Environmental Engineering Reference
In-Depth Information
substances (Fu et al.
2010
; Mostofa et al. (Manuscript In preparation); Hamanaka
et al.
2002
; Hayakawa
2004
; Farjalla et al.
2006
).
Second, H
2
O
2
, formed photolytically from water using UV radiation, can
react with CO
2
under abiogenic conditions to produce various organic substances
(CH
2
O, HCOOH, CH
3
OH, CH
4
, and C
6
H
12
O
6
; Eqs.
7.1
-
7.5
, respectively) in the
aqueous solutions (Lobanov et al.
2004
). The reactions between H
2
O
2
and CO
2
as
well as their thermodynamic parameters such as enthalphy changes (
Δ
H
0
) and the
Gibbs free energy changes (
Δ
G
0
) are mentioned as follows (Lobanov et al.
2004
):
H
2
O
2
+
CO
2
→
CH
2
O
+
3
/
2O
2
∆
H
0
=
465 kJ,
∆
G
0
=
402 kJ
(7.1)
∆
H
0
=
465 kJ,
∆
G
0
=
402 kJ
H
2
O
2
+
CO
2
→
HCOOH
+
O
2
∆
H
0
=
172 kJ,
∆
G
0
=
166 kJ
(7.2)
∆
H
0
=
172 kJ,
∆
G
0
=
166 kJ
2H
2
O
2
+
CO
2
→
CH
3
OH
+
5
/
2O
2
(7.3)
∆
H
0
=
530 kJ,
∆
G
0
=
464 kJ
2H
2
O
2
+
CO
2
→
CH
4
+
3O
2
(7.4)
∆
H
0
=
649 kJ,
∆
G
0
=
580 kJ
H
2
O
2
+
CO
2
→
1
/
6C
6
H
12
O
6
+
3
/
2O
2
∆
H
0
=
426 kJ
(7.5)
∆
H
0
=
426 kJ
Therefore, these organic substances produced photolytically may play an
important role in biogeochemical processes in natural waters.
Third, H
2
O
2
can react with nitrous acid to yield peroxynitrous acid, a power-
ful nitrating agent and an important intermediate in atmospheric chemistry (Vione
et al.
2003
). The kinetics of the reaction is compatible with a rate-determining
step involving either H
3
O
2
and HNO
2
, with rate constant 179.6
±
1.4 M
−
1
s
−
1
,
or H
2
O
2
and protonated nitrous acid, with rate constant 1.68
±
0.01
×
10
10
M
−
1
s
−
1
(diffusion-controlled reaction) (Vione et al.
2003
). Thus, H
2
O
2
might be a key
environmental factor in atmospheric oxidative chemistry.
+
8 Scope of the Future Challenges
The determination of H
2
O
2
and ROOH as well as their spatial-temporal varia-
tions, sources, production and decay mechanisms have been examined in natural
waters. Compared to H
2
O
2
, relatively little attention is paid to the determination
