Efficiency of carbon dioxide capture with metal substitutions in the MIL-88A metal-organic framework

Carbon dioxide capture is a vital approach for mitigating air pollution and global warming. In this context, metal-organic frameworks are promising candidates. Particularly, MIL-88A (M), where the metal nodes (M) are connected to fumarate linkers in its structure, has demonstrated significant potential for CO₂ capture. However, to date, no studies have investigated the effects of metal substitutions in MIL-88A (M) on CO₂ capture performance. Therefore, the present work aims to address this gap by examining metal substitutions with M = Al, Sc, Ti, V, and Ga. To quantitatively understand the CO₂ capture capabilities of MIL-88A (M), we employed grand canonical Monte Carlo simulations to study both excess and total CO₂ uptakes. Our findings indicated that MIL-88A with Al and Ga as metal nodes exhibited the best performance for CO₂ capture. Furthermore, the adsorption energy of the CO₂ molecule in MIL-88A (M), obtained through van der Waals-corrected density functional theory calculations, indicated the following order of preference for CO₂ adsorption: Ti > V > Sc > Ga ≈ Al. The adsorption strength of the CO₂ molecule in MIL-88A (Ga and Al) was the weakest among the considered metals. However, MIL-88A (Al) exhibited the largest specific surface area and hence offered the best excess and total gravimetric uptakes, while MIL-88A (Ga), together with MIL-88A (Al), had the largest pore volumes. Therefore, they exhibited the best excess and total volumetric uptakes. The electronic density of states revealed that the interaction between the 3σ , 2π , and 1π peaks of the CO₂ molecule and the O and C p and p orbitals of MIL-88A (M) was found to be significant for understanding the physical interaction between CO₂ and MIL-88A (M). Thus, our findings provide valuable insights for the rational design of metal-organic frameworks for gas capture and storage applications.