Molecular Insights\ninto the Microscopic Behavior of\nCO<sub>2</sub> Hydrates in Oceanic Sediments: Implications for Carbon\nSequestration

Knowledge of the microscopic behavior of CO<sub>2</sub> hydrates\nin oceanic sediments is crucial to evaluate the efficiency and stability\nof hydrate-based CO<sub>2</sub> sequestration in oceans. Here, systematic\nmolecular dynamics simulations are executed to investigate the growth\nand dissociation of CO<sub>2</sub> hydrates, and the mechanical instability\nof CO<sub>2</sub> hydrate-Illite interface in the brine-urea-Illite\nsystem. Simulation results show that the CO<sub>2</sub> hydrate growth\nis jointly affected by the confined space, Illite surface properties,\nand presence of urea. Specifically, the interfacial H<sub>2</sub>O\nand the ion layer on the Illite surface hinder the growth of CO<sub>2</sub> hydrate crystals toward Illite surfaces. Urea molecules can\nbind salt ions and increase CO<sub>2</sub> concentrations in the water,\nthus kinetically promoting CO<sub>2</sub> hydrate growth. The dissociation\nof the CO<sub>2</sub> hydrate is affected by Illite surface properties\nand the CO<sub>2</sub> hydrate structure. CO<sub>2</sub> hydrate \nstarts from the regions where hydrate particles are minimally in contact\nand extends on both sides. The mechanical tension and compression\nof the CO<sub>2</sub> hydrate-Illite interface exhibit nonlinear characteristics\nby changing the hydrogen bonds and the CO<sub>2</sub> hydrate structure.\nThe molecular insight into the microscopic behavior of CO<sub>2</sub> hydrates in the brine-urea-Illite system contributes to a broader\nunderstanding of hydrate-based CO<sub>2</sub> sequestration.