The role of adsorbate size on adsorption of Ne and Xe on graphite

• Published in: Journal of colloid and interface science Vol. 524; pp. 490 - 503
• Main Authors: Prasetyo, Luisa, Loi, Quang K., (Johnathan) Tan, Shiliang, Do, D.D., Nicholson, D.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.08.2018
• Subjects: Adsorption; Commensurate packing; Graphite; Neon; Simulation; Transition; Xenon; Neon; Adsorption; Simulation; Xenon; Graphite; Transition; Commensurate packing
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2018.03.091

Snapshot of Xe adsorption on the new graphite model at 65K for different loadings [Display omitted] •Correct description of the transition from fluid to incommensurate (IC) packing for neon.•For xenon, the transition from fluid to incommensurate (IC), followed by commensurate (C) packing.•The IC-to-C transition of xenon is opposite to the C-to-IC transition observed with Kr, N2, CH4.•The graphite model accounts for corrugation and anisotropy in polarizability.•Characteristic curve of the isosteric heat versus loading as a function of temperature. We have carried out an extensive grand canonical Monte Carlo simulation to investigate the adsorption of neon and xenon on graphite. The adsorbate collision diameters of neon and xenon are smaller and greater respectively, than the commensurate graphite lattice spacing λ=3×3R300 of 0.426 nm. Simulated isotherms and isosteric heats were obtained using a graphite model that has been shown to describe successfully the adsorbate transitions for krypton, methane and nitrogen by Prasetyo et al. (2017), which have collision diameters close to λ. Neon does not exhibit commensurate (C) packing because the gain in the intermolecular potential interactions in the incommensurate (IC) packing when molecules move away from carbon hexagon centres, does not compensate for the increase in the solid-fluid potential energy. Xenon, on the other hand, exhibits IC packing because its molecular size is greater than λ. Nevertheless, at a sufficiently high chemical potential, the first layer of xenon changes from the IC to C packing (in contrast to what is observed for krypton, nitrogen and methane). This transition occurs because the decrease in the xenon intermolecular interactions is sufficiently compensated by the increase in the solid-fluid interaction, and the increase in the fluid-fluid interactions between molecules in the first layer and those in the second layer. This finding is supported by the X-ray diffraction study by Mowforth et al. (1986) and Morishige et al. (1990).