Surface-Molecule Interaction Strength on CO2 Adsorption Capacity in Nanopores: Implications to Advance CO2 Sequestration Performance

CO 2 geological sequestration, injecting CO 2 into tight salt caverns or depleted oil/gas reservoirs where a diversity of nanopores exists, is recognized as a reliable and applicable approach to achieve efficient CO 2 reduction. The adsorption mechanism induced by the surface-molecule interaction is the underlying reason why nanopores have an obvious stronger CO 2 storage capacity than macropores. However, the magnitude that the CO 2 storage performance would be improved by intensifying the surface-molecule interaction strength is still a giant knowledge gap. A clear understanding of the relationship between surface-molecule interaction strength and the nanoconfined CO 2 adsorption capacity provides critical guidance on modifying surface composition aiming at better CO 2 sequestration performance. In this work, the simplified local density (SLD) theory in accordance with the equilibrium of chemical potential lays the fundamental basis, and the shift of CO 2 critical properties as the surface-molecule interaction strength varies is taken into account. Results indicate the following: (a) Manipulating surface-molecule interaction strength imposes a significant impact on CO 2 adsorption phase density in nanopores; the CO 2 storage amount in a 2 nm pore would improve by as much as 103%, while the interaction strength enhances from 100 to 500 K; (b) The discrepancy in terms of nanoconfined average CO 2 density due to changing interaction strength is fairly evident at low-pressure conditions but greatly mitigated under high-pressure conditions where the bulk CO 2 density approaches the adsorption phase density; (c) Neglecting the shift of CO 2 critical properties in nanopores leads to the overestimation in nanoconfined average CO 2 density, and a magnitude that could exceed 30% has a positive correlation with the rise of surface-molecule interaction strength as well as the decline in pore size. This work explores the key dependence of the nanoconfined CO 2 storage on surface-molecule interaction and highlights the huge potential to advance CO 2 sequestration efficiency by nanopore surface modification.