¾ Fuel Cellspkamat/pdf/assemblies.pdf · Role of nanometal in catalysis Size and support...
Transcript of ¾ Fuel Cellspkamat/pdf/assemblies.pdf · Role of nanometal in catalysis Size and support...
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Organic-Inorganic Hybrid Nanostructures
Prashant V. KamatRadiation Laboratory and
Dept Of Chemical & Biomolecular EngineeringUniversity of NotreDame
Notre Dame, Indiana 46556-0579Researchers/CollaboratorsAmy Dawson, Dr. T. Hirakawa Ella Jakob Dr. Girish KumarRavi Subramanian, Roxana Nicolaescu Dr. K. George Thomas (RRL, India)Istvan Robel Prof. Fukuzumi (Osaka U.)Said Barazzouk Prof. Imahori (Kyoto)T. Hasobe
Support: US DOE
Nanostructure Architectures for Energy Conversion
Photochemical Solar Cells− Assembly of molecular clusters
− Photoinduced charge separation
− Conversion of light energy into electricity
SS
S
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S
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S
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S
S
S
S
S
SS
SS
SS
SS
SS
S
S
S
S
S
S
SS
SS
SS
SS
e-
Pt
e-
OTEI-/ I3-
OTE: Optically Transparent Electrode
e-
hν
Porphyrin C60 Gold Nanoparticle
e-
Catalysis with Semiconductor and Metal Nanostructures− Design and characterization of new
materials− Photocatalytic production of hydrogen reactant products
hνe e
e
h hh
Ag
TiO2
reactant products
hνe e
e
h hh
reactant products
hνee ee
ee
hh hhhh
Ag
TiO2
Fuel Cells− Carbon nanotubes as a novel support
− Assembly of fuel cells and improving cell performance
CH3OH + H2O O2/air
H2OCO2
H+CH3OH + H2O O2/air
H2OCO2
H+O2/air
H2OCO2
H+
CO2
H+
Catalysis with Semiconductor and Metal Nanostructures
Synthesis Semiconductor Nanoparticles
Molecular Beam Epitaxy (MBE)
Metal Organic Chemical Vapor Deposition (MOCVD)
Colloidal Growth initiated by Chemical Reactions
Examples: Hydrolysis of titanium tetrachloride to produce TiO2
TiCl4 + 2H2O TiO2 + HCl
Reaction between cadmium and selenide compoundsCd2+ + Se2- CdSe (CdSe)n
A typical set up used in the synthesis of colloidal CdSe capped with TOPO. By controlling the temperature and arresting the colloidal growth one can control the size of the CdSe particles
2
Size control using reverse micellar system
Q-CdSeQ-CdSeQ-CdSe
Organic surfactants such as Aerosol-OT form reverse micelles in nonpolar solvents. Controlled addition of water yields desired size of particles
300 400 500 6000.0
0.2
0.4
0.6
0.8
1.0
Abs
orba
nce
Wavelength/nm
a
b c
300 400 500 6000.0
0.2
0.4
0.6
0.8
1.0
Abs
orba
nce
Wavelength/nm
a
b c
a
b c
Semiconductor Heterostructures
Cd2+ S2-TiO2
Cd2+
Cd2+
Cd2+
Cd2+
Cd2+
Cd2+
TiO2TiO2
CdS
Titanium
isopropoxide
HCl/H2O
Suspension ofSnO2 Colloids
Precipitation of SnO2@TiO2
Suspensionof SnO2@TiO2
TiO2@CdS
SnO2@TiO2
Organic capping or charge stabilization is important in achieving stable colloidal suspension
SnO2
TiOTiO22
CdSCdSSnOSnO22@TiO@TiO22@CdS@CdS
SnO2
TiOTiO22
SnO2
Confinement along 1, 2 and 3 dimensions. Analogous to a quantum well, quantum wire and quantum dot.
Quantum wells, wires and dots are often described using the analogy to a particle in a 1D box, a 2D box and a 3D box. This is because when the actual physical length scale of the system is smaller than the exciton Bohr radius or corresponding deBroglie wavelength, either or both the electron and hole experience confinment. In turn, theenergies of the carrier along that dimension of the material are no longer continuous as in the case where there is no confinement. The appearance of discrete states is one of the fundamental signatures of nanomaterials. Since solving the Schrodingerequation of a carrier to find its eigenvalues and eigenfunctions involves using boundary conditions one can also immediately predict that the actual shape of a quantum well, wire or dot will also play a role in dictating the ordering and spacing of states. A nanowire will have a similar but different progression of states than a quantum dot (or nanocrystal). The same applies to quantum wells as well as more exotic shapes of nanostructures.
For CdSe me = 0.13m0 , mh = 0.45m0 , ε = 9.4
Exciton Bohr Radius,
3
Schematic diagram of the molecular orbital model forband structure, adapted from ref 3.
Brus, Acc. Chem. Res., Vol. 23, 11990
The theoretical size dependence of the lowest excited state of four different semiconductors is shown in adjucentFigure. These curves can be approximated by
where me and mh are the effective masses and ε is the bulk optical dielectric coefficient. For every material, there is a diameter where the negative Coulombic attraction is balanced by the positive kinetic energy. In CdS this occurs at about a 70-A diameter, where each term is about 0.1 eV.
260 3403000
1.0
Abs.
Wavelength, nm
Bawendi, Acc. Chem. Res., 1999, 32, 389-396Kamat J. Phys. Chem., 1992, 96, 6829-34.
Size dependent absorption and emission spectra of colloidal CdSe quantum dots.
Examples of Size Quantization Effects
Emission from ZnO-quantum dots
CB
VB
S*
TiOTiO22
S+
O2
O2
Products
hν
hν
A
et ht
VB
–
+
+
–A−
B
B−
CB
Direct bandgap excitation of the semiconductor
Excitation of the molecules adsorbed on semiconductor substrate
Photocatalytic Activity of Semiconductor Nanoparticles
Emission
Charge Trapping
Interfacial Electron Transfer
4
Factors Controlling the Photocatalytic Activity
Bandgap energy determines minimum energy required to achieve charge separation
Energy levels of conduction and valence bands determine the energetics of electron transfer. (Quantized particles are more reductive/oxidative than the bulk semiconductors.)
Surface vacancies dictate the charge trapping and charge recombination processes
Interaction of molecules with surface and pH of the medium influence the charge transfer processes
H+/H2
-2.0
-1.0
0.0
+1.0
+2.0
+3.0
V vs. NHE
3.0 1.42.4 1.7
3.0
1.2
2.22.7 2.8 2.1 eV
VB
CBSIC
GaAsCdSe
CdSTiO2 MoS2Fe2O2
In2O3 WO3CdO
Eg
H+/H2
-2.0
-1.0
0.0
+1.0
+2.0
+3.0
V vs. NHE
3.0 1.42.4 1.7
3.0
1.2
2.22.7 2.8 2.1 eV
VB
CBSIC
GaAsCdSe
CdSTiO2 MoS2Fe2O2
In2O3 WO3CdO
Eg
400 500 600 700 800 9000.0
0.1
0.2
0.3
0.4
a
b
c
d
Abs
orba
nce
Wavelength, nm
0 100 200 300 400 5000.0
0.1
0.2
∆Abs
orba
nce
Time, s
Electron Accumulation/Trapping in TiO2 Colloids
Upon UV- irradiation TiO2 colloids prepared in ethanol turns blue as photogenerated electrons are trapped at the Ti4+ sites. These trapped electron survive charge recombination and exhibit long lifetimeSuch colorations are referred as photochromic effects –coloration induced by light
UV/N2 air
TiO2 TiO2(h + e) TiO2 (h) + ethanol TiO2 + productsTiO2 (e) TiO2 (etrap)TiO2 (etrap) + O2 TiO2 + O2
-
∆∆AA
0.015
0.051
0.033
Wavelength, nmWavelength, nm450 650550
50 ps
500 ps
2 ns
20 ns
Electron Accumulation/Trapping in ZnO Colloids
250 300 350 4000.0
0.2
0.4
0.6
0.8
1.0
Abso
rban
ce
Wavelength,nm
a,eb
cd
O2
O2
VB
CB
Vs2+/+
Electron accumulation in N2 + UV
–
+
VB hν
knrkr
Vs2+/+
CB– –– ––
+
Upon exposure to aira-d UV exposure of ZnO colloids in N2 for 30 min.e –Upon exposure to air
Electron accumulation causes band edge to shift to higher energies.
Photoinduced charge transfer between TiO2 semiconductor colloid and C60
hν
e
TiO2
C60CB
VB
hν
e
TiO2
C60CB
VB
0.00
0.05
0.10
0.15
0.20
400 500 600 700Wavelength (nm)
× 3
∆τ = 1 µs∆τ = 100 µs
0 50 100 150Time (µs)
420 nmC60 + TiO2
.01
∆A
Difference absorption spectra recorded following 308 nm laser pulse excitation of TiO2 colloidal suspension containing C60
5
hν
et ht
VB
–
+
+
–CB
2H2O+ O2
4OH−
H2
2H+2H+
H2
Pt
Hydrogen production is observed only in presence of a precious metal catalyst
Semiconductor (e.g., TiO2) nanoparticles for hydrogen production
What about gold and other noble metals?
Hydrogen Evolution rates for various Photocatalysts (µl/hr)
Pt/TiO2 7.7Pd/TiO2 6.7Rh/TiO2 2.8Ru/TiO2 0.2Sn/TiO2 0.2Ni/TiO2 0.1TiO2 <0.1
Toshima, J. Phys. Chem. 1985, 89, 1902
Photocatalytic water splitting reactions
TiO2
Pt
h
e
2H+
H2
4OH−
2H2O + O2hν
Role of nanometal in catalysis
Size and support dependency of catalytic activity of gold clusters on titania,
Haruta, et al Catal. Today, 1997, 36, 153
Structural and electronic properties of Au on TiO2(110), Yang, Z.X., R.Q. Wu, and D.W. Goodman,
Phys. Rev. B, 2000, 6, 14066-14071.
High-performance nanocatalysts for single-step hydrogenations. Thomas, J. M., Johnson, B. F. G., Raja, R., Sankar, G. and Midgley, P. A., Acc. Chem. Res., 2003, 36, 20-30.(Bimetallic nanoparticles (Ru6Pd6, Ru6Sn, Ru10Pt2, and Ru12Ag4) anchored within silica nanopores exhibit high activities)
Catalysis with TiO2/gold nanocomposites. Effect of metal particle size on the Fermi level equilibration,Subramanian, V., E. Wolf, and P.V. Kamat, J. Am. Chem. Soc. 2004, 126, 4943-4950
The Structure of Catalytically Active Au on Titania. Chen, M. S. and Goodman, D. W., Science, 2004, Published online
Powering Fuel Cells with CO via Aqueous Polyoxometalates and Gold Catalysts Won Bae Kim, T. Voitl, G. J. Rodriguez-Rivera, J. A. DumesicScience, 2004, 308, 1280-1283
+N-Br
Phase Transfer Catalyst in toluene+/-thiol
NaBH4
Hydrogen tetrachloro
aurate in water
NaBH4
toluene
Synthesis of Gold Colloids in Organic Solvents
A biphasic reduction method using alkanethiol and TOAB as stabilizers …….Brust et al, J. Chem. Soc., Chem. Commun. 1995, 1655-1656; Chemistry Materials, 1998, 10, 922.
N +
-Br
N +
N +N +
-Br
N+
-Br
N +-Br
-Br
-Br
25 nm
Au
400 500 600 700 8000.0
0.2
0.4
0.6
0.8
Abs
orba
nce
Wavelength,nm
Thiol:Aua 4:1*(8nm)b 2:1(5nm)c 4:1(<3nm)*After reduction
a
b
c
400 500 600 7000.00
0.25
0.50
0.75
1.00I,2-dichlorobenzeneCyclohexane
Abs
orba
nce
Wavelength, nm
The peak position, λs, for metal nanoclusters can be expressed as
λs2 ≈ λp
2 /(ε∝+2 εm) where εm is the dielectric constant, λp is the bulk plasmon wavelength and can be expressed in the form
λp = (Ne2/ε0meff)-½
N is the conduction band electron density, meff is the effective mass
Surface Plasmon Absorption of Gold Nanoparticles
Solvent R.I., n λmax(nm)cyclohexane 1.426 526toluene 1.496 530o-xylene 1.501 532chlorobenzene 1.524 533o-dichloro- 1.551 535benzene
N+
-Br
N+
N+ N+-Br
N+-Br
N+-Br
-Br
-Br
SS
SSS
S S
S S
S
518
Alkanethiolate Gold Cluster Molecules with Core Diameters from 1.5 to 5.2 nm: Core and Monolayer Properties as a Function of Core Size, Hostetler et al Langmuir, 1998, 14,17-30Surface binding properties of tetraoctylammonium bromidecapped gold nanoparticles, George Thomas and Kamat, Langmuir, 2002, 18, 3722ε(ω) = n2(ω)
6
400 500 600 700 8000.0
0.2
0.4
0.6
0.8
Abs
orba
nce
Wavelength,nm
Thiol:Aua 4:1*(8nm)b 2:1(5nm)c 4:1(<3nm)*After reduction
Controlling the sizeDifferent size Au particles can be prepared by adjusting thiol concentrations
SS
SSS
S S
S S
S
10 nm
(b)
10 nm10 nm
(a)
a
b
c5 nm5 nm
(c)
5 nm5 nm
(a)
N+
-Br
N+
N+ N+-Br
N+-Br
N+-Br
-Br
-Br
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NBr
N Br
NBrN
Br
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NBr
N Br
NBrN
Br
Au-ROD
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NBr
N Br
NBrN
Br
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NBr
N Br
NBrN
Br
Au-ROD
125 nm
125 nm400 500 600 700 800 900 1000
0.0
0.2
0.4
0.6
0.8
1.0a- Au-R0b- Au-R50c- Au-R100d- Au-R150
dcba
Abso
rban
ce
Wavelength, nm
AR1
AR2
AR3AR 5
Controlling the shape
Aspect ratio =l/wl
25 nm
Kim, et al, Photochemical Synthesis of Gold NanorodsJ. Am. Chem. Soc., 124, 14317 (2002) George Thomas, et al., Unidirectional Plasmon Coupling through Longitudinal Self-assembly of Gold Nanorods. J. Phys. Chem. B, 108, 13066 (2004)
w
400 600 800 1000 12000.0
0.1
0.2
0.3
0.4jd
cb
a
Abs
orba
nce
Wavelength, nm
Self Assembly of Gold Nanorods
CS O
O H
C SO
OHCS O
O H
C SO
OHAu Au
Longitudinal interplasmon coupling via hydrogen bonding
50 nm
50 nm
50 nm
50 nm
Linear Assembly HS-(CH2)n-CO2Hn = 2, 10
George Thomas, K., Barazzouk, S., Ipe, B. I., Shibu Joseph, S. T. and Kamat, P. V., Unidirectional Plasmon Coupling through Longitudinal Self-assembly of Gold Nanorods. J. Phys. Chem. B, 2004, 108, 13066-13068.
Catalytic Nanomotors
Paxton et al J. Am. Chem. Soc. 2004, 126, 13424-13431
7
HS
Spacer Photoresponsive molecule
S SS
SSSSS
George Thomas & Kamat Accounts of Chemical Research 2003, 36, 888-898
Controlling the surface property
NCH3
O
S
NH3C
O
S
N CH3
O
S
NH3C O
S
NCH3
O
S
NH3C
O
S
S
SS
SS
S Au
O
S
O
S
O
S
OS
O
S
O
S
S
SS
SS
S Au
S H
SA uS
S
S
S
S
S
S
SS
SS
S
S
S
S
N
N H N
H NN H C O ( C H
2)n
S H
( n = 5 , 1 1 )
Nano Lett., 2002, 2, 29-35
Adv. Mater., 2004, 16, 975-978J. Am. Chem. Soc, 2005, 127, 1216-1228.
J. Phys. Chem. B, 2002, 106, 18-21
ee e e eee
h
hν
TiO2
Au
C2H5OH
EF EF
eeee ee ee eeeeee
hh
hν
TiO2
Au
C2H5OH
EF EF
COO−
S-
S-S
S
−OOCS-
S
-SS
COO−
S-
S-S
S
TiO2
Au
Au
Au
COO−
S-
S-S
S
COO−
S-
S-S
S
−OOCS-
S
-SS
−OOCS-
S
-SS
COO−
S-
S-S
S
COO−
S-
S-S
S
TiO2
Au
Au
Au
Jakob, M.; Levanon, H.; Kamat, P.V., Charge Distribution between UV-Irradiated TiO2 and Gold Nanoparticles. Determination of Shift in Fermi Level,. Nano Lett. 2003, 3, 353-358.
Subramanian, V., Wolf, E. E. and Kamat, P. V., Catalysis with TiO2/Au Nanocomposites. Effect of Metal Particle Size on the Fermi Level Equilibration. J. Am. Chem. Soc., 2004, 126, 4943-4950.
Charge Distribution in TiO2-Metal System Photoinduced charging and discharging in TiO2 nanoparticles
ee e e eee
h
hν
TiO2
Au
C2H5OH
EF EF
eeee ee ee eeeeee
hh
hν
TiO2
Au
C2H5OH
EF EF
Decreased blue coloration confirms electron transfer from charged TiO2 to gold nanoparticles
300 400 500 600 700 8000.0
0.2
0.4
0.6
0.8
1.0
Abso
rban
ce
Wavelength,nm
TiO2a UV=0minb 30 minsc 60 minsd 120mins d
a
bc
TiO2 TiO2(h + e) C2H5OH TiO2(e)
TiO2(e) + Au TiO2 + Au(e)
300 400 500 600 700 8000.0
0.2
0.4
0.6
0.8
Abso
rban
ce
Wavelength,nm
[Au]8nm
a 0µMb 43µMc 85µMd 126µMe 166µMf 206µM
d
ba
c
ef
-2 0 2 4 6 8
0.00
0.01
0.02
0.03
0.04
0.05
∆A
Time (µs)
a TiO2b Au(8nm)c Au(5nm)
a
b
c
-2 0 2 4 6 8
0.00
0.01
0.02
0.03
0.04
0.05
∆A
Time (µs)
a TiO2b Au(8nm)c Au(5nm)
a
b
c
675 nm
8
C60
TiO2/Au(e) + C60 TiO2/Au+ C60− ..(c-f)
TiO2(e) + Au TiO2/Au(e) (b)
TiO2 TiO2(e) ….(a)400 600 800 1000 1200-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
Abso
rban
ce
Wavelength,nm
a TiO2,UV120b Au8,0.2mMc [C60]-5.9µMd [C60]-11.7µMe [C60]-17.5µMf [C60]-23.2µM
C60−
a
b
f
c
Au
Sequential Electron Transfer
e
ee
e
hν
e
TiO2
hC2H5OH
1 2 3 40
5
10
15
Red
uctio
n Ef
ficie
ncy
(%)
No Au8 nm Au
5 nm Au
3 nm Au
Effect of Gold Particle Size on the Catalytic Reduction Efficiency of TiO2 particles
10 nm
(b)
10 nm10 nm
(a)
a
b5 nm5 nm
(c)
5 nm5 nm
(c)
Vaidyanathan, Wolf, Kamat J. Am. Chem. Soc., 2004, 126, 4943-4950
E*f (TiO2)= Efb = -0.25 + 0.059 log ([C60]eq / [C60−])
[C60]eq = [C60]0 – [C60•⎯]
Determining the Fermi Level of the Composite Particles
MetalVB
CB
ee e
Redox couple
EfFEfhν
eE*fF
h
e e
e
E*f –Apparent Fermi Level
Efb –Flat band potential
-2706694TiO2 -Au(5nm)
-2907794TiO2 -Au(3nm)
-2505194TiO2 -Au(8nm)
-2303694TiO2
Ef*(mV)
[C60⎯](µM)
[C60]0(µM)
System
Subramanian, V., et al., Catalysis with TiO2/Au Nanocomposites. J. Am. Chem. Soc., 2004, 126, 4943-4950.
Particle Size Effect on the Shift in Flat Band Potential
Higher photocurrent observed with TiO2/Au composite confirms improved catalytic performance
A shift in the flat band potential is seen in TiO2 films deposited with metal nanoparticles
Larger shift observed with smaller particles parallel the Fermi level shift observed with particle systems
Cur
rent
(µA)
Voltage (V)
a TiO2b TiO2-Au(8nm)c TiO2-Au(5nm)
0 -1.2
ab
c
200
400
600
Vs. SCE
0.01 M NaOH
e
e
e
e
OTE TiO2 Au
h
h
h
RedOx
hν
9
Establishing the property of electron storage in metal Particles
reactant products
hνe e
e
h hh
Ag
TiO2
Ag+ NOOO
Ti O
DMFreflux
AgN
OOO
Ti ONOOO
Ti O
reflux
Ag
TiO2
NOOO
Ti ONOOO
Ti O
① Form TTEAIP-capped Ag metal
H2O② Form TiO2 shell
Ag+ NOOO
Ti O
DMFreflux
AgN
OOO
Ti ONOOO
Ti O
reflux
Ag
TiO2
NOOO
Ti ONOOO
Ti O
① Form TTEAIP-capped Ag metal
H2O② Form TiO2 shell
Hirakawa, Kamat Langmuir, 2004, 20, 5645-5647
e –
A−
N electrons N-1 electronsred shift
N+1 electronsblue shift
Metal – cluster
e –
B+
Effect of excess charge on the electronic properties
Kreibig et al Mie-plasmon spectroscopy: A tool of surface science.in Fine Particles Science and Technology,Ed. E. Pelizzetti,NATO, p499
Charge transfer between cluster atoms and the surrounding species alters the electron density
The plasmon frequency of metal clusters can be expressed as,
ωp = (Ne2/ε0meff)½
N is the conduction band electron density, meff is the effective mass
Wavelength , nm
Abs
orba
nce
0
0.4
0.8
1.2
1.6
2
300 400 500 600 700
0s
10s30s
60s
air
Wavelength , nm
Abs
orba
nce
0
0.4
0.8
1.2
1.6
2
300 400 500 600 700
0s
10s30s
60s
air
ethanol products
hνe e
e
h hh
Ag
TiO2
λp= 470 nm
e
e
eAg
TiO2
λp= 430 nm
ethanol products
hνe e
e
h hh
Ag
TiO2
λp= 470 nm
ethanol products
hνe e
e
h hh
ethanol products
hνee ee
ee
hh hhhh
Ag
TiO2
λp= 470 nm
e
e
eAg
TiO2
λp= 430 nm
ee
ee
eeAg
TiO2
λp= 430 nm
Photoinduced charge separation and charging of metal core in Ag@TiO2
25 nm
Wavelength, nm
Abs
.
Ag @SiO2
0
0.04
0.08
0.12
0.16
0.2
300 400 500 600 700 800
(B)
50nm
Wavelength, nm
Abs
.
Ag @SiO2
0
0.04
0.08
0.12
0.16
0.2
300 400 500 600 700 800
(B)
Wavelength, nm
Abs
.
Ag @SiO2
0
0.04
0.08
0.12
0.16
0.2
300 400 500 600 700 800
(B)
50nm
(A)
hν
AgSiO2
Hirakawa and Kamat, J. Am. Chem. Soc. 127, ASAP (2005)
ethanol products
hνe e
e
h hh
Ag
TiO2
λp= 470 nm
e
e
eAg
TiO2
λp= 430 nm
ethanol products
hνe e
e
h hh
Ag
TiO2
λp= 470 nm
ethanol products
hνe e
e
h hh
ethanol products
hνee ee
ee
hh hhhh
Ag
TiO2
λp= 470 nm
e
e
eAg
TiO2
λp= 430 nm
ee
ee
eeAg
TiO2
λp= 430 nm
Charging and Discharging of Electrons in the Metal Core
Hirakawa, T. and Kamat, P. V., Electron Storage and Surface Plasmon Modulation in Ag@TiO2 Clusters.Langmuir, 2004, 20, 5645-5647
Time, min
Peak
pos
ition
of p
lasm
on, n
m
OnIrradiation Off
420
440
460
480
0 10 20 30 40380
400
420
440
Ag @TiO2
Ag @SiO2
(A)
Peak
pos
ition
of p
lasm
on, n
m
Time, min
Peak
pos
ition
of p
lasm
on, n
m
OnIrradiation Off
420
440
460
480
0 10 20 30 40380
400
420
440
Ag @TiO2
Ag @SiO2
(A)
Peak
pos
ition
of p
lasm
on, n
m
0
1
2
3
300 400 500 600 700 800
Wavelength, nm
Abs
.
420
430
440
450
0 1 2 3 4 5Concentration of TH, µM
Peak
pos
ition
, nm
After irradiation.
After addition of TH
0
1
2
3
300 400 500 600 700 800
Wavelength, nm
Abs
.
420
430
440
450
0 1 2 3 4 5Concentration of TH, µM
Peak
pos
ition
, nm
After irradiation.
After addition of TH
10
420
440
460
480
0 0.2 0.4 0.6 0.8 10
10
20
30
40
50
Irradiation time , min
Plas
mon
pea
k , n
m
No.
of s
tore
d el
ectr
ons
per p
artic
leThe plasmon frequency of silver clusters can be expressed as,
ωp = (Ne2/ε0meff)½
N is the conduction band electron density, meff is the effective mass
Electron Storage in Silver Nanoclusters
Potential applications in Microcapacitors, Photocatalysts & Optoelectronics
Wavelength, nm
1µs
Ag @TiO2
∆Ab
s, 1
0-3
420 nm
540 nm
-8.0
-6.0
-4.0
-2.0
0
2.0
4.0
6.0
8.0
360 460 560 660 760
TiO2
4
8
12
16
0 0.5 1.0 1.5
∆Ab
s., 1
0-3
Time, 10-4 s
Ag @TiO2
420 nm
-12.0
-8.0
-4.0
0.00E+000 0.5 1.0 1.5
Time, 10-4 s
∆Ab
s., 1
0-3
Ag @TiO2
540 nm
Probing the charge equilibration process with laser pulse excitation
AuAu FluorophoreFluorophore−OOC− Electron DonorTiO2
Conductingelectrode
e
e
hνe
Nanostructure architectures for charge rectification
Au
OOC S--
OOC S--
OOC S--
OS
OS
OS
Hybrid Assembly on an Electrode Surface
AuAuOS
HOOCS--
30 nm30 nm
+AuAu OS
HOOCS--
TiO2
OTE
11
a1 τ1(ns)
a2 τ2(ns)
<τ> (ns)
Air 0.55 2 1.28 34 33.2
Tol 1.26 3.9 0.78 25.9 21.6
ACN 0.63 1.22 0.59 9.19 8.2
• Efficient quenching of singlet excited state on TiO2 surface.
• No significant quenching on silica
0 10 20 300
500
1000
1500
2000
d
c
b
a
Cou
nts
Lifetime, ns
a- Airb- Tolc- ACNd- Scatterer
OTE/TiO2/Au-S-Pyrene Electrode
350 400 450 500 5500.0
0.2
0.4
0.6
0.8
1.0
c
b
aN
orm
aliz
ed E
mis
sion
Wavelength, nm
a- Air
b- Tol
c- ACN
Au
OOC S--
OOC S--
OOC S--
OS
OS
OS
TiO2
OTE
hν
AuAuOS
hν
AuAuOS
e
No emission
e
Emission
hν
Modulation of Fluorophore Emission Using Electrochemical Bias
Electrolyte, TBAP in ACN (0.1 M) RE: SCE,
CE: Pt Scan Rate, 1mV/sec
350 400 450 5000.0
0.2
0.4
0.6
0.8
1.0 -1.2 V
- 1.0V
- 0.75 V
- 0.50 V- 0.25 V
0 V
Nor
mal
ized
Em
issi
on
Wavelength, nm
OTETiOTiO22
-(CH2)n-S- -SCOO–
-(CH2)n-S- -SCOO–
-(CH2)n-S- -SCOO–
0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.20.0
0.2
0.4
0.6
0.8
1.0
Nor
mal
ized
Em
issi
on
Potential, Volt
Em.@ 395 nm
e
P. V. Kamat; S. Barazzouk; S. Hotchandani, Electrochemical Modulation of Fluorophore Emission at a Nanostructured Gold Film. Angew. Chem. (Int. Ed.) 2002, 41, 2764-2767
600 650 700 750 8000.0
0.2
0.4
0.6
0.8
1.0
0 100 200 300
1
2
3
4
I 0/I
[Au], µM
e
f
h
g
d
cb
a
Nor
mal
ized
Em
issi
on
Wavelength, nm
[Au}0
0.35 mM
Chla/Chla+•
Au
e
EF
e ee
e ee
1Chla*/Chla+•3Chla*/Chla+•
isce
Chla/Chla+•
Au
e
EF
e ee
e ee
Chla*/Chla+•
Chla*/Chla+•isce
Chla/Chla+•
Au
hν
e
EF
e ee
e ee
Chla*/Chla+•
Chla*/Chla+•isce
-1
0
1
E vs. NHE
-1
0
1
E vs. NHE
-1
0
1
E vs. NHE
Electron transfer between Excited Chlorophyll a and Au Colloids
Barazzouk, S., Kamat, P. V. and Hotchandani, S., Photoinduced Electron Transferbetween Chlorophyll a and Gold Nanoparticles. J. Phys. Chem. B, 2005, 109, 716-723.
12
650 700 750 800 850 9000.0
0.2
0.4
0.6
0.8
1.0Potential, mV vs. SCE
0 200 400 600 800 10000.0
0.2
0.4
0.6
0.8
1.0-50-50 0-1000
λem= 750 nm
Nor
mal
ized
Em
issi
on
Time, sec
g
fe
d
c
b
a
Nor
mal
ized
Em
issi
on
Wavelength, nm
400 500 600 700 800 900 1000 1100-0.04
-0.02
0.00
0.02(A)b
a
∆A
Wavelength, nm
Excitation 532 nma. Chlab. Chla + Au
Electron Transfer in the Hybrid Assembly
Chla* + Au Chla+. + Au(e)
400 450 500 550 600 650 700 7500
4
8
12
16
20
Wavelength, nm
IPC
E, %
0.0
0.2
0.4
0.6
0.8
1.0
1.2
OTE/TiO2/Chla
Abs. Spec. Chl a
OTE/TiO2/Au/Chla
Abso
rban
ce
AuAu
h ν
e
AuAu
AuAuChl a
Chl a
Chl aAuAu
h ν
e
AuAu
AuAuChl a
Chl a
Chl ae
e
e
Photocurrent Action Spectrum of Chlorophyll Modified Electrodes
Semiconductor-metal-molecular assemblies can be engineered to tailor the properties of light harvesting assemblies
Gold nanoparticles improve the photocatalytic performance of semiconductor nanoparticles
Electrons can be stored in small nanoparticles using photolytic or electrochemical methods.
Charging of metal nanoparticles is convenient to modulate the catalytic properties of ordered assemblies
Hybrid Nanoassemblies for Energy Conversion