Effect of axial molecules and linker length on CO2 adsorption and selectivity of CAU-8: a combined DFT and GCMC simulation study

Abstract

Density Functional Theory (DFT) and Grand Canonical Monte Carlo (GCMC) calculations are performed to study the structures and carbon dioxide (CO₂) 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 (H₂BPDC) linker of CAU-8 is substituted by 4,4′-oxalylbis(azanediyl)dibenzoic acid (H₂ODA) and 4,4′-teraphthaloylbis(azanediyl)dibenzoic acid (H₂TDA) containing amide groups (–CO–NH- motif). Furthermore, MgO₆ octahedral chains where dimethyl sulfoxide (DMSO) decorating the axial position bridged two Mg²⁺ 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 CO₂ adsorptions and selectivities of Al-based MOFs are better than those of Mg-based MOFs, which is due to DMSO. Amide groups made CO₂ molecules more intensively distributed besides organic linkers. CO₂ uptakes and selectivities of MOFs containing H₂TDA linkers are better in comparison with those of MOFs containing H₂BPDC linkers or H₂ODA linkers.