Generation of Nanobubbles Using Alumina Nanopores and Bubble Coalescence

Nanobubbles (NBs), with their unique physicochemical properties and promising applications, have become an important research topic. Generation of monodispersed bulk NBs with specified gas content remains a challenge. We developed a simple method for generating bulk NBs, using porous alumina films with ordered straight nano-scaled holes. Nanoparticle tracking analysis (NTA) is used to confirm NB formation. The NTA data demonstrates that NB size is distributed discretely with a uniform increment factor of √2. To explain the observed characteristic size distribution of NBs, we propose a simple model in which two NBs of the same size are assumed to preferentially coalesce.