Sonochemistry

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In chemistry, the study of sonochemistry is concerned with understanding the effect of ultrasound in forming acoustic cavitation in liquids, resulting in the initiation or enhancement of the chemical activity in the solution. [1] Therefore, the chemical effects of ultrasound do not come from a direct interaction of the ultrasonic sound wave with the molecules in the solution.

Contents

History

The influence of sonic waves travelling through liquids was first reported by Robert Williams Wood (1868–1955) and Alfred Lee Loomis (1887–1975) in 1927. The experiment was about the frequency of the energy that it took for sonic waves to "penetrate" the barrier of water. He came to the conclusion that sound does travel faster in water, but because of the water's density compared to Earth's atmosphere it was incredibly hard to get the sonic waves to couple their energy into the water. Due to the sudden density change, much of the energy is lost, similar to shining a flashlight towards a piece of glass; some of the light is transmitted into the glass, but much of it is lost to reflection outwards. Similarly with an air-water interface, almost all of the sound is reflected off the water, instead of being transmitted into it. After much research they decided that the best way to disperse sound into the water was to create bubbles at the same time as the sound. Another issue was the ratio of the amount of time it took for the lower frequency waves to penetrate the bubbles walls and access the water around the bubble, compared to the time from that point to the point on the other end of the body of water. But despite the revolutionary ideas of this article it was left mostly unnoticed. [2] Sonochemistry experienced a renaissance in the 1980s with the advent of inexpensive and reliable generators of high-intensity ultrasound, most based around piezoelectric elements. [3]

Physical principles

Sound waves propagating through a liquid at ultrasonic frequencies have wavelengths many times longer than the molecular dimensions or the bond length between atoms in the molecule. Therefore, the sound wave cannot directly affect the vibrational energy of the bond, and can therefore not directly increase the internal energy of a molecule. [4] [5] Instead, sonochemistry arises from acoustic cavitation: the formation, growth, and implosive collapse of bubbles in a liquid. [3] The collapse of these bubbles is an almost adiabatic process, thereby resulting in the massive build-up of energy inside the bubble, resulting in extremely high temperatures and pressures in a microscopic region of the sonicated liquid. The high temperatures and pressures result in the chemical excitation of any matter within or very near the bubble as it rapidly implodes. A broad variety of outcomes can result from acoustic cavitation including sonoluminescence, increased chemical activity in the solution due to the formation of primary and secondary radical reactions, and increased chemical activity through the formation of new, relatively stable chemical species that can diffuse further into the solution to create chemical effects (for example, the formation of hydrogen peroxide from the combination of two hydroxyl radicals following the dissociation of water vapor within collapsing bubbles when water is exposed to ultrasound).

Upon irradiation with high intensity sound or ultrasound, acoustic cavitation usually occurs. Cavitation – the formation, growth, and implosive collapse of bubbles irradiated with sound — is the impetus for sonochemistry and sonoluminescence. [6] Bubble collapse in liquids produces enormous amounts of energy from the conversion of kinetic energy of the liquid motion into heating the contents of the bubble. The compression of the bubbles during cavitation is more rapid than thermal transport, which generates a short-lived localized hot-spot. Experimental results have shown that these bubbles have temperatures around 5000 K, pressures of roughly 1000 atm, and heating and cooling rates above 1010 K/s. [7] [8] These cavitations can create extreme physical and chemical conditions in otherwise cold liquids.

With liquids containing solids, similar phenomena may occur with exposure to ultrasound. Once cavitation occurs near an extended solid surface, cavity collapse is nonspherical and drives high-speed jets of liquid to the surface. [6] These jets and associated shock waves can damage the now highly heated surface. Liquid-powder suspensions produce high velocity interparticle collisions. These collisions can change the surface morphology, composition, and reactivity. [9]

Sonochemical reactions

Three classes of sonochemical reactions exist: homogeneous sonochemistry of liquids, heterogeneous sonochemistry of liquid-liquid or solid–liquid systems, and, overlapping with the aforementioned, sonocatalysis  [ fr ] (the catalysis or increasing the rate of a chemical reaction with ultrasound). [10] [11] [12] Sonoluminescence is a consequence of the same cavitation phenomena that are responsible for homogeneous sonochemistry. [13] [14] [5] The chemical enhancement of reactions by ultrasound has been explored and has beneficial applications in mixed phase synthesis, materials chemistry, and biomedical uses. Because cavitation can only occur in liquids, chemical reactions are not seen in the ultrasonic irradiation of solids or solid–gas systems.

For example, in chemical kinetics, it has been observed that ultrasound can greatly enhance chemical reactivity in a number of systems by as much as a million-fold; [15] effectively acting to activate heterogeneous catalysts. In addition, in reactions at liquid-solid interfaces, ultrasound breaks up the solid pieces and exposes active clean surfaces through microjet pitting from cavitation near the surfaces and from fragmentation of solids by cavitation collapse nearby. This gives the solid reactant a larger surface area of active surfaces for the reaction to proceed over, increasing the observed rate of reaction., [16] [17]

While the application of ultrasound often generates mixtures of products, a paper published in 2007 in the journal Nature described the use of ultrasound to selectively affect a certain cyclobutane ring-opening reaction. [18] Atul Kumar has reported multicomponent reaction Hantzsch ester synthesis in Aqueous Micelles using ultrasound. [19]

Some water pollutants, especially chlorinated organic compounds, can be destroyed sonochemically. [20]

Sonochemistry can be performed by using a bath (usually used for ultrasonic cleaning) or with a high power probe, called an ultrasonic horn, which funnels and couples a piezoelectric element's energy into the water, concentrated at one (typically small) point.

Sonochemistry can also be used to weld metals which are not normally feasible to join, or form novel alloys on a metal surface. This is distantly related to the method of calibrating ultrasonic cleaners using a sheet of aluminium foil and counting the holes. The holes formed are a result of microjet pitting resulting from cavitation near the surface, as mentioned previously. Due to the aluminium foil's thinness and weakness, the cavitation quickly results in fragmentation and destruction of the foil.

See also

Related Research Articles

<span class="mw-page-title-main">Cavitation</span> Low-pressure voids formed in liquids

Cavitation in fluid mechanics and engineering normally refers to the phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, called "bubbles" or "voids", collapse and can generate shock waves that may damage machinery. These shock waves are strong when they are very close to the imploded bubble, but rapidly weaken as they propagate away from the implosion. Cavitation is a significant cause of wear in some engineering contexts. Collapsing voids that implode near to a metal surface cause cyclic stress through repeated implosion. This results in surface fatigue of the metal, causing a type of wear also called "cavitation". The most common examples of this kind of wear are to pump impellers, and bends where a sudden change in the direction of liquid occurs. Cavitation is usually divided into two classes of behavior: inertial cavitation and non-inertial cavitation.

<span class="mw-page-title-main">Ultrasound</span> Sound waves with frequencies above the human hearing range

Ultrasound is sound with frequencies greater than 20 kilohertz. This frequency is the approximate upper audible limit of human hearing in healthy young adults. The physical principles of acoustic waves apply to any frequency range, including ultrasound. Ultrasonic devices operate with frequencies from 20 kHz up to several gigahertz.

Bubble fusion is the non-technical name for a nuclear fusion reaction hypothesized to occur inside extraordinarily large collapsing gas bubbles created in a liquid during acoustic cavitation. The more technical name is sonofusion.

<span class="mw-page-title-main">Sonoluminescence</span> Light emissions from collapsing, sound-induced bubbles

Sonoluminescence is the emission of light from imploding bubbles in a liquid when excited by sound.

<span class="mw-page-title-main">Antibubble</span> Droplet of liquid surrounded by a thin film of gas

An antibubble is a droplet of liquid surrounded by a thin film of gas, as opposed to a gas bubble, which is a sphere of gas surrounded by a liquid. Antibubbles are formed when liquid drops or flows turbulently into the same or another liquid. They can either skim across the surface of a liquid such as water, in which case they are also called water globules, or they can be completely submerged into the liquid to which they are directed.

<span class="mw-page-title-main">Sonication</span> Application of sound energy

Sonication is the act of applying sound energy to agitate particles in a sample, for various purposes such as the extraction of multiple compounds from plants, microalgae and seaweeds. Ultrasonic frequencies (> 20 kHz) are usually used, leading to the process also being known as ultrasonication or ultra-sonication.

<span class="mw-page-title-main">Ultrasonic cleaning</span> Method of cleaning using ultrasound

Ultrasonic cleaning is a process that uses ultrasound to agitate a fluid, with a cleaning effect. Ultrasonic cleaners come in a variety of sizes, from small desktop units with an internal volume of less than 0.5 litres (0.13 US gal), to large industrial units with volumes approaching 1,000 litres.

<span class="mw-page-title-main">Bubble (physics)</span> Globule of one substance in another, typically gas in a liquid

A bubble is a globule of a gas substance in a liquid. In the opposite case, a globule of a liquid in a gas, is called a drop. Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.

Sonophoresis also known as phonophoresis, is a method that utilizes ultrasound to enhance the delivery of topical medications through the stratum corneum, to the epidermis and dermis. Sonophoresis allows for the enhancement of the permeability of the skin along with other modalities, such as iontophoresis, to deliver drugs with lesser side effects. Currently, sonophoresis is used widely in transdermal drug delivery, but has potential applications in other sectors of drug delivery, such as the delivery of drugs to the eye and brain.

<span class="mw-page-title-main">Ultrasonic transducer</span> Acoustic sensor

Ultrasonic transducers and ultrasonic sensors are devices that generate or sense ultrasound energy. They can be divided into three broad categories: transmitters, receivers and transceivers. Transmitters convert electrical signals into ultrasound, receivers convert ultrasound into electrical signals, and transceivers can both transmit and receive ultrasound.

<span class="mw-page-title-main">Ultrasonic horn</span>

An ultrasonic horn is a tapering metal bar commonly used for augmenting the oscillation displacement amplitude provided by an ultrasonic transducer operating at the low end of the ultrasonic frequency spectrum. The device is necessary because the amplitudes provided by the transducers themselves are insufficient for most practical applications of power ultrasound. Another function of the ultrasonic horn is to efficiently transfer the acoustic energy from the ultrasonic transducer into the treated media, which may be solid or liquid. Ultrasonic processing of liquids relies of intense shear forces and extreme local conditions generated by acoustic cavitation.

Acoustic resonance spectroscopy (ARS) is a method of spectroscopy in the acoustic region, primarily the sonic and ultrasonic regions. ARS is typically much more rapid than HPLC and NIR. It is non destructive and requires no sample preparation as the sampling waveguide can simply be pushed into a sample powder/liquid or in contact with a solid sample.

<span class="mw-page-title-main">Kenneth S. Suslick</span>

Kenneth S. Suslick is the Marvin T. Schmidt Professor of Chemistry Emeritus at the University of Illinois at Urbana–Champaign. His area of focus is on the chemical and physical effects of ultrasound, sonochemistry, and sonoluminescence. In addition, he has worked in the fields of artificial and machine olfaction, electronic nose technology, chemical sensor arrays, and the use of colorimetric sensor arrays as an optoelectronic nose.

<span class="mw-page-title-main">Mechanism of sonoluminescence</span>

Sonoluminescence is a phenomenon that occurs when a small gas bubble is acoustically suspended and periodically driven in a liquid solution at ultrasonic frequencies, resulting in bubble collapse, cavitation, and light emission. The thermal energy that is released from the bubble collapse is so great that it can cause weak light emission. The mechanism of the light emission remains uncertain, but some of the current theories, which are categorized under either thermal or electrical processes, are Bremsstrahlung radiation, argon rectification hypothesis, and hot spot. Some researchers are beginning to favor thermal process explanations as temperature differences have consistently been observed with different methods of spectral analysis. In order to understand the light emission mechanism, it is important to know what is happening in the bubble's interior and at the bubble's surface.

<span class="mw-page-title-main">Sonodynamic therapy</span>

Sonodynamic therapy (SDT) is a noninvasive treatment, often used for tumor irradiation, that utilizes a sonosensitizer and the deep penetration of ultrasound to treat lesions of varying depths by reducing target cell number and preventing future tumor growth. Many existing cancer treatment strategies cause systemic toxicity or cannot penetrate tissue deep enough to reach the entire tumor; however, emerging ultrasound stimulated therapies could offer an alternative to these treatments with their increased efficiency, greater penetration depth, and reduced side effects. Sonodynamic therapy could be used to treat cancers and other diseases, such as atherosclerosis, and diminish the risk associated with other treatment strategies since it induces cytotoxic effects only when externally stimulated by ultrasound and only at the cancerous region, as opposed to the systemic administration of chemotherapy drugs.

<span class="mw-page-title-main">Timothy Leighton</span> Professor of Ultrasonics and Underwater Acoustics

Timothy Grant Leighton is the Professor of Ultrasonics and Underwater Acoustics at the University of Southampton. He is the inventor-in-chief of Sloan Water Technology Ltd., a company founded around his inventions. He is an academician of three national academies. Trained in physics and theoretical physics, he works across physical, medical, biological, social and ocean sciences, fluid dynamics and engineering. He joined the Institute of Sound and Vibration Research (ISVR) at the University of Southampton in 1992 as a lecturer in underwater acoustics, and completed the monograph The Acoustic Bubble in the same year. He was awarded a personal chair at the age of 35 and has authored over 400 publications.

Ultrasonic antifouling is a technology that uses high frequency sound (ultrasound) to prevent or reduce biofouling on underwater structures, surfaces, and medium. Ultrasound is just high frequency sound. Ultrasound has the same physical properties as human-audible sound. The method has two primary forms: sub-cavitation intensity and cavitation intensity. Sub-cavitation methods create high frequency vibrations, whilst cavitation methods cause more destructive microscopic pressure changes. Both methods inhibit or prevent biofouling by algae and other single-celled organisms.

Sonoelectrochemistry is the application of ultrasound in electrochemistry. Like sonochemistry, sonoelectrochemistry was discovered in the early 20th century. The effects of power ultrasound on electrochemical systems and important electrochemical parameters were originally demonstrated by Moriguchi and then by Schmid and Ehert when the researchers investigated the influence of ultrasound on concentration polarisation, metal passivation and the production of electrolytic gases in aqueous solutions. In the late 1950s, Kolb and Nyborg showed that the electrochemical solution hydrodynamics in an electrochemical cell was greatly increased in the presence of ultrasound and described this phenomenon as acoustic streaming. In 1959, Penn et al. demonstrated that sonication had a great effect on the electrode surface activity and electroanalyte species concentration profile throughout the solution. In the early 1960s, the electrochemist Allen J. Bard showed in controlled potential coulometry experiments that ultrasound significantly enhances mass transport of electrochemical species from the bulk solution to the electroactive surface. In the range of ultrasonic frequencies [20 kHz – 2 MHz], ultrasound has been applied to many electrochemical systems, processes and areas of electrochemistry both in academia and industry, as this technology offers several benefits over traditional technologies. The advantages are as follows: significant thinning of the diffusion layer thickness (δ) at the electrode surface; increase in electrodeposit/electroplating thickness; increase in electrochemical rates, yields and efficiencies; increase in electrodeposit porosity and hardness; increase in gas removal from electrochemical solutions; increase in electrode cleanliness and hence electrode surface activation; lowering in electrode overpotentials ; and suppression in electrode fouling.

Sonochemical synthesis is the process which utilizes the principles of sonochemistry to make molecules undergo a chemical reaction with the application of powerful ultrasound radiation (20 kHz–10 MHz). Sonochemistry generates hot spots that can achieve very high temperatures, pressures of more than 1000 atmospheres, and rates of heating and cooling that can exceed 10^11 K/s. High intensity ultrasound produces chemical and physical effects that can be used for the production or modification of a wide range of nanostructured materials. The principle that causes the modification of nanostructures in the sonochemical process is acoustic cavitation.

Ozone micro/nano-bubble technology overcomes the limitation of ozone oxidation and mass transfer of ozone and its utilization. It improves the oxidation efficiency of ozone. Ozone micro/nano-bubble technology improves the disinfectant capacity of ozone.

References

  1. ↑ Suslick, K. S. (1990). "Sonochemistry". Science. 247 (4949): 1439–45. Bibcode:1990Sci...247.1439S. doi:10.1126/science.247.4949.1439. PMID   17791211. S2CID   220099341.
  2. ↑ Wood, R.W.; Loomis, Alfred L. (1927). "The physical and biological effects of high-frequency sound-waves of great intensity". The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science. 4 (22). Informa UK Limited: 417–436. doi:10.1080/14786440908564348. ISSN   1941-5982.
  3. 1 2 Suslick, Kenneth S. (1989). "The Chemical Effects of Ultrasound". Scientific American. 260 (2). Springer Nature: 80–86. Bibcode:1989SciAm.260b..80S. doi:10.1038/scientificamerican0289-80. ISSN   0036-8733. S2CID   124890298.
  4. ↑ Suslick, K. S. (23 March 1990). "Sonochemistry". Science. 247 (4949). American Association for the Advancement of Science (AAAS): 1439–1445. Bibcode:1990Sci...247.1439S. doi:10.1126/science.247.4949.1439. ISSN   0036-8075. PMID   17791211. S2CID   220099341.
  5. 1 2 Suslick, Kenneth S.; Flannigan, David J. (2008). "Inside a Collapsing Bubble: Sonoluminescence and the Conditions During Cavitation". Annual Review of Physical Chemistry. 59 (1). Annual Reviews: 659–683. Bibcode:2008ARPC...59..659S. doi:10.1146/annurev.physchem.59.032607.093739. ISSN   0066-426X. PMID   18393682. S2CID   9914594.
  6. 1 2 Leighton, T.G. The Acoustic Bubble; Academic Press: London, 1994, pp.531–555.
  7. ↑ Suslick, Kenneth S.; Hammerton, David A.; Cline, Raymond E. (1986). "Sonochemical hot spot". Journal of the American Chemical Society. 108 (18). American Chemical Society (ACS): 5641–5642. doi:10.1021/ja00278a055. ISSN   0002-7863. S2CID   100496976.
  8. ↑ Flint, E. B.; Suslick, K. S. (20 September 1991). "The Temperature of Cavitation". Science. 253 (5026). American Association for the Advancement of Science (AAAS): 1397–1399. Bibcode:1991Sci...253.1397F. doi:10.1126/science.253.5026.1397. ISSN   0036-8075. PMID   17793480. S2CID   22549622.
  9. ↑ Suslick, K.S.; Doktycz, S.J. Adv. Sonochem. 1990, 1, 197–230.
  10. ↑ Einhorn, Cathy; Einhorn, Jacques; Luche, Jean-Louis (1989). "Sonochemistry - The Use of Ultrasonic Waves in Synthetic Organic Chemistry". Synthesis. 1989 (11). Georg Thieme Verlag KG: 787–813. doi:10.1055/s-1989-27398. ISSN   0039-7881.
  11. ↑ Luche, J.L.; Compets. Rendus. Serie. IIB 1996, 323, 203, 307.
  12. ↑ Pestman, Jolanda M.; Engberts, Jan B. F. N.; de Jong, Feike (1994). "Sonochemistry: Theory and applications". Recueil des Travaux Chimiques des Pays-Bas. 113 (12). Wiley: 533–542. doi:10.1002/recl.19941131202. ISSN   0165-0513.
  13. ↑ Crum, Lawrence A. (1994). "Sonoluminescence". Physics Today. 47 (9). AIP Publishing: 22–29. Bibcode:1994PhT....47i..22C. doi:10.1063/1.881402. ISSN   0031-9228. PMID   17771441.
  14. ↑ Putterman, S.J. Sci. Am. February 1995, p. 46.
  15. ↑ Suslick, Kenneth S.; Casadonte, Dominick J. (1987). "Heterogeneous sonocatalysis with nickel powder". Journal of the American Chemical Society. 109 (11). American Chemical Society (ACS): 3459–3461. doi:10.1021/ja00245a047. ISSN   0002-7863. S2CID   96340676.
  16. ↑ Zeiger, Brad W.; Suslick, Kenneth S. (21 September 2011). "Sonofragmentation of Molecular Crystals". Journal of the American Chemical Society. 133 (37). American Chemical Society (ACS): 14530–14533. doi:10.1021/ja205867f. ISSN   0002-7863. PMID   21863903. S2CID   12061434.
  17. ↑ Hinman, Jordan J.; Suslick, Kenneth S. (11 January 2017). "Nanostructured Materials Synthesis Using Ultrasound". Topics in Current Chemistry. 375 (1). Springer Nature: 12. doi:10.1007/s41061-016-0100-9. ISSN   2365-0869. PMID   28078627. S2CID   29099588.
  18. ↑ "Brute Force Breaks Bonds". Chemical & Engineering News. 22 March 2007.
  19. ↑ Atul Kumar, R.A.Muarya SYNLETT 1987, 109, 3459.https://www.organic-chemistry.org/abstracts/lit2/076.shtm
  20. ↑ González-García, José; Sáez, Verónica; Tudela, Ignacio; Díez-Garcia, María Isabel; Deseada Esclapez, María; Louisnard, Olivier (2 February 2010). "Sonochemical Treatment of Water Polluted by Chlorinated Organocompounds. A Review". Water. 2 (1). MDPI AG: 28–74. doi: 10.3390/w2010028 . ISSN   2073-4441.
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