【作者】 张晨光；

【导师】 李家俊； James M.Tour；

【作者基本信息】 天津大学 ， 材料学， 2013， 博士

【摘要】 碳纳米洋葱、碳纳米管与石墨烯是石墨的三种纳米级尺寸的同素异形体，分别为零维颗粒、一维线性和二维薄膜结构。它们都具有优良的导电与导热性能，高的比表面积及良好的力学性能，因此在电子器件、复合材料、储能介质与生物材料等领域有着重要的应用价值。目前，碳纳米材料的生长与应用领域仍有很多有待解决的问题，包括碳纳米材料的可控生长，新型碳纳米材料结构的合成，碳纳米材料的在储能领域的应用。本文首次采用NaBH4还原法制备Fe-Ni合金催化剂，并以氧化镁为载体，利用化学气相沉积法(CVD)催化合成了碳纳米洋葱(CNOs)，研究了催化剂含量、载体种类、生长温度与时间等工艺条件对CNOs结构与形貌的影响，考查了高温退火温度对空心CNOs生成的影响，并对空心CNOs合成工艺和生长机理进行了探索，研究了CNOs的电化学储氢性能。研究发现，当以MgO为载体，催化剂含量为10%，生长温度与时间分别为850°C和0.5h时，可获得分散良好且尺寸均匀的CNOs。由于Fe-Ni合金催化剂中对碳原子溶解度较小的Ni原子的存在，会推迟催化剂的失活，生成空心CNOs。在1100°C的高温退火条件下，包覆Fe-Ni合金的实心CNOs可生成大量的空心CNOs。空心CNOs的电化学储氢性能优于实心CNOs，其电化学储氢量达1.76%。本文还对比研究了浸渍法制备的Ni、Fe-Ni与Fe三种催化剂对合成CNOs的结构与形貌的影响，并研究了CNOs作为润滑油添加剂的减摩性能，同时初步研究了它们的磁存储性能。结果表明，5%的催化剂含量下，三种催化剂合成的产物为内包核的碳洋葱纳米颗粒，分别为Ni@CNOs、Fe0.64Ni0.36@CNOs与Fe3C@CNOs，产物的纯度高，无其他形式的碳产物。CNOs作为润滑剂在润滑油中的最佳添加量为0.1%，Fe3C@CNOs在500N的载荷下摩擦系数μ可达到0.026。磁学性能测试显示Ni@CNOs呈超顺磁性；Fe0.64Ni0.36@CNOs的Mr/Ms约为0.22，矫顽力Hc为228.4Oe，显示了其在高密度磁存储材料与存储介质包覆材料中的应用前景。本文首次利用单分散的颗粒平均直径为~4nm的AlFe2O4催化剂，采用CVD法合成了大直径单壁碳纳米管(SWCNT)阵列，研究了催化剂种类与浓度、载体的种类与涂覆量、气压与水蒸气通入量等生长条件对SWCNT阵列生长高度、质量与结构的影响，并通过透射电镜与原子力显微镜的表征和分子动力学模拟研究了少壁碳管的塌陷行为与临界直径。结果表明，AlFe2O4催化剂的催化活性优于Fe3O4催化剂，Al原子的掺杂可有效防止催化剂颗粒团聚，从而增加SWCNT阵列生长高度和质量。本实验条件下获得的生长SWCNT阵列最佳条件为乙炔、氢气与水蒸气混合气体的气压4.9Torr，溅射Al镀层为载体，AlFe2O4纳米颗粒为催化剂且催化剂溶液浓度为25nM，阵列底端的IG/ID达18.5，阵列高度达100μm。经实验表征与模拟证实，SWCNT与双壁碳管发生塌陷的临界直径分别为2.6nm和4.0nm。本文首次利用钾原子插层与展开法将多壁碳纳米管(Multi-Walled CarbonNanotubes, MWCNTs)阵列转化为石墨烯纳米带阵列，研究了展开处理之后MWCNT的结构变化、分析了其作为超级电容器电极材料的储能性质及机理。研究发现，展开后的MWCNT的结构为外层石墨烯纳米带-内层少壁碳管的复合结构。超级电容器的性能测试显示，展开后的MWCNT阵列的比容量为106.2F/g，是原始的MWCNT阵列的~4倍；其能量与功率密度均高于原始MWCNT阵列，在能量密度为5.2Wh/kg时功率密度达最大为103kW/kg；展开后的MWCNT的外层的石墨烯纳米带增加了有效可利用面积，内层的少壁碳管的优良的导电性提供了高效的电荷传输，且碳管垂直阵列的形貌为离子的传输提供了笔直的快速的通道。更多还原

【Abstract】 Carbon nano-onions (CNOs), carbon nanotubes (CNTs) and graphene are thethree allotropes for graphite at nanoscale. They are0-dimensional particle,1-dimensional wire and2-dimensional film structures, respectively. Due to theirexcellent electrical and thermal conductivity, high specific surface area, as well as thegood mechanical properties, they show great application potentialities in the fields ofelectronics device, composites, energy-storage media, biomaterials, and etc. However,at present there still remains a number of problems in the growth and applications ofcarbon nano-materials, including controllable growth of carbon nano-materials,synthesis of novel-structured carbon nano-materials and applications of carbonnano-materials in energy storage field.This study first reports the synthesis of Fe-Ni alloy catalyst from NaBH4reduction method and the use of Fe-Ni alloy catalyst and MgO substrate for growingcarbon nano-onions by CVD method. The influence of catalyst content, types ofsubstrate, growth temperature and growth time on the structure and morphology ofCNOs has been investigated. The influence of annealing temperatures on the growthof hollow CNOs, the growth mechanism of hollow CNOs and the mechanism of itsuse in electrochemical hydrogen storage have been also investigated. Studies haveshown that well-dispersed and uniform-sized CNOs can be obtained at the optimumconditions: catalyst content of10%, use of MgO substrate, growth temperature of850°C and growth period of0.5h. Due to the presence of Ni atoms which have a lowcarbon solubility, the deactivation of Fe-Ni alloy catalyst can be retarded, allowing forthe growth of hollow CNOs. By annealing at1100°C, large amounts of hollow CNOscan be obtained from the Fe-Ni alloy encapsulated CNOs. Hollow CNOs exhibit asuperior electrochemical hydrogen storage performance to the solid CNOs, with acapacity of1.76%. A comparative study of the influence of three types of catalysts: Ni,Fe-Ni alloy and Fe on the structure and morphology of CNOs was also carried out inthis study. The anti-friction properties of the CNOs as lubricants and their magneticstorage properties have also been investigated. Studies have shown that the CNOsgrown by different catalysts are Ni@CNOs, Fe0.64Ni0.36@CNOs and Fe3C@CNOs,respectively. By growing at a catalyst content of5%, a high purity of CNOs have been obtianed without any other carbon structures. As lubricants, the optimum additionamount in the oil of the CNOs is0.1%. A friction coefficient μ of0.026is achievedunder500N from Fe3C@CNOs. The magnetic propery tests show that the Ni@CNOsexhibit paramagnetic behavior, whereas the Fe0.64Ni0.36@CNOs exhibit a Mr/Ms andcoercive Hc of0.22and228.4Oe, respectively, indicating an application potentialityin high-density magnetic storage media and its encapsulating materials.This study first reports the synthesis of large-diameter SWCNT carpet by CVDmethod from monodispersed AlFe2O4nanoparticles with an average diameter of~4nm. The influence of types and concentrations of catakysts, types and coatingamounts of the substrate, growth pressure and water vapor amounts on the height,growth quality and structures of the SWCNT carpet have been investigated. Thecollapsing behavior and critical diameters of the few-walled CNTs have been studiedusing atomic force microscope, transmission electron microscope and moleculardynamics simulations. Studies show that the AlFe2O4nanoparticle has a highercatalyst activity Fe3O4nanoparticle, as the doping of Al atom is able to prevent thecoalescence of catalyst nanoparticles, thus providing a high-quality and tall SWCNTcarpet. The optimum conditions for growing the best quality SWCNT carpet is:pressure of mixing gas of acetylene, hydrogen and water vapor at4.9Torr, sputteredAl as substrate, concentration of AlFe2O4nanoparticles of25nM. The SWCNT carpethas a bottom IG/IDratio of18.5and a height of100μm. Through the experimentcharacterizations and simulation verifications, the critical diameterDe eqxepforSWCNT and DWCNT collapsing are2.6nm and4.0nm, respectively.This study first reports the splitting of MWCNT carpet by K atom intercalationapproach into graphene nano-ribbon carpet. The structural changing, supercapacitorproperties and charge storage mechanism of the split MWCNT carpet have beeninvestigated. Studies show that the split MWCNTs have a composite structureconsisting of outer graphene nanoribbons-inner few-walled CNTs.The split MWCNTcarpet as supercapacitor electrode materials exhibit a specific capacity of106.2F/g,~4times more than that of the original MWCNT capet. The split MWCNT carpet alsoshows higher power and energy densities than that of the original MWCNTs. Powerdensity of103kW/kg was obtained while maintaining an energy density of5.2Wh/kg.The split MWCNT carpets have increased their effective surface area for storing theions. The good conductivity of the inner few-walled CNTs and the vertical CNTarrays both accout for the efficient ions conducting and transportations.更多还原