2.1 Carbonaceous Quantum Dots
15
hydrothermal circumstances, GQDs are ultimately synthesized via a method with
chemical cutting and deoxidization in alkali medium (e.g., NaOH, NH 3 ) (Pan et al.
2010, 2012; Zhu et al. 2011; Shen et al. 2011). On the basis of GO sheets, Zhu et al.
illustrated the first sonication combined with solvent thermal preparation of GQDs,
with DMF acting as solvent. Because of superior edge influence and quantum restriction, GQDs own pronounced features of QDs and graphene (Chen et al. 2014; Dinari
et al. 2015). Consequently, GQDs, with their simple synthesis routes and great electrochemical performance (Low et al. 2013; Wang et al. 2014b). Chao et al. synthesized
the graphene foam (GF) that are supported GQD and anchored it on VO 2 array electrode, which was called GVG (Chao et al. 2015). The formation of the GVG is shown
in Fig. 2.1b. The growth mechanism includes the self-assembly and crystallographic
orientation processes. In the solvothermal reaction process, the VOC 2 O 4 nucleates
on the GF surface, and the particles bond with each other, reducing the overall
energy. Afterwards, a belt structure produced in the light of the strong anisotropy
of monoclinic VO 2 crystal. Eventually, two single belts combine together in order
to produce the intersected nanobelts structure according to the oriented attachment
mechanism. Park et al. (2016) reported that introducing the GQDs into the cathode
dramatically improved sulfur/sulfide utilization, realizing high performance. Additionally, the GQDs induced the integrity of sulfur-carbon electrode composite’s structure through oxygen-enriched functional groups. The hierarchical architecture made
charge transfer fast when reducing the wastage of lithium polysulfides, on account
of the physicochemical performance of GQDs. The mechanism through which great
cycling and rate properties are obtained was completely studied by the analysis of
capacity and voltage profiles. GQDs could be fabricated by an improved Hummers’
method, and then GQD-S and GQD-S/Carbon Black (CB) could be obtained through
the hydrothermal processes with simple hybrid. The TEM and scanning TEM images
of nanosized sulfur on the GQD electrodes in the Li 2 S 8 catholyte are shown in
Fig. 2.1b–e. GQDs tightly covered the nanosized sulfur particles’ surface, which
was demonstrated through lattice fringes in corresponding with (111) planes.
Electrochemical Exfoliation. GQDs and C-Dots can be prepared by electrochemical cutting of carbon precursors like carbon nanotubes, rGO film, graphite rods, and
3-dimensional (3D) CVD-grown graphene. Meanwhile, it has been suggested that
OH· radical and O· radical formed on the basis of oxidation of water at the anode
function as electrochemical “scissors” for the sake of the releasion of GQDs or C-dots
(Lu et al. 2009). Some corrosion processes could be started near the edges and sped
up at defect sites. When using organic solvents, Ananthanarayanan et al. ascribed
the desquamation process to the capability of the electrolytic anion to insert between
graphene layers and the electrical stress (Ananthanarayanan et al. 2014). Functional
groups or heteroatoms can be adhibited or doped on the synthetic carbon nanodots
lying on the used electrolyte (Li et al. 2012c). The abovementioned electrochemical
strategy is uncomplicated (mainly one step) and usually of high yield.
Physical Routes. Microwave extraction provides rapid and even heating for the
reaction medium, then considerably enhancing the reaction rate and making the
product yields and quality better (Li et al. 2012a) Ultrasound may generate alternant
high-pressure and low-pressure waves in fluid, resulting in the formation and severe
15
hydrothermal circumstances, GQDs are ultimately synthesized via a method with
chemical cutting and deoxidization in alkali medium (e.g., NaOH, NH 3 ) (Pan et al.
2010, 2012; Zhu et al. 2011; Shen et al. 2011). On the basis of GO sheets, Zhu et al.
illustrated the first sonication combined with solvent thermal preparation of GQDs,
with DMF acting as solvent. Because of superior edge influence and quantum restriction, GQDs own pronounced features of QDs and graphene (Chen et al. 2014; Dinari
et al. 2015). Consequently, GQDs, with their simple synthesis routes and great electrochemical performance (Low et al. 2013; Wang et al. 2014b). Chao et al. synthesized
the graphene foam (GF) that are supported GQD and anchored it on VO 2 array electrode, which was called GVG (Chao et al. 2015). The formation of the GVG is shown
in Fig. 2.1b. The growth mechanism includes the self-assembly and crystallographic
orientation processes. In the solvothermal reaction process, the VOC 2 O 4 nucleates
on the GF surface, and the particles bond with each other, reducing the overall
energy. Afterwards, a belt structure produced in the light of the strong anisotropy
of monoclinic VO 2 crystal. Eventually, two single belts combine together in order
to produce the intersected nanobelts structure according to the oriented attachment
mechanism. Park et al. (2016) reported that introducing the GQDs into the cathode
dramatically improved sulfur/sulfide utilization, realizing high performance. Additionally, the GQDs induced the integrity of sulfur-carbon electrode composite’s structure through oxygen-enriched functional groups. The hierarchical architecture made
charge transfer fast when reducing the wastage of lithium polysulfides, on account
of the physicochemical performance of GQDs. The mechanism through which great
cycling and rate properties are obtained was completely studied by the analysis of
capacity and voltage profiles. GQDs could be fabricated by an improved Hummers’
method, and then GQD-S and GQD-S/Carbon Black (CB) could be obtained through
the hydrothermal processes with simple hybrid. The TEM and scanning TEM images
of nanosized sulfur on the GQD electrodes in the Li 2 S 8 catholyte are shown in
Fig. 2.1b–e. GQDs tightly covered the nanosized sulfur particles’ surface, which
was demonstrated through lattice fringes in corresponding with (111) planes.
Electrochemical Exfoliation. GQDs and C-Dots can be prepared by electrochemical cutting of carbon precursors like carbon nanotubes, rGO film, graphite rods, and
3-dimensional (3D) CVD-grown graphene. Meanwhile, it has been suggested that
OH· radical and O· radical formed on the basis of oxidation of water at the anode
function as electrochemical “scissors” for the sake of the releasion of GQDs or C-dots
(Lu et al. 2009). Some corrosion processes could be started near the edges and sped
up at defect sites. When using organic solvents, Ananthanarayanan et al. ascribed
the desquamation process to the capability of the electrolytic anion to insert between
graphene layers and the electrical stress (Ananthanarayanan et al. 2014). Functional
groups or heteroatoms can be adhibited or doped on the synthetic carbon nanodots
lying on the used electrolyte (Li et al. 2012c). The abovementioned electrochemical
strategy is uncomplicated (mainly one step) and usually of high yield.
Physical Routes. Microwave extraction provides rapid and even heating for the
reaction medium, then considerably enhancing the reaction rate and making the
product yields and quality better (Li et al. 2012a) Ultrasound may generate alternant
high-pressure and low-pressure waves in fluid, resulting in the formation and severe