(185b) Hydrophobicity/Hydrophilicity Driven CO2 Solubility in Kaolinite Nanopores in Relation to Carbon Sequestration

Carbon capture and sequestration (CCS) is an urgent mission for human being due to the increasingly severe global warming crisis. Storing CO₂ in underground aquifers is a viable option to alleviate greenhouse gas effects. In this process, CO₂ solubility trapping in nanoporous media saturated with water may play an important role. CO₂ solubility in nanoporous media is determined by the mutual interactions among CO₂, water, and nano-confinement, which ultimately determine the CO₂ sequestration amount. However, the effects of nano-confinement surface characteristics are not well studied yet. In this study, we use molecular dynamics simulations to study the effects of surface characteristics on CO₂ solubility under nano-confinement by deploying kaolinite nanopores as a model under typical geological conditions (373 K and up to 400 bar). We find that, compared to the bulk solubility, CO₂ under-solubility is observed in hydrophilic kaolinite nanopores, while over-solubility is seen in hydrophobic kaolinite nanopores. From the microscopic view, in hydrophilic kaolinite nanopores, water forms strong adsorption layers on the pore surfaces, which repel CO₂ molecules. However, CO₂ and water can be co-adsorbed on the pore surfaces in hydrophobic kaolinite nanopores. In addition, CO₂ molecules align parallel to the pore surface in hydrophobic kaolinite nanopores, while water molecules align perpendicular to the hydrophilic one. CO₂ is less hydrated under the nano-confinement than in bulk, especially under the hydrophobic one. In conclusion, hydrophobic strata are more capable to sequestrate CO₂ than hydrophilic strata in terms of solubility trapping mechanism.