Ab initio calculations of CO₂ adsorption on β-C₂S(100) and M3-C₃S(001) surfaces: An exploration of early CO₂ sequestration pathways

Investigating CO₂ sequestration in cement-based materials is significant for achieving carbon neutrality in the cement and concrete industries. The early CO₂ sequestration pathways on cement-based materials are fundamental for CO₂ sequestration, which is not clear. Towards this, the adsorption behavior of CO₂ on β-C₂S(100) and M3-C₃S(001) was investigated at the atomic level using density functional theory calculations, which were then compared with water adsorption results. The molecular adsorption configurations of CO₂ on both β-C₂S(100) and M3-C₃S(001) were tilted from their initial configurations due to the influence of surface Ca and O atoms. The CO₂ adsorption energy on M3-C₃S(001) and β-C₂S(100) were −0.458 eV and −0.426 eV, respectively, indicating adsorption on M3-C₃S(001) was more energetically favorable. After CO₂ adsorption, electrons were transferred from the surface to the CO₂ molecule. Furthermore, the Ca–O bond orders of β-C₂S(100) and M3-C₃S(001) after CO₂ adsorption were maximally decreased by 2.79% and 6.99%, respectively. A more significant adsorption influence on surfaces was found for H₂O, with more negative adsorption energy, more evident electron transfer, and a greater decrease in bond order. The CO₂ adsorption on β-C₂S(100) and M3-C₃S(001) were still spontaneous at 298 K and 1 atm. This study provides important theoretical insights into early CO₂ sequestration at the atomic level, which has practical implications for the design of efficient CO₂ sequestration technologies.