Understanding CO ₂ adsorption on the surfaces of SrO and its hydroxylated variants Sr(OH) ₂ · <i>n</i> H ₂ O ( <i>n</i> = 0, 1, 8)

Strontium oxide (SrO) is a promising material for CO₂ capture through a reversible cycle of carbonation and calcination, where SrO reacts with CO₂ to form SrCO₃ and can be regenerated by calcination. In the presence of moisture, SrO forms strontium hydroxide and its hydrates (Sr(OH)₂·<i>n</i>H₂O). This study, which employs density functional theory, investigates the CO₂ adsorption mechanism of these processes on various crystal surfaces, including SrO, Sr(OH)₂, Sr(OH)₂·1H₂O, and Sr(OH)₂·8H₂O. A significant finding is that the interaction of CO₂ with these surfaces leads to carbonate/bicarbonate formation <i>via</i> electron transfer, with notable differences in CO₂ orientation and bond characteristics between SrO surfaces and its hydroxylated surfaces. To explore the effects of moisture on CO₂ adsorption, H₂O adsorption on these stable surfaces was investigated. The results showed that H₂O reacts with the SrO (100) surface to form hydroxyl (OH) groups while it bonds with the surfaces of Sr(OH)₂·<i>n</i>H₂O (<i>n</i> = 0, 1, 8) with hydrogen bonding. A small amount of H₂O can enhance CO₂ adsorption while a large amount of H₂O could decrease the capability of CO₂ adsorption.