2D Squaraine-Bridged Covalent Organic Polymers with Promising CO2 Storage and Separation Properties

Three hypothetical 2D porous covalent organic polymers, named SQ-COPs (i.e., SQ-COP-1, SQ-COP-2 and SQ-COP-3), have been proposed via the combination of linear squaraine unit and heterocyclic molecules (H3B3O3, H3B3N3 and H3C3N3). By using the first principle methods and grand cannonical Monte Carlo (GCMC) simulations, these SQ-COPs are predicted to possess big pore sizes (13.8-15.0 angstrom), large free volumes (5.07-10.94 cm(3) g(-1)) and high BET specific surface areas (8585-8938 m(2) g(-1)), which even exceed those of MOF-210 and PAF-1. As is expected, these SQ-COPs show promising gas storage and separation properties of H-2, CH4, N-2 and CO2 at ambient conditions. Especially at 298 K and 30 bar, their CO2 uptake reaches 804, 575 and 633 mg/g respectively, significantly higher than those of zeolites. Meanwhile, for separation of binary gas mixtures CO2/H-2, CO2/CH4, CO2/N-2, and CH4/H-2, SQ-COPs are comparable with most of COFs and MOFs. These porous SQ-COPs materials are not only environmental-friendly (metal-free), but also promising candidates for CO2 capture.