Plasmon Sensitized TiO2 Nanoparticles as a Novel Photocatalyst for Solar Applications

George Chumanov

Department of Chemistry, Clemson University, Clemson, SC 29634

e-

h+

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

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

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

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

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)

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

Titania coated Silver Nanoparticles

200nm

hνvisible

hνUV

++− −

Metal core shortens the electron-hole pairs generated in titania shell

SiO2 TiO2

Ag core SiO2/TiO2 Nanoparticles

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

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

UV-Vis Absorption Spectra of Fe3+-doped TiO2 : Effect of Fe3+ concentration

Electron Microscopy

TiO2 as prepared (amorphous) TiO2 after heat treatment (crystalline)

Electron Microscopy

Fe3+/TiO2 after heat treatment (semi-crystalline)

Fe3+/TiO2 as prepared (amorphous)

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

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

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-

Photocatalysis Experiments

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

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.

Current Member of the GroupDavid Evanoff, Katrina Daniels,

Amar Kumbhar, Steve Hunson,

Mark Kinnan, Sravanti Ambati,

Kenia Parga

EPA