Mechanistic insights into CO2 adsorption on cementitious surfaces: Coverage and pre-hydration effects from first-principles calculations

A deep understanding of the mechanisms of carbon dioxide (CO₂) adsorption on cementitious material surfaces is crucial for optimizing their CO₂ sequestration capabilities. In this study, we employed first-principles calculations to investigate the behaviour of CO₂ adsorption on the β-C₂S(100) and M3-C₃S(001) surfaces across multiple coverage levels. Results showed that the total adsorption energy became increasingly negative with higher CO₂ coverage, whereas the average adsorption energy per CO₂ molecule on the two surfaces displayed differing trends. At higher coverage levels, adsorption behaviour was influenced by site saturation, steric hindrance, and electrostatic interactions. The M3-C₃S(001) surface exhibited stronger and more stable CO₂ adsorption than the β-C₂S(100) surface, primarily due to the presence of oxygen ions (O_i). DFT analysis, including the partial density of states (PDOS) and crystal orbital Hamilton population (COHP) calculations, revealed a weakening of the Ca-O bonds at high coverages. CO₂ adsorption on pre-hydrated surfaces was also explored, showing a reduced CO₂ sequestration capacity on both materials. Overall, this study sheds light on the fundamental mechanisms of CO₂ adsorption on cementitious surfaces, providing atomistic insights into the interaction between surface pre-hydration and CO₂ adsorption, and therefore offering valuable guidance for developing more efficient CO₂ capture and storage methods in the cement industry.