Sonochemistry decomposition

A. Troia, D.M. Ripa, R. Spagnolo, V. Maurino, Single bubble sonochemistry Decomposition of alkyl bromide and the isomerization reaction of maleic acid. Ultrason. Sonochem. 13,429-432(2006)... 

Homogeneous non-aqueous sonochemistry is typified by the sonolysis of chloroform which has been studied using ultrasonic irradiation of frequency 300 kHz (I = 3.5 W cm ) to yield a large number of products amongst which are HCl, CCI4 and C2CI2 [42]. Decomposition was found to only occur in the presence of... 

In 1983 Suslick reported the effects of high intensity (ca. 100 W cm, 20 kHz) irradiation of alkanes at 25 °C under argon [47]. These conditions are of course, well beyond those which would be produced in a reaction vessel immersed in an ultrasonic bath and indeed those normally used for sonochemistry with a probe. Under these extreme conditions the primary products were H2, CH4, C2H2 and shorter chain alk-l-enes. These results are not dissimilar from those produced by high temperature (> 1200 °C) alkane pyrolyses. The principal degradation process under ultrasonic irradiation was considered to be C-C bond fission with the production of radicals. By monitoring the decomposition of Fe(CO)5 in different alkanes it was possible to demonstrate the inverse relationship between sonochemical effect (i. e. the energy of cavitational collapse) and solvent vapour pressure [48],... 

Photochemical decomposition can also be carried out in the presence of a suspension of photoactive material such as Ti02 where substrate absorption onto the uv activated surface can initiate chemical reactions e. g. the oxidation of sulphides to sul-phones and sulphoxides [37]. This technology has been adapted to the destruction of polychlorobiphenyls (PCB s) in wastewater and is of considerable interest in environmental protection. Using pentachlorophenol as a model substrate in the presence of 0.2 % TiOj uv irradiation is relatively efficient in dechlorination (Tab. 4.5) [38]. When ultrasound is used in conjunction with photolysis, dechlorination is dramatically improved. This improvement is the result of three mechanical effects of sonochemistry namely surface cleaning, particle size reduction and increased mass transport to the powder surface. 

Decatrienes, in intramolecular Alder-ene reactions, 10, 578 Dechlorination reactions, via cobalt(III) complexes, 7, 44 Decomposition pathways mixed metal carbonyls, via sonochemistry, 1, 310 in mononuclear ruthenium and osmium alkenyl formations, 6, 405... 

Nanostructured LaNiOs was prepared by co-precipitation under ultrasonic radiation [120], Using various characterization methods and evaluation of catalytic activity, the effects of ultrasound on the structural properties and catalytic activity of LaNiOs were studied. The TEM showed that the ultrasound could cause a decrease in the particle size. The average particle size of LaNiOs prepared by sonochemistry is 20 nm. The specific surface area of LaNiOs is 11.27 m g h Ultrasound could lead to increased surface oxide content and surface crystal oxygen vacancies. The TPR result showed that the LaNi03 prepared by sonochemistry has a lower reduction temperature and a higher ratio of surface oxygen to crystal oxygen. The evaluation of catalytic activity showed that ultrasound could increase the catalytic activity of LaNiOs for NO decomposition. 

In the above example, the decomposition ratio (for which the exact method of determination does not appear clearly in the paper) increases notably when the frequency reaches a critical value. The violent shock undergone by a surface hit by a cavitation bubble should be similar in nature if not in intensity to other mechanical shocks, with analogous chemical consequences. Such analogies of the sonochemistry of solids with mechanochemistry were suggested previously. ... 

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