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(a)
O 2 −•
O 2
HO
e - Conduction Band (CB)
h + Valence Band (VB)
Organics
H 2 O
Photooxidation
(b)
e -
O 2
CB
Organic*
O 2 −•
VB
Photooxidation
figure 24.1 Photoinduced charge-transfer processes in semiconductor nanoparticles (a) upon bandgap excitation. (b) Nanoparticles act
as mediators for the charge transfer between two adsorbed molecules.
for environmental remediation. Currently, much literature exists on the development of new photocatalytic nanomaterials with
regard to this aspect. in this section, we review the basic concepts of nanocrystalline photocatalysts and ways to enhance their
photocatalytic activities. Some examples of nanocrystalline semiconductors, used in the photocatalysis of organic compounds,
are mentioned here (Table 24.1; [9]) but the reader may refer to reference articles for a detailed discussion on basic synthesis
strategies and photocatalytic reaction conditions.
24.2.2
Nanocrystalline photocatalysts
As the size of the semiconductor particle is reduced below a critical diameter, splitting of the energy bands into discrete, quan-
tized levels occurs. Particles that exhibit these quantization effects are often called “Q-particles.” The optical, electronic, and
catalytic properties of Q-particles drastically differ from those of the corresponding macrocrystalline substance [10]. The band
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