Combined DFT and MD simulation approach for the study of SO2 and CO2 adsorption on graphite (111) surface in aqueous medium

In this study, density functional theory (DFT) calculations combined with molecular dynamics (MD) simulation have been used to understand the adsorption mechanism of sulfur dioxide (SO2) and carbon dioxide (CO2) on the graphite surface in aqueous medium, in view of analytical and environmental application. The global reactivity descriptors, such as the frontier molecular orbital energies (EHOMO and ELUMO), gap energy (ΔEgap), absolute hardness (η) and softens (σ), fraction of electrons transferred (ΔN) and electronegativity (χ) were evaluated. The dynamic descriptors calculated by the MD simulation such as the adsorption energy (Eads), total energy (Etot), deformation energy (Edef), rigid adsorption energy (RAE) and dEads/dNi were also calculated and discussed. The obtained results indicated strong electron acceptor ability and high adsorption energy, which can suggest good adsorption ability. The interaction energies (ΔEinteraction) were negative for both gases indicating strong attractive force between the molecules and the graphite surface. The highest values of the binding energy (ΔEbinding) indicate that the adsorption of each molecule is strong and stable, which is in agreement with the interaction energies. The values of EHOMO and Eads were negative, indicating that the complete chemical processes occur spontaneously. Furthermore, MD simulation was applied to investigate the most stable configuration of the molecules on the graphite (111) surface. The larger Eads and the smaller bond distances indicate that graphite exhibited higher sensitivity to interact with SO2 and CO2 molecules in an aqueous medium.