Computational Study on Metal-Ion-Decorated Prismane Molecules for Selective Adsorption of CO₂ from Flue Gas Mixtures

Selective adsorption of CO₂ from flue gas is extremely significant because of its increasing concentration in air and its deleterious effect on the environment. In this work, we have explored metal-ion-bound prismane molecules for selective CO₂ adsorption from the flue gas mixture. The Ca²⁺-bound prismane complex exhibits superior CO₂ selectivity and adsorption capacity. The calculated binding energy and molecular electrostatic potential (MESP) analysis showed that the rectangular face of prismane binds strongly with metal ions as compared to its triangular face. The CBS-QB3 and density functional theory-based functional M06-2X/6-311+G(d) calculations show that the prismane molecule can bind to one Li⁺, K⁺, Mg²⁺, and Ca²⁺ ion with favorable binding energy. The metal-ion-bound prismane complexes have been examined for their CO₂, N₂, and CH₄ adsorption capacity. Prismane-Ca²⁺ can bind with six CO₂ molecules strongly with an average binding energy of -18.1 kcal/mole as compared to six N₂ (-12.6) and five CH₄ (-13.4) gas molecules. The gravimetric density calculated for the CO₂-adsorbed prismane-Ca²⁺ complex has been found to be 69.1 wt %. The discrete hydrocarbon structure for selective separation of CO₂ is rare in the literature and can have potential applications for cost-effective CO₂ capture from the flue gas mixture.