Carbon Dioxide Capture by PAFs and an Efficient Strategy To Fast Screen Porous Materials for Gas Separation

We have systematically investigated the CO2 storage and separation in a new class of porous aromatic frameworks (PAFs) with diamond-like structure by molecular simulations. Because of the small pore size of 5.2 Å, PAF-301 exhibits not only much higher CO2 uptakes at low pressure (275 mg/g at 298 K and 1 bar) but also much higher selectivities for the CO2/H2, CO2/N2, CO2/CH4, and CH4/H2 mixtures than the other three PAFs. The uptakes of CO2 in PAF-303 and PAF-304 reach 3432 and 3124 mg/g at 298 K and 50 bar, respectively, which are larger than MOF-200 (2437 mg/g) and MOF-210 (2396 mg/g), suggesting the two PAFs are promising candidates for high-capacity CO2 storage. Interestingly, the selectivity of PAFs is closely related to the difference of isosteric heats (DIH) of two components and is independent with the molar fraction at zero pressure. Therefore, we proposed an efficient DIH approach to screen porous materials for separation of mixture gases and derived the relation between the selectivity and the difference of isosteric heats based on Langmuir adsorption theory. The derived DIH equation can quickly screen out promising porous materials (including PAFs, COFs, MOFs, etc.) for separation of mixture gases.