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nanomaterials such as nanocluster materials and nanodispersions, their photocatalytic activity is controlled by a series of factors such as the nanoparticle size, light
absorption efficiency, and surface area, which play an important role in augmenting
the production yield of CO 2 photoreduction. The currently huge challenge for these
kinds of materials is their agglomeration, leading to a decrease in surface area and
photocatalytic performance. However, several works attempted to introduce the use
of polymers as stable carriers to prevent agglomeration of these zero-dimensional
nanoparticles (Bard et al. 2002). Meanwhile, one-dimensional nanomaterials
including nanofiber and nanotube with 0.1–1.0 μm in length offer numerous applications in general and CO 2 photoreduction in particular. Li and co-workers examined the efficient adsorption and photocatalytic activities of heterostructure
CdS(Bi 2 S 3 )/TiO 2 nanotube composite in the CO 2 photoreduction to CH 3 OH (Li
et al. 2011). While two-dimensional nanomaterials, namely, films and coatings,
with nanometer thickness has paid much attention in term of their facet-dependent
properties for CO 2 reduction, three-dimensional nanomaterials show excellent optical, electronic, and photocatalytic properties. Because they offer a typical kind of
hierarchical architectures including high surface area, porosity, and crystallinity,
these photocatalysts were widely used for CO 2 photoreduction.
6.3.3 Enhanced Adsorption and Activation of Carbon Dioxide
The key to a noticeable enhancement in photocatalysis relies on improved CO 2
adsorption and activation because of strong CO 2 stability with high C=O bond
energy. To boost the absorbability towards CO 2 , photocatalysts need to be constructed with a highly porous structure. Therefore, structurally chemical modification should be important in the design of such materials. In addition, another main
target is to activate the CO 2 molecules efficiently, facilitating the photoreduction
process with higher performance. In fact, many studies in this context have concentrated on the following strategies.
Firstly, the design of novel photocatalysts with a higher surface area is one of
effective strategies. Metal-organic frameworks (MOFs), consisting of metal clusters
and organic ligands, have reportedly exhibited precious properties in terms of superhigh surface areas for CO 2 adsorption. Meanwhile, simple Ti/TiO 2 is presented as
wide bandgap energies. TiO 2 species based MOFs can, therefore, be promising candidates for potential new photocatalyst generations. For example, such Ti-based
NH 2 -MIL-125 frameworks exhibited outstanding photocatalytic performance for
the transformation of CO 2 into HCOO
−
anion (Yanghe et al. 2012). MOFs nanomaterials with other metal sites can boost CO 2 capture and improve electron transfers
(Chen et al. 2013). However, apart from high surface area, several MOFs show their
thermal and chemical instability in certain conditions; thus, they need to be improved
more structurally.
Secondly, modifying the surface with basic functional groups recently has
received much attention. Chemically, CO 2 molecules were represented as a weakly
T. D. Nguyen et al.
nanomaterials such as nanocluster materials and nanodispersions, their photocatalytic activity is controlled by a series of factors such as the nanoparticle size, light
absorption efficiency, and surface area, which play an important role in augmenting
the production yield of CO 2 photoreduction. The currently huge challenge for these
kinds of materials is their agglomeration, leading to a decrease in surface area and
photocatalytic performance. However, several works attempted to introduce the use
of polymers as stable carriers to prevent agglomeration of these zero-dimensional
nanoparticles (Bard et al. 2002). Meanwhile, one-dimensional nanomaterials
including nanofiber and nanotube with 0.1–1.0 μm in length offer numerous applications in general and CO 2 photoreduction in particular. Li and co-workers examined the efficient adsorption and photocatalytic activities of heterostructure
CdS(Bi 2 S 3 )/TiO 2 nanotube composite in the CO 2 photoreduction to CH 3 OH (Li
et al. 2011). While two-dimensional nanomaterials, namely, films and coatings,
with nanometer thickness has paid much attention in term of their facet-dependent
properties for CO 2 reduction, three-dimensional nanomaterials show excellent optical, electronic, and photocatalytic properties. Because they offer a typical kind of
hierarchical architectures including high surface area, porosity, and crystallinity,
these photocatalysts were widely used for CO 2 photoreduction.
6.3.3 Enhanced Adsorption and Activation of Carbon Dioxide
The key to a noticeable enhancement in photocatalysis relies on improved CO 2
adsorption and activation because of strong CO 2 stability with high C=O bond
energy. To boost the absorbability towards CO 2 , photocatalysts need to be constructed with a highly porous structure. Therefore, structurally chemical modification should be important in the design of such materials. In addition, another main
target is to activate the CO 2 molecules efficiently, facilitating the photoreduction
process with higher performance. In fact, many studies in this context have concentrated on the following strategies.
Firstly, the design of novel photocatalysts with a higher surface area is one of
effective strategies. Metal-organic frameworks (MOFs), consisting of metal clusters
and organic ligands, have reportedly exhibited precious properties in terms of superhigh surface areas for CO 2 adsorption. Meanwhile, simple Ti/TiO 2 is presented as
wide bandgap energies. TiO 2 species based MOFs can, therefore, be promising candidates for potential new photocatalyst generations. For example, such Ti-based
NH 2 -MIL-125 frameworks exhibited outstanding photocatalytic performance for
the transformation of CO 2 into HCOO
−
anion (Yanghe et al. 2012). MOFs nanomaterials with other metal sites can boost CO 2 capture and improve electron transfers
(Chen et al. 2013). However, apart from high surface area, several MOFs show their
thermal and chemical instability in certain conditions; thus, they need to be improved
more structurally.
Secondly, modifying the surface with basic functional groups recently has
received much attention. Chemically, CO 2 molecules were represented as a weakly
T. D. Nguyen et al.