Effect of axial molecules and linker length on CO 2 adsorption and selectivity of CAU-8: a combined DFT and GCMC simulation study.

Density Functional Theory (DFT) and Grand Canonical Monte Carlo (GCMC) calculations are performed to study the structures and carbon dioxide (CO 2 ) adsorption properties of the newly designed metal-organic framework based on the CAU-8 (CAU stands for Christian-Albrechts Universität) prototype. In the new MOFs, the 4,4'-benzophenonedicarboxylic acid (H 2 BPDC) linker of CAU-8 is substituted by 4,4'-oxalylbis(azanediyl)dibenzoic acid (H 2 ODA) and 4,4'-teraphthaloylbis(azanediyl)dibenzoic acid (H 2 TDA) containing amide groups (-CO-NH- motif). Furthermore, MgO 6 octahedral chains where dimethyl sulfoxide (DMSO) decorating the axial position bridged two Mg 2+ ions are considered. The formation energies indicate that modified CAU-8 is thermodynamically stable. The reaction mechanisms between the metal clusters and the linkers to form the materials are also proposed. GCMC calculations show that CO 2 adsorptions and selectivities of Al-based MOFs are better than those of Mg-based MOFs, which is due to DMSO. Amide groups made CO 2 molecules more intensively distributed besides organic linkers. CO 2 uptakes and selectivities of MOFs containing H 2 TDA linkers are better in comparison with those of MOFs containing H 2 BPDC linkers or H 2 ODA linkers.