22
2 Synthesis of Quantum Dots
was added to form a mixed solution. After vigorous stirring for 4 h at 60 °C, buff and
sticky polymer solution was obtained for the subsequent electrospinning process. As
for a typical electrospinning process, the spinneret had an inner diameter of 0.6 mm.
Grounded aluminum strips with parallel gaps of about 1 cm were used as collectors. A
distance of 15 cm and a direct current voltage of 18 kV were maintained between the
tip of the spinneret and the collector. The as-electrospinning SnCl 2 /PAN nanofibers
(denoted as SnCl 2 -PAN) were dried for 24 h in vacuum at 60 °C. The dried SnCl 2 -
PAN were further annealed in an air-circulated oven at 280 °C for 2 h at a heating
rate of 2 1C min
−1 , and then 62 Zhang et al. annealed in a N2 flow at 800 1C for
1 h at a heating rate of 5 1C min1. The annealed product was designated as Sn
QDs@CNFs. The preparation process of the N-doped CNFs was the same as the
method of Sn QDs@CNFs, just without the addition of SnCl 2 · 2H 2 O. Ag-LTO/TiO 2
NSs were synthesized by Ge et al. (2016) through a facile hydrothermal process, and
subsequently, AgNO 3 was then calcinated and thermally decomposed; ultrasonic
treatment was used to disperse Ag (Fig. 2.2f).
2.2.3 Hydrothermal Reaction
Due to the feature of high purity in the production of particles, good dispersion, good
and controllable crystal shape and low production cost, hydrothermal synthesis is
also an effective method (Zubair et al. 2017). Han and co-workers (2013) published
a two-step solution phase synthesis procedure to obtain the V 2 O 5 QD/graphene
hybrid (VQDG) nanocomposite by controlling the nucleation and growth procedures (Fig. 2.2 g). A two-step solution phase process was used to synthesize the
VQDG with the as-prepared rGO suspension (∼0.1 mg mL
−1 ). The vanadium sol
and aniline were mixed in a 100 mL beaker and stirred at room temperature for
30 min with the molar ratio of 1:0.03. Next, 13 mL rGO suspension was added into
the mixture and stirred at 80 °C for 24 h. The sample was then transferred into a
100 mL autoclave and heated at 180 °C for 48 h. After washed and dried at 80 °C
for 24 h, a blackish yellow powder was obtained.
2.3 Nonmetallic Quantum Dots
2.3.1 Mechanical Crushing Method
The mechanical crushing method is a direct method to grind bulk to nanometer
scale. Rangasamy et al. exhibited graphene/Si-CuO quantum dots (Gr/Si-CuO QD)
layered structure. Si nanopowder was prepared by mechanical crushing process.
In order to synthesize Si quantum dots (QD), the crushed Si powder (0.2 g) was
mixed with (100 mL) DI water: (10 mL) HF solution followed by sonication for
2 Synthesis of Quantum Dots
was added to form a mixed solution. After vigorous stirring for 4 h at 60 °C, buff and
sticky polymer solution was obtained for the subsequent electrospinning process. As
for a typical electrospinning process, the spinneret had an inner diameter of 0.6 mm.
Grounded aluminum strips with parallel gaps of about 1 cm were used as collectors. A
distance of 15 cm and a direct current voltage of 18 kV were maintained between the
tip of the spinneret and the collector. The as-electrospinning SnCl 2 /PAN nanofibers
(denoted as SnCl 2 -PAN) were dried for 24 h in vacuum at 60 °C. The dried SnCl 2 -
PAN were further annealed in an air-circulated oven at 280 °C for 2 h at a heating
rate of 2 1C min
−1 , and then 62 Zhang et al. annealed in a N2 flow at 800 1C for
1 h at a heating rate of 5 1C min1. The annealed product was designated as Sn
QDs@CNFs. The preparation process of the N-doped CNFs was the same as the
method of Sn QDs@CNFs, just without the addition of SnCl 2 · 2H 2 O. Ag-LTO/TiO 2
NSs were synthesized by Ge et al. (2016) through a facile hydrothermal process, and
subsequently, AgNO 3 was then calcinated and thermally decomposed; ultrasonic
treatment was used to disperse Ag (Fig. 2.2f).
2.2.3 Hydrothermal Reaction
Due to the feature of high purity in the production of particles, good dispersion, good
and controllable crystal shape and low production cost, hydrothermal synthesis is
also an effective method (Zubair et al. 2017). Han and co-workers (2013) published
a two-step solution phase synthesis procedure to obtain the V 2 O 5 QD/graphene
hybrid (VQDG) nanocomposite by controlling the nucleation and growth procedures (Fig. 2.2 g). A two-step solution phase process was used to synthesize the
VQDG with the as-prepared rGO suspension (∼0.1 mg mL
−1 ). The vanadium sol
and aniline were mixed in a 100 mL beaker and stirred at room temperature for
30 min with the molar ratio of 1:0.03. Next, 13 mL rGO suspension was added into
the mixture and stirred at 80 °C for 24 h. The sample was then transferred into a
100 mL autoclave and heated at 180 °C for 48 h. After washed and dried at 80 °C
for 24 h, a blackish yellow powder was obtained.
2.3 Nonmetallic Quantum Dots
2.3.1 Mechanical Crushing Method
The mechanical crushing method is a direct method to grind bulk to nanometer
scale. Rangasamy et al. exhibited graphene/Si-CuO quantum dots (Gr/Si-CuO QD)
layered structure. Si nanopowder was prepared by mechanical crushing process.
In order to synthesize Si quantum dots (QD), the crushed Si powder (0.2 g) was
mixed with (100 mL) DI water: (10 mL) HF solution followed by sonication for