Sonochemical treatment

Esclapez MD, Saez V, Milan-Yanez D et al (2010) Sonochemical treatment of water poulled with trichloroacetic acid from sonovoltammetry to pre-pilot plant scale. Ultrason Sonochem 17 1010-1020... 

Tauliq-Yap YH, Wong YC, Zainal Z, Hussein MZ (2009) Synthesis of self-assembled nanorod vanadium oxide bundles by sonochemical treatment. J Nat Gas Chem 18 312-318... 

Kruger O, Schulz Th L, Peters D (1999) Sonochemical treatment of natural ground water at different high frequencies preliminary results. Ultrason Sonochem 6(1) 123-128... 

The majority of systems studied have been aqueous solutions of either aromatic compounds or halogenated hydrocarbons. Such materials represent models for the major classes of organic pollutants in waste and ground water. The primary products resulting from the sonochemical treatment of phenol at 541 kHz (27 °C with bubbled air) are hydroquinone and catechol [22]. These compounds are easy to monitor and are clearly seen to be intermediates which disappear as the reaction progresses (Fig. 4.1). Similarly the sonolysis of aqueous 4-chlorophenol leads to products mainly characteristic of oxidation by OH radical e. g. 4-chlorocatechol but in both cases the final organic products are CO, CO2 and HCOOH (Scheme 4.2) [22-25]. 

A study of sonochemical treatment of chlorinated hydrocarbons in water demonstrated the homogeneous destruction of CH2CI2, CCI4, MeCCl3, and CICH = CCI2 in solution at concentrations of 100-1000 ppm by volume [29]. The method appears to be potentially quite powerful for the purification of contaminated water. In a separate study when saturated aqueous solutions of CH2CI2 (110 ppm) and MeCClj (1300 ppm) were sonicated for 20 min some 75 % of the contaminant was degraded [30]. 

An alternative arrangement would involve a number of probes inserted through the walls of a vessel allowing a much larger sonochemical treatment zone. Such a system will suffer from the same problems as the individual flow cell except that it will continue to function even if one or two probe units fail (Fig. 7.18). 

For all these reasons, most of the acoustical energy involved in generating the cavities and in their collapse is ultimately spent in decomposing water into H2 and 02. This is the main factor affecting sonochemical efficiency (i.e., the ratio between the rate of the reaction of interest and the applied power density, W/L). In order to improve the efficiency of a sonochemical process, chemical or physical modifications can be introduced into the system, which may reduce this loss (see Sec. IV.G). The efficiency can also be affected by the presence of other chemicals in the solution, which may react with the radicals, thus reducing the number of reactive species available to the target molecules. A preprocess might be conceived to separate some of these unwanted chemicals from the solution prior to sonochemical treatment. 

Sonochemical treatment during the synthesis also speeds up the process due to the cavitation effect, also providing conditions for control of interpenetration of different frameworks (catenation) [38,39]. If separate frameworks are self-assembled within each other, this effect is known as framework catenation [40]. It is divided into interpenetration and interweaving. In interpenetrated MOFs, frameworks are maximally displaced from each other in interwoven MOF structures, the distance between both frameworks is minimized (eg, IRMOF-13, Table 1). Catenation results in the enhancement of the rigidity of the material at the expense of its porosity, but increases the stability as well as may help in the case of adsorption and storage of small molecules due to the size selectivity. 

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