14
2 Synthesis of Quantum Dots
(León and Pacheco 2011) h-BN, (Beheshtian et al. 2013) layered double hydroxides (LDHs), (Tokudome et al. 2016) molybdenum diselenide (MoSe 2 ) and tungsten
diselenide (WSe 2 ), etc. (Huang and Kelley 2000). Such semiconductor nanoclusters
represent clear quantum confinement effects, and thus are also classified as “QDs”
(Mainwaring et al. 2006). The as-prepared QDs are usually regarded as zero dimensional (0D), however, they are just smaller forms of their native layered forms in
terms of the lateral length dimension. Their 2D lattices in the bulk form can be still
maintained by a certain degree when they are exfoliated into the nanoscale. Therefore, herein, “2D-QDs” is reasonably used as an abbreviation for “QDs derived from
2D inorganic materials” (Wang et al. 2016).
The burgeoning GQDs and C-dots have attained great attention due to their enormous development prospect with respect to biomedical applications. These illuminant carbon nanocrystals supply optical sensing and biological imaging with unprecedented opportunities. Owing to their small dimension and great biocompatibility,
they could also function as effective carriers in the application of drug delivery
when allowing isochronous visual control of releasing dynamics. What’s more, their
distinctive catalytic and physicochemical performance promise various applications
in field of biomedicine. There have been already several preeminent review articles
in regard to syntheses, performance, and application prospect of C-dots (Baker and
Baker 2010) and GQDs (Zhang et al. 2012b).
Meanwhile, preparation of C-dots and GQDs may be ordinarily split into “topdown” method and “bottom-up” method. The former involves making carbonaceous
materials cut or broken down through some approaches on basis of chemistry, electrochemistry, or physics. The latter is actualized by making small organic molecules thermally decomposed and carbonized or by making small aromatic molecules gradually
chemically fused (Zheng et al. 2015).
2.1.1 Top-Down Method
Acidic Oxidation. Some methods have been extensively used to make C-dots and
GQDs exfoliated from carbon fiber, carbon nanotube, (Tao et al. 2012) graphene
oxide (GO), (Wang et al. 2011) soot, (Liu et al. 2007) coal, (Ye et al. 2013) carbon
black, (Xia and Zheng 2012) and activated carbon, (Qiao et al. 2009) such as strong
acid treatment. These methods are suitable for large-scale processable production
from easily accessible low-cost carbon source. When using these methods, it is
unavoidable to introduce oxygenated groups with a negative charge on the resultant
C-dots, which makes them defective in graphitic structure and hydrophilic. One
problem often met is that it is difficult to make excess oxidizing agent (e.g., HNO 3 )
completely removed.
Hydrothermal or Solvothermal Synthesis. Hydrothermal synthesis quintessentially uses reduced GO (rGO) sheets working as the precursors with a thermal method,
and the precursors are heretofore treated with oxidizer (e.g., HNO 3 , O 3 ), introducing epoxy groups onto the carbon lattice and ascertaining the cutting sites. In
2 Synthesis of Quantum Dots
(León and Pacheco 2011) h-BN, (Beheshtian et al. 2013) layered double hydroxides (LDHs), (Tokudome et al. 2016) molybdenum diselenide (MoSe 2 ) and tungsten
diselenide (WSe 2 ), etc. (Huang and Kelley 2000). Such semiconductor nanoclusters
represent clear quantum confinement effects, and thus are also classified as “QDs”
(Mainwaring et al. 2006). The as-prepared QDs are usually regarded as zero dimensional (0D), however, they are just smaller forms of their native layered forms in
terms of the lateral length dimension. Their 2D lattices in the bulk form can be still
maintained by a certain degree when they are exfoliated into the nanoscale. Therefore, herein, “2D-QDs” is reasonably used as an abbreviation for “QDs derived from
2D inorganic materials” (Wang et al. 2016).
The burgeoning GQDs and C-dots have attained great attention due to their enormous development prospect with respect to biomedical applications. These illuminant carbon nanocrystals supply optical sensing and biological imaging with unprecedented opportunities. Owing to their small dimension and great biocompatibility,
they could also function as effective carriers in the application of drug delivery
when allowing isochronous visual control of releasing dynamics. What’s more, their
distinctive catalytic and physicochemical performance promise various applications
in field of biomedicine. There have been already several preeminent review articles
in regard to syntheses, performance, and application prospect of C-dots (Baker and
Baker 2010) and GQDs (Zhang et al. 2012b).
Meanwhile, preparation of C-dots and GQDs may be ordinarily split into “topdown” method and “bottom-up” method. The former involves making carbonaceous
materials cut or broken down through some approaches on basis of chemistry, electrochemistry, or physics. The latter is actualized by making small organic molecules thermally decomposed and carbonized or by making small aromatic molecules gradually
chemically fused (Zheng et al. 2015).
2.1.1 Top-Down Method
Acidic Oxidation. Some methods have been extensively used to make C-dots and
GQDs exfoliated from carbon fiber, carbon nanotube, (Tao et al. 2012) graphene
oxide (GO), (Wang et al. 2011) soot, (Liu et al. 2007) coal, (Ye et al. 2013) carbon
black, (Xia and Zheng 2012) and activated carbon, (Qiao et al. 2009) such as strong
acid treatment. These methods are suitable for large-scale processable production
from easily accessible low-cost carbon source. When using these methods, it is
unavoidable to introduce oxygenated groups with a negative charge on the resultant
C-dots, which makes them defective in graphitic structure and hydrophilic. One
problem often met is that it is difficult to make excess oxidizing agent (e.g., HNO 3 )
completely removed.
Hydrothermal or Solvothermal Synthesis. Hydrothermal synthesis quintessentially uses reduced GO (rGO) sheets working as the precursors with a thermal method,
and the precursors are heretofore treated with oxidizer (e.g., HNO 3 , O 3 ), introducing epoxy groups onto the carbon lattice and ascertaining the cutting sites. In