Gas Permeability and Selectivity of a Porous WS2 Monolayer

Atomically thin porous membranes display high selectivity for gas transport and separation. To create such systems, defect engineering of two-dimensional (2D) materials, e.g., via ion irradiation, provides an efficient route. Here, first-principles calculations are used to study the permeability of He, H2, N2, CO2, and CH4 molecules through WS2 monolayers containing vacancy-type defects. We found that (i) for most pores, regardless of the pore size, H2 exhibits large permeability (≃105 GPU), (ii) dissociation of H2 molecules and edge saturation occur when they approach the angstrom-size pores, (iii) the 1W6S pore (one W and six S atoms are removed from a WS2 monolayer) can separate H2 and N2 gases with high selectivity, and (iv) the 2W6S pore exhibits exceptionally high selectivity for separation of H2/CO2 (≃1013) and H2/CH4 (≃109). Our study advances the understanding of the mechanisms behind gas permeability and selectivity through sub-nanometer pores in WS2 and potentially other inorganic 2D materials.