利用密度泛函理论,研究了双层石墨烯层间一氧化碳(CO)与氧(O)的氧化反应,获得了双层石墨烯层间距与反应能垒的定量关系.计算结果表明反应初态、过渡态、末态体系总能以及反应能垒对层间距离变化敏感:随着层间距的逐渐缩小,反应能垒逐渐增加.因此,改变双层石墨烯层间间距可以实现反应能垒的原子级调控.通过差分电荷密度分析体系的电子结构,发现当双层石墨烯层间距较小时,过渡态O—C=O中碳原子与石墨烯上下层中的碳原子之间有明显的电荷堆积,出现sp轨道杂化,导致二者相互作用增强,在z轴方向受到束缚力,难以与吸附在石墨烯表面的氧原子形成较弱的O—C键,阻碍了过渡态O—C=O的形成.通过调控双层石墨烯间距,可以降低一氧化碳氧化反应能垒.该研究为石墨烯的应用,以及新型碳基插层复合材料的制备提供一定的理论支撑.

Graphene is a two-dimensional (2D) crystal of carbon atoms packed in a honeycomb lattice. Because of this unique structure, it shows a number of intriguing properties. Interface between neighboring 2D layers or between 2D overlayers and substrate surfaces provides confined space for chemical process. The interlayer spacing between bilayer graphenes of van der Waals material is expected to modify the properties of atoms and molecules confined at the atomic interfaces. In this paper, the carbon monoxide (CO) and oxygen (O) in bilayer graphene are studied by density functional theory (DFT). The quantitative relationship between the interlayer spacing of bilayer graphene (d) and the reaction energy barrier (E-a) is obtained. Five values of d between 4.7 angstrom and 5.9 angstrom are used. The calculated results show that the total energy of the initial state, the transition state, the final state system and the reaction barrier are sensitive to the variation of the interlayer distance: the reaction barrier increases gradually with interlayer distance decreasing. The calculated energy barrier is 1.13 eV when the interlayer distance is 4.7 angstrom, while the energy barrier is 0.39 eV when the interlayer distance is 5.9 angstrom. It is also found that adsorption energy between O and graphene at the top site and the bridge site increase gradually with interlayer distance decreasing. Therefore, the atomic-level regulation of the reaction barrier can be achieved by changing the interlayer spacing of bilayer graphene. The charge density difference shows that when the distance between two layers of graphene is small, there is an obvious charge accumulation between C atoms in transition state O-C=O and C atoms in the upper or lower layer of graphene. This results in sp orbital hybridization, which leads the interaction between two C atoms to be enhanced. It is difficult to form a weak O-C bond of transition state O-C=O with O atoms adsorbed on graphene because of a binding force which exists in the z-axis direction. The DFT calculation of CO oxidation reaction barrier can be reduced by adjusting the spacing of bilayer graphene, which provides a theoretical support for the application of graphene and the preparation of new carbon-based intercalated composites.