Metal/Semiconductor
Nanohetrostructures: Interfacial
Charge Transfer Dynamics and Their
Photoconversion Applications
Wei-T...
Outline
• Au-CdS Core−Shell Nanocrystals with Controllable Shell Thickness and
Photoinduced Charge Separation Property and...
Chem. Mater. 2008, 20, 7204–7206

J. Phys. Chem. C 2010, 114, 11414–11420
Introduction
• Why metal/semiconductor hetrostructures?
CdSe-Au
Ultrafast charge transfer!
Long-live charge separation tim...
Motivation
1. Prevention of Chemical poisoning

2. Visible-Light-Driven Catalytic Activity

Sunlight Driven!

[V. Iliev, D...
Synthesis of Au-CdS core-shell nanocrystals

• Tri-functional reagent, L-Cysteine (Cys):
- SH : complexing with Cd2+ (Cys/...
Photophysical properties
UV spectra

TEM images

A

B
red shift

C

D

Theoretical calculation of SPR position for AuCdS :...
Excited state interaction studies
Photocurrent measurement
PL spectra

hv

e- h+

CdS emission

Au
CdS
Electron transfer!!
Au-CdS excited state interaction studies
A

Time-resolved PL spectra

Electron transfer rate constant , ket
ket =

B

1
<t...
Photocatalytic applications
A
Au–CdS + hν  Au(e–)–CdS(h+) (1)
Au(e–)–CdS(h+) + H2O  Au(e–)–CdS + H+ + ·OH (2)
RhB + ·OH ...
Department of Materials Science and Engineering, National Chiao Tung
University, Hsinchu, Taiwan 30010, Republic of China....
TEM images of Au-ZnS core-shell nanocrystals
A
A
EDAX analysis

Core component

100 nm

B
B

ZnS (203)
ZnS (103)
Au (111)
...
Electrophotocatalysis oxidation of methanol
Effective degradation containment catalyst!
Methylene blue
+ neThionine

Convert to harmless form

Langmuir 2010, 26, 5918...
Photocatalytic applications
A
ZnS- Au + hν  Au(e–)–ZnS(h+) (1)
Au(e–)–ZnS(h+) + TH ZnS(h+) + Au + TH. (colorless
form) (...
Conclusions
• The results show that the Au/CdS and ZnS core-shell structure
provides excellent oxidation reaction efficien...
ACS Nano, 2012, 6, 4418–4427
Synthesis of Au-TiO2 and Au-SiO2 core-shell
nanocrystals
Photophysical properties
TEM images

UV spectra
1.2
Au
Au@TiO2
Au@SiO2

Absorbance

0.9

c

Red shift

0.6
b
a

0.3

0.0
4...
Dye-Sensitized Solar Cell by Incorporating with Au/TiO2 and Au/SiO2
I-V curve measurment
24

A
Current density (mA/cm 2)

...
Distinguish the role of core/shell nanocrystals in solar cell devices
Conclusions
By incorporating these Au core@oxide shell nanoparticles in the DSSC, we have succeeded in
identifying the inf...
Radiation Laboratory, Department of
Chemistry and Biochemistry, University of
Notre Dame, Notre Dame, Indiana 46556,
Unite...
Synthesis of DHLA protected Ag8 cluster
Sonication
NaBH4
α-Lipoic acid

DHLA(light yellowish solution)

+ AgNO3

Ag-DHLA c...
Photophysical properties
UV spectra
b
a

QY=4.62%

Clusters size larger than theory of Ag8 ?
Why?
MV+

Ag8
TEM images

e

...
Charge transfer between Ag8 and MV2+

Ag8 - MV2+ -light
MV2+ -dark
MV2+ -light

Ag8 - MV2+ -dark

Formation of MV.+
e- tra...
Ag8-MV2+ Interfacial charge transfer dynamics
A

Ag8

B

Ag8 + MV2+

Formation of MV.+

C

D
Conclusions
• Ag8 cluster excited state electron transfer event have
successfully demonstrated.
• The photochemical activi...
Thank you!
Those papers can be found in
Chemistry of Materials 2008, 20, 7204-7206
Journal of Physical Chemistry C 2009, 1...
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Summary of Wei-Ta's work

  1. 1. Metal/Semiconductor Nanohetrostructures: Interfacial Charge Transfer Dynamics and Their Photoconversion Applications Wei-Ta Chen Advisor : Dr. Yung-Jung Hsu 10.19.2013
  2. 2. Outline • 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
  3. 3. Chem. Mater. 2008, 20, 7204–7206 J. Phys. Chem. C 2010, 114, 11414–11420
  4. 4. Introduction • Why metal/semiconductor hetrostructures? CdSe-Au Ultrafast charge transfer! Long-live charge separation time! CdSe-Pt [Wu et al., J. Am. Chem. Soc. 2012, 134, 10337] [Costi et al., Nano lett. 2008, 8, 637]
  5. 5. Motivation 1. Prevention of Chemical poisoning 2. Visible-Light-Driven Catalytic Activity Sunlight Driven! [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.]
  6. 6. Synthesis of Au-CdS core-shell nanocrystals • Tri-functional reagent, L-Cysteine (Cys): - SH : complexing with Cd2+ (Cys/Cd) - NH2 : coupling Cys/Cd with Au - COOH : promoting the dispersion of Au N1= Au-N N2= CN N3=NH2 C1= C-C C2= C-N C3=COO-
  7. 7. Photophysical properties UV spectra TEM images A B red shift C D Theoretical calculation of SPR position for AuCdS : Volume thickness λest λexp 1 mL 555 552 2 mL 11.9 nm 558 558 4 mL [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.] 9.0 nm 13.9 nm 560 562 8 mL 18.6 nm 562 578
  8. 8. Excited state interaction studies Photocurrent measurement PL spectra hv e- h+ CdS emission Au CdS Electron transfer!!
  9. 9. Au-CdS excited state interaction studies A Time-resolved PL spectra Electron transfer rate constant , ket ket = B 1 <t > (Au - CdS) - 1 <t > (CdS)
  10. 10. Photocatalytic applications A 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) B
  11. 11. Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan 30010, Republic of China. Photo-assisted direct methanol fuel cell Hole participates methanol oxidation reaction Reduce precious metal usage by light irradiation!! Efficient hole exaction process by coupling metal with semiconductor!! Chem. Commun., 2013, 49, 8486-8488
  12. 12. TEM images of Au-ZnS core-shell nanocrystals A A EDAX analysis Core component 100 nm B B ZnS (203) ZnS (103) Au (111) ZnS (002) 0.31 nm ZnS(002) 0.24 nm Au(111) 5 nm Shell component
  13. 13. Electrophotocatalysis oxidation of methanol
  14. 14. Effective degradation containment catalyst! Methylene blue + neThionine Convert to harmless form Langmuir 2010, 26, 5918–5925
  15. 15. Photocatalytic applications A 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) B
  16. 16. Conclusions • 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 photoassisted methanol oxidation applications, photocatalysis, electron storage, nonvolatile memory device, etc.
  17. 17. ACS Nano, 2012, 6, 4418–4427
  18. 18. Synthesis of Au-TiO2 and Au-SiO2 core-shell nanocrystals
  19. 19. Photophysical properties TEM images UV spectra 1.2 Au Au@TiO2 Au@SiO2 Absorbance 0.9 c Red shift 0.6 b a 0.3 0.0 400 500 600 700 800 Wavelength (nm) Increasing n value by coating shell layer A Absorbance 0.8 Au/TiO2 f g 0.6 0.4 a. 0min b. 1min c. 3min d. 6min e. 10min f. 15min g. Air 0.6 a. 0min b. 1min c, 3min d. 6min e. 10min f. 15min Au/SiO2 a-f 0.4 0.3 a 0.2 0.2 300 B 0.5 Absorbance 1.0 400 500 600 Wavelength (nm) 700 800 400 500 600 Wavelength (nm) Increasing Au core charge density 700 800
  20. 20. Dye-Sensitized Solar Cell by Incorporating with Au/TiO2 and Au/SiO2 I-V curve measurment 24 A Current density (mA/cm 2) A B 20 c 16 a b 12 TiO2 + N719 TiO2 + Au@TiO2 + N719 8 TiO2 + Au@SiO2 + N719 4 0 0.0 0.2 Table 1 0.4 0.6 0.8 Voltage (V) 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
  21. 21. Distinguish the role of core/shell nanocrystals in solar cell devices
  22. 22. Conclusions 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.
  23. 23. Radiation Laboratory, Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
  24. 24. Synthesis of DHLA protected Ag8 cluster Sonication NaBH4 α-Lipoic acid DHLA(light yellowish solution) + AgNO3 Ag-DHLA complex Ag-DHLA complex NaBH4 Ag Ag8 cluster
  25. 25. Photophysical properties UV spectra b a QY=4.62% Clusters size larger than theory of Ag8 ? Why? MV+ Ag8 TEM images e MV2+ Ag h h ’ Ag core/Ag8 Shell
  26. 26. Charge transfer between Ag8 and MV2+ Ag8 - MV2+ -light MV2+ -dark MV2+ -light Ag8 - MV2+ -dark Formation of MV.+ e- transfer occurred
  27. 27. Ag8-MV2+ Interfacial charge transfer dynamics A Ag8 B Ag8 + MV2+ Formation of MV.+ C D
  28. 28. 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. e- hν ket = 2.74 x 1010 s-1 e- e- h + h+ MV2+ h+ MV .+ τav= 28.7ps Ag8
  29. 29. Thank you! Those papers can be found in Chemistry of Materials 2008, 20, 7204-7206 Journal of Physical Chemistry C 2009, 113, 17342-17346 Chem. Comm. 2013, 2013, 49, 8486-8488 Langmuir 2010, 26, 5918-5925 Journal of Physical Chemistry C 2010, 114,11414-11420 ACS Nano 2012, 6, 4418–4427 J. Phys. Chem. Lett. 2012, 3, 2493–2499 Acknowledgement

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