Environmental Engineering Reference
In-Depth Information
Despite the instability of all these species and their tendency to recombine
(to form water and hydrogen peroxide), some of them rapidly react with
organic molecules, while some are ejected into the bulk solution to initiate
aque ous phase oxidation reactions. A summary of chemical reactions tak-
ing place in sonicated water (saturated with air) is given in the following
sequence, where the symbol “)))” represents ultrasonic irradiation [30]:
H
2
O (g) + )))
HO + H
(7.1)
HO + H
H
2
O
(7.2)
HO + HO
H
2
O
2
(7.3)
O
2
+ )))
O
2
-
(7.4)
2N
2
+ O
2
2N
2
O
(7.5)
2N
2
O + H
2
O
2HNO
2
+ 2N
2
(7.6)
H + N
2
O
N
2
+ OH
(7.7)
OH + N
2
O 2NO + H (7.8)
HNO
2
+ H
2
O
2
HNO
3
+ H
2
O (7.9)
HNO
3
+ ))) OH + NO
2
(7.10)
HNO
3
+ ))) H + NO
3
(7.11)
It is these properties of ultrasound that offer a unique medium for the
oxidative and/or thermal destruction of organic compounds without the
addition of chemical reagents and generation of hazardous sludge that
makes it a promising means of “green technology.” On the other hand,
mineralization or conversion of organic carbon to CO
2
by ultrasound
alone is time-consuming and this is why recent studies with ultrasound
generally focus on the addition of small quantities of soluble or insol-
uble catalysts to generate additional nucleation and reaction sites and/
or to provide excess radical species. The method provides an excellent
synergy based on the presence of excess nucleation/reaction sites, and
the ubiquitous properties of ultrasound for accelerating rates of mass
transfer and chemical reactions and for improving surface properties of
solid particles [31-33].
7.2.1
Sonochemical Degradation of Azo Dyes
The majority of published literature on sonochemical destruction of
color and dyestuff is carried out with reactive azo dyes due to their
Search WWH ::
Custom Search