【作者】 鞠治成；

【导师】 钱逸泰；

【作者基本信息】 山东大学 ， 纳米材料化学， 2011， 博士

【摘要】 本论文首先综述了纳米材料的结构、性质、应用及制备方法,重点阐述了纳米结构碳化硅及碳材料的研究进展及发展趋势。在对碳化硅及碳材料的制备、应用等方面的发展现状进行了充分调研的基础上采用硫辅助方法低温制备出了高品质的晶态立方碳化硅纳米线,并发现纳米线的生长过程符合VLS生长机理；以废塑料为原料,与硅粉在升华硫粉辅助条件下制备出了立方碳化硅六角片及纳米线,这不但可以变废为宝,充分利用固体废弃物,还对废塑料污染环境给出了一种可能的解决方案；采用高温裂解方法在不锈钢高压釜中,于铜及镁基底上实现了从一维碳纳米线到二维树叶状碳片,再到三维实心碳球及丁香花状碳包覆四氧化三铁分级结构材料的控制合成。论文主要工作内容概括如下：1.采用高压釜技术,以硅粉作为硅源,四氯乙烯为碳源,金属钠为还原剂,升华硫粉为反应辅助剂,在130℃得到了结晶品质良好的3C-SiC内米线,其直径主要集中在30纳米,长度可达数十微米,高分辨电镜照片显示该纳米线生长方向为[111]；不加入硫粉,于270℃也能获得直径为40-120纳米的立方相碳化硅纳米线,但是线的产率相对于加硫粉辅助的要低的多。延长反应时间一定程度上有益于纳米线的形成；过高的反应温度并不能明显增加纳米线的含量,反而使得纳米线尺寸分布变宽；增加或减少升华硫粉的用量都会降低碳化硅纳米线的产率。此外,根据试验结果并结合相关文献报道我们发现,该实验中碳化硅纳米线的具体形成机理为气-液-固(VLS)生长机制。2.利用硅粉和废塑料作为原料,金属钠和镁粉为还原剂,硫粉为辅助剂在不锈钢高压釜中于350-500℃得到了结晶品质良好的立方碳化硅纳米材料。当所用废塑料为高密度聚乙烯(HDPE:洗发水及化妆品包装瓶、矿泉水瓶等)时,所得产物中有部分为3C-SiC六方片(约占40%),其尺寸主要集中在300-500纳米,厚度约50纳米；当所用废塑料为低密度聚乙烯(LDPE:各种废塑料袋、农用地膜等)时,所得产物中有部分为3C-SiC纳米线(约占35%),其直径约为50纳米,长度可达数十微米；当所用废塑料为聚对苯二甲酸乙二醇酯(PET：透明汽水及饮品瓶)时,所得产物大部分为带有褶皱的厚度约100纳米的二维片状结构,并伴随有少量类六角片(约20%)共存。当废塑料主要成分为HDPE及LDPI时,所得碳化硅均为立方相；而当废塑料主要成分为PET时,所得碳化硅材料为立方和六方混合相且伴随有堆垛层错现象。通过系统地观察采用HDPE作碳源时其不同时间段条件下样品的形貌,我们认为立方相碳化硅六角片状结构的形成过程属于自组装的定向聚集机制。3.利用高温分解路线,在铜及镁基底上,以二茂铁为催化剂,高温氯化分解二氯甲烷,分别制备出了树叶状碳片及碳纳米线阵列,通过调节反应参数对二维碳片厚度于50-200纳米之间可控。当我们以其它卤代烷烃替代二氯甲烷时可以获得单分散的或相互粘连的微米级实心碳球；如果以甲醇、乙醇取代二氯甲烷并适当增加二茂铁的用量可以得到仙人掌状及丁香花状碳包覆四氧化三铁分级结构材料。通过选择不同的反应体系,我们可以很容易地实现：从一维碳纳米线到二维树叶状碳片,再到三维实心碳球及丁香花状碳包覆四氧化三铁分级结构材料的控制合成。借助于扫描电镜仔细观察二维碳材料的具体生长过程我们发现,其符合扩散限制聚集分型生长机制。此外,我们将附着碳材料的铜基底裁切成所需的电极片形状,以金属锂片为对电极,组装成模拟电池,在电压区间为0.01-3 V,电流密度为100 mA/g条件下进行充放电测试,其首次放电比容量为730 mAh/g,而充电比容量达到321mAh/g。经过简单的几次充放电循环,其比容量稳定在340 mAh/g以上；当电流密度为300 mA/g,充放电循环50圈后其比容量稳定在220 mAh/g左右。更多还原

【Abstract】 In this dissertation, the structures, properties, applications and fabrication methods are summarized at first; the research developments of nano-structured SiC and carbon materials are mainly discussed. After investigating the synthesis routes and applications of SiC and carbon materials thoroughly, we prepared crystalline cubic SiC nanowires via a sulfur-assisted approach at low temperature; the growth mechanism of the nanowires accord with the vapor-liquid-solid (VLS) growth process. Cubic SiC hexagonal platelets and nanowires were also fabricated by waste plastics and Si powder via sulfur-assisted; this method could make the best of the waste plastics and provide a possible way to solve the plastic pollution. In addition, carbon materials with various morphologies were prepared on the copper and magnesium substrate by pyrolysis of dichloromethane and ferrocene in stainless steel autoclave. In this process, the morphology was controlled to transform from 1-D nanowires to 2-D leaf-like carbon sheets then to 3-D nanospheres and lilac shaped carbon-coated iron oxide hierarchical structures. The dissertation is summarized as follows:1. Highly crystalline 3C-SiC nanowires were fabricated in an autoclave at 130℃by silicon powder as Si source, tetrachlorethylene as carbon source, metallic Na as reductant and sulfur powder as assistant agent. The average diameter of the 3C-SiC nanowires was about 30 nm and the length was up to tens of micrometers. High-resolution TEM photos indicate that preferential growth of the nanowires was along [111] crystal direction. The cubic SiC nanowires with the length of 40-120 nm could also be prepared at 270℃ without sulfur powder additive; however, the ratio of the nanowires was much lower than the typical reaction with sulfur powder. Increasing the reaction time could improve the yield of the nanowires in a certain extent; excessively high temperature could not enhance the content of the nanowires, and the size distribution would broaden instead; either increasing or decreasing the dosage of sulfur powder would reduce the yield of SiC nanowires. In addition, based on the experiment results and related reports, we can draw a conclusion that the possible growth mechanism of SiC nanowires was vapor-liquid-solid(VLS) growth process.2. The cubic SiC nanomaterials were synthesized in the autoclave at 350-500℃by silicon powder and waste plastics as reagents, metallic Na and Mg powder as reductants, sulfur powder as assistant agent. When the waste plastic was high-density polyethylene(HDPE:detergent bottles or beverage bottles), hexagonal platelets of 3C-SiC (about 40%) could be observed; the length of SiC hexagonal platelet-like crystals was 300-500 nm, and the thickness of these platelets was about 50 nm. If the low-density polyethylene (all kinds of waste plastic bags, agricultural film, etc.) was applied as carbon source instead,3C-SiC nanowires (about 35%) were found in the final product; the average diameter of the nanowires was about 50nm and the length was up to tens of micrometers. When the waste plastic was polyethylene terephthalate(PET:beverage, food and other liquid containers), most of the product were two-dimensional crapy lamellas with the thickness of about 100 nm and about 20% hexagonal platelet-like crystals were observed. When the carbon source was HDPE and LDPE, the as-obtained SiC was cubic; however, when the waste plastic was PET, the as-obtained SiC was a mixture of cubic and hexagonal with the phenomenon of stacking fault. Based on the observation of the morphologies of SiC fabricated in different time by HDPE, we supposed that the growth process of cubic SiC hexagonal platelets was self-assembled oriented aggregation mechanism.3. Leaf-like carbon sheets and carbon nanowires array were synthesized through a pyrolysis route on copper and magnesium substrates by ferrocene as catalyzer and dichloromethane as carbon source; the thickness of the 2-D nanosheets could be controlled from 50 nm to 200 nm by adjusting the experimental parameters. When the carbon source was replaced by other halogenated alkanes, monodispersed or chained-like solid carbon spheres could be obtained; if methanol or ethanol was applied instead of dichloromethane and the dosage of ferrocene was increased appropriately, the cactus-like and lilac shaped carbon-coated iron oxide hierarchical structure material could be obtained. We could easily achieved the controlled synthesis from 1-D nanowires to 2-D leaf-like carbon sheets then to 3-D nanospheres and lilac shaped carbon-coated iron oxide hierarchical structures by choosing different reaction system. The growth process of the 2D carbon materials was carefully observed by SEM, and it is considered that Diffusion-Limited-Aggregation mechanism could be responsible for the growth.In addition, we cut the copper attached by carbon materials into desired electrode shape, applied lithium metal piece as the counter electrode, assembled into a simulation lithium-ion battery. The voltage range was the 0.01-3 V, and current density was 100 mA /g for the charge and discharge test. The first discharge capacity was 730 mAh/g, while the charge capacity can be to 321 mAh/g. After several charge and discharge cycles, its specific capacity stabilized at 340 mAh/g or more; when the current density was 300 mA/g, after 50 cycles, its capacity also stabilized at about 220 mAh/g.更多还原