1. Oxidation–Halogenation Method
Metallic Ag with different morphologies, foil, nanowire, or nanotube, can be
utilized as the Ag source. In the oxidation–halogenation processes, an oxidation
reaction (Ag
0 + oxidant ! Ag
+ + reductant) and a halogenation reaction (Ag
+ + X
À
! AgX) will occur together.[46–54] Firstly, metallic Ag is oxidized into Ag
+ ion in
the presence of oxidant such as Fe
3+ or H 2 O 2 . Meanwhile, the dissolved X
À ion
immediately combines with the released Ag
+ ion to form AgX. For example, Ye
et al. largely synthesized uniform AgBr nanowires using commercial silver foils at
room temperature [46]. It was revealed that the towerlike AgBr nanowire was
produced by the following pathway: Firstly, the uniform AgBr nanocrystals with
octahedron-like structures formed tidily on the surfaces of Ag foils. Then, with
prolonging the reacting time, the formed AgBr nanocrystals attached to each other
and self-assembled into towerlike nanostructure arrays under the direction of PVP
(Fig. 13.6a, b). Using Ag nanowires as Ag source and FeCl 3 as oxidant, Huang et al.
fabricated necklace-like Ag/AgCl nano-heterostructures [50]. By adjusting the addition of FeCl 3 , the amount of AgCl in Ag/AgCl nanowires can be conveniently
controlled, in Fig. 13.6c. They found that the ratio of Ag and AgCl plays an
important role in determining the photocatalytic activity of Ag/AgCl nanowires.
When the ratio of AgCl and Ag is 85:15, the Ag/AgCl nanowires exhibit the optimal
photocatalytic activity for the decomposition of organic pollutants and water splitting to produce oxygen.
Fig. 13.6 (a) Schematic illustration of the heteroepitaxial growth process of AgBr nanowires on
Ag substrates; (b) SEM images of AgBr nanowires during growth process at different reaction times
(0, 0.5, 1, 2, 4, and 6 h) [46]. Reproduced from Ref. [46] by permission of John Wiley & Sons Ltd.
(c) SEM images of the necklace-like Ag/AgCl nano-heterostructures with different AgCl amount
(10%, 30%, 80%, 85%, and 100%) and EDS analysis of Ag/AgCl with 85% AgCl
[50]. (Reproduced from Ref. [50] by permission of John Wiley & Sons Ltd)
312
13 Syntheses and Applications of Silver Halide-Based Photocatalysts
Metallic Ag with different morphologies, foil, nanowire, or nanotube, can be
utilized as the Ag source. In the oxidation–halogenation processes, an oxidation
reaction (Ag
0 + oxidant ! Ag
+ + reductant) and a halogenation reaction (Ag
+ + X
À
! AgX) will occur together.[46–54] Firstly, metallic Ag is oxidized into Ag
+ ion in
the presence of oxidant such as Fe
3+ or H 2 O 2 . Meanwhile, the dissolved X
À ion
immediately combines with the released Ag
+ ion to form AgX. For example, Ye
et al. largely synthesized uniform AgBr nanowires using commercial silver foils at
room temperature [46]. It was revealed that the towerlike AgBr nanowire was
produced by the following pathway: Firstly, the uniform AgBr nanocrystals with
octahedron-like structures formed tidily on the surfaces of Ag foils. Then, with
prolonging the reacting time, the formed AgBr nanocrystals attached to each other
and self-assembled into towerlike nanostructure arrays under the direction of PVP
(Fig. 13.6a, b). Using Ag nanowires as Ag source and FeCl 3 as oxidant, Huang et al.
fabricated necklace-like Ag/AgCl nano-heterostructures [50]. By adjusting the addition of FeCl 3 , the amount of AgCl in Ag/AgCl nanowires can be conveniently
controlled, in Fig. 13.6c. They found that the ratio of Ag and AgCl plays an
important role in determining the photocatalytic activity of Ag/AgCl nanowires.
When the ratio of AgCl and Ag is 85:15, the Ag/AgCl nanowires exhibit the optimal
photocatalytic activity for the decomposition of organic pollutants and water splitting to produce oxygen.
Fig. 13.6 (a) Schematic illustration of the heteroepitaxial growth process of AgBr nanowires on
Ag substrates; (b) SEM images of AgBr nanowires during growth process at different reaction times
(0, 0.5, 1, 2, 4, and 6 h) [46]. Reproduced from Ref. [46] by permission of John Wiley & Sons Ltd.
(c) SEM images of the necklace-like Ag/AgCl nano-heterostructures with different AgCl amount
(10%, 30%, 80%, 85%, and 100%) and EDS analysis of Ag/AgCl with 85% AgCl
[50]. (Reproduced from Ref. [50] by permission of John Wiley & Sons Ltd)
312
13 Syntheses and Applications of Silver Halide-Based Photocatalysts