| Popis: |
Recent years have seen a surge of interest in layered materials, mainly because of their numerous applications, prominently in gas sorption. These materials are highly anisotropic, because of the coexistence of covalent bonds within the individual layers and weak van der Waals (vdW) interactions between layers. Although the anisotropy makes layered materials appealing for many technological applications, it also makes their full theoretical and experimental description difficult. This study has addressed some of the major gaps in our understanding of layered materials using a combination of theoretical and experimental techniques. Computationally, newly developed functionals able to treat both short and long range interactions within density functional theory have been used to look at the structure, energetics, dynamics and adsorption properties of layered materials. Neutron scattering experiments have been used to further our understanding of the atomic dynamics in graphite and to set up a preliminary study of the hydrogen adsorption in doped graphite. The present results underline strong similarities of the vdW-dominated properties of the systems examined. The interlayer binding energies and the hydrogen adsorption capabilities have been found to be surprisingly similar. Analysis shows that this is due to a fine balance between attractive and repulsive forces and, more specifically between atomic polarizabilities and volumes of the material components. The comparison between experimental and predicted atomic displacements in graphite highlights that the carbon dynamics is affected by nuclear quantum effects at temperatures lower than 300 K. These temperatures are common for many technological applications, especially those related to gas adsorption. Thus, the presented results pose some questions on what could be the correct model and computational technique to use in order to gain a better understanding of the sorptive properties of layered materials, especially carbon based, and move forward in the design of new gas storage materials. |
