【作者】 李娜；

【导师】 陈丽；

【作者基本信息】 兰州理工大学 ， 应用化学， 2017， 硕士

【摘要】 石墨烯是一种由单层碳原子紧密排列成二维蜂窝状结构的碳材料。石墨烯展现出很多优异的物理化学性能,从发现开始就受到各个领域的广泛关注。然而,石墨烯仍然存在一些不足。例如,石墨烯片层易发生团聚,采用化学剥离法制备的石墨烯缺陷多。此外,石墨烯是一种能带隙为零的半导体,一定程度上限制了石墨烯应用于电学器件。研究表明,通过化学掺杂可以有效调节石墨烯的电子结构,改善其物理化学性质。基于以上问题,本论文采用石墨以及氟化石墨为原料,通过不同方法制备石墨烯及掺杂石墨烯,考察所得石墨烯及掺杂石墨烯的形貌、结构、电导率及电化学性能。主要研究内容包括以下几个方面:(1)以石墨为原料,通过三种不同的氧化方法制备氧化石墨烯(Graphene O xide,GO),以水合肼为还原剂将GO还原为石墨烯,考察GO氧化程度对石墨烯在有机溶剂中分散性能及电化学性能的影响。结果表明,调控氧化剂的用量和种类,可以改变GO的氧化程度;以氧化程度最高的GO还原所得的石墨烯,在有机溶剂中的分散性能最好,电化学性能最佳。(2)化学剥离法是以石墨为原料,通过氧化和还原过程制备石墨烯,由于存在过度氧化以及不彻底还原,所得石墨烯存在较多的结构缺陷,进而影响石墨烯的性能。因此,选用氟化石墨为原料,通过超声法,静置法以及加热回流法三种方法制备石墨烯,对所得石墨烯进行形貌、结构表征及电化学性能测试。结果表明,三种方法均可制备出单晶结构的石墨烯,其中加热回流法制备的石墨烯晶体有序度最高,电化学性能最佳。(3)以氟化石墨为原料,尿素为氮源,通过高温固相反应制备氮掺杂石墨烯(N-Gr),探讨了反应温度对N-Gr的结构及电化学性能的影响。结果表明,氮元素以吡咯氮、吡啶氮和石墨化氮三种形式掺入石墨烯晶格结构中。500℃下制备的N-Gr具有最佳的电化学性能,此外,其电导率可达9475 S/m,远远大于以GO为原料在相同条件下制备的氮掺杂石墨烯(N-RGO)的电导率(200 S/m)。(4)以氟化石墨为原料,Na HSO3、Na2S2O3·5H2O、Na2SO3以及N a2S·9H2O为硫源,采用高温固相反应制备硫掺杂石墨烯(S-Gr),探讨不同硫源对S-Gr的结构及电化学性能影响。结果表明,硫元素以C-S-C、C-SOx-C两种结构掺杂进入石墨烯晶格结构中。其中以Na2S·9H2O作为掺杂剂制备的硫掺杂石墨烯的硫含量最高(3.35%),电导率最高(21720 S/m),电化学性能最佳。更多还原

【Abstract】 Graphene, a single-atom-thick sheet with a honeycomb lattice of carbon atoms,has generated tremendous attention in recent years. However, graphene is easy to reunite, and the chemical exfoliation of graphite to graphene via oxidation and reduction will introduce many defects into graphene sheets. In addition, graphene is a zero bandgap semiconductor, which hindered the application of graphene in electrical devices. It can effectively adjust the electronic structure of graphene by chemical doping, which improved its physical and chemical properties, and then optimized electrochemical performance of graphene. In order to solve these issues, looking for a suitable method to prepare graphene is putting on the schedule. In this paper, severial feasible methods are developed to prepare graphene and doped graphene with graphite and fluorinated graphite, and the influence of dispersion stability, the structure,electric conductivity and electrochemical performance were investigated. The main research contents and results are as follows:(1) Three chemical oxidation reduction methods, including Hummers method,modified Hummers method, and improved method, were used to prepare GOs and graphene sheets. The influence of preparation methods on the structure, dispersion stability in organic solvents, and electrochemical properties of graphene sheets were investigated. The results showed that the amount and kind of oxidizing agent, may be varied the oxidation degree of GO. In addition, graphene prepared by improved method exhibits excellent dispersity and stability in organic solvents without any additional stabilizer or modifier, which is attributed to the completely exfoliation and regular structure. Moreover, cyclic voltammetric (CV) and electrochemical impedance spectroscopy (EIS) measurements showed that graphene prepared by improved method exhibits superior electrochemical properties than that prepared by the other two methods.(2) One of the key problems with the chemical exfoliation of graphite to graphene via oxidation and reduction, is the excessive oxidation of graphite and incomplete reduction of graphene oxide, which introduce many defects into graphene sheets. Therefore, fluorinated graphite (FGi) was chosen to prepare graphene sheets,ultrasonic method, static method and refluxing method are selected. The results showed that graphene prepared by refluxing method emerges outstanding crystal structure and electrochemical properties.(3) A series of Nitrogen-doped graphene sheets (N-Gr) with discrepant electrochemical performance were prepared through a high-temperature solid state reaction method by controlling reaction temperature on reaction reagent of fluorinated graphite and urea. Nitrogen was successfully doped into graphene with three forms of pyrrolic nitrogen, pyridinic nitrogen and graphitic nitrogen. The results showed that N-Gr-500 presented the best crystal structure, and largest CV curve area. As a contrast,the mixture of GO and urea is employed to produce Nitrogen-doped reduction of graphene oxide (N-RGO). The most dramatic discovery of this study is that the electric conductivity of N-Gr-500 achieved 9475 S/m, whlie the electric conductivity of N-RGO-500 was only tested to be 200 S/m.(4) Another experiment is regard to the synthesis of Sulphur-doped graphene sheets (S-Gr) and its electrical properties. A sequence of Sulfur reagents, such as NaHSO3, Na2S2O3·5H2O, Na2SO3 and Na2S·9H2O were selected for reductants and dopants to prepare S-Gr at 500℃. The doped materials were characterized by XPS and demonstrated that sulfur in the form of C-S-C and C-SOx-C successfully doped into graphene, and the sulfur content of sulfur doped graphene prepared by Na2S·9H2O (S-Gr-4) is reach to 3.35%. Furthermore, S-Gr-4 exhibits superhigh electric conductivity. The electric conductivity of S-Gr-4 is 21720 S/m.更多还原