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 (Oi). 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.