460
S. Das et al.
2.4 Graphene-Based Nanocomposites
Graphene possesses a plane monolayered two-dimensional (2D) arrangement of carbon atoms in the form of a honeycomb. They are the major building blocks for 0D
fullerenes, 1D carbon nanotubes, and 3D graphite. Graphene acquires a high thermal
conductivity, electrical properties (π-conjugation), mobile charge carriers at room
temperature, and exceptionally high theoretical specific surface area (2600 m
2 /g).
This had resulted in their exploitation as photocatalyst support for enhanced photocatalytic activity. The ground-breaking reports by Kamat et al., where they created
graphene oxide (GO)-TiO 2 nanocrystalline composites demonstrated for the first time
the feasibility of using graphene in photocatalytic nanocomposites, inspiring intensive research on their development of next-generation photocatalysts (Williams et al.
2008). Graphene alone possesses antimicrobial activity owing to its which is physicochemical properties related to size, morphology, and surface functional groups.
Reports by Akhavan et al. suggested antibacterial action of graphene nanosheets
against E. coli as well. According to them, the bacterial inactivation in this case is
due to a “suicidal mechanism”. Normal GO was capable of proliferating the bacterial growth until it was found that components of the bacteria reduce the GO to
generate bactericidal and hence suicidal molecules (Akhavan and Ghaderi 2012;
Williams et al. 2008). In another study by the group, biocompatible antioxidant
melatonin was used for reduction of GO. The bacteria captured within the aggregated GO nanosheets were biologically detached from their surroundings and subsequently killed. Also, if required, photothermal therapy using near-infrared irradiation at 808 nm, could also kill the bacteria. Since the GO does not serve detrimental
until reduced, they are applied as an encapsulating material for transport of preferred microorganisms, surface sterilizing agents, and smart-coat technologies for
inactivation of microorganisms (McGuinness et al. 2016).
Salient application of graphene in accelerating photocatalytic disinfection is in the
form of hybrid nanocomposites with conventional photocatalysts like TiO 2 and ZnO.
This could be done by the direct embedding of the semiconductors on the GO surface or crystal lattice. As per Cao et al., graphene/TiO 2 NCs photocatalysts displayed
better visible light absorption and also superior photocatalytic inactivation toward E.
coli when irradiated under visible light, where pure TiO 2 actions were reported negligible (McGuinness et al. 2016). The visible light PCD of these reduced GO/TiO 2 has
not been restricted to common Gram-negative organisms, but has also been reported
against MDR E. coli. As per Prasad et al., it took 120 min for complete disinfection
of E. coli with detrimental loss to the bacterial genetic component and antibiotic
resistance (Prasad et al. 2017). Sun and coworkers constructed GO–TiO 2 –Ag NCs
with GO sheets (2D) with TiO 2 nanorods (1D) and Ag quantum dots(0D) using a
facile two-phase method. These GO–TiO 2 –Ag NCs displayed tremendous intrinsic
disinfection and biocidal properties against E. coli cells. This may be attributed to
easy transfer of photo-generated electrons from TiO 2 to GO sheets (Liu et al. 2013).
Since the work function of surface-deposited Ag NPs has a Fermi level lower than
that of GO the photo-generated electrons might further be transferred from GO to
S. Das et al.
2.4 Graphene-Based Nanocomposites
Graphene possesses a plane monolayered two-dimensional (2D) arrangement of carbon atoms in the form of a honeycomb. They are the major building blocks for 0D
fullerenes, 1D carbon nanotubes, and 3D graphite. Graphene acquires a high thermal
conductivity, electrical properties (π-conjugation), mobile charge carriers at room
temperature, and exceptionally high theoretical specific surface area (2600 m
2 /g).
This had resulted in their exploitation as photocatalyst support for enhanced photocatalytic activity. The ground-breaking reports by Kamat et al., where they created
graphene oxide (GO)-TiO 2 nanocrystalline composites demonstrated for the first time
the feasibility of using graphene in photocatalytic nanocomposites, inspiring intensive research on their development of next-generation photocatalysts (Williams et al.
2008). Graphene alone possesses antimicrobial activity owing to its which is physicochemical properties related to size, morphology, and surface functional groups.
Reports by Akhavan et al. suggested antibacterial action of graphene nanosheets
against E. coli as well. According to them, the bacterial inactivation in this case is
due to a “suicidal mechanism”. Normal GO was capable of proliferating the bacterial growth until it was found that components of the bacteria reduce the GO to
generate bactericidal and hence suicidal molecules (Akhavan and Ghaderi 2012;
Williams et al. 2008). In another study by the group, biocompatible antioxidant
melatonin was used for reduction of GO. The bacteria captured within the aggregated GO nanosheets were biologically detached from their surroundings and subsequently killed. Also, if required, photothermal therapy using near-infrared irradiation at 808 nm, could also kill the bacteria. Since the GO does not serve detrimental
until reduced, they are applied as an encapsulating material for transport of preferred microorganisms, surface sterilizing agents, and smart-coat technologies for
inactivation of microorganisms (McGuinness et al. 2016).
Salient application of graphene in accelerating photocatalytic disinfection is in the
form of hybrid nanocomposites with conventional photocatalysts like TiO 2 and ZnO.
This could be done by the direct embedding of the semiconductors on the GO surface or crystal lattice. As per Cao et al., graphene/TiO 2 NCs photocatalysts displayed
better visible light absorption and also superior photocatalytic inactivation toward E.
coli when irradiated under visible light, where pure TiO 2 actions were reported negligible (McGuinness et al. 2016). The visible light PCD of these reduced GO/TiO 2 has
not been restricted to common Gram-negative organisms, but has also been reported
against MDR E. coli. As per Prasad et al., it took 120 min for complete disinfection
of E. coli with detrimental loss to the bacterial genetic component and antibiotic
resistance (Prasad et al. 2017). Sun and coworkers constructed GO–TiO 2 –Ag NCs
with GO sheets (2D) with TiO 2 nanorods (1D) and Ag quantum dots(0D) using a
facile two-phase method. These GO–TiO 2 –Ag NCs displayed tremendous intrinsic
disinfection and biocidal properties against E. coli cells. This may be attributed to
easy transfer of photo-generated electrons from TiO 2 to GO sheets (Liu et al. 2013).
Since the work function of surface-deposited Ag NPs has a Fermi level lower than
that of GO the photo-generated electrons might further be transferred from GO to