Theoretical investigation of CO2 capture in the MIL-88 series: effects of organic linker modification.

CO2 capture is a crucial strategy to mitigate global warming and protect a sustainable environment. Metal-organic frameworks with large surface area, high flexibility, and reversible adsorption and desorption of gases are good candidates for CO2 capture. Among the synthesized metal-organic frameworks, the MIL-88 series has attracted our attention due to their excellent stability. However, a systematic investigation of CO2 capture in the MIL-88 series with different organic linkers is not available. Therefore, we clarified the topic via two sections: (1) elucidate physical insights into the CO2@MIL-88 interaction by van der Waals-dispersion correction density functional theory calculations, and (2) quantitatively study the CO2 capture capacity by grand canonical Monte Carlo simulations. We found that the 1πg, 2σu/1πu, and 2σg peaks of the CO2 molecule and the C and O p orbitals of the MIL-88 series are the predominant contributors to the CO2@MIL-88 interaction. The MIL-88 series, i.e., MIL-88A, B, C, and D, has the same metal oxide node but different organic linkers: fumarate (MIL-88A), 1,4-benzene-dicarboxylate (MIL-88B), 2,6-naphthalene-dicarboxylate (MIL-88C), and 4,4'-biphenyl-dicarboxylate (MIL-88D). The results exhibited that fumarate should be the best replacement for both the gravimetric and volumetric CO2 uptakes. We also pointed out a proportional relationship between the capture capacities with electronic properties and other parameters.