Synthesis of i III VI semiconductor nanoparticles and their applications

SYTHESIS OF I-III-VI SEMICONDUCTOR
NANOPARTICLES AND THEIR APPLICATIONS



TANG XIAOSHENG
(Master of Engineering, University of Science and
Technology of China)




A THESIS SUBMITTED
FOR THE DOCTOR OF PHILOSOPHY
DEPARTMENT OF MATERIALS SCIENCE &
ENGINEERING
NATIONAL UNIVERSITY OF SINGAPORE
2013



i

Acknowledgements
First and foremost, I would like to express my deepest and sincerest gratitude to
my supervisor, Dr. Xue Junmin, for offering me this wonderful opportunity to pursue
my PhD degree. His enthusiasm, integrity, and dedication for scientific research have
been a major influence on me. I have benefited tremendously from his immense

knowledge, insightful intuition, patient guidance and encouragements throughout of
years of my study.
Secondly, I would like to thank my co-supervisor, Dr. Gregory K.L. Goh, from
Institute of Materials Research and Engineering. He helped me so much on my
research work.
I will take this opportunity to appreciate the friendship and support from my
group colleagues, Dr. Eugene Choo Shi Guang, Sheng Yang, Yuan Jiaquan, Chen Yu,
Erwin, Li Meng and Lee Wee Siang Vincent. Thanks to Dr. Eugene Choo Shi Guang,
he gave me some good advice and taught me how to operate equipments in our
department.
I wish to express my sincere gratitude to our department staffs, Mr. Chen Qun,
Ms. Lim Mui Keow Agnes, Dr. Zhang Jixuan, Dr. Yin Hong, Ms. Yang Fengzhen, Mr.
Henche Kuan, Ms. Chooi Kit Meng Serene, Ms. He Jian, and Mr. Chan Yew Weng
for their support. They have always been helpful, providing trainings for utilizing the
technical facilities. Without their support my research work would not have been
possible to proceed.
ii

My Sincere thanks to Miss. Tay Qiuling, from Nanyang Technological University,
Miss Tan Hui Ru, from Institute of Materials Research and Engineering, and Dr. Yu
Kuai, from NUS Graduate School for Integrative Sciences and Engineering; they
warmly helped and discussed with me in the photocatalystic testing and TEM
characterization.
I am grateful to my dear friends, Dr. Wang Yu, Dr. Yuan Du, Dr. Zhang Xiaoxin,
Dr. Ma Yuwei, Dr. Wang Yinxiao, Mrs. Ran Min, Mr. Neo Chin Yong, … The joyful
conversations with them and encouragement from them in the past a few years.
Last but not least, I deeply owe to my dear parents for their unconditional love and
to my wife Liu Congrong for her endless support and loving care, and my son Tang
Jixuan.

iii

Table of Contents
Acknowledgements i
Table of Contents iii
Summary vi
List of Tables and Schemes ix
List of Figures x
List of Abbreviations xvi
List of Symbols xviii
Chapter 1 Introduction 1
1.1 General properties of semiconductor nanomaterials 1
1.1.1 Size dependent optical properties of semiconductor nanoparticles 1
1.2 Current progress of semiconductor nanoparticles 3
1.2.1 Core-shell semiconductor nanoparticles 3
1.2.2 Doping of semiconductor nanoparticles 5
1.2.3 Composition of semiconductor nanoparticles 5
1.3 I-III-VI semiconductor nanoparticles 7
1.3.1 Methods to prepared I-III-VI nanoparticles 7
1.4 Design and applications 9
1.4.1 QDs as in vivo probes 9
1.4.2 Two-photon cell labeling by QDs 11
1.4.3 Semiconductor nanomaterials for hydrogen production 12
1.5 Research objectives 13
Chapter 2 Experimental techniques 24
2.1 Materials 24
2.2 Phase transfer of hydrophobic nanoparticles 24
2.2.1 Phase Transfer of the hydrophobic CuInS
2
-ZnS nanocubes 24

2.2.2 Phase transfer of hydrophobic Zn-doped AgInS
2
nanocrystals 25
2.2.3 Preparation of water-soluble AgInS
2
-ZnS nanoparticles 25
2.3 Characterization 26
2.3.1 Chemical analysis 26
iv

2.3.2 Morphological study 27
2.3.3 Optical properties 28
2.3.4 Cell viability assays 29
2.3.5 Cell labeling 30
2.3.6 Photocatalytic reactions 31
Chapter 3 CuInS
2
–ZnS Nanocubes with High Tunable Photoluminescence 33
3.1 Introduction 33
3.2 Synthesis of CuInS
2
-ZnS nanocrystals 34
3.3 Results and discussion 35
3.3.1 Characterization of the structure of CuInS
2
-ZnS nanocubes 35
3.3.2 Optical property of CuInS
2
-ZnS cube 41
3.3.3 Biological application of CuInS

2
-ZnS nanocubes 44
3.4 Summary 47
Chapter 4 Zn doped AgInS
2
Nanocrystals and Their Fluorescence Properties 51
4.1 Introduction 51
4. 2 Experiment procedures 53
4.2.1 Synthesis of AgInS
2
and Zn-doped AgInS
2
nanocrystals 53
4.3 Results and discussion 54
4.3.1 Characterization of the structure of Zn-doped AgInS
2
nanoparticles 54
4.3.2 Optical property of Zn-doped AgInS
2
nanocrystals 61
4.3.3 Biological application Zn-doped AgInS
2
nanocrystals 66
4. 4 Conclusions 67
4.5 References 69
Chapter 5 AgInS
2
-ZnS Heterodimers with Tunable Photoluminescence 71
5.1 Introduction 71
5.2 Synthesis of AgInS

2
-ZnS nanocrystals 72
5.3.1 Characterization of the structure of AgInS
2
-ZnS heterodimer 73
5.3.2 Optical properties of AgInS
2
-ZnS heterodimer 83
5.3.3 Cell labeling using AgInS
2
-ZnS heterodimer 88
Chapter 6 Cu-In-Zn-S Nanoporous Spheres for Highly Efficient Hydrogen Evolution 96
v

6.1 Introduction 96
6.2 Preparation of CIZS nanoporous spheres 98
6.3 Results and discussions 98
6.3.1Characterization of the structure of CuInZnS spheres 98
6.3.2 Hydrogen production using CuInZnS spheres as photocatalyst 104
6.4 Conclusions 105
Chapter 7 CuInZnS-Decorated Graphene Nanocomposites for Highly Efficient
Hydrogen Production 108
7.1 Introduction 108
7.2 Experimental 110
7.2.1 Preparation of CuInZnS nanospheres 110
7.2.2 Preparation of graphene oxides (GO) 110
7.2.3 Preparation of CIZS-rGO nanocomposites 111
7.3 Results and discussion 112
7.3.1Characterization of the structure of CuInZnS-Decorated Graphene
nanocomposites 112

7.3.2 Hydrogen production using CuInZnS-Decorated Graphene nanocomposites as
photocatalyst 124
7.4 Conclusions 130
7.4 References 132
Chapter 8 Conclusions and Future Work 134
8.1 Conclusions 134
8.2 Future Work 137
8.3 References 139


vi

Summary
In this thesis, the research work focused on the fabrication of I-III-VI
semiconductor nanoparticles and their applications on biological cell labeling and
hydrogen production by water splitting. Firstly, zinc-doped CuInS
2
and AgInS
2
nanoparticles with different shapes including the cube, sphere and heterodimer
structures were prepared by hot-injection method. Corresponding photoluminescent
(PL) properties of Zn-doped AgInS
2
and CuInS
2
nanoparticles were studied by
lifetime measurement and ultrafast laser. The high quality two-photon PL was further
used in the application of two-photon cell labeling. Secondly, Cu-In-Zn-S
nanospheres and CuInZnS microstructures-graphene composites were prepared
through a template-free hydrothermal method. The as-prepared product with tunable

absorption was used as a photocatalyst for hydrogen production under the illumination
of visible light, which displayed high photocatalytic efficiency.
For the I-III-VI alloy semiconductor nanoparticles, three studies were done. The
first study investigated CuInS
2
-ZnS alloyed nanocubes. The CuInS
2
-ZnS nanocubes
with tunable emissions from 548 to 678 nm were prepared by diffusing Zn ions into
CuInS
2
nanocrystal seeds. They also displayed high quality two-photon fluorescence.
Based on the strong PL, the cell imagings excited by either 365 nm UV or 800 nm
infrared lasers were demonstrated. The successful synthesis of the CuInS
2
-ZnS
alloyed nanocubes provided the premise for future investigation of alloyed systems
arising from the I-III-VI
2
group semiconductors. The second study developed a facile
solution method to synthesize Zn-doped AgInS
2
nanoparticles. The as-obtained
vii

Zn-doped nanoparticles showed strong PL emissions in the visible band from 520 to
680 nm. The nanocrystals with high quantum yield demonstrate promising
applications in cell imaging. The third study discussed AgInS
2
–ZnS heterodimer

nanostructures. PL emission of the AgInS
2
–ZnS heterodimers was finely tuned from
green to red by the diffusion Zn into AgInS
2
nanoparticles through adjusting the
intermediate temperature from 90
o
C to 180
o
C. Moreover, the heterodimers showed
well defined two photon fluorescence (TPF) properties. Finally, the cell imaging using
AgInS
2
-ZnS excited by either UV or infrared light was successfully demonstrated.
For the I-III-VI semiconductor microstrues, two main studies were conducted. In
the first study, we synthesized Cu-In-Zn-S nanospheres by a template free and facile
method. The band gap of the Cu-In-Zn-S nanospheres could be tuned by the amount
of Cu doping. Moreover, the mesopous nanostructure of the Cu-In-Zn-S nanospheres
exhibited excellent photocatalytic activity for hydrogen production from water
without any co-catalyst. This work demonstrated the potential of industrial hydrogen
production with a low-cost method in the field of solar energy conversion. In the
second study, we synthesized CuInZnS-rGO nanocomposites with high efficiency of
the photocatalytic H
2
from water splitting under visible light by a solvothermal
method. The CuInZnS-rGO nanocomposites displayed a high visible light
photocatalytic H
2
production rate of 3.8 mmol/h·g with 0.5 wt% Pt as a co-catalyst,

which was the highest productivity for the Cu-In-Zn-S system. Furthermore, this work
demonstrated the use of graphene as a support for Cu-In-Zn-S microstructure in
photocatalytic hydrogen production. This provided a potential application of
viii

graphene-based materials in the field of solar energy conversion.

ix

List of Tables and Schemes
Table 3. 1 Elemental Analysis of the CuInS
2
-ZnS nanocubes by ICP-OES. 37

Scheme 4. 1 Schematic illustration showing the synthesis of Zn-doped AgInS
2

nanocrystals at different diffusion temperatures. 54

Scheme 5. 1 Schematic illustration showing the synthesis of AgInS
2
-ZnS
heterodimers using a hot injection method. 73

Table 5. 1 ICP analysis of chemical compositions of the heterodimers using
different intermediate temperatures. 81
Table 5. 2 EDX analysis of chemical compositions of the heterodimers obtained
using different intermediate temperatures 82

Table 6. 1 BET specific surface area analysis of the spheres with different

amounts of Cu-doping. 103

Table 7. 1 BET surface areas of the obtained CIZS-rGO nanocomposites. 123


x

List of Figures
Figure 1. 1 A), Wide field HRTEM micrograph of Zn
0.67
Cd
0.33
Se nanocrystals. B)
PL spectra with excitation of 365 nm for the Zn
x
Cd
1-x
Se nanocrystals with
Zn mole fractions of (a) 0, (b) 0.28, (c) 0.44, (d) 0.55, (e) 0.67 [77] 7
Figure 1. 2 A) HRTEM image of single ZnS-AgInS
2
solid solution nanoparticle,
B) photographs of UV-illuminated ZAIS nanoparticles solutions. [36] 8
Figure 1. 3 Photoluminescence properties of CuInS2/ZnS core-shell nanocrystals
[80]. 9
Figure 1. 4 Cross section of dual-labeled sample examined with a Bio-Rad 1024
MRC laser-scanning confocal microscope with a 40x oil 1.3 numerical
aperture objective. [73] 10
Figure 1. 5 Two-photon fluorescence labeling of HeLa cancer cells after
uptaking water solube CdSe@AsS QDs for 2h. [99] 11

Figure 1. 6 Low and high magnification TEM images and XEDS maps (orange
= Zn, green = In and yellow = Ag) for ZnIn
0.23
Ag
0.04
S
1.365.
[117] 13

Figure 3. 1 XRD pattern of CuInS
2
seeds formed at 120
o
C. (Tetragonal CuInS
2
,
JCPDS card No. 85-1575) 36
Figure 3. 2(A) XRD pattern of the obtained CuInS
2
-ZnS alloyed nanocubes with
zinc mole fraction of 62%. (B) TEM images of the as-obtained CuInS
2
-ZnS
alloyed nanocubes. Inset: Corresponding SAED pattern of the sample. (C)
The magnified TEM image of CuInS
2
-ZnS alloyed nanocubes. Inset is the
cubic model. (D) EDX spectrum of the obtained CuInS
2
-ZnS nanocubes

with zinc mole fraction of 62%. Four elements, Cu, In, Zn S were detected.
(E) HRTEM of a single CuInS
2
-ZnS alloyed nanocube. (F) The
corresponding fast Fourier transform (FFT) image from area (E). 39
Figure 3. 3 Histograms of size distributions of the CuInS
2
-ZnS alloyed
nanocubes with different mole fractions of zinc, (A) 62%, (B) 52%,(C) 38%,
respectively. 39
Figure 3. 4 TEM images of the CuInS
2
-ZnS alloyed nanocubes with zinc mole
fractions of (A) 52% and (B) 38%, respectively. 40
Figure 3. 5 The absorption spectra of the CuInS
2
-ZnS alloyed nanocubes with
different zinc mole fractions (A) 62%, (B) 52% and (C) 38%, respectively.
41
Figure 3. 6 (A) PL spectra of the CuInS
2
-ZnS alloyed nanocubes with different
zinc mole fractions of 62%, 52% and 38%, respectively. The measurements
were under excitation of 365 nm UV. The inset is the digital photograph of
the samples in toluene under excitation of 365 nm. (B) Upconversion
spectra of the CuInS
2
-ZnS alloyed nanocubes with different zinc mole
fractions of 62%, 52% and 38%, respectively. The measurements were
under excitation of 800 nm laser. The inset is the digital photograph of the

samples in toluene under excitation of 800 nm. 42
xi

Figure 3. 7 PL emission spectra of the CuInS
2
-ZnS alloyed nanocubes with zinc
mole fractions (A) 62%, (B) 52% and (C) 38 %, respectively, in comparison
with the standard rhodamine 6G ethanol solution (QY=95%) or rhodamine
101 ethanol solution (QY=100%). The quantum yields of the nanocubes
were (A) 39%, (B) 37% and (C) 34%, respectively. 42
Figure 3. 8 PL relaxation of the nanocubes with zinc mole fraction of 38%, as
compared to that of the pure CuInS
2
nanoparticles. Inset is the photograph
of pure CIS nanoparticles under UV-365nm lamp. 43
Figure 3. 9 (A) Upconversion emission of the CuInS
2
-ZnS alloyed nanoparticles
with zinc mole fraction of 52% with various input powers. (B) The
corresponding quadratic dependence of integrated fluorescence intensity
with the input power of laser, showing that the upconversion mechanism is
two- photon. 44
Figure 3. 10 (A) Digital photographs of the CuInS
2
-ZnS alloyed nanocubes
dispersed in water under excitation of 365 nm UV. (B) The digital
photographs of the nanocubes with zinc mole fraction of 38% dispersed in
water and toluene mixtures, demonstrating that the nanocubes could be
dispersed in water completely after phase transfer. (C) PL spectra of the
CuInS

2
-ZnS nanocubes after phase transfer, in comparison with those of the
nanocubes before phase transfer. (D) The fluorescent image of the OCA17
cells labeled with the CuInS
2
-ZnS nanocubes with zinc mole fraction of 62%
under 365 nm UV excitation. (E) Multi-photon fluorescent image of
NIH/3T3 cells labeled with the nanocubes with zinc mole fraction of 38%
upon excitation of 800 nm laser. 46

Figure 4. 1 (A) XRD pattern of the AgInS
2
nanocrystals obtained at 120
o
C, (B)
XRD pattern of the Zn-doped AgInS
2
nanocrystals by diffusing Zn into the
pre-formed AgInS
2
at 120
o
C, (C) EDX spectra of the pure AgInS
2
and
Zn-doped AgInS
2
nanocrystals, (D) TEM image of the AgInS
2
nanocrystals

obtained at 120
o
C (Inset: digital photograph showing the weak red emission
of the pure AgInS
2
nanocrystals under UV excitation) and (E) TEM image
showing the Zn-doped AgInS
2
nanocrystals obtained at 120
o
C (Inset:
histogram showing the size distribution of the nanocrystals). 56
Figure 4. 2 XPS spectra of (A) Ag 3d, (B) In 3d, (C) S 2p, (D) Zn 2p3. 57
Figure 4. 3 (A) ICP analysis showing the chemical compositions of the Zn-doped
AgInS
2
nanocrystals prepared at different diffusion temperatures. (B, C and
D) TEM images of Zn-doped AgInS
2
nanoparticles prepared at 150
o
C, 180
o
C and 210
o
C, respectively (Insets: histograms showing the size
distribution of the nanocrystals). 59
Figure 4. 4 (A) The absorption spectra (B) PL spectra of the Zn-doped AgInS
2

nanocrystals prepared at 120
o
C, 150
o
C, 180
o
C and 210
o
C, respectively,
(C) the corresponding digital photographs of the Zn-doped AgInS
2

nanocrystals dispersed in toluene under excitation of 365 nm UV. 60
Figure 4. 5 (A) PL emission spectra of the aqueous Zn doped AgInS
2
alloy
xii

nanoparticles prepared at 210
o
C versus the standard rhodamine 6G ethanol
solution (QY=95%), (B) PL emission spectra of the Zn doped AgInS
2
alloy
nanoparticles at 180
o
C versus the standard rhodamine 6G ethanol solution
(QY=95%), (C) PL emission spectra of the Zn doped AgInS
2
alloy

nanoparticles at 150
o
C, versus the standard rhodamine 101 ethanol solution
(QY=100%) and (D) PL emission spectra of the Zn doped AgInS
2
alloy
nanoparticles at 120
o
C, versus the standard rhodamine 101 ethanol solution
(QY=100%). The quantum yields of the four alloy nanoparticles were 17%,
16%, 15% and 12%, respectively. 62
Figure 4. 6 (A) PL relaxations of the Zn-doped AgInS
2
nanocrystals prepared at
120
o
C, 150
o
C, 180
o
C and 210
o
C, respectively and (B) Table showing the
fit parameters of the relaxation plots. The fit parameters are derived from
the equation: I(t) = A
1
exp(-t/

1
) + A

2
exp(-t/

2
). 64
Figure 4. 7 Transient absorption spectra of Zn-doped AgInS
2
nanocrystals at
different time delays. 64
Figure 4. 8 Single-wavelength dynamics of Zn-doped AgInS
2
nanocrystals.
Pump wavelength used is 400 nm, Probe wavelengths are indicated in the
figure. 65
Figure 4. 9 (A) PL spectra of the Zn-doped AgInS
2
nanocrystals in water under
excitation of 365 nm UV, (B) the digital photograph showing the emissions
of the Zn-doped AgInS
2
nanocrystals in water under 365 nm UV excitation
and (C) The fluorescent image of the NIH/3T3 cells labeled with Zn-doped
AgInS
2
nanocrystals with green emission under 365 nm UV excitation
(Inset: cell imaging with higher magnification). 67

xiii

Figure 5. 1 TEM images of (A) AgInS

2
nanoparticles synthesized at 90
o
C, (B)
AgInS
2
-ZnS heterodimers prepared at 210
o
C for 2 hours. The zinc source
was injected at 90
o
C. (C) HRTEM of an AgInS
2
-ZnS heterodimer and the
inset is the schematic representation of the heterodimer. (D) XRD patterns
of (a) pure AgInS
2
nanoparticles and (b) AgInS
2
-ZnS heterodimers. 74
Figure 5. 2 The XRD pattern of the AgInS
2
-ZnS heterodimers synthesized using
the intermediate temperature of 90
o
C, in comparison with the standard
XRD patterns of chalcopyrite AgInS
2
and cubic ZnS. 76
Figure 5. 3 EDX spectrum of the AgInS

2
-ZnS heterodimers prepared at 210
o
C
for 2 h. The zinc source was injected at 90
o
C. 76
Figure 5. 4 (A) PL spectra of (a) the pure AgInS
2
nanoparticles without visible
emission observed, represented by the dashed line (b) the AgInS
2

nanoparticles at 210
o
C for 30 s upon zinc injection (c) the AgInS
2

nanoparticles synthesized at 210
o
C for 30 mins upon zinc injection (d) the
AgInS
2
-ZnS heterodimers synthesized at 210
o
C for 2 hours upon zinc
injection. (B) The corresponding digital photographs of the four samples
under excitations of day light and UV, respectively. 78
Figure 5. 5 A series of HRTEM images of a typical heterodimer at different
focus stages, presenting the structure evolution of the heterodimer with

electron beam energy input. 79
Figure 5. 6 TEM images of AgInS
2
-ZnS heterodimers prepared using different
intermediate temperatures (A) 120
o
C, (B) 150
o
C and (C) 180
o
C
respectively; Insets are HRTEM images of the single AgInS
2
-ZnS
heterodimer circled by red dot line. The scale bar is 2 nm. (D) XRD patterns
of AgInS
2
-ZnS heterodimers prepared using different intermediate
temperatures of 90
o
C, 120
o
C, 150
o
C, 180
o
C, respectively. 83
Figure 5. 7 The absorption spectra of AgInS
2
-ZnS heterodimers synthesized

using the intermediate temperature of 90
o
C, 120
o
C, 150
o
C and 180
o
C,
respectively. 84
Figure 5. 8 (A) Photography pictures and (B) PL spectra of the AgInS
2
-ZnS
heterodimers with different emissions dispersed in toluene under excitation
of 365 nm. 85
Figure 5. 9 (A) PL emission spectra of the AgInS
2
-ZnS heterodimers at 90
o
C
versus the standard rhodamine 6G ethanol solution (QY=95%), (B) PL
emission spectra of the AgInS
2
-ZnS heterodimers at 120
o
C versus the
standard rhodamine 6G ethanol solution (QY=95%), (C) PL emission
spectra of the AgInS
2
-ZnS heterodimers at 150

o
C versus the standard
rhodamine 101 ethanol solution (QY=100%) and (D) PL emission spectra
of the AgInS
2
-ZnS heterodimers at 180
o
C versus the standard rhodamine
101 ethanol solution (QY=100%). The quantum yields of the four
heterodimers were 31%, 28%, 35% and 38%, respectively. 86
Figure 5. 10 TEM image of AgInS
2
nanoparticles (blue emission) prepared using
intermediate temperature of 60
o
C. 86
Figure 5. 11 The upconversion fluorescence spectra of the obtained heterodimers
xiv

in toluene excited by 800 nm laser. 87
Figure 5. 12 (A) Two-photon emission of the AIZS-ZS heterodimers (150
o
C)
with various input powers. (B) Quadratic dependence of integrated
fluorescence intensity with the input power of laser. 88
Figure 5. 13 (A) Digital photographs of the obtained AgInS
2
-ZnS heterodimers
with different emissions in water; (B) PL spectra of the AgInS
2

-ZnS
heterodimers in water. 90
Figure 5. 14 (A) TEM image of obtained AgInS
2
-ZnS clusters (150
o
C) after
phase transfer; (B) A magnified TEM image of single copolymer coated
AgInS
2
-ZnS heterodimers. 90
Figure 5. 15 Images of Hela cells labeled with the heterodimers with different
emission under UV excitation (A) green, (B) yellow, (C) red. (D) Magnified
Images of Hela cells labeled by heterodimers with green emission. 91
Figure 5. 16 (A) The bright microscopy picture of the heterodimers (dry powder
form) under excitation of 800 nm laser. (B) The dark image without 800 nm
laser excitation. 92
Figure 5. 17 (A) TPF image of NIH/3T3 cells labeled with the heterodimers with
red emission. (B) The dark image without 800 nm laser excitation. 92

Figure 6. 1 XRD patterns of CIZS spheres with different amounts of Cu-doping.
(a. Cu
0.01
In
0.25
ZnS
1.38
, b. Cu
0.02
In

0.25
ZnS
1.385
, c. Cu
0.04
In
0.25
ZnS
1.395
, d.
Cu
0.08
In
0.25
ZnS
1.415
). 99
Figure 6. 2 (A) Low magnification FESEM image of Cu
0.04
In
0.25
ZnS
1.395
spheres;
(B) High resolution FESEM image of Cu
0.04
In
0.25
ZnS
1.395

nanospheres; (C)
Low-resolution TEM image of Cu
0.04
In
0.25
ZnS
1.395
spheres; (D)
High-resolution TEM image of Cu
0.04
In
0.25
ZnS
1.395
spheres, and (E)
HRTEM image of the single Cu
0.04
In
0.25
ZnS
1.395
nanoparticles. 99
Figure 6. 3 EDX spectrum of the CIZS spheres. 101
Figure 6. 4 (A) High angle annular dark field (HAADF) image of an
individual Cu
0.04
In
0.25
ZnS
1.395

sphere. (B) Line profile analysis of S (yellow),
Cu (red), Zn (green) and In (blue-green), along axis of one single sphere;
(C), (D) ,(E) and (F) are XEDS maps (orange=Cu, blue=In , green=Zn and
yellow=S ) for one Cu
0.04
In
0.25
ZnS
1.395
sphere. 102
Figure 6. 5 The XPS spectrum of Cu 2p of the CIZS spheres. 102
Figure 6. 6 Nitrogen adsorption-desorption isotherms of Cu
0.04
In
0.25
ZnS
1.395

nanoporous spheres. 103
Figure 6. 7 (A) UV-Vis absorption spectra of the CIZS spheres with different
amounts of Cu. (B) Hydrogen evolution from an aqueous solution
containing 1.2 moldm
-3
Na
2
SO
3
and 0.7 moldm
-3
Na

2
S

catalyzed by CIZS
spheres with different amount of doped Cu. 104

Figure 7. 1 (A) XRD patterns of CIZS-rGO nanocomposites with different
weight ratios of rGO to CIZS. (B) Low magnification TEM image of CG2
nanocomposites. (C) and (D) Magnified TEM image of CG2
xv

nanocomposites, showing that CIZS nanospheres wrapped in rGO sheets. (E)
Magnified TEM image of CG2 nanocomposites, revealing that the
nanospheres were porous and comprised of numerous nanoparticles. (F)
High-resolution TEM image of the CIZS nanospehres in the
nanocomposites. 114
Figure 7. 2 EDS spectrum of Cu
0.02
In
0.3
ZnS
1.47
-rGO nanocomposites. 115
Figure 7. 3 (A) Line profile analysis of S (orange), Cu (red), Zn (green) and In
(blue), along axis of one single CIZS nanosphere in the CG2
nanocomposites. (B), (C) and (D): XEDS maps (orange=Cu, blue=In and
green=Zn) of CIZS nanospheres in the CG2 nanocomposites. 115
Figure 7. 4 XPS data from the surface of the CIZS nanospheres in CG2
nanocomposites: (A) Cu 2p core-level spectrum, (B) Zn 2p core-level
spectrum; (C) In 3d core-level spectrum; (D) S 2p core-level spectrum. 117

Figure 7. 5 AFM image of graphene oxide nanosheet. 118
Figure 7. 6 XPS spectra of C 1s from (A) GO and (B) CG2 nanocomposites. 118
Figure 7. 7 Raman spectra of graphene oxide and CIZS-rGO. 119
Figure 7. 8 (A) Low magnification TEM image of CIZS nanospheres (Inset:
XRD pattern of CIZS nanospheres). (B) Magnified TEM image of pure
CIZS nanospheres. 120
Figure 7. 9 TEM image of Cu
0.02
In
0.3
ZnS
1.47
nanospheres. 121
Figure 7. 10 Nitrogen adsorption-desorption isotherms (A) and corresponding
pore size distribution curves (B) of samples Cu
0.02
In
0.3
ZnS
1.47
solid powders.
122
Figure 7. 11 Nitrogen adsorption-desorption isotherms (A) and corresponding
pore size distribution curves (B) of samples Cu
0.02
In
0.3
ZnS
1.47
-rGO

composites (CG2) solid powders. 122
Figure 7. 12 UV-Vis absorption spectra for the CG1, CG2 and CG5, as well as
the pure CIZS nanospheres. Inset: the corresponding digital photographs of
CG1, CG2, CG5 and pure CIZS nanospheres. 125
Figure 7. 13 Comparison of the visible-light photocatalytic activity of sample
rGO, CIZS, CG0.5, CG1, CG2, CG5 and CG20 for hydrogen production
using 1.2 mol·L
-1
Na
2
SO
3
and 0.7 mol·L
-1
Na
2
S

solution

as sacrificial
reagent and 0.5 wt% Pt as a co-catalyst; 800 W Xe-Hg lamp was used as the
light source. 125
Figure 7. 14 Mott-Schottky plot obtained at different frequencies for CuInZnS
film electrode with Ag/AgCl, saturated KCl reference electrode and Pt
counter electrode immersed in 0.1 M NaOH electrolyte with pH 12.5. 127
Figure 7. 15 Schematic illustration of the charge separation and transfer in the
Cu
0.02
In

0.3
ZnS
1.47
-rGO composites system under visible light. The
photoexcited electrons transfer from the conduction band of the
semiconductor Cu
0.02
In
0.3
ZnS
1.47
not only to Pt, but also to the carbon atoms
on the graphene sheets, which is accessible to protons that could readily
react to form H
2.
130

xvi

List of Abbreviations
XRD X-ray diffractometer
EDS X-ray energy dispersive spectrometer
TEM Transmission electron microscopy
HRTEM High resolution transmission electron microscopy
SAED Selected area electron diffraction
UV-Vis-NIR Ultra violet-visible-near infrared spectroscopy
ICP-OES Inductively coupled plasma-optical emission spectrometry
XPS X-ray photoelectron spectroscopy
STEM Scanning transmission electron microscopy
PL Photoluminescence

BET Brunauer-Emmett-Teller
FTO Fluorine-Tin Oxide
NHE Normal Hydrogen Electrode
AIZS Silver indium zinc sulfide
CIZS Copper indium zinc sulfide
CIS Copper indium sulfide
QDs Quantum Dots
LEDs Light-Emitting Diodes
FFT Fast Fourier Transform
GO Graphene Oxide
xvii

rGO Reduced Graphene Oxide
TPF Two Photon Fluorescence
xviii

List of Symbols
E
g
Band gap energy

QY Quantum yield

a, b, c Lattice constant of unit cell

θ Bragg's diffraction angle

d Spacing between adjacent crystal planes
Abs Absorbance
m Meter

cm Centimeter
μm Micrometer
mm Millimeter
nm Nanometer
Å Angstrom
ml Milliliter
M Mol per liter, mol/L
min Minute
s Second
℃ Centigrade, which is the temperature unit
eV Electron volt
rpm Revolution per minute

xix

List of Publications
1, Synthesis of ZnO Nanoparticles with Tunable Emission Colors and Their Cell
Labeling Applications
Xiaosheng Tang , Eugene Shi Guang Choo , Ling Li ,Jun Ding, Junmin
Xue* Chemistry of Materials 2010, 22, 3383
2, Synthesis of CuInS
2
–ZnS alloyed nanocubes with high luminescence
Xiaosheng Tang , Wenli Cheng , Eugene Shi Guang Choo, Junmin Xue* Chemical
Communication
，
2011,47, 5217
3 Synthesis and characterization of AgInS2–ZnS heterodimers with tunable
photoluminescence
Xiaosheng Tang , Kuai Yu , Qinghua Xu , Eugene Shi Guan Choo , Gregory K. L.

Goh and Junmin Xue*, Journal of Materials Chemistry, 2011, 21, 11239
4 One-Pot Synthesis of Water-Stable ZnO Nanoparticles via a Polyol Hydrolysis
Route and Their Cell Labeling Applications
Xiaosheng Tang , Eugene Shi Guang Choo , Ling Li ,Jun Ding and Junmin Xue* ,
Langmuir 2009, 25(9), 5271
5 Synthesis of Zn doped AgInS
2
Nanocrystals and Their Fluorescence Properties
Xiaosheng Tang , Wenxi Bernice Ailsa Ho, Jun Min Xue*, The Journal of Physical
Chemistry C 2012, 116, 9769
6 Highly Efficient Visible-Light-Driven Photocatalytic Hydrogen Production of
CuInZnS-Decorated Graphene Nanosheets
Xiaosheng Tang, Qiuling Tay, Zhong Chen, Yu Chen, Gregory K.L. Goh,

Junmin
xx

Xue* Journal of Materials Chemistry A, 2013, Accepted
7 A facile method to synthesize CuInZnS micostructure for hydrogen production by
water splitting
Xiaosheng Tang, Qiuling Tay, Yu Chen, Zhong Chen,

Gregory K.L. Goh,

Junmin
Xue* New Journal of Chemistry, under revision
8 Synthesis of AIZS@SiO
2
core–shell nanoparticles for cellular imaging Applications
Sheng Yang, Tang Xiaosheng, Xue junmin*, Journal of Materials Chemistry 2012,

22, 1290
9 One-step Synthesis of Hollow Porous Fe
3
O
4
Beads/reduced Graphene Oxide
Composites with Superior Battery Performance
Yu Chen, Xiaosheng Tang, Bohang Song, Li Lu, and Jumin Xue*，Journal of
Materials Chemistry
，
2012, 22, 17656
Chapter 1 Introduction
1

Chapter 1 Introduction
1.1 General properties of semiconductor nanomaterials
It is well-known that nanomaterials display lots of novel physical and chemical
properties, as compared to their bulk materials, because of their reduced dimension
and increased surface area [1-3]. Therefore, nanomaterials have attracted the interests
of a large number of scientists during the past two decades [4-7]. The size of
nanomaterial ranges from a few nanometers to consisting of a few thousand atoms, in
which the electron motion is confined by potential barriers in all dimensions. Three
effects can be observed due to this size effect. For semiconductor nanoparticles, also
called quantum dots (QDs) are normally highly fluorescent with a narrow emission
bandwidth, which makes them highly attractive as fluorescent dyes in biological
labeling applications [8, 9].Semiconductor nanoparticles, have been widely used in
different areas including biological imaging, solar cell and photocatalyst because of
their tunable optical properties [10-12]. Hence, achieving tunable optical properties
was the most pivotal step to determine the detailed application of QDs. The following
subsections provide a literature summary of QDs, which points out three major factors

which would affect the optical properties of QDs including particles’ size, particles’
shape and the composition [13-16].
1.1.1 Size dependent optical properties of semiconductor
nanoparticles
Semiconductor nanoparticles have an increasement in the band gap energy with
decreasing particles size due to quantum size effect [14, 15, 17, 18]. Therefore,
Chapter 1 Introduction
2

different photoluminescence emissions could be achieved by changing the particles
size. The detail mechanism can be described as follows. When a semiconductor
nanoparticle is excited by the light which has a greater energy than Eg, the excited
electron leaves an orbital hole in the valence band [13, 19]. The negative electron and
positive charged hole forms an electron-hole pair. Following this, radiative
recombination accompanied with relaxation of the excited electron back to the
valence band annihilates the exciton which will emit a relatively sharp emission band
at the band gap energy [13, 19]. Based on the quantum confinement effect, when the
size of nanoparticles was close to the Bohr radius, the states of free charge carrier in
semiconductor NCs become quantized. The movement of these electrons and holes is
then determined by quantum mechanics. In general, the exciton has a finite size
within the crystal defined by the Bohr exciton diameter, which could range from 1 nm
to more than 100 nm. If the size of semiconductor nanoparticles is smaller than the
size of the exciton, the charge carriers will become spatially confined and increase in
energy [13]. Therefore, the different photoluminescence wavelength could be tuned
by changing the particles size.
Furthermore, the photoluminescence is also sensitive to the surface of
nanoparticles. If the surface of semiconductor nanoparticles was passivated, the PL
wavelength maximum will be close to the absorption band edge with little red-shift
[20, 21]. Otherwise, the surface traps would lead to red-shift and lower quantum
yield.

Chapter 1 Introduction
3

1.1.2 Shape dependent optical properties of semiconductor
nanoparticles
For semiconductor nanoparticles, the shape effect is also an important topic [22,
-24]. Mona et al. studied the shape dependent ultrafast relaxation dynamics of CdSe
nanodots and nanorods [22]. In their study, they found the carrier relaxation dynamics
of the higher energy states in CdSe nanorods was faster than nanodots as the delay
time increased [22]. The reasoning was that lowering the symmetry from spheres to
rods led to splitting of the energy level degeneracy. Increasing the density of states
along the long axis of rods would induce a speed up in the relaxation process which
involves either electron-phonon or electron-hole coupling. CdSe nanorods have a
longer axis than nanodots, which results in a faster relaxation process [22].
1.2 Current progress of semiconductor nanoparticles
1.2.1 Core-shell semiconductor nanoparticles
In 1982, A. Henglein published his work on the emitting semiconductor CdS
nanocrystals (NCs), which he discovered by chance when he was studying the surface
chemistry and catalytic processes of colloidal semiconductor particles [25, 26]. In this
experiment, he observed that the light was emitted upon the excitation at 390 nm [25,
27]. Later, L. Brus firstly presented quantum mechanical effect as the correct
interpretation for blue-shift in the absorption spectrum of NCs [28, 29]. Based on
these pioneer scientists’ efforts, more and more research groups have begun to focus
on nanomaterials [30-33].
Over the past two decades, several approaches were developed to prepare