chemical vapor deposition method (In 2 S 3 powder and Au/WO 3 were placed in
quartz furnace separately, the temperature of the furnace will be increased to
800
C with certain Ar flow, and the deposition time is 10 min).
12.3.1.4 Carbon-Based Cocatalysts
Besides the metal nanoparticles and semiconductors cocatalysts, there are intensive
research works focusing on the carbon-based cocatalysts in CO2PR. Graphene,
carbon nanotube, carbon nanodots, carbon nanosheet layer, metal organic frameworks (MOFs), metal–ligand complex, etc. are common carbon-based cocatalysts in
recent years (Table 12.1).
Graphene, owing to its flexible mechanical strength, remarkable electric conductivity, high surface area, etc., has been applied to many fields. In photocatalysis,
graphene can transfer the photo-generated electrons, hence improving the electronhole separation efficiency and prolonging the lifetime of charge carriers (Fig. 12.5).
Tu et al. [49] fabricated a sandwich structure TiO 2 –graphene nanosheet over a
one-step hydrothermal method. The graphene oxide (GO) was prepared according
to Hummers’ method which is a common method for many reported graphene–
semiconductor composites. During the hydrothermal process, the GO, Ti precursor,
and solvent (ethylenediamine abbreviated as En/H 2 O) underwent an in situ simultaneous reduction–hydrolysis process, the GO was reduced by En, and the Ti precursor hydrolyzed to form TiO 2 NPs. Different weight ratios of TiO 2 /graphene were
obtained by varying the GO amount during the synthesis. Ong et al. [58] adopted the
electrostatistic self-assembly strategy to prepare the reduced graphene oxide (rGO)/
protonated C 3 N 4 (pCN) composites. Owing to abundant CN motifs existing on the
g-C 3 N 4 surface, the surface protonation by HCl could be easily conducted. After the
HCl treatment, the pCN was positively charged according to the Zeta potential test,
which could spontaneously assemble on the negative-charged GO (prepared by
Hummers’ method). Finally, the GO was reduced to rGO by NaBH 4 to form
2D/2D rGO/pCN composite. Unlike 2D graphene–semiconductor composites,
Zhang proposed that encapsulation by graphene-like carbon sheet could enhance
the confinement effect of the core nanoparticles compared with its naked counterparts. Therefore, Fe@C NPs were fabricated for the use of MIL-101 as selfsacrificing template and precursor. During the synthesis, two-step calcination
method was utilized; first, MIL-101(Fe) was collapsed and formed Fe 3 C and
Fe 3 O 4 in Ar-500
C; meanwhile, the Fe species could avoid sintering into large
NPs and , subsequently, the temperature raised to 700
C to obtain the Fe@C NPs. It
should be noted that rational regulate the calcination temperature and retention time
is the key to control the particle size and graphite carbon layer’s thickness.
Metal organic frameworks (MOFs), as one class of porous nanocrystals, possess
huge surface area, tunable surface functional groups, and alternative compositions
which have been applied to multiple fields such as catalysis, gas capture and
separation, drug delivery, molecule identification, etc. Due to strong CO 2 adsorption
capability of UiO-66, cooperation with some narrow bandgap semiconductor could
12.3 Cocatalysts in Semiconductor-Based CO 2 Photoreduction
289
quartz furnace separately, the temperature of the furnace will be increased to
800
C with certain Ar flow, and the deposition time is 10 min).
12.3.1.4 Carbon-Based Cocatalysts
Besides the metal nanoparticles and semiconductors cocatalysts, there are intensive
research works focusing on the carbon-based cocatalysts in CO2PR. Graphene,
carbon nanotube, carbon nanodots, carbon nanosheet layer, metal organic frameworks (MOFs), metal–ligand complex, etc. are common carbon-based cocatalysts in
recent years (Table 12.1).
Graphene, owing to its flexible mechanical strength, remarkable electric conductivity, high surface area, etc., has been applied to many fields. In photocatalysis,
graphene can transfer the photo-generated electrons, hence improving the electronhole separation efficiency and prolonging the lifetime of charge carriers (Fig. 12.5).
Tu et al. [49] fabricated a sandwich structure TiO 2 –graphene nanosheet over a
one-step hydrothermal method. The graphene oxide (GO) was prepared according
to Hummers’ method which is a common method for many reported graphene–
semiconductor composites. During the hydrothermal process, the GO, Ti precursor,
and solvent (ethylenediamine abbreviated as En/H 2 O) underwent an in situ simultaneous reduction–hydrolysis process, the GO was reduced by En, and the Ti precursor hydrolyzed to form TiO 2 NPs. Different weight ratios of TiO 2 /graphene were
obtained by varying the GO amount during the synthesis. Ong et al. [58] adopted the
electrostatistic self-assembly strategy to prepare the reduced graphene oxide (rGO)/
protonated C 3 N 4 (pCN) composites. Owing to abundant CN motifs existing on the
g-C 3 N 4 surface, the surface protonation by HCl could be easily conducted. After the
HCl treatment, the pCN was positively charged according to the Zeta potential test,
which could spontaneously assemble on the negative-charged GO (prepared by
Hummers’ method). Finally, the GO was reduced to rGO by NaBH 4 to form
2D/2D rGO/pCN composite. Unlike 2D graphene–semiconductor composites,
Zhang proposed that encapsulation by graphene-like carbon sheet could enhance
the confinement effect of the core nanoparticles compared with its naked counterparts. Therefore, Fe@C NPs were fabricated for the use of MIL-101 as selfsacrificing template and precursor. During the synthesis, two-step calcination
method was utilized; first, MIL-101(Fe) was collapsed and formed Fe 3 C and
Fe 3 O 4 in Ar-500
C; meanwhile, the Fe species could avoid sintering into large
NPs and , subsequently, the temperature raised to 700
C to obtain the Fe@C NPs. It
should be noted that rational regulate the calcination temperature and retention time
is the key to control the particle size and graphite carbon layer’s thickness.
Metal organic frameworks (MOFs), as one class of porous nanocrystals, possess
huge surface area, tunable surface functional groups, and alternative compositions
which have been applied to multiple fields such as catalysis, gas capture and
separation, drug delivery, molecule identification, etc. Due to strong CO 2 adsorption
capability of UiO-66, cooperation with some narrow bandgap semiconductor could
12.3 Cocatalysts in Semiconductor-Based CO 2 Photoreduction
289