【作者】 张璐；

【导师】 李峰；

【作者基本信息】 北京化工大学 ， 化学， 2010， 博士

【摘要】 碳纳米管及碳纤维作为碳基材料中最重要的组成部分,不仅传承了纳米材料优越的物理化学性能,并且由于自身特殊的石墨层结构产生了许多优异的电子传导、高抗腐蚀性和高稳定性等优势广泛的应用于诸多领域中,例如传感器、半导体、催化剂及其催化剂载体、储氢材料、超级电容器、生物医药等领域。对于发展简单、绿色、高效、可控的制备方法,获得多功能、结构可调,性能可控的此类碳基材料,具有重要的科学价值与实践意义。在众多影响碳基材料生长的各种因素当中,碳基材料所用催化剂的性质、组成及其微观结构最为关键。而这将影响所得碳基材料的形貌、结构等性质,最终决定碳基材料在应用方面的各种性能。因此,人们不断地积极探索多种形貌碳基材料和所用催化剂的简易制备方法和对其结构与组成的影响,从而进行碳基材料的可控制备,以期获得高质量、高性能的碳基材料。水滑石(Layered Double Hydroxide,简写为LDHs)是一类具有特殊层状结构的层状双羟基金属氢氧化物材料。由于LDHs存在着晶格能最低效应及晶格定位效应,使不同种类的金属离子以一定方式均匀分布在层板上。水滑石前驱体在高温焙烧后得到的复合金属氧化物中金属离子保持与前驱体一致的分布。因此,利用LDHs作为前驱体可以制备得到均匀分散的活性金属粒子,高效的生长碳基材料。本论文利用水滑石层板中金属离子在原子级别上高度分散的特点制备了一系列含特定活性组分的LDHs材料,并提出了水滑石焙烧产物LDO为前驱体,通过化学气相沉积法(CCVD)的制备,合成一系列管径均匀的多壁碳纳米管(直壁碳纳米管和螺旋碳纳米管)。通过研究不同温度和不同活性组分对水滑石焙烧产物的影响,进而研究对其碳纳米管形貌和结构的影响。水滑石前驱体法制备碳材料不仅克服了单元活性金属粒子容易在反应过程中烧结,使催化剂失去活性的缺点,还可以通过控制水滑石中不同比例的金属组分来实现对碳纳米管形貌生长的控制。此种制备方法操作简便,可控、环境友好。本论文还提供一种原位制备碳纳米管的方法。此方法利用水滑石直接作为催化剂,乙炔作为还原剂和碳源,一步法生长碳基材料。在反应中以原位生长得到的尖晶石型金属氧化物作为载体支持所还原的金属粒子分散,而金属氧化物也在此过程中被生长的碳纳米管所分散,负载在碳纳米管管壁的表面。原位合成的碳基材料中碳纳米管和金属氧化物之间均匀分散,相互作用力较强,且各组分之间的比例可以通过控制反应条件来得到。此方法操作简便,表面含有大量的缺陷和含氧官能将有利于提高碳纳米管材料的性能。利用水滑石层板组成和结构的可调控性向层板中引入不同的活性组分和助活性组分,一步法生长具有特殊结构的碳纤维。通过对不同反应条件的研究,最优化制备多种形貌碳纤维,包括亚微米级直壁碳纤维(SSCFs)、螺旋碳纤维(扭状螺旋碳纤维CNCs和双螺旋碳纤维CMCs)、花边型碳纤维(LCFs)。最后利用以上合成的多形貌碳基材料作为Pt粒子载体制备复合电催化剂应用于甲醇、乙醇电催化氧化当中,拥有较高的电化学活性和抗中毒性能。这是由于所合成的碳基材料不同的形貌、微观结构以及表面所负载的含氧官能团共同作用而导致的。更多还原

【Abstract】 Carbon nanotubes and carbon fibers as the most important parts of carbon materials, they not only inherit excellent physical and chemical properties from the nanomaterials, but also have superior electronic conductivity, high resistance to corrosion and high stability origined form unique structure of the graphite layer. They are broadly applied as sensors, semiconductors, catalysts and catalyst supports, energy storage materials, super capacitors, biomedicine and other fields. At prsent, it is scientific valuable and has important practical significance to develop a facile, green, efficient and controllable method to prepare this class of materials. The carbon materias can be synthesized by controlling the experimental parameters, such as used catalysts, carbon sources, reaction temperatures, gas flow rates and feedstock pressures. Among them, the type and character of utilized catalyst is the most important factor in the formation of helical nanostructures. The catalysts act as the seeds for the nucleation and growth of nanotubes. Therefore, many researchers actively explore facile preparation methods of multi-morphology carbon materials and catalysts and investigate the effect on the structure and composition of carbon materials, in order to obtain carbon materials with high-quality and superior performance.Layered double hydroxides (LDHs), also known as anionic clay with brucite (Mg(OH)2)-like structure, consist of positively charged layers and negative anions in the interlayer. The metal ions are bonded to hydroxyl groups to form two-dimensional brucite-like layers and are uniformly distributed on an atomic level without segregation. Thus, highly dispersed metal particles over oxides matrix can be obtained by designing an appropriate LDHs precursor containing the desired metal cations and subsequent thermal treatment followed by reduction, originating from the ordered prearrangement of metal cations in the layers of LDHs precursor at an atomic level.In this thesis, utilizing good dispersion of cation within the LDHs’layered, multi-walled carbon nanotubes with uniform outer diameters has been grown over a series of catalysts derived from calcined LDHs by the CCVD method. The investigation of reaction temperature and compositions of LDHs in order to research the effect on the compositions of LDO and the growth of CNTs. To prepare metal-supported catalysts from calcined LDHs for the growth of CNTs not only overcome the shortcomings of active metal particles easily sinter during the reaction, but also control varying compositions of LDHs with different proportions to control the morphologies of CNTs. This method is simple, controllable, and environmentally friendly.Carbon nanotubes have been prepared by one-step synthesis over LDHs. In the system, LDHs is used directly as catalysts and acetylene act both as reducing agent and carbon source. Multi-walled CNTs were synthesized catalytically by active Ni nanoparticles derived from LDHs, and that the co-growing spinel-type NixMg1-xAl2O4 complex metal oxides from LDHs could be highly dispersed in the CNTs matrix. The as-synthesized spinel particles have good crystallinity and uniform particle size result in strong interaction between complex metal oxides and CNTs. This method is simple, effective and controllable. Moreover, the defect and the special surface modification by complex metal oxides on CNTs in favor of better performance of CNTs.Carbon fibers with different morphologies were prepared via CCVD of acetylene over LDHs. Carbon fibers including submicrometer fibers(SSCFs), helical carbon fibers (twist-shaped nanocoils CNCs and herringbone-type double microcoils CMCs) and lace-type carbon fiber (LCFs) could be controllably obtained only by varying compositions of LDHs.Finally, the electrocatalytic activity of electrodes modified with platinum particles supported on as-synthesized a series of carbon materials were studied for the oxidation of methanol/ethanol, as to demonstrate the feasibility of applying carbon materials as Pt electrocatalyst supports in direct alcohol fuel cells. The electrochemical investigation indicates that all as-fabricated electrodes showed superior electrocatalytic properties. The significantly enhanced electrochemical properties were believed to be strongly related to the special microstructure as well as the composition of as-grown carbon-based support materials. Moreover, the method of highly dispersed Pt nanoparticles supported on carbon nanotubes synthesized by a facile and green carbothermal reduction has been proposed. The as-fabricated hybrid Pt-CNTs composite exhibited excellent electrocatalytic property for ethanol oxidation.更多还原