This article reviews the preparation methods of graphene, analyzes and compares the advantages and disadvantages of various methods, and briefly introduces the mechanical, optical, electrical and thermal properties of graphene.

　　Graphene has become a research hotspot in the field of materials with its excellent properties and unique two-dimensional structure. This article reviews the preparation methods of graphene, analyzes and compares the advantages and disadvantages of various methods, and briefly introduces the mechanical, optical, electrical and thermal properties of graphene. Graphene-based composite materials are an important research direction in the field of graphene applications. This article describes in detail the preparation and application of graphene polymer composites and graphene-based inorganic nanocomposites, and specifically discusses graphene/bulk metals The preparation method of matrix composite material and its excellent performance.

　　In order to make better use of these properties of graphene, researchers have adopted a variety of methods to prepare graphene. With the advent of low-cost chemically modified graphene, people can make better use of its properties to prepare graphene composites with different functions. This article will focus on the latest research progress of graphene composites, especially bulk graphene metal matrix composites. 1. The preparation of graphene. The preparation of graphene has gradually developed a variety of preparation methods from the earliest mechanical peeling method, such as: crystal epitaxial growth method, chemical vapor deposition method, liquid phase direct peeling method, high temperature deoxidation and chemical reduction method, etc. . Researchers in my country have carried out research work on the preparation of graphene earlier. An overview of the research progress of graphene is shown in Table 1. Chemical vapor deposition is a common method for preparing large-area graphene. At present, most hydrocarbon gases (such as CH4, C2H2, C2H4, etc.) are used as precursors to provide carbon sources, and solid carbon aggregates can also be used to provide carbon sources. For example, Sun, etc., use chemical vapor deposition to deposit polymer films on metal catalyst substrates. On the above, a high-quality graphene with a controllable number of layers was prepared. Compared with chemical vapor deposition, plasma-enhanced chemical vapor deposition can produce single-layer graphene at a lower deposition temperature and shorter reaction time. In addition, the crystal epitaxial growth method removes Si by heating single crystal 6H-SiC, thereby obtaining graphene epitaxially grown on the SiC surface. However, the surface of SiC crystal will be reconstructed during the high temperature process, which makes the surface structure more complicated, so it is difficult to obtain graphene with large area and uniform thickness. The solvothermal method has attracted more and more attention from researchers because of its characteristics that high-quality graphene can be prepared under high temperature and high pressure closed systems. Compared with other methods, graphene nanoribbons with no defects and a definite structure can be prepared by organic synthesis.

　　"Table 1 Overview of the preparation method of graphene" "Different from the above bottom-up synthesis method, the top-down method can increase the yield of graphene and is easy to prepare. Such as simple and easy chemical exfoliation method and graphite oxide reduction method, the latter has become the easiest method to prepare graphene in the laboratory. The solvent stripping method developed next is less toxic than the redox method and will not damage the structure of graphene. In addition to the chemical reduction method, graphite oxide can also be reduced to graphene by electrochemical methods, but the ratio of C and O atoms in the graphene prepared by this method is low. In addition, the microwave method has also been used to prepare graphene. For example, Chen et al. first disperse graphene oxide (GO) in a mixed solvent of NN-dimethylacetamide and water (DMAc/H2O), and then mix the reaction solution. Microwave thermal reduction, the conductivity of graphene obtained is 104 times that of graphene oxide. Lu Yan of the University of Science and Technology Beijing used the arc method to prepare graphene with an open mesoporous structure, with a specific surface area of 77.8m2/g and a mesoporosity of 74.7%, which can be used as an electrode material.　　2, excellent properties of graphene 　　 single-layer graphene and its derivatives are shown in Figure 1. It is a two-dimensional periodic honeycomb lattice structure composed of carbon six-membered rings with a bond length of 0.141nm. Graphene can be crimped into zero-dimensional fullerenes, one-dimensional carbon nanotubes or stacked into three-dimensional graphite.

　　2.1, electrical properties　　One of the most important properties of graphene is its unique carrier properties and massless Dirac fermion properties. The valence band and conduction band of graphene overlap at the Fermi level. It is a two-dimensional semiconductor with a zero energy gap. The carriers can move in a sub-micron distance without scattering. It is the material with the smallest resistivity found so far. . The anti-interference ability of electron transport inside graphene is very strong, and its electron mobility can exceed 15000cm2/(V·s) at room temperature. The electron mobility was found for the first time to be close to 200,000 cm2/(V·s) [48]. The carrier mobility in single-layer graphene is almost unaffected by chemical doping and temperature. In addition, the half-integer quantum Hall effect of electron carriers and hole carriers in graphene can be changed by changing the chemical potential by the action of an electric field. Observed, and Novoselov et al. [50] observed the quantum Hall effect of graphene at room temperature. Burghard et al. found that the conductivity of the chemically reduced multilayer graphene oxide flakes is between 0.05-2S/cm, and the field-effect mobility at room temperature is 2~200cm2/(V·s). Concluding remarks Graphene has become a research hotspot as soon as its excellent properties appear. Its preparation process has gradually developed from the earliest mechanical peeling method, such as: chemical vapor deposition, redox method, liquid phase peeling method, crystal epitaxial growth method, etc. It is a kind of preparation method, but the preparation of large quantities, low-cost and high-quality graphene is still a focus of future graphene preparation research. At present, the research of graphene composite materials mainly focuses on the application research of graphene polymer materials and graphene surface loaded inorganic nanoparticles and its catalysis, biosensors, spectroscopy and other fields, while the research of bulk graphene metal matrix composite materials Relatively few, the excellent reinforcement effect of graphene and its unique interface with the metal matrix will make this type of composite material a research hotspot for graphene composite materials in the future.