Characteristics and Application of Ultrafine Bubbles

Ultrafine bubbles (bulk nanobubbles), small bubbles less than 1 µm in diameter, have attracted academic and industrial attention because they have numerous advantages, including chemical-free nature and extraordinarily long lifetime. Since Brownian motion velocity is much higher than buoyancy, ultrafine bubble lifetime is more than several months. But stable mechanism is still unclear, even though their inside is highly pressured. They have several characteristics, such as pH-dependent surface charge and reduction in friction. Ultrafine bubbles are generated and removed by selecting the ultrasonic frequency. This review discusses the fundamental characteristics of ultrafine bubbles and their applications. Ultrafine bubbles effectively remove proteins, dyes, and inorganic salts from solid surfaces. Ultrafine bubbles promote adsorption, desorption and extraction. Gold nanoparticles, nanocomposites of CaCO3 and pulp fiber, and follow nanoparticles are synthesized using ultrafine bubbles. Thus, ultrafine bubbles have been shown to be powerful, environmentally friendly, safe, clean, simple, and inexpensive methods.