Multiscale investigation of metal substitution and diffusion mechanisms for enhanced CO2 adsorption: A case study of SIFSIX-3-Cu MOFs

Abstract

Carbon capture through adsorption is acknowledged as a promising engineering solution, notable for its low energy consumption, high controllability, and compatibility with renewable energy sources. Metal-organic frameworks (MOFs) have gained significant attention as sorbents for low-energy CO₂ separation from flue gases. In this study, we conducted molecular dynamics (MD) simulations to study the charge distribution of atoms in SIFSIX-3-M (where M = Ni, Co, Cu, Zn, Fe) with various pore parameters. Results indicated that SIFSIX-3-Cu possesses a large van der Waals surface and improved accessible solvent surface, suggesting the enhanced gas adsorption capabilities. Further analysis of the charge distribution and differential density maps for CO₂ adsorption revealed that the primary adsorption site for CO₂ within the pore is largely influenced by the strong interactions with the fluorine atoms in the framework. By calculating the radial distribution function (RDF) of the carbon atoms in CO₂ relative to the silicon atoms in SIFSIX-3-Cu, we observed a notably strong interaction between the carbon atoms and the neighboring fluorine atoms near the silicon atoms at 5.75 Å, that provides a critical binding site for CO₂ adsorption. Additionally, we employed computational fluid dynamics (CFD) simulations to study the breakthrough curves of N₂CO₂ gas mixture passing through a porous packed bed constructed by SIFSIX-3-Cu. The results demonstrated effective separation of N₂ and CO₂, highlighting the strong selectivity of SIFSIX-3-Cu for CO₂ adsorption. Moreover, SIFSIX-3-Cu exhibited excellent thermal stability, maintaining consistent CO₂ uptake across multiple temperature swing adsorption (TSA) cycles. This study provides a solid foundation for further optimization of the SIFSIX series MOFs for advanced carbon capture applications.