Multifunctional strain-controlled graphdiyne membrane for gas separation: a theoretical study

Graphdiyne (GDY) membrane with intrinsic pore has potential for gas separation. Here we report a multistage gas separation of H2/CO2/N2/CH4 gas mixture through graphdiyne by applying tensile strain using molecular dynamics simulation. The results indicate that gas permeability is remarkably enhanced through tensile strain. H2 molecules have always been able to penetrate GDY membrane, while all CH4 molecules are blocked during the progress of tensile strain up to ultimate strain. An ultrahigh H2 permeance of ∼106 GPU (gas permeation unit) and H2 selectivity towards CO2/N2/CH4 was obtained, which is larger than the acceptable value in industrial applications. As the tensile strain is between 7.5% and 10% (ϵx)–15%(ϵy), the membrane adopted in this work can be utilised for separating CO2 from CO2/N2/CH4 mixture. When the strain level is beyond 10% (ϵx)–15% (ϵy), the strained GDY can be served as a CH4 upgrading membrane. The ultrahigh gas permeance is ascribed to the ultrathin membrane and high-density pore, and the size sieving effect of GDY membrane with small pores is responsible for the excellent gas selectivity. The results suggest that these two-dimensional membranes with intrinsic pores could serve as the ideal multifunctional size-selective membrane for gas separation towards different separation requirements.