Revealing the different performance of Li₄SiO₄ and Ca₂SiO₄ for CO₂ adsorption by density functional theory

To reveal the difference between Li₄SiO₄ and Ca₂SiO₄ in CO₂ adsorption performance, the CO₂ adsorption on Li₄SiO₄ (010) and Ca₂SiO₄ (100) surfaces was investigated using density functional theory (DFT) calculations. The results indicate that the bent configuration of the adsorbed CO₂ molecule parallel to the surface is the most thermodynamically favorable for both Li₄SiO₄ and Ca₂SiO₄ surfaces. The Li₄SiO₄ (010) surface has greater CO₂ adsorption energy (E _ads = -2.97 eV) than the Ca₂SiO₄ (100) surface (E _ads = -0.31 eV). A stronger covalent bond between the C atom of adsorbed CO₂ and an O_S atom on the Li₄SiO₄ (010) surface is formed, accompanied by more charge transfer from the surface to CO₂. Moreover, the Mulliken charge of O_S atoms on the Li₄SiO₄ (010) surface is more negative, and its p-band center is closer to the E _f, indicating O_S atoms on Li₄SiO₄ (010) are more active and prone to suffering electrophilic attack compared with the Ca₂SiO₄ (100) surface.