Oxidative Reactions
Typical photocatalysts, i.e., metal oxides (MO), such as oxides of titanium, zinc,
tungsten, vanadium, chromium, and vanadium, can absorb photons to generate the
photo-excited electrons and positive holes as expressed in Eq. (1.20). In the presence
of water molecules, hydroxyl radicals (HO
•
) are produced by a reaction between
positive holes and H 2 O according to Eq. (1.21) (Fig. 1.3). Furthermore, H 2 O 2 is
possibly formed through the oxidative pathway, leading to the HO
• generation from
the cleavage of H 2 O 2 under photolysis as shown in Eqs. (1.22)–(1.23) (Li et al.
2014).
Photocatalyst þ h υ ! Photocatalyst e
À CB
ð Þþh
þ VB
ð Þ
ð
Þ
ð 1:20Þ
H 2 O þ h
þ
! H
þ
þ HO
•
ð1:21Þ
Fig. 1.2 Hydrogen
production from water using
heterogeneous powder
photocatalysts. The
photocatalysts are dispersed
in a reactor with water. Sun
or light shines at the
dispersed photocatalysts,
and then hydrogen is
obtained (modified after
(Kudo and Miseki 2009))
Table 1.2 Typical
photocatalysts for
photocatalysis
Photocatalyst
Band gap (eV)
Spectral region
ZnS
3.80
UV
SnO 2
3.80
UV
TiO 2 (anatase)
3.24
UV
ZnO
3.20
UV
TiO 2 (rutile)
3.02
UV and Visible
CdS
2.40
UV and Visible
Cu 2 O
2.20
UV and Visible
1 Photocatalytic Remediation of Organic Pollutants in Water
9
Typical photocatalysts, i.e., metal oxides (MO), such as oxides of titanium, zinc,
tungsten, vanadium, chromium, and vanadium, can absorb photons to generate the
photo-excited electrons and positive holes as expressed in Eq. (1.20). In the presence
of water molecules, hydroxyl radicals (HO
•
) are produced by a reaction between
positive holes and H 2 O according to Eq. (1.21) (Fig. 1.3). Furthermore, H 2 O 2 is
possibly formed through the oxidative pathway, leading to the HO
• generation from
the cleavage of H 2 O 2 under photolysis as shown in Eqs. (1.22)–(1.23) (Li et al.
2014).
Photocatalyst þ h υ ! Photocatalyst e
À CB
ð Þþh
þ VB
ð Þ
ð
Þ
ð 1:20Þ
H 2 O þ h
þ
! H
þ
þ HO
•
ð1:21Þ
Fig. 1.2 Hydrogen
production from water using
heterogeneous powder
photocatalysts. The
photocatalysts are dispersed
in a reactor with water. Sun
or light shines at the
dispersed photocatalysts,
and then hydrogen is
obtained (modified after
(Kudo and Miseki 2009))
Table 1.2 Typical
photocatalysts for
photocatalysis
Photocatalyst
Band gap (eV)
Spectral region
ZnS
3.80
UV
SnO 2
3.80
UV
TiO 2 (anatase)
3.24
UV
ZnO
3.20
UV
TiO 2 (rutile)
3.02
UV and Visible
CdS
2.40
UV and Visible
Cu 2 O
2.20
UV and Visible
1 Photocatalytic Remediation of Organic Pollutants in Water
9