High CO2 adsorption capacities in UiO type MOFs comprising heterocyclic ligand

Abstract

For equilibrium-based CO2 capture, a high CO2 adsorption amount and working capacity of adsorbents to fulfill different conditions are desired. In this work, we investigated the CO2 adsorption in four UiO type MOFs comprising N, S, and O heterocyclic ligands. Our grand canonic Monte Carlo (GCMC) simulation results show that the CO2 adsorption amount in MOFs comprising N (UiO(BPYDC)), S (Zr-BTDC), and O (Zr-BFDC) heterocyclic ligands is higher than that in their parent MOF, UiO-67. The MOFs comprising O-heterocyclic ligand (Zr-BFDC) shows the highest CO2 adsorption amount, which is 4 times higher than that of UiO-67 at 1 bar. In addition, we also found that by changing the heteroatoms on the ligands, the CO2 working capacity can be precisely tuned. For post-combustion CO2 capture, Zr-BFDC shows the highest working capacity due to the relative steepness isotherms. However, for syngas purification, due to the higher partial pressure of CO2, the relative steepness of the CO2 isotherms for Zr-BFDC is less of an advantage, resulting in working capacities that are less than those of Zr-BTDC and UiO(BPYDC). For biogas stream purification, UiO(BPYDC) shows the highest working capacity. Furthermore, density functional theory (DFT) calculations revealed that the incorporation of heteroatoms alters the distribution of charge in the system, introducing regions of negative charge around heteroatoms, leading to enhanced interactions between framework atoms and CO2 molecules.