Molecular insights into the formation of carbon dioxide hydrates on the external surface of sodium montmorillonite in the presence of various types of organic matters

Abstract

To address the urgent challenge of global climate change due to the greenhouse effect resulting from increasing carbon dioxide (CO₂) emissions, viable technologies for geological CO₂ storage must be developed. Of such technologies, CO₂ hydrates holds significant promise for CO₂ storage in seabed sediments, which typically contain clay minerals and organic matter (OM). Thus, investigating the structure of clay mineral interfaces and their interactions with OM is crucial for understanding the nucleation and growth of CO₂ hydrate in seabed sediments. In this study, molecular dynamics simulations were used to investigate CO₂ hydrate formation on the external surface of sodium montmorillonite (Na-Mnt) in the presence of various types of OM. The results show that the Na-Mnt surface adsorbed certain numbers of sodium ions (Na⁺) and OM molecules. The hydration of Na ⁺ disrupted of the hydrogen bond structure of CO₂ hydrates, while hydrogen bonds that formed between OM and H₂O molecules hindered CO₂ hydrate formation. Consequently, CO₂ hydrates predominantly formed in the bulk-like solution away from the Na-Mnt. However, the electrostatic interaction between the carboxyl groups of OM and Na⁺ mitigated the inhibitory effect of Na⁺ on CO₂ hydrate formation. Over all, these findings can serve as a fundamental theoretical basis for understanding the formation and occurrence characteristics of CO₂ hydrates in seabed sediments with a rich Mnt content. Such understanding will help to advance the development of CO₂ storage technologies utilizing CO₂ hydrates in seabed sediments.