The Function Of Supercritical CO₂in The Solution Preparation Of Graphene:First-principles Calculations

Graphene is a kind of stable,single-layer two-dimensional crystal. It has superior electrical conductivity, high opacity, and at room temperature it has a high thermal conducticity. These unique properties have make it become the hottest star material. Along with the extensive application of graphene, its preparation methods are also increasingly important. At present, the preparation of graphene has improvement a lot. The preparation of graphene has many experiments. The widely used stripping methods of graphite have some disadvantages,and the obtained graphene is found to be either too little in quantity, or have serious defects. But the solution method has solved the two problems. Experimentally some people obtained graphene by intercalating and stripping of graphite. When they are studying the method, they take1-pyrenecarboxylic acid as a "molecular wedge". Besides we can also exfoliate graphene from graphite well by using supercritical CO2and pyrene derivatives. We can see that in the process of solution preparation of graphene, small molecules, such as H2O, supercritical CO2that cannot be ignored also play a important role, besides pyrene derivatives.Based on the above analysis and consideration, in the solution preparation of graphene, the role of small molecules is important. It is the auxiliary function of these small moleculars to make it easier for exfoliating graphene from graphite, and also make the separated graphene basically no defect, and so we can obtain perfect graphene. This paper theoretically studies the mechanism of solution preparation of graphene, especially the auxiliary function of these small molecular.We study the CO2molecule adsorption on the monolayer graphene and double-layer graphene by using the first-principles calculations based on density functional theory. We found that either monolayer graphene and double-layer graphene, the most stable position is all bridge position(B). And then we aslo study the CO2molecules diffusion between double-layer graphene. We found that the spread of CO2on each path is easy, and diffusion barrier is small. It provides a theoretical basis for the experiment which exfoliate graphene from graphite well by using supercritical CO2and pyrene derivatives. Finally we have theoretical simulated energy variation of supercritical CO2from far and near double-layer graphene. On the one hand, we analyzes the supercritical CO2from far and near double-layer graphene in vertical and parallel two typical ways. On the other hand, we also study AA graphene configuration and make a comparison with AB graphene configuration. We found that supercritical CO2prefer the vertical way between the vertical and parallel two typical ways.