Ananda J. Jadhav, Aniruddha Bhalchandra Pandit
Bulk nanobubbles (BNBs), or ultrafine bubbles, have attracted significant attention due to their unexpected long-term stability and unusual physicochemical behavior. Classical models, including the Epstein–Plesset framework, predict rapid dissolution of nanoscale bubbles; however, numerous studies now confirm that BNBs persist for weeks to months, challenging established theories and stimulating renewed interest in their mechanistic origins. This review provides a comprehensive synthesis of current understanding, beginning with the historical evolution of BNB research and the primary pathways proposed for their formation, including nucleation-driven processes and microbubble shrinkage. Major generation strategies such as cavitation, electrolysis, pressurization–decompression, membrane permeation, and microfluidics are critically evaluated with respect to scalability, efficiency, and gas selectivity. The physicochemical attributes of BNBs, encompassing interfacial charge stabilization, enhanced gas solubility, radical generation, and mass-transfer effects, are discussed alongside recent advances in theoretical, atomistic, and continuum-level modeling that seek to reconcile their anomalous stability. Progress in characterization techniques, from light scattering and acoustic detection to nanopore- and fluorescence-based methods, is also assessed.