Effect of Modified Metal Center in Ligand for CO2 Capture in Novel Zr-Based Porphyrinic Metal–Organic Frameworks: A Computational Investigation

A combination of grand canonical Monte Carlo (GCMC) and density functional theory (DFT) simulations was used to investigate the effect of modified metal center in ligand for CO2 capture in novel Zr-based porphyrinic metal–organic frameworks (PCN-224-Ms, M = Mg, Fe, Co, Ni, Mn, and Zr). The results show that the MTCPP ligands (TCPP = tetrakis(4-carboxyphenyl)porphyrin) provide more favorable adsorption sites than the inorganic Zr6 nodes for CO2 molecules. The modification of metal center in MTCPP ligand has a remarkable effect on the single-component adsorption of CO2 compared to CH4 and thus enhances the adsorption of CO2 and the selectivity of CO2 over CH4. Furthermore, Coulomb interaction between adsorbate and framework plays a dominant role compared with non-Coulomb interaction in the process of adsorption and separation. Among various modified metal centers, the Zr-MTCPP is found to be the best for enhancing the adsorption and selectivity of CO2. In addition, a small amount of water has a negative effect on the selectivity of CO2/CH4, and its influence follows the order PCN-224-Zr > PCN-224-Mn > PCN-224-Ni, depending on the strength of Coulomb interaction between H2O molecules and frameworks.