Environmental Engineering Reference
In-Depth Information
H
2
O
2
+ TiO
2
(e)
•OH + OH
−
(7.9)
Dye•
+
+ O
2
(or O
2
•−
or •OH)
peroxylated or hydroxylated
(7.10)
intermediates
degraded or mineralized products
Photocatalytic degradation of rhodamine 6G (R-6G), methyl red, mal-
achite, 4-nitrophenol, yellow 27, yellow 50, violet 51 and bisphenol-A.
Photocatalytic degradation of the diuron by TiO
2
and by Pt/TiO
2
, also on Au/
TiO
2
for diuron as well as its didemethylatedproduct,3,4-dichlorophenyl-
urea, has been reported.h e photocatalytic degradation of s-triazines her-
bicides (atrazine, simazine, trietazine, prometon and prometryn) was i rst
studied by Pelizzetti
et al.
[6]. Several studies were published about the solar
TiO
2
photocatalyzed oxidation of s-triazines (2-chloro-, 2-methoxy and
2-methylthio-s-triazines) and the mechanistic pathways of the observed pho-
toproducts [7-13]. Recently, other three herbicides belonging to the triazine
group, irgarol [2-methylthio-4-(tert-butylamino)-6-(cyclopropylamino)-s-
triazine], cyromazine [
N
-cyclopropyl- 1,3,5-triazine-2,4,6-triamine] and
metamitron {4-amino-6-phenyl-3-methyl-1,2,4-triazin-5(4
H
)-one}, were
studied and similar results were observed.
h e photocatalytic degradation of four representative compounds of
anilide and amide herbicides (3,4-dichloropropioamide, propanil, ala-
chlor, propachlor) have been studied [14-17].
p
-Chloraniline, tetrachlorohydroquinone, H
2
O
2
, tetrachlorocatechol
and
o
-chloraniline were identii ed as the principal intermediates in the
photocatalytic destruction of PCP in the presence of TiO
2
[18-21]. h e
major PCP intermediates detected were 2,3,5,6-tetrachloro-1,4-benzoqui-
none, 2,3,5,6-tetrachloro-1,4-hydroquinone and 2,3,5,6-tetrachlorophenol
[22]. h e pesticide permethrin can be easily photodecomposed into CO
2
and Cl
−
ions in a l uoro surfactant/TiO
2
aqueous dispersion [23].
Atrazine
{
2-chloro-4-ethyl-amino-6-isopropylamino-1,3,5-triazine
}
is
one of the most common pesticides found in groundwater sources and
drinking water supplies. McMurray
et al.
[24] studied the photocatalytic
decomposition of this herbicide by TiO
2
i lms in industrial water.
TiO
2
nanoparticles were used for preconcentration of trace arsenite
and arsenate in natural water. Adsorption of Pb, Cd, Cu, Zn, and Ni to
titanium dioxide nanoparticles was studied by Engates
et al
. [25]. TiO
2
had also been used for the preconcentration of metal ion such as Cu, Cr,
Zn, Cd, Se, Ho, Au, Nd, Tm, La, Y, Tb, Eu, Dy from various environ-
mental samples such as wastewater, sediments, coal ash, vehicle exhaust
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