Environmental Engineering Reference
In-Depth Information
excitation. The energy band diagram of TiO
2
is shown in Figure 25.1. The reaction mecha-
nism of photocatalysis by semiconductors is presented in Figure 25.2.
The reactions occurring on the surface of the catalyst can be represented as follows.
−
+
TiOh eh
cb
2
+→+
vb
−
−
Oe
+→
O
2
cb
2
+
+
hHO
+ →+
2
HH
vb
∙
OH +
∙
OH → H
2
O
2
−
−
OHO
+ →+
HOHO
+
2
2
2
2
−
+→
OH
OOH
2
∙
OH + Organic compounds or microbes + O
2
→ CO
2
+ H
2
O
UV
O
2
e
-
CB
O
-
3.2 eV
OH
-
h
+
VB
OH
•
FIGURE 25.1
Energy band diagram of TiO
2
.
H
2
O +
•
OH
UV light
Reduction
reaction
+
Conduction band
O
2
Pollutant
e
-
Oxidation
reaction
-
Valence band
H
2
O + CO
2
FIGURE 25.2
Reaction mechanism of photocatalysis by semiconductors.
