Chemistry Reference
In-Depth Information
SO
2
−
+ →
h
ν
•
SO
−
(5.46)
3
3
SO
2
−
+
•
OH
→
•
SO OH
−
+
−
k
=
5 5 10
.
×
9
/M/s
.
(5.47)
3
3
47
The formation of
• −
SO
3
in the solution was confirmed by a single-line spec-
trum [352]. The optical absorption of
•
SO
3
has an absorption at 255 nm
−
(ε
255 nm
= 1000/M/cm). The decay of
•
SO
3
followed second-order kinetics (Eq.
−
5.48) [352]:
2
•
SO
−
→
S O or SO SO
2
−
+
2
−
2
k
=
1 1 10
.
×
9
/M/s
.
(5.48)
3
2
6
3
3
48
SO
3
with different substrates is studied by moni-
toring the radicals produced from the reaction [352].
The sulfate radical (
SO
•−
) has been generated by hemolytic scission of the
peroxide of persulfate (PS) or peroxymonosulfate (PMS) by transition metal
activation, thermal activation, and photolytic and radiolytic methods [353-
357]. The catalytic decomposition of PMS in a homogeneous pathway uses
transition metals as an aid (M: Ag
+
, Fe
2+
, Co
2+
, Ni
2+
, and Mn
2+
) (Eq. 5.49):
generally, the kinetics of
•
−
2
+
−
3
+
•−
−
.
(5.49)
M HSO
+
→
M SO
+
+
OH
5
4
An approach of using Fe-Co mixed oxide nanocatalysts for the heteroge-
neous activation of PMS has also been suggested to produce the
SO
•−
radical
[358]. Thermal activation of PS yields the
SO
•−
radical (Eq. 5.50):
2
−
•−
S O
+
heat
→
2
SO
.
(5.50)
2
4
Reaction (5.50) was recently studied in detail using an EPR spin trapping
technique [359]. A mechanism of the reaction (5.50) has also been studied in
the temperature range of 60-80°C in the presence and absence of sodium
formate [360]. The rate constant was measured as (0.7−1.0) × 10
−4
/second at
80°C [360]. A chemical probe to differentiate HO
•
and
SO
•−
radicals in thermal
activation of PS has been developed [357].
In the radiolytic method, the reduction of PS by a hydrated electron pro-
duces sulfate radicals (Eq. 5.51):
S O
2
−
+
e
−
→
SO
•−
+
SO
2
−
.
(5.51)
2
8
(
aq
)
4
4
The spectrum obtained at pH 7.0 using this method is shown in Figure 5.18
[353]. The absorption spectrum has a peak at 450 nm. The sulfate radical has
a weak absorption (ε
450 nm
= 1100/M/cm). The photolysis of PS generates the
sulfate radical (Eq. 5.52) [354, 361]:
S O
2
−
+
h
ν λ
(
<
300
nm
)
→
SO
•−
.
(5.52)
2
8
4
Similarly, sulfate and hydroxyl radicals are produced in the degradation of
PMS upon UV irradiation (λ < 260 nm) [354]. The decay kinetics of
SO
•−
in
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