Efficient storage and separation of methane using the metal–organic frameworks M2(m-dobdc)(M = Fe, Co, Ni, and Cu): a first-principles study

Abstract

Methane (CH₄) storage media play a crucial role in promoting sustainable development. However, current materials encounter challenges related to storage capacity and operational conditions. Therefore, it is essential to develop new and innovative materials for capturing and storing CH₄. The versatility of metal-organic frameworks (MOFs) allows for significant opportunities in this area due to their ease of functionalization. This inclusive innovation study explores the adsorption properties of CH₄ in M₂(m-dobdc) MOFs (M = Fe, Co, Ni, Cu; m-dobdc⁴⁻=4,6-dioxido-1,3-benzenedicarboxylate) through first-principles calculations. Strong orbital interactions between the M and surrounding oxygens result in notable charge depletion on the metal atoms, making them potential sites for CH₄ adsorption. The strength of CH₄ adsorption at each metal site is evaluated by analyzing the adsorption energy, charge transfer, charge density difference map, and partial density of states. The type of metal atom has a minimal influence on the CH₄ storage capacity of M₂(m-dobdc) frameworks. The findings reveal that M₂(m-dobdc) can hold up to 18 CH₄ molecules (per unit cell) with an average adsorption energy of about − 0.44 eV. The M₂(m-dobdc) frameworks can efficiently store and separate CH₄ molecules at moderate temperatures and pressures. Furthermore, M₂(m-dobdc) frameworks demonstrate outstanding capability for separating CH₄ from CH₄/CF₄, CH₄/N₂, CH₄/CO_2, and CH₄/H₂ binary mixtures. This study could pave the way for advancing functionalized MOFs that possess a significant capacity for CH₄ capture.