18
2 Synthesis of Quantum Dots
simple combustion, plasma (Wang et al. 2012; Kim and Suh 2014) and microwave
(Yin et al. 2013) can be used. These approaches are uncomplicated, cost-efficient,
extensible, and allow heteroatoms to naturally inherit from the precursors.
2.1.3 Synthetic or Post-synthetic Strategies
2.1.3.1 Size and Shape Control
As described by Sk and his co-workers, PL transmission of a GQD is determined
by its size in large part, and its shape to some extent (Sk et al. 2014). Stepwise
organic synthesis can control both shape and size of synthetic GQDs precisely. Lu
et al. prepared well-defined GQDs by mean of cage-opening of C60 molecules with
ruthenium catalysis (Yan et al. 2010b). The appearance of the GQDs could be tailored
to various shapes, such as triangular, parallelogram, trapezoid, hexagon, mushroom,
and so on, with the different density of carbon clusters and the change in annealing
temperature. C-dots with well defined and controllable size have been achieved by
templated pyrolysis on the basis of organic precursors (Lu et al. 2011). While a copolymer serves as soft template to provide C-dots with restrictions, the structure of
mesoporous silica with order that functions as hard template prevents aggregation.
C-dots prepared upon the foundation of single-chain polymeric nanoparticles as
well have narrow distribution of size (Liu et al. 2011). Post-synthesis separation
techniques like dialysis, gel electrophoresis, (Zhu et al. 2013) ultra-filtration, (Xia
and Zheng 2012) column chromatography, (Zheng et al. 2013) or anion-exchange
high-performance liquid chromatography (Li et al. 2010) can be used in order to
reduce the dimensional changes. For instance, polyacryalamide gel electrophoresis
(PAGE) already has been applied to split as-prepared C-dots up into fluorescent
bands of nine with the emission peak range of 415 nm (violet) to 615 nm (orangered), which indicates the advantage of gel electrophoresis to obtain multicolor C-dots
with monodisperse (Vinci et al. 2013).
2.1.3.2 Surface Engineering
Controlling Oxidation. On the one side, oxygenated functional groups upon
C-dots make them hydrophilic and supply further functionalization with convenient
chemical handles. On the other side, these groups serve as surface emissive traps,
causing the decrease of the PL efficiency. Hence, the characters of these nanodots
could be tailored by the control of the degree of their oxidation. Besides, it has been
illustrated that reducing oxygenated GQDs can improve quantum yield (QY) while
oxidizing GQDs makes the emission red-shift. For instance, the green microwavesynthesized GQDs with NaBH 4 reducing made the emission shift to blue and a
onefold increase in the QY.
2 Synthesis of Quantum Dots
simple combustion, plasma (Wang et al. 2012; Kim and Suh 2014) and microwave
(Yin et al. 2013) can be used. These approaches are uncomplicated, cost-efficient,
extensible, and allow heteroatoms to naturally inherit from the precursors.
2.1.3 Synthetic or Post-synthetic Strategies
2.1.3.1 Size and Shape Control
As described by Sk and his co-workers, PL transmission of a GQD is determined
by its size in large part, and its shape to some extent (Sk et al. 2014). Stepwise
organic synthesis can control both shape and size of synthetic GQDs precisely. Lu
et al. prepared well-defined GQDs by mean of cage-opening of C60 molecules with
ruthenium catalysis (Yan et al. 2010b). The appearance of the GQDs could be tailored
to various shapes, such as triangular, parallelogram, trapezoid, hexagon, mushroom,
and so on, with the different density of carbon clusters and the change in annealing
temperature. C-dots with well defined and controllable size have been achieved by
templated pyrolysis on the basis of organic precursors (Lu et al. 2011). While a copolymer serves as soft template to provide C-dots with restrictions, the structure of
mesoporous silica with order that functions as hard template prevents aggregation.
C-dots prepared upon the foundation of single-chain polymeric nanoparticles as
well have narrow distribution of size (Liu et al. 2011). Post-synthesis separation
techniques like dialysis, gel electrophoresis, (Zhu et al. 2013) ultra-filtration, (Xia
and Zheng 2012) column chromatography, (Zheng et al. 2013) or anion-exchange
high-performance liquid chromatography (Li et al. 2010) can be used in order to
reduce the dimensional changes. For instance, polyacryalamide gel electrophoresis
(PAGE) already has been applied to split as-prepared C-dots up into fluorescent
bands of nine with the emission peak range of 415 nm (violet) to 615 nm (orangered), which indicates the advantage of gel electrophoresis to obtain multicolor C-dots
with monodisperse (Vinci et al. 2013).
2.1.3.2 Surface Engineering
Controlling Oxidation. On the one side, oxygenated functional groups upon
C-dots make them hydrophilic and supply further functionalization with convenient
chemical handles. On the other side, these groups serve as surface emissive traps,
causing the decrease of the PL efficiency. Hence, the characters of these nanodots
could be tailored by the control of the degree of their oxidation. Besides, it has been
illustrated that reducing oxygenated GQDs can improve quantum yield (QY) while
oxidizing GQDs makes the emission red-shift. For instance, the green microwavesynthesized GQDs with NaBH 4 reducing made the emission shift to blue and a
onefold increase in the QY.