Sub-micrometer gas-containing cavity, or bubble, in aqueous solutions
A nanobubble 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][3][4] Nanobubbles generally measure between 70-150 nanometers in size [5][6] and less than 200 nanometers in diameter[7][8] 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.[4][9][10][11]
Nanobubbles can be formed by injecting any gas into a liquid.[12][13] Because of their unique properties, they can interact with and affect physical, chemical, and biological processes.[14] They have been used in technology applications for industries such as wastewater, environmental engineering, agriculture, aquaculture, medicine and biomedicine, and others.[9][15][16]
Background
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.[14] Stable nanobubbles in bulk about 30-400 nanometers in diameter were first reported in the British scientific journal Nature in 1982.[14] Scientists found them in deep water breaks using sonar observation.[14]
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.[17]
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.[15]
Nanobubbles and nanoparticles are often found together in certain circumstances,[18] but they differ in that nanoparticles have different properties such as density and resonance frequency.[19][20]
The study of nanobubbles faces challenges in understanding their stability and the mechanisms behind their formation and dissolution.[21]
Properties
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.[21][22]
High Internal Pressure: The small size of nanobubbles leads to high internal pressure, which influences their behavior and interactions with the surrounding liquid.[21]
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.[21]
Usage
In aquaculture, nanobubbles have been used to improve fish health and growth rates[23][24][25] and to enhance oxidation.[26][27][28] Nanobubbles can improve health outcomes for fish by increasing the dissolved oxygen concentration of water,[23] reducing the concentration of bacteria and viruses in water,[24] and triggering the nonspecific defense system of species such as the Nile tilapia, improving survivability during bacterial infections.[29] The use of nanobubbles to increase dissolved oxygen levels can also promote plant growth and reduce the need for chemicals.[30] Nanobubbles have also been shown as effective in increasing the metabolism of living organisms including plants.[28] In regards to oxidation, nanobubbles are known for generating reactive oxygen species, giving them oxidative properties exceeding hydrogen peroxide.[27] Researchers have also proposed nanobubbles as a low-chemical alternative to chemical-based oxidants such as chlorine and ozone.[28][29]
References
↑ Svetovoy, Vitaly B. (April 2021). "Spontaneous chemical reactions between hydrogen and oxygen in nanobubbles". Current Opinion in Colloid & Interface Science. 52 101423. arXiv:2102.03126. doi:10.1016/j.cocis.2021.101423.
↑ Michailidi, Elisavet D.; Bomis, George; Varoutoglou, Athanasios; Efthimiadou, Eleni K.; Mitropoulos, Athanasios C.; Favvas, Evangelos P. (2019). "Fundamentals and applications of nanobubbles". Advanced Low-Cost Separation Techniques in Interface Science. Interface Science and Technology. Vol.30. pp.69–99. doi:10.1016/B978-0-12-814178-6.00004-2. ISBN978-0-12-814178-6.
1 2 Nirmalkar, N.; Pacek, A. W.; Barigou, M. (18 September 2018). "On the Existence and Stability of Bulk Nanobubbles". Langmuir. 34 (37): 10964–10973. doi:10.1021/acs.langmuir.8b01163. PMID30179016.
1 2 Foudas, Anastasios W.; Kosheleva, Ramonna I.; Favvas, Evangelos P.; Kostoglou, Margaritis; Mitropoulos, Athanasios C.; Kyzas, George Z. (January 2023). "Fundamentals and applications of nanobubbles: A review". Chemical Engineering Research and Design. 189: 64–86. Bibcode:2023CERD..189...64F. doi:10.1016/j.cherd.2022.11.013.
↑ Parker, John L.; Claesson, Per M.; Attard, Phil (August 1994). "Bubbles, cavities, and the long-ranged attraction between hydrophobic surfaces". The Journal of Physical Chemistry. 98 (34): 8468–8480. doi:10.1021/j100085a029.
↑ Alheshibri, Muidh; Al Baroot, Abbad; Shui, Lingling; Zhang, Minmin (October 2021). "Nanobubbles and nanoparticles". Current Opinion in Colloid & Interface Science. 55 101470. doi:10.1016/j.cocis.2021.101470.
↑ Alheshibri, Muidh; Craig, Vincent S. J. (27 September 2018). "Differentiating between Nanoparticles and Nanobubbles by Evaluation of the Compressibility and Density of Nanoparticles". The Journal of Physical Chemistry C. 122 (38): 21998–22007. doi:10.1021/acs.jpcc.8b07174.
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