Nanoscale\nUnderstanding on CO<sub>2</sub> Diffusion\nand Adsorption in Clay Matrix Nanopores: Implications for Carbon Geosequestration

Carbon\ncapture and storage (CCS) in subsurface reservoirs represents\na highly promising and viable strategy for mitigating global carbon\nemissions. In the context of CCS implementation, it is particularly\ncrucial to understand the complex molecular diffusive and adsorptive\nbehaviors of anthropogenic carbon dioxide (CO<sub>2</sub>) in the\nsubsurface at the nanoscale. Yet, conventional molecular models typically\nrepresent only single-slit pores and overlook the complexity of interconnected\nnanopores. In this work, finite kaolinite lamellar assemblages with\nabundant nanopores (<i>r</i> < 2 nm) were used. Molecular\ndynamics simulations were performed to quantify the spatial distribution\ncorrelations, adsorption preference, diffusivity, and residence time\nof the CO<sub>2</sub> molecules in kaolinite nanopores. The movement\nof the CO<sub>2</sub> molecules primarily occurs in the central and\nproximity regions of the siloxane surfaces, progressing from larger\nto smaller nanopores. CO<sub>2</sub> prefers smaller nanopores over\nlarger ones. The diffusion coefficients increase, while residence\ntimes decrease, with the pore size increasing, differing from typical\nslit-pore models due to the pore shape and interconnectivity. The\nperspectives in this study, which would be challenging in conventional\nslit-pore models, will facilitate our comprehension of the CO<sub>2</sub> molecular behaviors in the complex subsurface clay sediments\nfor developing quantitative estimation techniques throughout the CCS\nproject durations.