Preparation, Modification, And Application Of Coal-based-graphene

Attributed to the unique two-dimensional crystal sp2 carbon structure, graphene has exhibited extraordinary mechanical, electrical, and optical properties. These properties give graphene great potential applications in functional materials, catalysts, sensors, and plenty of other fields. However, the key factors on the development and application of graphene are due to its controllable production and functionalization.As a natural carbon source, coal, containing polycyclic aromatic hydrocarbons, plays an important role in the preparation of various new carbon materials. With the purpose of controllable preparation and application of graphene using coal as a raw carbon source, this thesis focuses on studying the factors which significantly affect the structure and properties of graphene, including the coal structure, graphitization degree, coal powder size and coal type. The main work is to investigate the coal-based-graphene composite materials and study their applications in CO2 photocatalytic process and electrochemical performance. These results have demonstrate dimportant theoretical and practical valueby clarifying main factors that affect the structure and properties of graphene, which will open a new way for applying coal as acarbon source material for large-scale production of graphene and graphene-based different applications.First, the key factors on the graphitization of coal and production of graphene are studied. A novel technology is developed to prepare graphene from coal as a source material, which includes graphitization and chemical oxidation combined with plasma reduction. The results show that the organic macromolecular structure of coal is modulated by catalytic graphitization at 2500 °C and 1500 °C,and the graphitization of coal-based-graphites is higher than 65.0%. Specifically, the graphitization of coal-based-graphites is further increased to 71.63% by combining a graphitization at 1500 °C with ferric chloride/boric acid as a catalyst. Therefore, the graphitization productivity significantly depends on the coal sources. The graphitization product with anthracite as raw material is easily graphitized because of their large-scale aromatic layers in organic molecule structural unit. The mechanism of coal catalytic graphitization shows that boron atoms weaken the crosslink of bridges between aromatic layers in coal. The corresponding carbides were obtained due to the chemical reaction between iron and the aromatic layers, and when disordered carbon becomes saturated, carbon partially deposited and formed coal-based-graphite at low energy level.Furthermore, Zn O/graphene-oxide composites are fabricated and applied as catalysts in CO2 photocatalytic process study. The results demonstrate that Zn O/graphene-oxide composites, which are obtained from Zn O and different coal source produced grapheme oxide, shows effective performance in CO2 photocatalytic process and the superior catalytic activity as well as selectivity in the visible region is higher than in the ultraviolet region. The key factors are found to attribute to the structure and characteristics of graphene oxide. The catalytic activity follows Zn O/KCGO composites >Zn O/TXGO composites >Zn O/JCGO composites while the mass ratio between Zn O and coal-based-graphene-oxide is 7:3 and the addition was 1g/L. The formic acid had high selectivity and is 34.36 times higher than the yield of methanol. The main reason that absorption capacity of composites in visible region is enhanced is due to the coal-based-graphene-oxide having high band gap energy, and it further improves the reducing ability of photo-electrons.Finally, the coal-based-graphene composites are employed in supercapacitors. The sheet size effects and structural defects of coal-based-graphene are systematically investigated. The first charge-discharge capacity order is KCG>>TXG>>JCG when graphene is used as cathode material. Then, the electrical performance of Mn O2/graphene composites is studied. The results show that the first charge-discharge capacity of Mn O2/graphene composites has greatly improved compared to the pure Mn O2 and graphene. The strong synergy is generated due to Mn O2 and coal-based-graphene compound having excellent electrical properties. The electrical property of Mn O2/TXG composite is increased remarkably and the first charge-discharge capacity reaches 159.05 F/g, which is 3 times higher than TXG. This is mainly due to TXG having larger graphene sheet than the other coal-based-graphene, and the Mn O2 dispersing into graphene layers evenly to form a smooth electron transport channel to improve the electrical performance of Mn O2/TXG composite.