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Plasmon Sensitized TiO2 Nanoparticles as a Novel Photocatalyst for Solar Applications
George Chumanov
Department of Chemistry, Clemson University, Clemson, SC 29634
e-
h+
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Titania Photocatalyst
e-
h+
cb
vb
Reduction
Oxidation~3.2ev (UV light)
Electron-Hole recombination is on the order of < 30ps, hence efficiency is low (< 5%).
Efficiency of photocatalysis depends on how well one can preventthis charge recombination
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Role of metal in metal/titania nanocomposites
e-
h+
cb
vbOxidation
O2
O2-
e-
metal
~3.2ev (UV light)
Metal nanoparticles act as an electron sink, promoting interfacial charge transfer reducing charge recombination
P. V. Kamat. J. Phys.Chem. B., 2002, 106, 7729-7744
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Plasmon Resonance (PR) in Metal Nanoparticles
PR – collective oscillations of conducting electrons in metal nanostructures
++− − ++
− −
E
Ek
HE
ωp = (ne2/ε0me)1/2
εmetal (ωp) = 0
Ag, Au, Cu nanoparticles exhibit PR in the visible spectral range
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Optical Properties of Silver Nanoparticles
hν
Local Field is Enhanced Several Orders of Magnitude!
Extinction Spectra of Ag Nanoparticles as a Function of Size
200 300 400 500 600 700 800 900
quadrupole dipole
Wavelength (nm)
Opt
ical
dens
ity
Dipole
H
E
Quadrupole Hexapole Octapole
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Ag Nanoparticles as Efficient Antennae for Capturing of Solar Energy
200 300 400 500 600 700 800
Wavelength (nm)
2.5
0.5
1.0
1.5
Sola
r Spe
ctra
l Irr
adia
nce
(W /
m n
m)
2
2.5
0.5
1.0
1.5
Abs
orba
nce
200 300 400 500 600 700 800
Wavelength (nm)
2.5
0.5
1.0
1.5
Sola
r Spe
ctra
l Irr
adia
nce
(W /
m n
m)
2
2.5
0.5
1.0
1.5
Abs
orba
nce
Solar Spectrum is from J.H.Seinfeld and S.N.Pandis”Atmospheric Chemistry and Physics” John Wiley &Sons, Inc. New York, Chichester, Brisbane, Singapore, Toronto (1998)
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Titania Coated Metal Nanoparticles
Ag Au
Ag/Au5 ÷ 150 nm
TiO2 1 – 5 nm
Pt Pt
Pt
Pt
PtRuO2
RuO2
RuO
2
RuO 2
RuO 2
hν
++− −
Plasmon Enhanced Electron-Hole Pair Generation
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Titania coated Silver Nanoparticles
200nm
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hνvisible
hνUV
++− −
Metal core shortens the electron-hole pairs generated in titania shell
SiO2 TiO2
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Ag core SiO2/TiO2 Nanoparticles
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Metal Ion Doped-Titania Photocatalyst
cb
vbFe3+/4+
Fe2+/3+
e-
h+ Oxidation
Reduction
Migrate to the surface
e-
h+
(Visible light)
Dopants influences intrinsic properties of titania resulting in lowering theband gap and shifting light absorption into visible spectral rangeDopants should be both good electron and hole traps
Efficiency of photocatalysis depends on various charge transfer events and migration of charges to the surface
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Synthesis of Fe3+-doped TiO2
sonicate
Titanium Butoxide/Ethanol
Hydrolysis
Condensation
Fe(III) salt/Ethanol
sonicate
Centrifuging
Drying at 100°C
Heating at >450°C
12 hours
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UV-Vis Absorption Spectra of Fe3+-doped TiO2 : Effect of Fe3+ concentration
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Electron Microscopy
TiO2 as prepared (amorphous) TiO2 after heat treatment (crystalline)
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Electron Microscopy
Fe3+/TiO2 after heat treatment (semi-crystalline)
Fe3+/TiO2 as prepared (amorphous)
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EDX spectra and Mapping of Fe3+-doped TiO2
EDX spectra shows the presence of iron at >8 atomic % which arises from both surface and bulk Fe3+ sites
EDX mapping studies indicate the uniform dispersion of iron within the TiO2 matrix
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Photocatalysis Using UV light
Degradation of chromophore structure(diethylamine, N,N-diethylacetamide, etc)
Valence Band
Conduction Band
TiO2(Eg = 3.2 eV)
UV light
e-
h+
O2
O2-
SRBSRB•++ O2 SRBOO•+
h+ or •OH
SO42-, NH4
+, CO2, H2O
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Photosensitization Using Visible light
G. Liu, L. J. Zhao. New. J. Chem., 2000, 24, 411-417
Valence Band
Conduction Band
TiO2(Eg = 3.2 eV)Visible light
e-
h+
O2
O2-
SRB•++ O2 SRBOO•+
Degradation of chromophore structure(diethylamine, N,N-diethylacetamide, etc)
SO42-, NH4
+, CO2, H2O+
SRB*
SRB
e-
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Photocatalysis Experiments
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Role of metal in Metal/Doped-Titania Photocatalyst
Oxidation
Reductioncb
vb
e-
h+Fe3+/4+
Fe2+/3+
e-
h+
(Visible light)
Silver
At the plasmon resonance frequency there would be efficient resonance lightabsorption.
Band-gap excitation wavelength should reasonably match silver plasmon resonance frequency
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Conclusions
Titania coated silver nanoparticles were synthesized using sol-gel technique.
Fe3+- doped Titania that is sensitive to visible light was synthesized.
From the degradation of sulforhodamine dye experiments true doping effect was observed in the Fe3+- doped Titania photocatalyst
Efforts are underway to coat silver nanoparticles with Fe3+- doped Titania .
Photocatalytic activity of Fe3+- doped Titania and silver coated with Fe3+- doped Titania will be compared.
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Current Member of the GroupDavid Evanoff, Katrina Daniels,
Amar Kumbhar, Steve Hunson,
Mark Kinnan, Sravanti Ambati,
Kenia Parga
EPA