Progress in Preparation and Application of Functional Graphene

Graphene is a honeycomb monolayer carbon structure composed of carbon atoms that form planar Covalent bonds with SP2 hybridization. It is also a basic structural unit of many Nano carbon structures such as fullerenes and carbon nanotubes. Since it was successfully prepared by Geim et al. in 2004, graphene has become a star material in recent years with extremely high mechanical strength, carrier mobility and conductivity, thermal conductivity, light permeability, and chemical stability. Has received extensive attention from academic and industrial circles.

However, in contrast to these unparalleled properties, graphene materials that are actually used in production and life require a variety of properties. For example, graphene is a material with a theoretical surface area of up to 2630 M2 / g, and has great application potential in surface chemistry, adsorption and other fields. However, the surface of the eigengraphene is a flat large π bond structure, which has a considerable degree of chemical inertia and hydrophobicity, and it is easy to stack and aggregate, which is not conducive to the performance of graphene.

In order to solve the above problems and meet the needs of the application, scholars added other components and structures on the basis of graphene to form a new class of new materials that function graphene. They maintain most of the basic properties of graphene while having different properties. The new properties of the eigengraphene. Due to the introduction of various modification methods, functional graphene can gradually be reasonably designed for actual needs, and its application potential has gradually been developed. In recent years, its research has been rapidly developed!

This paper reviews the latest progress of functional graphene. At first, according to the chemical structure, the preparation method of Covalent binding and non-covalent binding are described. Secondly, according to the specific application field, the latest research results of functional graphene in recent years are summarized.

1, preparation method

Functional graphene is derived from graphene. In the past decade or so, the preparation method of graphene has been continuously developed, gradually forming graphene thin films represented by chemical vapor deposition and graphene powders represented by Redox, as shown in Figure 1, 2. The former is characterized by graphene having higher crystalline quality, less functional group content, and electronic properties with intrinsic semiconductors. The latter is characterized by graphene surface containing certain oxygen-containing functional groups and loose structure., It is conducive to the performance of the larger specific surface area and can be mass-produced. Correspondingly, the preparation of functionalized graphene is also based on eigengraphene and graphene oxide as raw materials.

1.1 Covalent functionality of graphene

The eigengraphene surface consists entirely of SP2 carbon atoms. This is a very stable structure that gives graphene a strong chemical inertia under normal circumstances. At the same time, this structure makes it easy to stack and aggregate between graphene, and the nature of hydrophobic also makes graphene difficult to disperse in solvents such as water, reducing the operability of graphene in applications.

The covalency of graphene is designed to destroy this stable structure, so that graphene's surface activity is easy to disperse in solvents, and it is also conducive to its role in applications such as adsorption, and the destruction of planar π bond structures. The conductivity and thermal conductivity of covalently functional graphene are generally significantly lower than the intrinsic graphene.

1.1.1 Functional use of small organic molecules

Although the intrinsic graphene is chemically inert, its π bond can also undergo certain types of chemical changes under strong chemical conditions. Similar to carbon nanoparticle Guandeng, the SP2 carbon structure of graphene can react directly with free radical reagents such as diazonium salts. By selecting the appropriate reaction Matrix, the functional groups required for surface modification of various types of graphene can be achieved., as shown in Figure 3. In addition, the eigengraphene can also undergo cycloaddition with the diene body, opening the SP2 carbon bond to produce a functional product. In this way, a complex ring system containing heteroatoms such as nitrogen can be easily introduced into graphene to enable it to play a role in a variety of application fields. This is consistent with its carbon Guandeng.

Xu et al. reacted with acetylenone as a reducing agent and graphene oxide, using the active carbon atoms in acetylacetone. In the one-step reaction, both reduction and functionalization were achieved at the same time, and functional graphene was obtained with highly coordinated acetylacetone units on the surface. This graphene can not only be dispersed in various solvents such as water, but also has a strong adsorption capacity for CO2 + and Cd2 + plasma.

1.1.2 Covalent bond grafting of polymers

In addition to organic small molecules, many polymers or their precursors can also be attached to the surface of graphene in a similar manner. Fang et al. connected the aryl group with a diazonium salt reaction on the graphene surface and then performed free radical polymerization, in which the free radicals produced by the diazonium salt were directly used as the initiator of the reaction, resulting in the connection of graphene to the surface of polystyrene. The polymer connection effectively separates the graphene sheet and avoids aggregation. At the same time, due to the action of graphene, the polymer forms a well-arranged membrane.

Similarly, the polymerization of many polymer precursors can be carried out in the suspension of graphene oxide, and graphene oxide naturally plays a role in cross-linking polymers, not only the properties of graphene itself. Play, The overall performance of polymer complexes has also been improved to varying degrees.

In addition to self-polymerization, polymers can also use active functional groups at their chain ends to connect to the surface of graphene oxide, which makes up for some of the disadvantages of in-situ polymerization, such as the ability to graft a variety of polymers on the surface of CA Moene., Including polymers that can not be polymerized on the surface of graphene. Yu et al. connect P3HT molecules with hydroxyl groups on GO by chemical reaction, and peak the electrical properties of graphene through these conductive branched chains.

One of the biggest features of graphene and polymer interconnections is that graphene and polymers are easily cross-linked to each other, forming a grid-like structure. In addition, graphene requires only a small amount of mass due to its relatively rich surfactant groups. fraction, Can make a significant change in polymer holding. Many graphene polymer complexes exhibit a gel state in solution, and for complexes that can form solids, they are often accompanied by significant changes in physical properties. For example, in the graphene polyvinyl alcohol system, only 1 yttrium of graphene oxide can greatly increase the mechanical properties of polyethylene, the tensile strength and elastic modulus are increased by 88 yttrium and 150 yttrium, respectively, and due to its Covalent bond connection, The fracture elongation rate also has a certain increase.

1.2 Non-covalent modification of graphene

In the practical application of functionalized graphene, it is usually required to improve the dispersion of graphene, avoid excessive aggregation, and maintain the inherent conductive and thermal conductivity of graphene, while the Covalent bond modification produces a graphene. The destruction of the car Junction, It is difficult to fully meet these two requirements, so the non-covalent bond modification method has received widespread attention.

1.2.1 Nanoparticles load modification

Graphene, as a material with a large specific surface area, can easily be combined with various particles that have been proved to have excellent properties through surface adsorption. Typical particles here include nanoparticles of metals or oxides such as Ag and Fe3O4, which are usually directly connected to functional groups on the surface of graphene oxide, or are non-covalently connected to the surface of the eigengraphene through a class of stabilizers. As shown in Figure 6, After heating, these nanoparticles are still firmly bonded to the surface of graphene.

In addition to the Covalent binding of hydroxyl and graphene, polyvinyl alcohol is also a typical example of hydrogen bonding and graphene oxide. The addition of appropriate amounts of polyvinyl alcohol can connect graphene oxide tablets to form complex networks. Structure, form a gel in aqueous solution.

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