微尺度碳/无机复合材料及氮化物的制备、结构和性能

【作者】 罗巍；

【导师】 谢毅；

【作者基本信息】 中国科学技术大学 ， 无机化学， 2008， 博士

【摘要】 本文旨在探索微尺度碳/无机复合材料、碳材料的化学合成新方法,研究反应机理。利用超临界流体技术,成功制备了多种微尺度碳/硫化物复合材料,含硫富碳材料以及碳纳米纤维,并进一步研究了电化学储锂性质;采用简单的低温溶剂热路线得到了多种形态的非晶碳纳米管、三维非晶碳纳米管网格;通过醇热催化路线大量制备了高质量的包裹金属钴的碳纳米管和竹节状的碳纳米管。此外,还通过低温固相反应的方法制备了多种铬族氮化物纳米材料。详细内容归纳如下:1.创新性的提出一种超临界CS₂体系制备碳纳米管填充金属硫化物复合材料的方法。a)采用二茂铁作为催化剂,通过一步合成的方法在超临界CS₂中成功制备了碳纳米管连续填充单晶FeS₂纳米线复合材料,在分析实验结果的基础上详细对其形成机理进行了研究,并对这种新颖的复合材料热稳定性、光学和电化学性质进行了测试和分析;b)在制备碳纳米管填充FeS₂纳米线复合材料的基础上,通过选用二茂钴作为催化剂和调整实验参数,我们还合成了包裹球形CoS₂颗粒碳球和碳纳米管填充CoS₂纳米棒复合材料。该方法还可能被用来合成其他的硫化物/碳复合材料;c)在超临界CS₂中还合成了花状和棒状的含硫富碳材料、碳纳米纤维,电化学性能测试表明花状含硫富碳材料具有较高的放电容量,有可能成为一种新型的正极材料。2.发展了一条简单的低温溶剂热路线制备多种形态的非晶碳纳米管。a)通过二茂铁与CCl₄、C₂Cl₄或C₄Cl₆之间的反应在180℃大量制备了多种形态的非晶碳纳米管,研究发现反应副产物Fe起到重要的模板作用;b)在以上体系中通过引入多孔泡沫镍,进一步合成了夹角为90°的三维碳纳米管网格,我们对其反应机理进行了初步的研究。这些新颖的网格结构具有很大的比表面积,在催化剂载体、储氢、纳米器件等方面有着潜在的应用前景。通过溶液化学还原方法在三维碳纳米管网格上成功均匀沉积了金属Ag颗粒制得三维碳纳米管网格/银复合材料,并对其常温下对NH₃的气敏性进行了测试;c)采用二茂钴代替二茂铁,类似条件下合成了触角状非晶碳纳米管,丰富了对碳材料的认识。3.提出了醇热催化路线,以甲醇或无水乙醇作为碳源和溶剂,二茂钴作为催化剂,在500℃大量制备了高质量的包裹金属钴的碳纳米管或竹节状的碳纳米管。这些工作对理解碳纳米管的催化生长机制作出了有益的帮助。4.在不使用溶剂的情况下,我们利用NaNH₂与无水金属氯化物MCl_n在低温下（220—250℃）反应,制备了多种铬族氮化物纳米材料。在250℃制备了CrN树枝晶和纳米线束,并对其反应机理进行了仔细的研究;通过调节反应体系的散热速度,我们成功控制合成了高温立方相W₂N薄片和低温六方相WN实心球,为合成亚稳相化合物提供了很好的借鉴;此外,在类似的条件下,我们还合成了空球状和花生状的立方相Mo₂N。该反应体系的设计对于低温合成氮化物具有重要的意义。更多还原

【Abstract】 The point of this dissertation is to explore new synthetic methods for micro-scale carbon/inorganic composites and carbon materials and study their reaction mechanism. We have successfully synthesized various micro-scale carbon/metal sulfide composites, sulfur-doped carbon materials and carbon nanofilaments by supercritical fluid technology, and studied their electrochemical properties; a low-temperature solvothermal route was proposed to prepare amorphous carbon nanotubes （CNTs） and three-dimensional （3D） CNT networks; CNTs encapsuled with cobalt nanoparticles and bamboo-shaped CNTs with high-quality were synthesized in large scale by a catalytic pyrolysis method. In addition, several group VIB nitrides were obtained by rapid solvent-free route at low temperature. The details are summarized as follows:1. Metal sulfide filled CNTs composites were obtained in supercritical CS₂ for the first time. a) Large-scale long continuous FeS₂ nanowire filled CNTs were one-step synthesized in the presence of NaN₃ in supercritical CS₂ at 500℃using ferrocene as the iron source. On the basis of the experiments, a possible mechanism has been proposed, and the thermal, optical, electrochemical properties were studied, b) Based on the synthesis of FeS₂ nanowire filled CNTs, we prepared carbon hollow spheres encapsuled with CoS₂ nanospheres and CoS₂ nanorods filled CNTs. This novel approach may be potentially extended to fill other technologically important sulfides into CNTs in supercritical CS₂. c) Flower-like and rod-like sulfur-doped carbon materials were also obtained in supercritical CS₂. The electrochemical properties of flower-like sulfur-doped carbon materials demonstrate that it delivers a large discharge capacity, showing its promise for application in new electrode materials.2. A simple low-temperature solvothermal route was proposed to prepare amorphous CNTs with novel structures. a) Several amorphous CNTs were obtained by the reactions between ferrocene and CCl₄, C₂Cl₄ or C₄Cl₆ at temperature range from 180-200℃, and the experimental results indicated that Fe derived from the decomposition of ferrocene plays a template for the formation of CNTs. b) By introducing porous nickel into above reactions, novel three-dimensional （3D） CNT networks with the included angle of 90°were also obtained. These interesting structures have relatively large specific surface areas, showing their promise for application in catalyst carriers, hydrogen storage, nanodevices. 3D CNT networks coated with Ag nanoparticles were also obtained for the study of its gas sensitive characteristics in NH₃ at room temperature. c) Carbon nanoantennae have been synthesized through the reaction of cobaltocene and CCl₄ in the presence of porous nickel at 240℃.3. Developed the ethanol thermal route. CNTs encapsuled with cobalt nanoparticles and bamboo-shaped CNTs with high-quality were synthesized in large scale at 500℃, in which methanol or ethanol acted as carbon resource and solvent, cobaltocene acted as catalyst. It is useful to understand the formation mechanism of CNTs.4. A rapid solvent-free route has been successfully developed for the synthesis of group VIB nitrides by the reaction of anhydrous metal chlorides and sodium amide, and it is found that the reaction temperature, initiated forms, the material of reaction container and the amount of reagents play important roles in the composition, phase, and morphology of the nitrides. This approach may be potentially extended to obtain other transition metal nitrides at low temperature.更多还原