CO2 nanobubbles in aqueous phases for improving geological carbon storage efficiency: Enhanced dissolution and influence of ions

Reliable geological carbon storage requires technologies that can enhance CO 2 dissolution and retention in subsurface environments. CO 2 nanobubble (NB) technology has received increasing attention for its potential to enhance storage efficiency. This study employs molecular dynamics simulations to investigate stability of the CO 2 NBs and enhanced dissolution in the presence of NBs with diameters of 3–10 nm in pure water and 1 mol/kg brines (NaCl, KCl, CaCl 2 , and MgCl 2 ) under 313.15 K and 20 MPa. First, the calculated CO 2 -water interfacial tension and CO 2 solubility in bulk phase agreed well with experimental data, validating reliability of CO 2 -aqueous solution model system. Second, dissolution behaviors of CO 2 NBs in aqueous solutions were studied. Monovalent ions (Na + , K + ) have little effect on the dissolution, while divalent ions strongly inhibit it. Increasing CO 2 initial concentration from 0 to 3% gradually slows dissolution process. Compared with pure water, monovalent cations have only minor effects on NB lifetimes, whereas divalent cations markedly prolong them, indicating a strong stabilizing role. Importantly, our study supports a dynamic equilibrium state of NBs: the number of CO 2 molecules in NBs fluctuates, challenging classical dissolution theory. CO 2 concentrations dissolved into the aqueous phases increase in the presence of NB with the decreasing size, showing 1.1–2.4 times enhancement with 3–10 nm of diameter. Finally, a new term CO 2 “blob” was introduced to describe the local structure of oversaturation state. Blob populations decrease with increasing NB size and are strongly suppressed by dissolved ions, with divalent cations exerting the greatest effect, showing similar tendency with solubility changes. This work provides practical insight into the effects of NB size and ion composition on CO 2 dissolution and stability and offers a blob-based mechanistic understanding of oversaturation. • CO 2 nanobubble in water and four saline environments were studied at molecular scale. • Nanobubble can enhance CO 2 solubility in aqueous solutions by 1.1–2.4 times. • Nanobubble has good stability in brines, especially Mg 2+ and Ca 2+ divalent cations. • Fluctuation nature of CO 2 nanobubble explains the flaws of Epstein-Plesset model. • The role of CO 2 blobs in elucidating supersaturation was proposed for the first time.