Adsorption of Argon on MFI Nanosheets: Experiments and Simulations

Argon adsorption on zeolite nanosheets has been studied using molecular simulations and experiments. Zeolite nanosheets are thin sheets of zeolite, with a thickness on the nanometer length scale. Zeolite nanosheets have a large surface area compared to the mass of the zeolite crystal. No part of the zeolite nanosheet can be characterized as bulk zeolite. The pores, channels, and cages of the zeolite are still present, so adsorption can take place inside the nanosheet as well as on the external surface of the zeolite nanosheet. Capillary condensation can take place between parallel zeolite nanosheets, and this can occur at pressures below saturation pressure of the adsorbent. The large space on the external surfaces, as well as void space between surfaces of different nanosheets, can significantly increase the porosity of the system. This results in a different adsorption isotherm compared to the regular bulk zeolite structure, where adsorption on the external surfaces has only a minor contribution to the overall adsorption. In this paper, we develop a simulation model for studying adsorption of argon on the external surface of zeolite nanosheets and between layered zeolite nanosheets. Using molecular simulation, we study the effect of capillary condensation with different distances between the nanosheets. Results from molecular simulations are compared to adsorption isotherms from experiments. The comparison between bulk zeolite and zeolite nanosheets helps to distinguish adsorption on external surfaces from adsorption in the zeolite framework. We find that experimental data can be described using a simple nanosheet model in molecular simulations. In addition, the density profile around the external surface of the zeolite is studied. The density profile across the external surface is calculated and used to determine the Gibbs surface excess concentration of the gas/zeolite interface.