Recent Advancements in Aqueous CO₂ Nanobubbles

Aqueous nanobubble dispersion of carbon dioxide (CO2) is an emerging science with great potential in developing novel nanomaterials that impact various industries. Nanobubbles (NBs), due to their nanoscale dimensions and unique hollow shell–core structure, exhibit a high surface/volume ratio and high internal pressure in addition to low buoyancy. This results in a highly efficient mass transfer rate with a swift dispersion of the CO2 NBs in aqueous media. The application of NB technology in different gas–liquid mixtures has been demonstrated to improve the efficiency of several chemical and biological processes, ranging from biomedical applications to wastewater treatment. The distinctive characteristics of NBs make them suitable for applications such as carbon capture, utilization, and storage (CCUS), particularly carbon sequestration in enhanced oil recovery or depleted oil reservoirs or deep saline aquifers, and the food and beverage industries. Here, we review recent advancements in CO2 NBs in aqueous media, focusing on methods for generating and characterizing them as well as the key factors affecting their formation, long-term stability, and potential applications. Various techniques for NB generation, such as cavitation, membrane dispersion, and pressurization-depressurization, were summarized. Additionally, state-of-the-art characterization techniques, including dynamic light scattering, nanoparticle tracking analysis, zeta potential analysis, nuclear magnetic resonance, cryo-scanning electron microscopy, and atomic force microscopy, were highlighted in this review. The diversity of emerging CO2 aqueous NB technologies holds great promise for various applications supported by different additives in aqueous solutions and warrants further investigations. Future directions include developing scalable, environmentally friendly methods for NB generation, emphasizing improving stability and optimizing their performance through artificial intelligence and machine learning-enabled systems. Additionally, integrating this technology with the existing CCUS infrastructure could address specific industrial and environmental needs, driving the adoption of CO2 NB technology on a broader scale.