Density Functional Simulation of Adsorption Behavior within the Dicalcium Silicate-Accelerated Carbonation System

In this study, the adsorption behavior of various molecules, including H2O, CO2, and H2CO3, on the C2S surface in the carbonation system was systematically compared to elucidate the microscopic mechanism in early accelerated carbonation using density functional theory and ab initio molecular dynamics. The electronic structures on beta-C2S and gamma-C2S surfaces differ, in that the valence band maximum is contributed by the 0 p orbital and Ca s orbital, respectively. This difference results in different proton-surface interactions. The protons hydroxylated the [SiO4](4-) tetrahedra on the beta-C2S surface. On the gamma-C2S surface, the protons enter the interior surface to form a three-coordination configuration with Ca atoms in addition to bonding with the [SiO4](4-) tetrahedra. The adsorption energy for the dissociative adsorption of H2CO3 on both beta-C2S and gamma-C2S surfaces is significantly higher than that of H2O, and the dissociative adsorption configurations are also more stable. CO2 only has a strong adsorption tendency on the gamma-C2S surface, where it acquires electrons from the surface Ca atoms to become activated. In the molecular adsorption phase, gamma-C2S interacts more strongly with CO2, H2CO3, and its dissociation products.