In this presentation, we extend the work of a number of investigators [1] to develop a new model for graphite that accounts for two important factors: (1) an energetic corrugation of the surface that is stronger than that given by the usual Steele model for the carbon in a graphene layer, and (2) the distinction between the top graphene layer and the lower layers because the former is in contact with only one neighbouring graphene layer. This model gives rise to a distribution of the interlayer spacing with the bulk interlayer spacing (for second and higher graphene layers) consistent with experimental XRD measurements and improves the modelling of experimental isotherms and isosteric heat. We illustrate the potential of this new model for graphite with a systematic and comprehensive study of adsorption of noble gases over a range of temperatures, from below the triple point to the boiling point. This study highlights the differences between the new model and the Steele model, especially at temperatures below the triple point where the corrugation is more strongly manifested, and the improved agreement between simulation results using the new model and experimental data. Anisotropy of the graphene layer also accounts for a shift in the 2D-transition for the first two layers and the sub-steps in the isotherm, associated with the spike in the plot of the isosteric heat versus loading. By decomposing the isotherm and the isosteric heat into contributions from the first and second layers, we can determine the mechanisms underlying these transitions. Adsorption of linear molecules, such as nitrogen, carbon dioxide and ethylene, and polar molecules, such as methanol and ammonia, will also be discussed in the presentation.
References:
[1] M. Cole and J. Klein, â??The interaction between noble gases and the basal plane surface of graphiteâ?, Surf. Sci., 124 (1983) 547; R. J. Gooding, B. Joos and B. Bergersen, â??Krypton on graphite: Microstructure at zero temperatureâ?, Phys. Rev. B, 27 (1983) 7669; M. L. Klein, S. F. Oâ??Shea and Y. Ozaki, â??Interaction potentials and the properties of xenon overlayers physisorbed on the graphite basal planeâ?, J. Phys. Chem. B, 88 (1984) 1420; G. Vidali and M. Cole, â??Lateral variation of the physisorption potential for noble gases on graphiteâ?, Phys. Rev. B, 29 (1984) 6736; M. Schobinger and F. Abraham, â??Energetics of the incommensurate phase of krypton on graphite: a computer simulation studyâ?, Phys. Rev. B, 31 (1985) 4590; E. Ustinov, â??Effect of crystallization and surface potential on the nitrogen adsorption isotherm on graphite: A refined Monte Carlo simulationâ?, Carbon, 100 (2016) 52.
Acknowledgement: This work is supported by the Australian Research Council, DP160103540, CF acknowledges the support from Decra, DE160100959.
