Ultrasound degradation

The role of cavitation in ultrasound degradation has been confirmed repeatably in most experiments where cavitation was prevented, either by applying an external hydrostatic pressure, by degassing the solution, by reducing the sound intensity or the temperature, polymer chain scission was also largely suppressed [117]. 

Ultra-sound emissions typically occur when male rodents are exposed to female odours or altricial neonates to maternal sources (Whitney, 1974 Conely and Bell, 1978). Without the VNO, sexually inexperienced male mice do not utter emissions at ultra-high frequencies (UHF), whereas those with prior experience vocalise after VN-x, as discussed above (Chap. 5). Female mouse urine contains a unique UHF-eliciting component which is non-volatile but ephemeral (Sipos et al., 1995). The signal is degraded by oxidation and disappears within 15 to 18 hours of deposition. Direct contact with freshly voided urine must occur before males will vocalise (sexually experienced or inexperienced). At least one of the olfactory systems is needed for UHF to be elicited by fresh urine complete deafferentation abolishes the response (Sipos et al., 1993). Exposure to females permits UHF to be elicited by other than chemical cues (Labov and Wysocki, 1989). Nocturnal or cryptic species conceivably use ultrasound to advertise male presence whether this is to deter other males or assist with female location is unclear. 

Fig. 8. Behaviour of molar mass vs. time of irradiation for methylhydroxyethylcellulose exposed to ultrasound degradation...

Sivakumar M, Pandit AB (2001) Ultrasound enhanced degradation of Rhodamine B Optimization with power density. Ultrason Sonochem 8 233-240... 

Reactions (9.88-9.91) proceeded in steps and depended largely on the number of activated chloride ions available in the solution. Formation of such activated chlorine radicals was also reported elsewhere during the degradation of CCI4 in aqueous solution by ultrasound [88]. 

P Christian, Dominick C (2001) The sonochemical degradation of aromatic and chloroaro-matic contaminants. In Mason TJ and Tiehm A (eds) Advances in sonochemistry ultrasound in environmental protection, Elsevier 6 102-103... 

Entezari Mohammad H, Christian P, Pierre D (2003) Degradation of azo dyes by hybrid ultrasound-Fenton reagent. Ultrason Sonochem 10(2) 103-108... 

Hung H-M, Hoffmann MR (1998) Kinetics and mechanism of the enhanced reductive degradation of CC14 by elemental iron in the presence of ultrasound. Environ Sci Technol 32(19) 3011—3016... 

Cravotto G, Binello A, Di Carlo S, Orio L, Zhi-Lin Wu, Ondmschka B (2010) Oxidative degradation of chlorophenol derivatives promoted by microwaves or power ultrasound a mechanism investigation. Environ Sci Poll Res 17(3) 674-687... 

Tai Li Ji, Ya-Li S (2009) Degradation of AR 97 aqueous solution by combining ultrasound and Fenton reagent. Environ Prog Sustain Energy 29(1) 101-106... 

Abstract Degradation of phenol in its aqueous solutions, using various techniques, including ultrasound, have been examined and discussed to better understand the mechanisms involved therein and the advantages as well as the disadvantages associated with the use of inorganic catalytic materials. 

Wu et al. [12] used both microwave (MW) and ultrasound (US) methods individually and in combination to examine the combined effect. The rapid thermal effect of MW could be seen on polar chemicals and more OH radicals were produced due to US. Microwave irradiations have shown enhanced degradation effect when applied with sonication in absence of additional catalyst though the rate increased more in presence of H2O2. The rate order was found to be MW-US > MW > US. 

Many workers have since tried ultrasound induced Fenton s reagent methods to degrade phenol. Papadaki et al. [83] reported the lower efficiency of Fenton s reagent for phenol degradation due to competition of both Fe2+ and ultrasound for H202, resulting in the reduction of concentration of Fenton s reagent in solution. 

In the experiment involving oxidative enzyme HRP (EC 1.11.1.7, RZ 1.9, 240 purpuro gallin (units/mg)) [89] for the enzymatic treatment and ultrasonic waves of 423 kHz and 5.5 W, the phenol degradation rate was found to increase. The ultrasound assisted biodegradation method has been found to be more efficient method than the sonolysis and enzyme treatment when operated individually. 

After the review of literature, we report here the results of the degradation of phenol, carried out in our laboratory in the presence of ultrasound, Ti02, rare earths and transition metal ions to highlight our interpretation of the mechanism. Various transition metal salts are known for their catalytic properties due to partly filled d-orbital of the metal atom. Mesoporous transition metal oxides are used not... 

Thus to conclude, it can be inferred that the ultrasound alone is less effective in degrading phenol compared to the photocatalyst, TiC>2. However, when the two techniques are combined, the result is most effective. Nevertheless, the role of transition and inner transition metal ions is still not clear although their effect could be seen - may be the lower concentrations of these ions could not play any effective role as of now until a further study is carried out. 

Wu Z-L, Dondruschka B, Cravotto G (2008) Degradation of phenol under combined irradiation of microwaves and ultrasound. Environ Sci Technol 42 8083-8087... 

Chen Y-C, Smimiotis P (2002) Enhancement of photocatalytic degradation of phenol and chlorophenols by ultrasound. Ind Eng Chem Res 41 5958-5965... 

Abstract Hazardous effects of various amines, produced in the environment from the partial degradation of azo dyes and amino acids, adversely affect the quality of human life through water, soil and air pollution and therefore needed to be degraded. A number of such studies are already available in the literature, with or without the use of ultrasound, which have been summarized briefly. The sono-chemical degradation of amines and in the combination with a photocatalyst, TiC>2 has also been discussed. Similar such degradation studies for ethylamine (EA), aniline (A), diphenylamine (DPA) and naphthylamine (NA) in the presence of ultrasound, Ti02 and rare earths (REs) La, Pr, Nd, Sm and Gd, in aqueous solutions at 20 kHz and 250 W power have been carried out and reported, to examine the combinatorial efficacy of ultrasound in the presence of a photocatalyst and rare earth ions with reactive f-electrons. 

For the sonochemical mineralization of reactive dye Cl Reactive Black 5 with 20, 279 and 817 kHz irradiation, the discoloration and radical formation both are directly dependent upon ultrasonic frequency, acoustic power and irradiation time and indirectly on the number of free radicals thus generated, as their suppression decreased the discoloration rate due to radical scavenging effect. Although ultrasound alone is capable of decolorizing Reactive Black 5 but inefficient in mineralization as only 50% degradation was observed after 6 h of ultrasonic irradiation [121]. The sonochemical... 

This facilitates the flow of degradable species through these tunnels onto the surface of the TiC>2 where electron could be donated to the holes of the anatase phase and the photocatalytic action in combination with the cavitational effect of the ultrasound can accelerate the fragmentations of pollutants. The details of this mechanism are however discussed at the end of chapter. Ultrasound also breaks TiC>2 particles to still smaller size and increases the active surface area manifold. 

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