13.5 Synthesis and Application of AgX-Based
Heterojunction Structure
The most common heterojunction structure is based on a semiconductorsemiconductor architecture in which a p-type semiconductor usually closely contacts
with an n-type semiconductor. This structure will result in a space charge region and
an electric field at the interface, causing the directed flow of electrons to the CB of
n-type semiconductor and holes to the VB of p-type semiconductor. This charge
transfer can enhance the separating efficiency, charge carrier lifetime, and reaction
rates [76–83]. Since AgX materials are prone to be reduced by the photo-generated
electrons, combining with other semiconductor not only improves the separation rate
of charge carriers but also promotes the photostability of AgX materials. Based on
the structure, the AgX-based heterojunction structures can be classified into two
types: AgX-Y and Ag-AgX-Y (Y is another semiconductor).
13.5.1 AgX–Y
AgX-Y is composed of AgX and another semiconductor Y. The closely contacting
interface between AgX and Y can be produced via ion exchange method. For
example, Huang et al. fabricated AgI–BiOI hierarchical hybrids by ion exchange
between BiOI hierarchical microspheres and AgNO 3 (Fig. 13.15a) [77]. It was found
that AgI nanoparticles were uniformly anchored on the surface of BiOI nanosheets
and the particle size of AgI can be toiled from 55–16 nm by the addition of poly
(vinylpyrrolidone) surfactant molecules. Besides ion exchange method, adsorption
of organics with halogen or Ag(NH 3 ) 2
+ beforehand can also create the close contact
between AgX and semiconductor Y. For instance, [C 16 min]Br ionic liquid was used
to adsorb on the surface of BiPO4 to form AgBr/BiPO 4 heterojunction structure
[83]. Beneficial from the close contact, the photo-generated charges can be efficiently separated, as shown in Fig. 13.15b, c. Some of the synthesized AgX–Y
photocatalysts are summarized in Table 13.2.
13.5.2 Ag–AgX–Y
Compared to AgX–Y, Ag–AgX–Y can more effectively absorb visible light by the
surface plasmon resonance effect (SPR) of Ag nanoparticles formed on the surface
of AgX. Therefore, Ag–AgX–Y not only can respond to visible light but also has
higher electron–hole separation rate. According to the substrates (Y), Ag–AgX–Y
can be classified into several classes as follows.
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13 Syntheses and Applications of Silver Halide-Based Photocatalysts
Heterojunction Structure
The most common heterojunction structure is based on a semiconductorsemiconductor architecture in which a p-type semiconductor usually closely contacts
with an n-type semiconductor. This structure will result in a space charge region and
an electric field at the interface, causing the directed flow of electrons to the CB of
n-type semiconductor and holes to the VB of p-type semiconductor. This charge
transfer can enhance the separating efficiency, charge carrier lifetime, and reaction
rates [76–83]. Since AgX materials are prone to be reduced by the photo-generated
electrons, combining with other semiconductor not only improves the separation rate
of charge carriers but also promotes the photostability of AgX materials. Based on
the structure, the AgX-based heterojunction structures can be classified into two
types: AgX-Y and Ag-AgX-Y (Y is another semiconductor).
13.5.1 AgX–Y
AgX-Y is composed of AgX and another semiconductor Y. The closely contacting
interface between AgX and Y can be produced via ion exchange method. For
example, Huang et al. fabricated AgI–BiOI hierarchical hybrids by ion exchange
between BiOI hierarchical microspheres and AgNO 3 (Fig. 13.15a) [77]. It was found
that AgI nanoparticles were uniformly anchored on the surface of BiOI nanosheets
and the particle size of AgI can be toiled from 55–16 nm by the addition of poly
(vinylpyrrolidone) surfactant molecules. Besides ion exchange method, adsorption
of organics with halogen or Ag(NH 3 ) 2
+ beforehand can also create the close contact
between AgX and semiconductor Y. For instance, [C 16 min]Br ionic liquid was used
to adsorb on the surface of BiPO4 to form AgBr/BiPO 4 heterojunction structure
[83]. Beneficial from the close contact, the photo-generated charges can be efficiently separated, as shown in Fig. 13.15b, c. Some of the synthesized AgX–Y
photocatalysts are summarized in Table 13.2.
13.5.2 Ag–AgX–Y
Compared to AgX–Y, Ag–AgX–Y can more effectively absorb visible light by the
surface plasmon resonance effect (SPR) of Ag nanoparticles formed on the surface
of AgX. Therefore, Ag–AgX–Y not only can respond to visible light but also has
higher electron–hole separation rate. According to the substrates (Y), Ag–AgX–Y
can be classified into several classes as follows.
322
13 Syntheses and Applications of Silver Halide-Based Photocatalysts