Physicochemical Properties of Water in Contact with Nanobubbles Generated by CO₂‐Hydrate Dissociation: An Investigation from Experiment and Molecular‐Dynamics Simulation

Abstract

The study investigates CO2‐nanobubbles (NBs) generated from gas‐hydrate dissociation, exploring their impact on the physicochemical properties of liquid water. Raman spectroscopy evidenced a slight increase in the Raman‐band intensity, suggesting enhanced total hydration‐layer water‐dipole moment and polarity without affecting water molecule structuring. Furthermore, an overall decreasing trend for the zeta potential of NB solution can be observed due to the strong electron affinity on the surface of CO2 bulk NBs, probably caused by a negative charge accumulation. These findings are in good qualitative accord with molecular‐dynamics (MD) simulation results, wherein water can induce a small dipole moment of about 0.16 D for CO2 NBs, thereby increasing the polarity of the system. Due to the interaction between water molecules, the Coulombic or electrostatic forces increase in the presence of NBs compared to pure water, which can reflect the increase in the dipole moment of water molecules in the presence of NBs. The presence of NBs strengthens the local hydrogen‐bond network, leading to higher‐frequency vibrations. Additionally, NBs amplify the intrinsic electric field of the aqueous solution, causing the gas‐water interface to exhibit negatively charged characteristics, dependent on NB size. Molecular simulations agree qualitatively with experiments, emphasizing their utility in studying NB evolution in water.