quantum dots employing CX-72 carbon black as the starting material by refluxing
with conc. HNO 3 for 24 h (Dong et al. 2012). Single-layered graphene quantum dots
can effectively penetrate the cell without any bio-conjugation which enables them to
be utilized in bio-imaging and drug delivery, whereas multilayered graphene quantum dots exhibit broad solar absorption, rendering promising candidate in optoelectronic devices.
Ultrasonic Exfoliation
The synthesis of carbon quantum dots through ultrasonication can generate alternate
waves in liquids of low and high pressure liable for the generation and collapsing of
vacuum bubbles in the reaction medium. It also prevents agglomeration and creates
strong hydrodynamic shear forces. Li et al. (2012) synthesize carbon quantum
dot-based Cu 2 O nanostructure via facile one-step ultrasonic treatment using glucose
as carbon precursor in alkali medium. Higher productivity of nanostructure is due to
the high light reflecting capability of Cu 2 O and up-conversion photoluminescence of
carbon quantum dots. IR light comprises nearly 53% of solar spectrum which has not
been utilized effectively. For the first time, Li et al. (2012) demonstrated that carbon
quantum dot-based Cu 2 O photocatalytic system could harness the near-infrared
region of the solar spectrum. The photocatalytic activity of nanostructure was
evaluated against methyl blue. The spherical-shaped nanostructure protruding
Cu 2 O particle could be clearly seen in scanning electron microscope images in
Fig. 3.6.
The ultrasonic waves had the potential to convert macroscopic carbonaceous
material into nanoscale carbon quantum dots. Li et al. (2011a) synthesize watersoluble fluorescent carbon quantum dots by using hydrogen peroxide-assisted ultrasonic method using activated carbon as precursor. The hydrophilic character of
carbon quantum dots was attributed to the occurrence of hydroxyl group. To prepare
a suitable amount of activated carbon, an appropriate amount of H 2 O 2 was added and
subjected to 40 KHz ultrasonic treatment for 2 h at room temperature. The obtained
suspension was then vacuum-filtered using 20 nm pore cellulose membrane. Park
et al. (2014) described green synthesis based on carbon quantum dots using waste
food via ultrasonic method at room temperature (Scheme 3.1). The usage of renewable resources for large-scale production of carbon quantum dots is a cost-effective
method and useful in energy conversion and biomedical and industrial application.
The synthetic procedure involves the following steps: dehydration, polymerization,
carbonization, and passivation (Jeong et al. 2012). In a typical procedure, waste food
and ethanol were mixed followed by ultrasonication to 45 min at 40 KHz. The
obtained sample was centrifuged to separate heavy and agglomerated particle. The
supernatant was then filtered twice through 0.22 μm membrane to separate carbon
quantum dots and further dried at 45
C. The uniform spherical shape carbon
quantum dots with average size of 4.6 nm were synthesized and further confirmed
by high-resolution transmission electron microscope and atomic force microscopy
images Fig. 3.7.
92
P. Shandilya et al.
with conc. HNO 3 for 24 h (Dong et al. 2012). Single-layered graphene quantum dots
can effectively penetrate the cell without any bio-conjugation which enables them to
be utilized in bio-imaging and drug delivery, whereas multilayered graphene quantum dots exhibit broad solar absorption, rendering promising candidate in optoelectronic devices.
Ultrasonic Exfoliation
The synthesis of carbon quantum dots through ultrasonication can generate alternate
waves in liquids of low and high pressure liable for the generation and collapsing of
vacuum bubbles in the reaction medium. It also prevents agglomeration and creates
strong hydrodynamic shear forces. Li et al. (2012) synthesize carbon quantum
dot-based Cu 2 O nanostructure via facile one-step ultrasonic treatment using glucose
as carbon precursor in alkali medium. Higher productivity of nanostructure is due to
the high light reflecting capability of Cu 2 O and up-conversion photoluminescence of
carbon quantum dots. IR light comprises nearly 53% of solar spectrum which has not
been utilized effectively. For the first time, Li et al. (2012) demonstrated that carbon
quantum dot-based Cu 2 O photocatalytic system could harness the near-infrared
region of the solar spectrum. The photocatalytic activity of nanostructure was
evaluated against methyl blue. The spherical-shaped nanostructure protruding
Cu 2 O particle could be clearly seen in scanning electron microscope images in
Fig. 3.6.
The ultrasonic waves had the potential to convert macroscopic carbonaceous
material into nanoscale carbon quantum dots. Li et al. (2011a) synthesize watersoluble fluorescent carbon quantum dots by using hydrogen peroxide-assisted ultrasonic method using activated carbon as precursor. The hydrophilic character of
carbon quantum dots was attributed to the occurrence of hydroxyl group. To prepare
a suitable amount of activated carbon, an appropriate amount of H 2 O 2 was added and
subjected to 40 KHz ultrasonic treatment for 2 h at room temperature. The obtained
suspension was then vacuum-filtered using 20 nm pore cellulose membrane. Park
et al. (2014) described green synthesis based on carbon quantum dots using waste
food via ultrasonic method at room temperature (Scheme 3.1). The usage of renewable resources for large-scale production of carbon quantum dots is a cost-effective
method and useful in energy conversion and biomedical and industrial application.
The synthetic procedure involves the following steps: dehydration, polymerization,
carbonization, and passivation (Jeong et al. 2012). In a typical procedure, waste food
and ethanol were mixed followed by ultrasonication to 45 min at 40 KHz. The
obtained sample was centrifuged to separate heavy and agglomerated particle. The
supernatant was then filtered twice through 0.22 μm membrane to separate carbon
quantum dots and further dried at 45
C. The uniform spherical shape carbon
quantum dots with average size of 4.6 nm were synthesized and further confirmed
by high-resolution transmission electron microscope and atomic force microscopy
images Fig. 3.7.
92
P. Shandilya et al.