Mechanical and gas adsorption properties of graphene and graphynes under biaxial strain

Abstract

The exceptional properties of two-dimensional (2D) solids have motivated extensive research, which revealed the possibility of controlling many characteristics of these materials through strain. For instance, previous investigations demonstrated that compressive deformation could be used to direct the chemisorption of atomic hydrogen and oxygen. Still, to our knowledge, there is no work detailing how strain affects the adsorption isotherms of 2D materials and the adsorption properties of materials such as the graphynes, which are monolayers composed of sp and sp2 carbon atoms. In the present work, we analyze how biaxial tensile deformation changes the adsorption properties of four 2D materials (graphene, α-graphyne, β-graphyne, and γ-graphyne). To achieve this, we perform Monte Carlo Grand Canonical calculations to obtain the adsorption isotherms of H2, CO2, and CH4 on the monolayers with and without strain. And, to apply the deformation, we carry out Molecular Dynamics simulations. We find a substantial reduction in the amount of gas adsorbed on the monolayers for nearly all gas–solid combinations. This is particularly true for graphene, where 14.5% strain reduces the quantity of H2/CO2/CH4 by 44.7/64.1/41.7% at P = 1 atm. To understand the results, we calculate adsorption enthalpies and analyze the gas distribution above the monolayers. We also characterize the mechanical properties of the considered solids under biaxial deformation. Finally, a comparison of pore sizes with the kinetic diameters of various gases suggests applications for the graphynes, with and without strain, in gas separation.