photocatalysts, the study of the reaction mechanism of CO2PR remains
challengeable.
12.3 Cocatalysts in Semiconductor-Based CO 2
Photoreduction
12.3.1 Preparations
12.3.1.1 Metal–Semiconductor Composites
There are numerous methods that are involved with the metal precursors’ reduction
and further deposit metal NPs on the semiconductors’ surface, leading to the
formation of metal–semiconductor composite. The common methods include
photo-deposition method, alcohol reduction method, chemical reduction method
(common reducing agents such as NaBH 4 , ascorbic acid, glucose, trisodium citrate,
hydrazine, etc.), deposition–precipitation (DP) method, atomic layer deposition
(ALD) method, etc. (Table 12.1).
Xie et al. [10] synthesized Pt–TiO 2 composites with the use of three different
methods: (1) photo-deposition of Pt NPs on titania with 300 W Xe lamp as light
source and methanol as the sacrificial reagent, (2) impregnation of Pt precursor with
titania and followed by calcination treatment in H 2 at 673 K, and (3) hydrazine
reduction of H 2 PtCl 6 an aqueous solution containing titania. The TEM results
indicate that the photo-deposition method and hydrazine reduction method both
result in smaller-sized Pt particles (mean size, 3.7 and 4.2 nm, respectively) and
the impregnation method followed by H 2 calcination will result in bigger-sized Pt
particles (6.8 nm). Wang et al. [9] adopted a unique tilted-target sputtering (TTS)
method for the ultrafine Pt cluster deposition on 1D TiO 2 single-crystal film. The
loading amount of Pt and cluster size (0.5–2 nm) were manipulated by adjusting the
deposition time (5–60s). Song et al. [15] studied the shape-dependent Pd/C 3 N 4
few-layer composites in CO2PR. During the synthesis process, the author used
HCHO and Na 2 C 2 O 4 to promote the formation of Pd (111) facets, while the Br
À
and I
À were introduced to stabilize the Pd (100) facet. As a result, Pd cube/C 3 N 4 and
Pd nanotetrahedron/C 3 N 4 can be well obtained through a solution-phase
solvothermal method. Despite their shape, these two Pd polyhedrons have comparable particle size (4–6 nm), which are the smallest Pd nanocrystals with specific
facets obtained in aqueous phase by now.
Compared with single-unit metal–semiconductor composite, binary metal alloy
NPs with diverse surface active sites and metal-support interfaces thus could possess
more potential in photocatalysis. In the synthesis of alloy NPs involved with at least
two metal precursors, Long et al. [18] synthesized a series of PdxCu1 fcc-phased
NPs in situ growth on the TiO 2 nanosheet in the presence of ascorbic acid and PVP.
Through varying the ratio of K 2 PdCl 4 to CuCl 2 , sphere-like NPs of CuPd1Cu1,
Pd3Cu1, Pd5Cu1, Pd7Cu1, and Pd11Cu1 could be obtained. Neaţu et al. [14]
12.3 Cocatalysts in Semiconductor-Based CO 2 Photoreduction
285
challengeable.
12.3 Cocatalysts in Semiconductor-Based CO 2
Photoreduction
12.3.1 Preparations
12.3.1.1 Metal–Semiconductor Composites
There are numerous methods that are involved with the metal precursors’ reduction
and further deposit metal NPs on the semiconductors’ surface, leading to the
formation of metal–semiconductor composite. The common methods include
photo-deposition method, alcohol reduction method, chemical reduction method
(common reducing agents such as NaBH 4 , ascorbic acid, glucose, trisodium citrate,
hydrazine, etc.), deposition–precipitation (DP) method, atomic layer deposition
(ALD) method, etc. (Table 12.1).
Xie et al. [10] synthesized Pt–TiO 2 composites with the use of three different
methods: (1) photo-deposition of Pt NPs on titania with 300 W Xe lamp as light
source and methanol as the sacrificial reagent, (2) impregnation of Pt precursor with
titania and followed by calcination treatment in H 2 at 673 K, and (3) hydrazine
reduction of H 2 PtCl 6 an aqueous solution containing titania. The TEM results
indicate that the photo-deposition method and hydrazine reduction method both
result in smaller-sized Pt particles (mean size, 3.7 and 4.2 nm, respectively) and
the impregnation method followed by H 2 calcination will result in bigger-sized Pt
particles (6.8 nm). Wang et al. [9] adopted a unique tilted-target sputtering (TTS)
method for the ultrafine Pt cluster deposition on 1D TiO 2 single-crystal film. The
loading amount of Pt and cluster size (0.5–2 nm) were manipulated by adjusting the
deposition time (5–60s). Song et al. [15] studied the shape-dependent Pd/C 3 N 4
few-layer composites in CO2PR. During the synthesis process, the author used
HCHO and Na 2 C 2 O 4 to promote the formation of Pd (111) facets, while the Br
À
and I
À were introduced to stabilize the Pd (100) facet. As a result, Pd cube/C 3 N 4 and
Pd nanotetrahedron/C 3 N 4 can be well obtained through a solution-phase
solvothermal method. Despite their shape, these two Pd polyhedrons have comparable particle size (4–6 nm), which are the smallest Pd nanocrystals with specific
facets obtained in aqueous phase by now.
Compared with single-unit metal–semiconductor composite, binary metal alloy
NPs with diverse surface active sites and metal-support interfaces thus could possess
more potential in photocatalysis. In the synthesis of alloy NPs involved with at least
two metal precursors, Long et al. [18] synthesized a series of PdxCu1 fcc-phased
NPs in situ growth on the TiO 2 nanosheet in the presence of ascorbic acid and PVP.
Through varying the ratio of K 2 PdCl 4 to CuCl 2 , sphere-like NPs of CuPd1Cu1,
Pd3Cu1, Pd5Cu1, Pd7Cu1, and Pd11Cu1 could be obtained. Neaţu et al. [14]
12.3 Cocatalysts in Semiconductor-Based CO 2 Photoreduction
285