Hydrophobic nanoconfinement enhances CO2 conversion to H2CO3

An understanding of the formation of H2CO3 in water from carbon dioxide is important in many environmental, biological, and industrial processes, and in the global carbon cycle. Although numerous computational and experimental investigations have focused on understanding these interactions, the conversion of CO2 to H2CO3 in nanopores, and how this conversion differs from that in bulk water, has not been understood. In this study, we use ReaxFF metadynamics molecular simulations to demonstrate striking differences in the free energy of CO2 conversion to H2CO3 in bulk water compared with that in water confined in pyrophyllite nanopores. We find that the nanoconfinement not only reduces the energy barrier, but also reverses the reaction from endothermic in bulk water to exothermic in nanoconfined water. In addition, charged species are observed more often under nanoconfinement than in bulk water. The higher number of reactive encounters, stronger solvation, and more favorable proton transfer with increasing confinement enhance the thermodynamics and kinetics of the reaction. As carbonation in nanopores is important in the carbon cycle and a complicated problem that depends on confinement, surface chemistry, pore chemistry, and concentration of CO2, our results provide a mechanistic understanding to an important step in this process.