Funnel mechanism for the filtration of gases through nanopores in layered membranes of carbon materials

Abstract

Ab initio molecular dynamics simulations provide novel information on the mechanisms of filtration of CO2 and CH4 gases through the nanopores of graphdiyne (GDY) and boron-graphdiyne (BGDY) layered materials. The molecules follow a funnel mechanism, in which molecules falling in the catchment area of the funnel (the wide upper region) deviate from their original path and cross the pore through a region around the center of the pore (the narrow tube at the bottom of the funnel). The critical parameter for a successful crossing is the size ratio of molecule and pore. The relevant pore size is not its geometrical size but an effective size accounting for the extension of the electronic cloud of the carbon chains bounding the pore. Very important is also the anisotropy in the form of the molecule. The linear CO2 molecule can take advantage of the orientation of its axis to decrease the effective size when crossing the narrow pores of GDY. The simulations reveal the relevance of the vibrational motion of the molecules, because the vibrations modulate the effective dynamical size of the molecules.