(a) A low percentage of light absorption up to the photocatalysts band gap
(b) Returned reaction of water formation
Beyond three interface kinds of heterojunction semiconductors, only type II bears
acceptable photocatalytic activity. The conversion of type II with a direct Z-scheme
mechanism can more increase the efficiency and suggests the solution for the
abovementioned disadvantages. The system includes two photocatalysts coupled
through redox charges carrying. The mentioned system is a biomimetic mechanism
occurred in the photosynthesis reactions for transferring of the photo-induced
electron of H 2 O to nicotinamide adenine dinucleotide phosphate. The formed couple
of heterojunction includes several photocatalysts species as the relevant redox
potentials of the generated charges are held at higher capacity. Therefore, a recombination reaction of a small amount of electronÀhole pairs causes them to be
sacrifice that makes the excited charges with higher energies leave behind (see
Fig. 9.10). The interesting mechanism provides the capability for visible photons
with relatively low energies to promote an efficient degradation process. Since
Z-scheme mechanism donates the mentioned benefits to a single photocatalyst
having wide band gap, the respected studies have been greatly increased. Some of
them are summarized in Table 9.3. One of notable study reports Pt-loaded in ZrO 2 –
TaON and Pt-loaded in WO 3 that demonstrate permanent photocatalytic H 2 generation from water with high apparent quantum yield at 420 nm. ZrO 2 extends the
lifetime of the photogenerated charges and inhibition of the recombination because
of modification of TaON n-type semiconductor (Maeda et al. 2010). A modified
silver chromate with graphene oxide as binary Ag 2 CrO 4 –GO photocatalyst has
shown notable degradation of methylene blue and phenol under visible light
(Xu et al. 2015). The energy levels of conduction band and valence band for single
Ag 2 CrO 4 and graphene oxide were measured ca. 0.47 V and 2.27 V vs. NHE and
ca. –0.75 V and 1.75 V vs. NHE, respectively. The photogenerated electrons of the
conduction band of silver chromate combine with cavities of valence band from
graphene oxide resulted in leaving of conduction band electrons of graphene oxide
with higher potential and more negatively potential than the À0.28 V as potential
value of O 2
*À
/O 2 . In some recent studies, the effective Z-scheme heterojunctions
Table 9.2 Photocatalysts coupled heterogeneously and the related usage
No. Photocatalyst
Usage
References
1.
TiO 2 /Pt/RuO 2
Water splitting/Rhodamine B
Duonghong et al. (1981)
2.
TiO 2 /Ag x O
Hydrogen evolution
Park and Kang (2007)
3.
Nb 2 O 5 /Pt
Hydrogen production
Chen et al. (2007)
4.
POP-HE
Benzyl alcohol oxidation
Xu et al. (2019a)
5.
TiO 2 /Pd
Suzuki-Miyaura coupling
Koohgard and Hosseini-Sarvari
(2018)
6.
BiVO4/Ag2O
Methyl Orange
Li et al. (2015a)
7.
g-C 3 N 4 /
BiOCl x Br 1Àx
Rhodamine B and Rhodamine
640
Shi et al. (2014)
8.
Bi 5 O 7 I/Bi 2 O 3
Malachite Green
Cheng and Kang (2015)
298
M. Chahkandi and M. Zargazi
(b) Returned reaction of water formation
Beyond three interface kinds of heterojunction semiconductors, only type II bears
acceptable photocatalytic activity. The conversion of type II with a direct Z-scheme
mechanism can more increase the efficiency and suggests the solution for the
abovementioned disadvantages. The system includes two photocatalysts coupled
through redox charges carrying. The mentioned system is a biomimetic mechanism
occurred in the photosynthesis reactions for transferring of the photo-induced
electron of H 2 O to nicotinamide adenine dinucleotide phosphate. The formed couple
of heterojunction includes several photocatalysts species as the relevant redox
potentials of the generated charges are held at higher capacity. Therefore, a recombination reaction of a small amount of electronÀhole pairs causes them to be
sacrifice that makes the excited charges with higher energies leave behind (see
Fig. 9.10). The interesting mechanism provides the capability for visible photons
with relatively low energies to promote an efficient degradation process. Since
Z-scheme mechanism donates the mentioned benefits to a single photocatalyst
having wide band gap, the respected studies have been greatly increased. Some of
them are summarized in Table 9.3. One of notable study reports Pt-loaded in ZrO 2 –
TaON and Pt-loaded in WO 3 that demonstrate permanent photocatalytic H 2 generation from water with high apparent quantum yield at 420 nm. ZrO 2 extends the
lifetime of the photogenerated charges and inhibition of the recombination because
of modification of TaON n-type semiconductor (Maeda et al. 2010). A modified
silver chromate with graphene oxide as binary Ag 2 CrO 4 –GO photocatalyst has
shown notable degradation of methylene blue and phenol under visible light
(Xu et al. 2015). The energy levels of conduction band and valence band for single
Ag 2 CrO 4 and graphene oxide were measured ca. 0.47 V and 2.27 V vs. NHE and
ca. –0.75 V and 1.75 V vs. NHE, respectively. The photogenerated electrons of the
conduction band of silver chromate combine with cavities of valence band from
graphene oxide resulted in leaving of conduction band electrons of graphene oxide
with higher potential and more negatively potential than the À0.28 V as potential
value of O 2
*À
/O 2 . In some recent studies, the effective Z-scheme heterojunctions
Table 9.2 Photocatalysts coupled heterogeneously and the related usage
No. Photocatalyst
Usage
References
1.
TiO 2 /Pt/RuO 2
Water splitting/Rhodamine B
Duonghong et al. (1981)
2.
TiO 2 /Ag x O
Hydrogen evolution
Park and Kang (2007)
3.
Nb 2 O 5 /Pt
Hydrogen production
Chen et al. (2007)
4.
POP-HE
Benzyl alcohol oxidation
Xu et al. (2019a)
5.
TiO 2 /Pd
Suzuki-Miyaura coupling
Koohgard and Hosseini-Sarvari
(2018)
6.
BiVO4/Ag2O
Methyl Orange
Li et al. (2015a)
7.
g-C 3 N 4 /
BiOCl x Br 1Àx
Rhodamine B and Rhodamine
640
Shi et al. (2014)
8.
Bi 5 O 7 I/Bi 2 O 3
Malachite Green
Cheng and Kang (2015)
298
M. Chahkandi and M. Zargazi