Summary of Wei-Ta's work
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Transcript of Summary of Wei-Ta's work
Metal/Semiconductor Nanohetrostructures: Interfacial Charge Transfer Dynamics and Their
Photoconversion Applications
Wei-Ta ChenAdvisor : Dr. Yung-Jung Hsu
10.19.2013
• Au-CdS Core−Shell Nanocrystals with Controllable Shell Thickness and Photoinduced Charge Separation Property and Interfacial Charge Carrier Dynamics Interfacial Charge Carrier Dynamics
• Au/ZnS Core/Shell Nanocrysals As an Eficient Anode Photocatalyst in Direct Methanol Fuel Cells
• L-Cysteine-Assisted Growth of Core-Satellite ZnS-Au Nanoassembles with Remarkable Photocatalytic Efficiency
• Know Thy Nano Neighbor. Plasmonic versus Electron Charging Effects of Metal Nanoparticles in Dye-Sensitized Solar Cells
• Realizing Visible Photoactivity of Metal Nanoparticles. Excited State Behavior and Electron Transfer Properties of Silver (Ag8) Clusters
Outline
Chem. Mater. 2008, 20, 7204–7206
J. Phys. Chem. C 2010, 114, 11414–11420
• Why metal/semiconductor hetrostructures?
Introduction
Ultrafast charge transfer!
Long-live charge separation time!
CdSe-Au
CdSe-Pt
[Wu et al., J. Am. Chem. Soc. 2012, 134, 10337][Costi et al., Nano lett. 2008, 8, 637]
[V. Iliev, D. Tomova, L. Bilyarska, G. Tyuliev, J. Mol. Catal. A: Chem. 2007, 263, 32.][P. V. Kamat et. al., J. Phys. Chem. C 2007, 111, 2834.]
[J. Qi et. al., ACS nano 2011, 5, 7108.]
Motivation
1. Prevention of Chemical poisoning
2. Visible-Light-Driven Catalytic Activity
Sunlight Driven!
• Tri-functional reagent, L-Cysteine (Cys):
Synthesis of Au-CdS core-shell nanocrystals
- SH : complexing with Cd2+ (Cys/Cd)
- NH2 : coupling Cys/Cd with Au - COOH : promoting the dispersion of Au
N1= Au-NN2= CNN3=NH2
C1= C-CC2= C-NC3=COO-
Photophysical properties
A B
C D
Volume
thickness
λest λexp
1 mL 9.0 nm 555 552
2 mL 11.9 nm
558 558
4 mL 13.9 nm
560 562
8 mL 18.6 nm
562 578
Theoretical calculation of SPR position for Au-CdS :
red shift
[T. Hirakawa et. al., J. Am. Chem. Soc. 2005, 127, 3928.] [G. Oldfield et. al., Adv. Mater. 2000, 12, 1519.]
[A. C. Templeton,et. al., J. Phys. Chem. B 2000, 104, 564.]
TEM images UV spectra
Electron transfer!!
e-
Au
CdS
hvh+ CdS emission
Excited state interaction studies
PL spectra
Photocurrent measurement
Au-CdS excited state interaction studies
Electron transfer rate constant , ket
A
B
Time-resolved PL spectra
Au–CdS + hν Au(e–)–CdS(h+) (1)
Au(e–)–CdS(h+) + H2O Au(e–)–CdS + H+ + ·OH (2)
RhB + ·OH oxidation products (3)
Au(e–)–CdS + O2 Au-CdS + ·O2– (4)
Photocatalytic applications
A
B
Reduce precious metal usage by light irradiation!!
Hole participates methanol oxidation reaction
Efficient hole exaction process by coupling metal with semiconductor!!
Photo-assisted direct methanol fuel cell
Department of Materials Science and Engineering, National Chiao Tung
University, Hsinchu, Taiwan 30010, Republic of China.
Chem. Commun., 2013, 49, 8486-8488
100 nm
A
5 nm
ZnS(002)
Au(111)
BZnS (002)Au (111)ZnS (103)ZnS (203)
0.31 nm
0.24 nm
A
B
TEM images of Au-ZnS core-shell nanocrystals
EDAX analysis
Core component
Shell component
Electrophotocatalysis oxidation of methanol
Effective degradation containment catalyst!
Methylene blue Thionine + ne- Convert to harmless form Langmuir 2010, 26, 5918–5925
ZnS- Au + hν Au(e–)–ZnS(h+) (1)
Au(e–)–ZnS(h+) + TH ZnS(h+) + Au + TH. (colorless form) (2)
ZnS(h+) + EtOH ZnS + EtOH.(3)
Photocatalytic applicationsA
B
• The results show that the Au/CdS and ZnS core-shell structure provides excellent oxidation reaction efficiency because the electron-hole pathway results in oxidation(reduction) reaction, rather than self-recombination.
• Reaction rate and electron transfer rate significantly enhances increasing CdS shell thickness.
• Our study provides an alternative design for such photo-assisted methanol oxidation applications, photocatalysis, electron storage, nonvolatile memory device, etc.
Conclusions
ACS Nano, 2012, 6, 4418–4427
Synthesis of Au-TiO2 and Au-SiO2 core-shellnanocrystals
400 500 600 700 8000.0
0.3
0.6
0.9
1.2
c
b
Abso
rban
ce
Wavelength (nm)
Au Au@TiO
2
Au@SiO2
a
Photophysical properties
Red shift
TEM images UV spectra
Increasing n value by coating shell layer
300 400 500 600 700 800
0.2
0.4
0.6
0.8
1.0
g
f
a. 0min b. 1min c. 3min d. 6min e. 10min f. 15min g. Air
Abso
rban
ce
Wavelength (nm)
a
A
400 500 600 700 800
0.2
0.3
0.4
0.5
0.6
Abso
rban
ce
Wavelength (nm)
a. 0min b. 1min c, 3min d. 6min e. 10min f. 15min
B
a-f
Au/TiO2 Au/SiO2
Increasing Au core charge density
0.0 0.2 0.4 0.6 0.80
4
8
12
16
20
24
Curr
ent den
sity
(m
A/c
m2 )
Voltage (V)
TiO2 + N719
TiO2 + Au@TiO
2 + N719
TiO2 + Au@SiO
2 + N719
A
ab
c
Table 1
Dye-Sensitized Solar Cell Performance
Support/Dye Jsc (mAcm-2) Voc (V) FF η (%)
TiO2/N719 18.28 0.729 0.697 9.29
TiO2+Au@TiO2/N719 18.281 0.771 0.694 9.78
TiO2+Au@SiO2/N719 20.31 0.727 0.691 10.21
Performances of DSSCs were measured with 0.18 cm2 working area under AM 1.5 illumination. Electrolyte: 0.6 M
DMPImI, 0.05 M I2, 0.1 M LiI, and 0.5 M tert-butylpyridine in acetonitrile. Au@TiO2 and Au@ SiO2 loadings were kept
at 0.7% by weight. FF and correspond to fill factor and power conversion efficiency respectively.
Dye-Sensitized Solar Cell by Incorporating with Au/TiO2 and Au/SiO2
I-V curve measurment
A B
Distinguish the role of core/shell nanocrystals in solar cell devices
By incorporating these Au core@oxide shell nanoparticles in the DSSC, we have succeeded in identifying the influence of these effects.
The examples discussed in the presents study provides a convenient way to isolate the two effects. The surface plasmon resonance effects increases the photocurrent of DSSC while the charging effects leads to increase in photovoltage.
These observations opens up new opportunity to introduce both these paradigms and synergetically enhance the photocurrent and photovoltage of DSSC.
Conclusions
Radiation Laboratory, Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
Synthesis of DHLA protected Ag8 cluster
α-Lipoic acid DHLA(light yellowish solution)
+ AgNO3
Ag
Sonication
Ag-DHLA complex
Ag-DHLA complex
NaBH4
NaBH4
Ag8 cluster
QY=4.62%a
b
Clusters size larger than theory of Ag8 ?Why?
Ag
Ag8
hn
eMV2+
MV+
hn’
Ag core/Ag8 Shell
Photophysical properties
TEM images
UV spectra
Charge transfer between Ag8 and MV2+
Ag8 - MV2+ -light
Ag8 - MV2+ -darkMV2+ -darkMV2+ -light
Formation of MV.+
e- transfer occurred
Ag8-MV2+ Interfacial charge transfer dynamics
B
C D
A Ag8 Ag8 + MV2+
Formation of MV.+
Conclusions • Ag8 cluster excited state electron transfer event have
successfully demonstrated.• The photochemical activity established in the present study
offers another dimension to the fascinating properties of small metal nanostructures.
• Basic understanding of excited state processes in fluorescent metal clusters paves the way towards the development of biological using and catalysts in energy conversion devices.
MV2+
MV .+
e-
e- e-
h+ h+ h+
Ag8
hνket = 2.74 x 1010 s-1
τav= 28.7ps
Thank you!Those papers can be found in
Chemistry of Materials 2008, 20, 7204-7206 Journal of Physical Chemistry C 2009, 113, 17342-17346Chem. Comm. 2013, 2013, 49, 8486-8488 Langmuir 2010, 26, 5918-5925 Journal of Physical Chemistry C 2010, 114,11414-11420ACS Nano 2012, 6, 4418–4427 J. Phys. Chem. Lett. 2012, 3, 2493–2499
Acknowledgement