dispersity, while the produced BiO
+ ions would dissolve in the solvent (BiOBr + Ag
+
¼ AgBr + BiO
+
) (Fig. 13.19b). By this process, the AgX would be in situ formed
on the surface of BiOX. This intimate connection between BiOX and AgX is
beneficial to the transfer of photo-generated carriers (Fig. 13.19c). Besides this
method, AgX–BiOX can also be obtained via the direct reaction of Bi
3+
, Ag
+ and X
À
in the hydrothermal process [101–103].
13.5.2.4 Ag–AgX–AgY
Similar to AgX, the other Ag salts (Ag–AgX–AgY), such as Ag 3 PO 4 , Ag 2 O,
Ag 2 CO 3 , AgVO 3 , etc., are also visible light-driven photocatalysts with high
photocatalytic activity. Combining with these Ag salts to construct heterojunction
can greatly improve the photocatalytic performance of AgX [104–107]. As we all
know, the solubility product (Ksp) of AgX is much lower than the most of other Ag
salts. Consequently, it is feasible to construct the heterojunction of AgX–AgY by the
means of ion exchange method. For example, Wu et al. utilized NaBr solution to
exchange the PO 4
3+ ions in Ag 3 PO 4 to form AgBr–AgPO 4 (Fig. 13.20a). In addition,
Ag–AgCl–Ag 2 O [105], Ag–AgBr–AgVO 3 [106], and Ag–AgBr–Ag 2 CO 3 [107] can
also be prepared by this ion exchange method (Fig. 13.20b, c). Being benefited from
this heterojunction, photo-generated carriers can be effectively separated
(Fig. 13.20d).
13.6 Z-Scheme Structure
Constructing Z-scheme structure is another effective way to promote the separation
rate of photo-generated carriers. Moreover, beneficial from the special transfer
process of electrons and holes, the higher redox ability of photocatalytic composites
can be reserved via Z-scheme structure [108–113]. In Z-scheme structured AgX-AgY photocatalytic material, the semiconductor Y has the same metallic element with
AgX, which can facilely be in situ generated via photo-reduction process. The in situ
formed Ag nanoparticles can be stably anchored on the surface of AgX inhibiting the
exfoliation of Ag nanoparticles from AgX surface [111]. Moreover, the tight solidsolid contact interface between Ag nanoparticles and AgX can reduce the electric
resistance, beneficial to forming Ohmic contact. Interestingly, different from the
conventional Z-scheme structure, the role of Ag nanoparticles, electron mediator or
photosensitizer, is determined by the energy band structure of AgX and semiconductor Y. According to the energy levels of the two semiconductors, the visible
light-driven Z-scheme AgX–Ag–Y can be classified into three types, as shown in
Fig. 13.21.
328
13 Syntheses and Applications of Silver Halide-Based Photocatalysts
+ ions would dissolve in the solvent (BiOBr + Ag
+
¼ AgBr + BiO
+
) (Fig. 13.19b). By this process, the AgX would be in situ formed
on the surface of BiOX. This intimate connection between BiOX and AgX is
beneficial to the transfer of photo-generated carriers (Fig. 13.19c). Besides this
method, AgX–BiOX can also be obtained via the direct reaction of Bi
3+
, Ag
+ and X
À
in the hydrothermal process [101–103].
13.5.2.4 Ag–AgX–AgY
Similar to AgX, the other Ag salts (Ag–AgX–AgY), such as Ag 3 PO 4 , Ag 2 O,
Ag 2 CO 3 , AgVO 3 , etc., are also visible light-driven photocatalysts with high
photocatalytic activity. Combining with these Ag salts to construct heterojunction
can greatly improve the photocatalytic performance of AgX [104–107]. As we all
know, the solubility product (Ksp) of AgX is much lower than the most of other Ag
salts. Consequently, it is feasible to construct the heterojunction of AgX–AgY by the
means of ion exchange method. For example, Wu et al. utilized NaBr solution to
exchange the PO 4
3+ ions in Ag 3 PO 4 to form AgBr–AgPO 4 (Fig. 13.20a). In addition,
Ag–AgCl–Ag 2 O [105], Ag–AgBr–AgVO 3 [106], and Ag–AgBr–Ag 2 CO 3 [107] can
also be prepared by this ion exchange method (Fig. 13.20b, c). Being benefited from
this heterojunction, photo-generated carriers can be effectively separated
(Fig. 13.20d).
13.6 Z-Scheme Structure
Constructing Z-scheme structure is another effective way to promote the separation
rate of photo-generated carriers. Moreover, beneficial from the special transfer
process of electrons and holes, the higher redox ability of photocatalytic composites
can be reserved via Z-scheme structure [108–113]. In Z-scheme structured AgX-AgY photocatalytic material, the semiconductor Y has the same metallic element with
AgX, which can facilely be in situ generated via photo-reduction process. The in situ
formed Ag nanoparticles can be stably anchored on the surface of AgX inhibiting the
exfoliation of Ag nanoparticles from AgX surface [111]. Moreover, the tight solidsolid contact interface between Ag nanoparticles and AgX can reduce the electric
resistance, beneficial to forming Ohmic contact. Interestingly, different from the
conventional Z-scheme structure, the role of Ag nanoparticles, electron mediator or
photosensitizer, is determined by the energy band structure of AgX and semiconductor Y. According to the energy levels of the two semiconductors, the visible
light-driven Z-scheme AgX–Ag–Y can be classified into three types, as shown in
Fig. 13.21.
328
13 Syntheses and Applications of Silver Halide-Based Photocatalysts