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P. Veerakumar et al.
for nitroreductase to accept electrons. Here, RGO plays the role of “extended
nanowire.” The activation of NB by Gr has been proposed using DFT calculations,
and the unsaturated carbon atoms at the edges of Gr and defects on Gr might possess
catalytic activity [87].
7.4 Porous Carbon-Based Functional Nanomaterials
Porous carbon materials including traditional activated carbons (ACs), carbon
nanotubes (CNTs), ordered mesoporous carbon (OMCs), carbon black (CBs),
nanofibers (NFs), and recently emerged novel structured carbons synthesized by
hard and soft templating methods have been widely used in a variety of applications
[94]. Due to their high specific surface areas, micro−/mesoporous structure, tunable
pore size, electronic conductivity, excellent accessibility to active sites, enhanced
mass transport and diffusion. These properties make them a special and unique
choice for various applications in divergent fields such as energy storage, fuel cells,
adsorption/separation, heterogeneous catalysts, catalyst supports, photocatalysis,
CO 2 capture, electrochemical sensors, and so forth [95–97]. However, to improve
their catalytic properties, surface modification, heteroatom doping, chemical activation, and defects on graphic layers are necessary and have been extensively
investigated [98–100]. It is well known that various surface groups, impurities
and surface irregularities (i.e., surface heterogeneity), as well as fine pores of
different sizes and shapes (i.e., structural heterogeneity) will contribute to the
reaction mechanisms. An uneven distribution of functional groups creates surface
heterogeneity. Another reason for heterogeneity is the presence of heteroatoms
(commonly O, N, and S). However, the emission resulting from graphene has been
attributed to C-oxygen-, C-nitrogen-, and/or C-sulfur-related localized states [101].
To induce ripples on the graphene surface can probably alter the local electrical
and optical properties of graphene; thus, modified ripple engineering can be used
for various applications [102]. Among the elements of complexity are the high
surface area resulting from an intricate pore structure, significant differences in the
physicochemical parameters among the heterogeneous surface sites, the occurrence
of partial delocalization of the π-electrons, and the ability of certain surface sites to
react with water and other solvents [103]. Some authors suggest that the distribution
of the functional groups on the surface of ACs depends on pore size. The surface
area is characterized among microporous materials (<2 nm), mesoporous materials
with pore diameter between 2 and 50 nm, and nonporous or macroporous materials
with pore diameter >50 nm [104]. The surface reactions of carbon nanomaterials are
generally initiated from reactions of C atoms at the edges of the layers or at other
lattice defects or reactions of functional groups that are bound to such C atoms.
Surface reactions based on carbon as metal-free catalysts are of particular interest.
The catalytic performance is significantly increased with an increase in the number
of surface oxygen groups present, which are responsible for the enhancement in
reaction rate, higher catalytic performance, and yield of the products [105]. Metal-
P. Veerakumar et al.
for nitroreductase to accept electrons. Here, RGO plays the role of “extended
nanowire.” The activation of NB by Gr has been proposed using DFT calculations,
and the unsaturated carbon atoms at the edges of Gr and defects on Gr might possess
catalytic activity [87].
7.4 Porous Carbon-Based Functional Nanomaterials
Porous carbon materials including traditional activated carbons (ACs), carbon
nanotubes (CNTs), ordered mesoporous carbon (OMCs), carbon black (CBs),
nanofibers (NFs), and recently emerged novel structured carbons synthesized by
hard and soft templating methods have been widely used in a variety of applications
[94]. Due to their high specific surface areas, micro−/mesoporous structure, tunable
pore size, electronic conductivity, excellent accessibility to active sites, enhanced
mass transport and diffusion. These properties make them a special and unique
choice for various applications in divergent fields such as energy storage, fuel cells,
adsorption/separation, heterogeneous catalysts, catalyst supports, photocatalysis,
CO 2 capture, electrochemical sensors, and so forth [95–97]. However, to improve
their catalytic properties, surface modification, heteroatom doping, chemical activation, and defects on graphic layers are necessary and have been extensively
investigated [98–100]. It is well known that various surface groups, impurities
and surface irregularities (i.e., surface heterogeneity), as well as fine pores of
different sizes and shapes (i.e., structural heterogeneity) will contribute to the
reaction mechanisms. An uneven distribution of functional groups creates surface
heterogeneity. Another reason for heterogeneity is the presence of heteroatoms
(commonly O, N, and S). However, the emission resulting from graphene has been
attributed to C-oxygen-, C-nitrogen-, and/or C-sulfur-related localized states [101].
To induce ripples on the graphene surface can probably alter the local electrical
and optical properties of graphene; thus, modified ripple engineering can be used
for various applications [102]. Among the elements of complexity are the high
surface area resulting from an intricate pore structure, significant differences in the
physicochemical parameters among the heterogeneous surface sites, the occurrence
of partial delocalization of the π-electrons, and the ability of certain surface sites to
react with water and other solvents [103]. Some authors suggest that the distribution
of the functional groups on the surface of ACs depends on pore size. The surface
area is characterized among microporous materials (<2 nm), mesoporous materials
with pore diameter between 2 and 50 nm, and nonporous or macroporous materials
with pore diameter >50 nm [104]. The surface reactions of carbon nanomaterials are
generally initiated from reactions of C atoms at the edges of the layers or at other
lattice defects or reactions of functional groups that are bound to such C atoms.
Surface reactions based on carbon as metal-free catalysts are of particular interest.
The catalytic performance is significantly increased with an increase in the number
of surface oxygen groups present, which are responsible for the enhancement in
reaction rate, higher catalytic performance, and yield of the products [105]. Metal-