Sub-micrometer gas-containing cavity, or bubble, in aqueous solutions
Ananobubble is a small sub-micrometer gas-containing cavity, or bubble, in aqueous solutions with unique properties caused by high internal pressure, small size and surface charge.[1][2] Nanobubbles generally measure between 70-150 nanometers in size [3][4] and less than 200 nanometers in diameter[5][6] and are known for their longevity and stability, low buoyancy, negative surface charge, high surface area per volume, high internal pressure, and high gas transfer rates.[2][7][8][9]
Nanobubbles can be formed by injecting any gas into a liquid.[10][11] Because of their unique properties, they can interact with and affect physical, chemical, and biological processes.[12] They have been used in technology applications for industries such as wastewater, environmental engineering, agriculture, aquaculture, medicine and biomedicine, and others.[7][13][14]
Nanobubbles are nanoscopic and generally too small to be observed using the naked eye or a standard microscope, but can be observed using backscattering of light using tools such as green laser pointers.[12] Stable nanobubbles in bulk about 30-400 millimeters in diameter were first reported in the British scientific journal Nature in 1982.[12] Scientists found them in deep water breaks using sonar observation.[12]
In 1994, a study by Phil Attard, John L. Parker, and Per M. Claesson further theorized about the existence of nano-sized bubbles, proposing that stable nanobubbles can form on the surface of both hydrophilic and hydrophobic surfaces depending on factors such as the level of saturation and surface tension.[15]
Nanobubbles can be generated using techniques such as solvent exchange, electrochemical reactions, and immersing a hydrophobic substrate into water while increasing or decreasing the water’s temperature.[13]
Nanobubbles and nanoparticles are often found together in certain circumstances,[16] but they differ in that nanoparticles have different properties such as density and resonance frequency.[17][18]
The study of nanobubbles faces challenges in understanding their stability and the mechanisms behind their formation and dissolution.[19]
Nanobubbles possess several distinctive properties:
Stability: Nanobubbles are more stable than larger bubbles due to factors such as surface charge and contaminants that reduce interfacial tension, allowing them to remain in liquids for extended periods.[19][20]
High Internal Pressure: The small size of nanobubbles leads to high internal pressure, which influences their behavior and interactions with the surrounding liquid.[19]
Large Surface-to-Volume Ratio: This property is crucial for efficient gas transfer between the nanobubbles and the liquid, which is beneficial for various applications.[19]
Inaquaculture, nanobubbles have been used to improve fish health and growth rates[21][22][23] and to enhance oxidation.[24][25][26] Nanobubbles can improve health outcomes for fish by increasing the dissolved oxygen concentration of water,[21] reducing the concentration of bacteria and viruses in water,[22] and triggering the nonspecific defense system of species such as the Nile tilapia, improving survivability during bacterial infections.[27] The use of nanobubbles to increase dissolved oxygen levels can also promote plant growth and reduce the need for chemicals.[28] Nanobubbles have also been shown as effective in increasing the metabolism of living organisms including plants.[26] In regards to oxidation, nanobubbles are known for generating reactive oxygen species, giving them oxidative properties exceeding hydrogen peroxide.[25] Researchers have also proposed nanobubbles as a low-chemical alternative to chemical-based oxidants such as chlorine and ozone.[26][27]
^ abLiu, Shu; Oshita, S.; Makino, Y.; Micro, th (2014). "Reactive oxygen species induced by water containing nano-bubbles and its role in the improvement of barley seed germination". S2CID55453522. {{cite journal}}: Cite journal requires |journal= (help)
