The role of gas composition in nanobubbles: Generation, characterization, applications, and future directions for sustainable technologies

Nanobubbles (NBs) are gas-filled entities under 1000 nm with unique physicochemical properties, including longevity and high gas-liquid mass transfer, making them suitable for diverse environmental, agricultural, medical, and energy applications. However, previous analyses often treat NBs monolithically, failing to connect the encapsulated gas core to the specific application mechanism, stability, and concentration. This review provides a targeted, mechanistic analysis establishing that gas composition is the primary design parameter defining NB functionality. We concisely link scalable generation methods and gas-specific methods to their influence on achievable NBs concentration. We demonstrate how the gas composition dictates physicochemical properties, from the high stability of O 2 and O 3 NBs to the inherent instability of CO 2 NBs. Most critically, this review re-frames applications based on a new gas-defined redox framework. (1) Oxidative: O 2 NBs for sustained oxygenation; O 3 NBs as an Advanced Oxidation Process, (2) Reductive: H 2 NBs for remediation, and (3) Physical/Inert: N 2 NBs for physical stripping. This is the first analysis to centralize the role of gas composition from a mechanistic, rather than descriptive, perspective, bridging fundamental properties with how applications function. Future research should prioritize optimizing gas-specific stability and concentration in complex real-world matrices and scaling generation to unlock the full potential of this technology for sustainable solutions. • Gas composition is the primary design parameter for nanobubble functionality. • Gas core dictates nanobubble stability, concentration, and redox potential. • Applications re-framed by a new gas-defined redox mechanism. • Nanobubble stability and size are critically linked to gas type.