Full life circle of micro-nano bubbles: Generation, characterization and applications

Micro-nano bubbles (MNBs) usually refer to ultrafine bubbles less than 100 μm in diameter, exhibiting extraordinary physical and chemical properties compared with those of macro-bubbles, and are attracting increasingly attention in both academia and industry. In the current paper, the full life circle of MNBs was reviewed, from emerging MNBs generation approaches to the advanced characterization techniques, and finally to their recently booming applications. The MNBs generation techniques were classified into two categories: the chemical approaches (e.g., electrolysis and chemical reaction, etc.) and the physical approaches (e.g., cavitation, dispersion of gas, solution mixing, temperature alteration, EHD effect, etc.). As to MNBs characterization, both the static and dynamic characterization techniques were discussed, e.g., optical microscope, high-speed photography, rheology, AFM, DLS, NTA, optical flow cytometry, electron microscope, etc., depending on their operating principles. Merits and demerits of those generation and characterization techniques for MNBs were compared and highlighted, as well as their own characteristics and application scopes. The burgeoning applications of MNBs in functional material preparation were subsequently reviewed in details, including material preparation mechanism, properties and application scenarios. While, the MNBs-based surface cleaning, hydrogen production and carbon neutrality were also emphasized. With the development of basic MNBs theory and the booming scientific and industrial demands, the MNBs-related science and technology will flourish, and MNBs will certainly exhibit broader application prospects in the near future.