Expanded Porphyrins as Two-Dimensional Porous Membranes for CO₂ Separation

Porphyrin-based two-dimensional polymers have uniform micropores and close to atom-thin thicknesses, but they have not been explored for gas separation. Herein we design various expanded porphyrin derivatives for their potential application in membrane gas separation, using CO₂/N₂ as an example. Pore sizes are determined based on both van der Waals radii and electron density distribution. Potential energy curves for CO₂ and N₂ passing through are mapped by dispersion-corrected density functional theory calculations. The passing-through barriers are used to evaluate CO₂/N₂ separation selectivity. Promising subunits for CO₂ separation have been selected from the selectivity estimates. 2D membranes composed of amethyrin derivatives are shown to have high ideal selectivity on the order of 10⁶ for CO₂/N₂ separation. Classical molecular dynamics simulation yields a permeance of 10⁴-10⁵ GPU for CO₂ through extended 2D membranes based on amethyrin derivatives. This work demonstrates that porphyrin systems could offer an attractive bottom-up approach for 2D porous membranes.