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Ab Initio Study of Gas Adsorption in Metal–Organic Frameworks Modified by Lithium: The Significant Role of Li-Containing Functional Groups C
- Gu, Chenkai, Liu, Yang, Liu, Jing, Hu, Jianbo, Wang, Weizhou
- Journal of physical chemistry 2018 v.122 no.32 pp. 18395-18404
- adsorption, benzene, binding sites, carbon dioxide, carbon monoxide, cations, coordination polymers, electrostatic interactions, energy, gases, hydrogen, hydrogen sulfide, lithium, metal ions, methane, moieties, nitrogen, sulfur dioxide
- Metal–organic frameworks (MOFs) are promising materials for gas adsorption. Introducing metal cations, for example, lithium cations (Li⁺), in the framework is an effective way to alter the gas adsorption features of MOFs. In this work, Li⁺ carried by different functional groups was incorporated onto a benzene linker, which is one type of the most common liker used in MOF synthesis. The interactions between the Li-modified linkers and various gas molecules were studied using MP2 method. Compared to the original benzene ring, the structures and orbitals of Li-modified linkers were significantly changed toward the direction of enhancing gas adsorption. For nonpolar gas species (CH₄, H₂, N₂, and CO₂), the induced polarizations greatly enhance the interactions between gas molecules and MOF linkers. Particularly, the expanded binding energy differences of H₂/N₂, CH₄/CO₂, and N₂/CO₂ will make them easier to get separated. For polar gas species (H₂O, H₂S, SO₂, and CO), the electrostatic interactions between gas molecules and Li⁺ play a significant role in enhancing gas adsorption. The strong affinities between polar gases and Li-modified linkers denote that the binding sites around Li⁺ can be first occupied by polar molecules such as H₂O and SO₂ during the practical adsorption process. This can result in the reduced adsorption capacities of other gases, such as CO₂.