can be attributed to more available space for the growth of carbon nanotubes and more uniform temperature and concentration profiles.     

Bundles of identical double-walled carbon nanotubes

In a sample produced by catalytic chemical vapor deposition (CCVD), the structure of the carbon nanotubes (diameter and helicity) which governs their electronic properties, is determined by electron diffraction. We found that most of the smallest bundles are constituted of identical double-walled carbon nanotubes.     

Gram-scale CCVD synthesis of double-walled carbon nanotubes

Synthesis of clean double-walled carbon nanotubes by a catalytic chemical vapour deposition (CCVD) method is reported; the catalyst is a Mg(1 - x)Co(x)O solid solution containing additions of Mo oxide; this MgO-based catalyst can be easily removed, leading to gram-scale amounts of clean carbon nanotubes, 77% of which are double-walled carbon nanotubes.     

Production of Carbon Nanotubes on Different Metal Supported Catalysts

Multiwall carbon nanotubes have been prepared by catalytic chemical vapor deposition (CCVD) method in high yield using various metals supported on different supports. Measurements by transmission electron microscopy (TEM) revealed the presence of high quality nanotubes on each catalyst, however, comparing the different catalysts in nanotube production it can be stated that beyond metals, the support also affects both the quality and the quantity of nanotubes.     

Nanotubes as polymer composite reinforcing additive materials – A comparative study

Nitrogen-doped bamboo-shaped carbon nanotubes (N-BCNTs) and their non-doped conventional counterparts, multiwalled carbon nanotubes (MWCNTs) were compared as polymer reinforcing additives in polyvinyl chloride (PVC) matrix. The nanotubes were synthetized by catalytic chemical vapor deposition (CCVD) method. The purity of both nanotubes was measured by thermogravimetric analysis (TGA) and found to be >91%. Further analysis on the morphology and size of the carbon nanotubes (CNTs) were performed by transmission electron microscopy (TEM). The PVC powder was impregnated with CNTs in ethanol by using tip ultrasonicator. The dispersion media was evaporated, and the CNT/PVC powder was used to produce polymer fibers. The orientation of carbon nanotubes in the PVC matrix was characterized by scanning electron microscopy (SEM), and the presence of nanotubes were confirmed in case of all PVC samples. It can be observed on the SEM images that the nanotubes are fully covered with PVC. The tensile strength of the nanotube containing samples was tested and the N-BCNT/PVC composite was found to be better in this sense, thanks to the extraordinary structure of the nanotube. In case of the N-BCNT/PVC composite the measured young modulus was 39.7% higher, while the elongation at brake decreased by 33.6% compare to the MWCNT/PVC composite. These significant differences in the mechanical properties of the composites can be explained with the stronger interaction between N-BCNTs and PVC.     

螺旋纳米碳纤维的制备与表征

利用氢电弧等离子体法制备了纳米铜-镍合金作为催化剂,通过乙炔的催化热解制备了对称生长的螺旋纳米碳纤维.并用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和红外(IR)对其进行表征,发现在单个纳米铜-镍合金粒子上对称生长出两根螺旋纳米碳纤维,它们的旋向相反,但是具有相同的螺旋直径、螺旋长度和碳纤维直径,而且纳米铜-镍合金粒子也有各种不同的形状.此外,这两根对称生长的螺旋纳米碳纤维之间的夹角也不同,分别为60°,90°,110°和160°.IR结果表明,螺旋纳米碳纤维分子结构中既含有不饱和的CC双键,又含有饱和的-CH₂-和-CH₃-基团.然而,利用氢电弧等离子体法制备的纳米铜和纳米镍作为催化剂,催化热解乙炔,得到的产物均是直线型碳纤维.     

Acetylene Sorption Dynamics in Carbon Nanotubes

Single‐walled and multi‐walled carbon nanotubes (SWNT and MWNT, resp.) were prepared by applying the catalytic chemical vapor deposition (CCVD) technique. Different nanotube samples were obtained from the as‐synthesized carbon/catalyst composites by treatments applied to remove the catalyst and the amorphous carbon. The dynamic and equilibrium adsorption properties of the samples were compared. Acetylene was used as an adsorptive probe. The sorption mass‐transport properties have been characterized by applying the frequency response (FR) technique. Results reflected that the surface functional groups, generated by an oxidative treatment, have significant influence on both the static and the dynamic acetylene sorption properties of the carbon nanotube materials. The rate of acetylene mass transport was governed by the rate of sorption in all the samples, except in MWNT after oxidative treatment, where the intracrystalline diffusion in the nanotubes was the rate‐controlling process.     

Carbon Nanotubes: An Example of Multiscale Development—A Mechanistic View from the Subnanometer to the Meter Scale

We summarize the catalytic synthesis of multiwall carbon nanotubes (MWCNTs). The current understanding of the reaction mechanism is presented, in particular the catalyst design for the CCVD process is analyzed. To complement that, kinetics and reaction engineering aspects are discussed along with the impact of the reaction and reactor operation on the product properties. All these issues are analyzed from the perspective of the industrial synthesis and implications for the application of carbon nanotubes. Carbon‐nanotube technology is a perfect example of multi‐scale development and covers challenges from the nanometer to the meter scale. Problems, methods, and solutions characteristic for different scales will be highlighted. The Co/Mn catalyst is used as reference as one of the first commercially used technologies for the scalable production of multiwall carbon nanotubes.     

Influence of diameter on the degradation profile of multiwall carbon nanotubes

Nanofluid and coiled tubes have been employed as two passive methods for enhancing the heat transfer. In the present study, the turbulent flow of CuO–water nanofluid in helical and conical coiled tubes was numerically investigated with constant wall temperature through mixture model. The thermophysical properties of base fluid (water) were considered as temperature-dependent functions, while Brownian effects were adopted in thermal conductivity and dynamic viscosity of nanofluid. Simulation results were validated using experimental data for heat transfer coefficient and pressure drop in helical coiled tube for different Reynolds numbers. Four different geometries were simulated and compared. The first one was a conical coiled tube; the others were helical coiled tubes whose coil diameters were minimum, maximum, and median of the conical coiled tube pitch coil diameter. The velocity profiles indicated stronger secondary flow in conical coiled tube at a specified Dean number. The obtained results also showed higher heat transfer enhancement in the conical coiled tube in comparison with helical coiled tube with the same average pitch coil diameter. Moreover, the nanoparticle-induced heat transfer enhancement was more effective in conical coiled tube.