Shelnutt Powerpoint Presentation H generation for KAIST program 06282012

1. Cooperative Binary Ionic Solids for
Artificial Photosynthesis of Fuels
John A. Shelnutt, Kathleen E. Martin, Yongming Tian,
Julian Y.-T. Shelnutt, Tito Busani, Zhongchun Wang, Yan Qiu,
John Jacobsen, Craig J. Medforth
Advanced Materials Laboratory
Sandia National Laboratories, Albuquerque, NM 87106
Department of Chemistry, University of Georgia, Athens, GA 30602
Department of Chemistry, University of California, Davis, CA
Department of Chemical & Nuclear Engineering
University of New Mexico, Albuquerque, NM
Yongming
Tian

2. Photosynthesis
6H2O + 6CO2 -------> C6H12O6+ 6O2
• Efficient utilization of solar energy (efficiency is 28% to ATP & NADPH).
– 30% loss of photons in the 400-700 nm range.
• Legacy of evolution explains part of the inefficiency of biological photosynthesis.
• The pigments evolved from pre-photosynthetic molecular machinery – heme biosynthetic pathway.
– Further 32% loss in converting to glucose (9% as sugar); 7-8% sugarcane to biomass.
• Areas for improved efficiency in artificial photosynthesis.
– Capture more of photons in the 400-700 nm range – better or additional pigments.
– Extent spectral range – out to 900 nm.

3. Photosynthetic Pigments
Phycoerythrin
Chlorophyll a & b
• Biosynthesis of chlorophyll is a branch off the evolutionarily much
earlier synthetic pathway for synthesis of related heme proteins.

4. Photosynthetic Reaction Center
• Light-harvesting complex I & II and the photosynthetic reaction center
– site of charge separation.

5. Photosynthetic Reaction Center
OEC
• Light-harvesting complex I & II and the photosynthetic reaction center
– site of charge separation.

6. Reaction Center
3 ps
e-
<1 ps
200 ps
<10 s
• ~100% efficient charge separation.

7. Light Harvesting
100-200 fs
35 ps
3-5 ps
• Rapid energy transfer among light-harvesting proteins
and into reaction center.

8. Chlorosomes
• Chlorosomes of green bacteria are the most
efficient light-harvesting structures known.
Chlorosomes
100 nm

9. Photosystems of Green Bacteria
Freeze-fracture
Chlorosomal
Bacteriochlorophyll TEM image of BChl-
rods
c aggregates from
Chl. vibrioforme
NCIB 8327 C
(from Saga et al. J.
Biosci. Bioeng.
2006, 102, 118-
123.)
Chlorosomes and
chlorosomal rods:
Light-harvesting is done
by the chlorosomal rods,
which are composed of
100 nm self-assembled bacterio-
chlorophyll molecules.
• These organisms use bacteriochlorophyll nanostructures light harvesting.
• Most efficient biological light-harvesting structures known.

10. Biomimetic Water-splitting Devices
Using Porphyrin Pigments
N
N X N
N M N h
N X' N Light
Harvesting
Porphyrin Antenna
N Pt
H2 O H2
CatOx D Receptor A CatRed
O2, H+ H+
e- e- e- e-
D = EDTA
Receptor = AA =
Chlorophyll COOH
+ +
A= MV2+ = H3C N N CH3
Monodisperse Porphyrin Nanospheres Synthesized by Coordination Polymerization, Wang, Z.; Lybarger, L. E.; Wang, W.;
Medforth, C. J.; Miller, J. E.; Shelnutt, J. A., Nanotechnology 2008, 19, 395604.

11. Porphyrin Nanospheres
Cl Cl
Pt
Cl Cl
N 100 nm
Cl Cl N Cl N Cl Cl
Pt N Sn N Pt
Cl Cl N Cl N Cl Cl
N Cl Cl
Cl Cl Cl Cl Pt
Pt Pt Cl Cl
Cl Cl Cl Cl
N N N
Cl Cl N Cl N Cl Cl N Cl N Cl Cl N Cl N Cl Cl
Pt N Sn N Pt N Sn N Pt N Sn N Pt
Cl Cl N Cl N Cl Cl N Cl N Cl Cl N Cl N Cl Cl
N
Cl Cl
Pt
Cl Cl
Cl
N
Cl
Cl Pt Cl
N
N
Cl Cl
Pt
Cl Cl 300 nm
Cl
Cl Cl N N Cl Cl
Pt N Sn N Pt
Cl Cl N Cl N Cl Cl
Cl
Cl
N
Pt
Cl
Cl
• Porphyrin nanospheres prepared from
SnTPyP-coordination polymer.
• Structure of the porphyrin
• TEM image of platinized nanospheres
coordination polymer, in this
prepared by chemical reduction by 0.1 M
case polymerized by Pt4+
NaBH4 and the structure of the
ions.
coordination polymer.

12. Energetics of Energy Trapping and Electron
Transfer by Anthracene Carboxylic Acid
S1
S2
S1
X e
T1
Triplet-triplet transfer
T1
X +
H3C N
+
N CH3
3.0 eV 2.0 eV 3.2 eV
1.8 eV 1.8 eV
S0 S0
N
N X N
N M N
N X' N
COOH
N

13. Platinized porphyrin nanospheres
50 nm K2PtCl4 + Ascorbic acid
STEM image

14. H2-production using platinized porphyrin
nanospheres for light harvesting
½ H2 + MV2+ 30
H+ + MV +.
25
Hydrogen ( mol)
Platinum
particles
MV2+ 20
15
3AA–*
AA 10
5
AA– EDTAox
0
SnT(4-Py)P spheres EDTA 0 20 40 60 80 100 120 140 160 180 200
Irradiation time (min)
• H2 evolution by the platinized nanospheres.
• C = anthracene carboxylic acid, D = EDTA, the electron donor, A = MV2+
(methylviologen), the primary acceptor.
• Reduced methylviologen generates H2 at the surface of the Pt nanoparticles.

15. Solar Fuels Approaches
Artificial Photosynthesis:
Porphyrin nanostructure Light
serves as light-harvesting h Harvesting
Antenna
array--bioinspired approach.
H2 O H2
CatOx D Receptor A CatRed
O2, H+ H+
e- e- e- e-
H2
Two Optimized Photocatalysts: Visible light CB e- Pt
Porphyrin nanostructure can CB e- Rred H+
serves as one of the Visible light
photocatalysts (semiconductors). R h+ VB
H2 O h+ VB Electron relay
O2, H+ H2O oxidation H2O reduction
• Two types of water-splitting nanodevice designs.
• Are hybrid solar fuels devices using porphyrin nanostructures possible?

16. Binary Nanostructures from Ionic
Self-Assembly of Porphyrins
SO3- H
+
N
N N N N
+
N+
- H - IV
O 3S H
SO3 H N Sn H
N N N N
- N+
SO3 H
H4TPPS4 SnIVTPyP
• Porphyrin analogs of chlorophyll

17. Porphyrin Nanotubes
• Formed by ionic self-assembly
70 nm
Transmission electron micrograph (TEM) images of porphyrin
nanotubes on holey carbon TEM grid.

18. Small Diameter Porphyrin Nanotubes
5 0 n m
x80000
N N
N X N N N X N
N SnIV N SnIV
N X N N
N X N
N
N
• Replacing SnT(4-Py)P with SnT(3-Py)P gives nanotubes of about half
the diameter (60 to 30 nm). SnT(2-Py)P does not give nanotubes.
• Co, Fe, V, and Ti porphyrins also form nanotubes.

19. Optical Properties of Porphyrin Nanotubes
Monomer-like Soret
bands
A J-aggregate bands
b
s
o
r
b
a
n
c
e
200 300 400 500 600 700 800
Wavelength (nm)
UV-visible absorption spectrum of Porphyrin nanotubes in transmitted white
porphyrin nanotubes composed of light (left) and viewed perpendicular to a
SnTPyP and H4TPPS. beam of white light (right).
• Resonance light scattering gives the bright green color.

20. Resonance Raman spectroscopy: Sn porphyrins
do not participate in J-aggregation
Monomer-like band resonance J-band resonance
4 b
a 2 H4TPPS4 4
413.1 nm 2
SnT4PyP
496.5 nm
Raman Intensity (arb. units)
Raman Intensity (arb. units)
SnT4PyP
413.1 nm H4TPPS4
496.5 nm
Nanotubes
413.1 nm
Nanotubes
496.5 nm
Nanotubes
406.7 nm Nanotubes
* 501.7 nm
1300 1400 1500 1600 1300 1400 1500 1600
-1 -1
Frequency (cm ) Frequency (cm )
Excitation at resonance with the J-band yields only
features of TPPS Raman spectrum.
Franco, R.; Jacobsen, J.; Wang, H.; Wang, Z.; Istvan, K.; Schore, N. E.; Song, Y.;
Medforth, C. J.; Shelnutt, J. A., Phys. Chem. Chem. Phys. 2010, 12, 4072–4077.

21. Photocatalytic Solar H2 Cell
Visible light H2
CB e- Pt
Visible light
CB e- Rred H+
R h+ VB
H2O h+ VB Electron relay
O2, H+ H2O oxidation H2O reduction
• Two-step photocatalytic water splitting, with small band gap semiconductors
optimized for the O2 or H2 half-reactions—maximum solar efficiency = 41%.
• Uses entire visible light spectrum, not just UV as in a typical single-photocatalyst
device (e.g., one based on TiO2).
• Usually uses two types of semiconductor nanoparticles and a solution redox
couple.

22. Porphyrin nanotube-Pt composites
• Platinum
nanoparticles on
outer surface of
porphyrin nanotubes. 100 nm
• Add ascorbic acid as an electron donor and the
platinized tubes produce hydrogen in the presence
of light, but works only for a few minutes.

23. H2 Generation by Platinized Porphyrin Nanotubes
• Platinum catalyzes H2O reduction to H2 using electrons from
the SnP anion generated by the photocycle.

24. Hybrid Artificial Photosynthesis Systems
Zn Porphyrin CBI electron donor-acceptor
h h
Electron Donor nanostructure
D
H2
e- Dox
Pt H2
H+ Visible light h+ e-
H2
D
e- h+
CB e- Pt e-
Pt H+
Visible light
CB e-- Rred H+
D ox Sn Porphyrin Electron Acceptor
R
Electron relay h+ VB
+
H2O h+ VB Electron relay
O2, H+ H2O oxidation H2O reduction
• Two-semiconductor device using a donor-acceptor binary
ionic porphyrin nanostructure as one of the photocatalysts.

25. Binary Materials for Solar Fuels Applications
Self-organizing Cooperative Binary Ionic (CBI) Solids:
• Tunable with multiple functionalities SEM
• Crystalline molecular packing order
• High surface area
• High visible and UV light absorptivities
• Exciton and charge carrier mobilities
• Catalytic functionality
NaCl
Segregated Stacking: Interleaved Stacking:
Columns of positive and negative Usually leads to insulators.
charges at corners of the porphyrin
molecules.
e -
• SEM image of CBI ‘micro-clovers’ composed of
n-type and p-type porphyrins—SnTPPS and
ZnT(N-EtOH-Py)P.
The microscale clovers are composed of
porphyrin molecules with electron donor
and acceptor characteristics. Such
structures can lead to conductors,
Acceptor Donor semiconductors, superconductors, and
photochemical properties that are useful
in many applications such as solar
energy harvesting and conversion.
SnTPPS ZnT(N-EtOH-Py)P

26. Porphyrin ‘Micro-clovers’
• SEM, TEM, and confocal fluorescence microscope images of porphyrin ‘micro-clovers’ formed by ionic self-
assembly of two porphyrins, one of which is photocatalytic—Sn tetra(sulfonatophenyl)porphyrin (SnTPPS) and
Zn tetra(N-ethanol-pyridinium)porphyrin (ZnT(N-EtOHPy)P).
• Fluorescence micrograph shows regio-specific emission from one of the ‘clovers’.

27. Microclovers at various times during growth
a b
c d
• SEM images of the SnTPPS and ZnT(N-EtOH-4-Py)P microclovers sampled at various
times during growth: 30 seconds (a), 5 minutes (b), 30 minutes (c), and 2 hours (d).
• Suggests clover-like dendritic growth by diffusion limited crystallization.

28. Ionic Strength Alters Morphology
Sn/Zn clovers: SnTPPS-ZnT(N-EtOHPy)P
• Increasing NaCl 5 mM 10 mM
concentration makes
clovers smoother,
15 mM 20 mM
• But with increasing
disorder in the clover-like
morphology.
5 mM 10 mM 15 mM 20 mM

29. Effect of Growth Temperature on Morphology
• Growth temperature dependence of SnTPPS4- and ZnT(N-EtOH-4-Py)P4+ structures.
• SEM images obtained for growth at 10 C (blue), 23 C (green), 60 C (gold), and 80
C (pink).

30. Metals can be interchanged without
drastically altering morphology
Switching metals in the porphyrins still gives clover-like morphology.
SnTPPS & ZnT(NEtOHPy)P gives microclovers with Switching metals (ZnTPPS & SnT(NEtOHPy)P) between
‘stems’. (SEM image) porphyrins also gives microclovers but without the
‘stems’. (SEM image)
• Switching metals puts donor and acceptor molecules in channels of opposite charge.
• Biomorphic shape of the porphyrin ‘four-leaf clovers’ may result partly from the
flexibility of the N-ethanol substituents or porphyrin-based impurities.

31. Family of Morphologies:
Zn/Sn clovers
ZnTPPS SnTNEtOHPyP
• Zn/Sn clovers at 10 , 20 , 40 , 60 , 80 C.

32. Clovers Extended Family
ZnTPPS SnTNEtOHPyP Growth temperatures:
20 C 60 C 80 C
Zn/Sn ‘clovers’
Sn/Zn ‘clovers’
10 C 20 C 40 C 60 C 80 C
• A common family of dendritic four-fold symmetric morphologies is obtained by
growing at different temperatures.
• Changing the metals in the porphyrins merely shifts the temperature at which a
particular morphology grows.
• Similar family of structures for other metal combinations.
• Structures form by diffusion limited crystallization.

33. Same metals in both porphyrins give a
different type CBI material (redox pairs).
SnTPPS & SnT(NEtOHPy)P) also gives ZnTPPS & ZnT(NEtOHPy)P give clover-like
microclovers with stems (SEM image). dendritic structures (SEM image).
• Still get clover-like structures.
• Porphyrin redox potentials are different because of substituents.

34. Clover crystal structures are similar for all
glass vs Col 2
combinations of Zn and Sn in these porphyrins
300
800 1600 800
Si 250 Glass substrate
Intensity
200
1200
Intensity
150
600 600 100
800
50
Intensity
Intensity
400 0
2 4 6 8 10 12 14 16 18 20
400 400 2Theta
0
2 4 6 8 10 12 14 16 18 20
2 Theta (degrees) Zn/Zn
200
Zn/Sn 200
Sn/Zn Sn/Sn
0 0
2 4 6 8 10 12 14 16 18 20 2 4 6 8 10 12 14 16 18 20
2 (degrees) 2 (degrees)
• XRD data obtained for dry room-temperature samples on glass or Si substrates.
• Highly crystalline (narrow peaks) when grown at elevated temperatures (not shown).

35. Metals can be substituted to alter properties
Sn/Zn Zn/Sn
Sn/Sn Zn/Zn
Mn/Zn Zn/Co
2.0 m 2.0 m
• Similar morphologies for 6-coordinate metals, TPPS/TNEtOHPyP combinations.
• Mn(III) and Co(III) likely have OH- as one of the axial ligands

36. Zn/Co CBI family of structures
a b c
d e f
• Zn/Co clovers (metals in the porphyrins in Fig. 1) prepared at different
temperatures (a-f): 10 , 20 , 40 , 50 , 60 , and 80 C, respectively.
• ZnTPPS/CoT(NEtOH-4-Py)P.

37. Altering the porphyrin substituents SnT(NMePy)P
SnT(NEtOHPy)P
changes the morphology.
Zn/Sn microclovers (ZnTPPS & SnT(NEtOHPy)P) Substituting Me for EtOH as the N-pyridyl
SEM image. substituent group (i.e., ZnTPPS & SnT(NMePy)P
gives a different morphology – nano-sheets (SEM).
• Drying gives crack pattern for ZnTPPS/SnT(NMePy)P nanosheets (but not for the wet sheets).
• ZnTPPS/SnT(NMePy)P gives crystals that may be large enough for single-crystal structure
determination (in progress at synchrotron with UC Davis).

38. Energetics: Water Splitting
• Sn porphyrin is acceptor; Zn porphyrin is donor.
• Sn porphyrin gives reductive cycle; Zn porphyrin gives oxidative cycle.

39. Electrostatic Channels in CBI Solids
e -
h+ h+
With segregated stacking, the four
charged groups at the corners of the
porphyrin rings form electrostatic
channels for formation and transfer
of free charge carriers.
By switching the metals, we can
make a material that has the
acceptor in either the positive or
negative channel.

40. Bulk Heterojunction Solar Cell
ITO
Bulk Heterojunction h+ PEDOT
Active Layer
e- BCP
Al
Acceptor Stacks
• Can we make solar devices
from a solid that has the
nanoscale interpenetrating
donor and acceptor
channels, e.g., the
Donor Stacks e- heterojunction active layer of
an organic solar cell?

41. Zn/Sn clovers show J-aggregate bands.
Monomer-like
Absorbance
bands
J-aggregate bands
200 300 400 500 600 700 800
Wavelength
• UV-visible absorption spectra of a suspension of the Zn/Sn clovers (green),
and the constituent porphyrins ZnTPPS (blue) and SnIVT(N-EtOH-4-Py)P (red).

42. Photoconductivity of Zn/Sn Microclovers
Dark
Light
AFM image (Inset: SEM) and I-V curves for ZnTPPS & SnT(NEtOHPy)P microclovers (CINT/CHTM).
Donor-Acceptor Biomorphs from the Ionic Self-assembly of Porphyrins, Martin, K. E.; Wang, Z.; Busani, T.; Garcia, R. M.; Chen, Z.; Jiang, Y.; Song, Y.;
Jacobsen, J. L.; Vu, T. T.; Schore, N. E.; Swartzentruber, B. S.; Medforth, C. J.; Shelnutt, J. A., J. Am. Chem. Soc. 2010, ASAP articles on web.

43. Nanomanipulator conductivity measurements
Clover
ZnTPPS
• No dark current detected either in-
Donor
plane or through the clover .
• Nanomanipulator is being modified
SnT(N-EtOHPy)P to provide visible light illumination
capability for photoconductivity
Acceptor measurements.
T. Busani (UNL), B. Swartzentruber, CINT/SNL.

44. Growth of Metal Nanostructures by Photocatalytic
Reduction of Aqueous Metal Ions by Porphyrins
N N
IV
Sn
N N
SnOEP
• Metal ions are continually reduced to metal and
deposited near the tin-porphyrin molecule.

45. Photo-initiated Processes Leading to
Metal Ion (Au+) Reduction for the Zn/Sn clovers
h
Au+
h Au+
Zn Porphyrin Donor
Au+
Au+
Au0 Au0 Au+
Au+ h+
e
D e h+
e D
Pt2+
Dox Dox
Sn Porphyrin Acceptor
• Three of the four processes are illustrated.

46. Zn/Sn Clover Photocatalytic
Reduction of Gold(I) Thiosulfate
• After 14 hours in dark • After 15 minutes in white light
• No reduction in dark reaction.
• Concentration of gold nanoparticles at periphery of the clovers (where charging
is seen in the SEM images)

47. Zn/Sn Clover Photocatalytic
Reduction of Gold(I) Thiourea
• SEM images of Zn/Sn CBI 20 ⁰C structures showing the reduction of aqueous Au(I) thiourea
complex by after 1 hour in the dark (a) and after 1 hour of exposure to white light.
• No gold metal is observed for the dark reaction.
• Gold particles are mostly at the edges of the clovers.

48. Reduction of Platinum Complex
Chemical reduction with ascorbic acid
OH
O
Pt2+ + AA Pt0 + AAox O
slow
OH
HO OH
by photocatalytic reduction AA
N N SnP + h → SnP*
SnIV
N N
SnP* + AA → SnP · + AAox
2SnP · + Pt2+ → 2SnP + Pt0
SnOEP
by autocatalytic reduction
Pt0
Pt2+ + AA Pt0 + AAox
fast

49. Photocatalytic Pt Reduction by Zn/Sn Clovers
70 C structure,
3-hr reaction
time
1-hr
reaction
time
Dark Light

50. H2 Generation by Platinized Porphyrin Nanotubes
• Platinum catalyzes H2O reduction to H2 using electrons from
the SnP anion generated by the photocycle.

51. Hydrogen Generation with the Zn/Sn Clovers
h
h
Zn Porphyrin Light-
Harvesting Donor
D
H2
e- Dox
Pt H2
h+ e-
H+ D e- h+ e- Pt
H+
Dox
Sn Porphyrin Light-
Harvesting Acceptor
• Three of the four energy/electron-transfer processes are shown.
• Hydrogen has been produced for at least 2 hours by the
platinized Zn/Sn clovers (20 C) without added relay.

52. Electrocatalytic CO2 reductionCO2 Co/TPP Electrodes
M edium/Low Loadings vs Blanks
30 0.5M NaHCO3
25
Graphite Blank
Graphite/Py ridine Blank
20 Co/TPP Medium Loading 100
CoTPP #1 0.5
Co/TPP Low Loading 90 (KHCO3)
CoTPP #3 0.5
80 mg/CS2 (KHCO3)
I, mAmp s/cm2
CO Conversion
70 CoTPP #3 [CS2]
15 (KOH)
60
CoTPP #2 5.0
50 (KOH)
40 CoTPP #1 [py]
(KOH)
10 30
20
10
0
5 -0.85 -1.05 -1.25 -1.45
E (V)
0
0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4 -1.6 -1.8
ECO , Volts vs. Ag/AgCl
2
Comparison of 0.7 mg ( ) CoTPP vs. 0.375 mg ( )
CoTPP loaded onto 2.5 cm2 graphite electrode.

53. CO2 Reduction Reactions
o
E (Volts vs. NHE)
pH 0 pH 7 pH 14
0.197 Ag/AgCl, KCl (sat'd) 0.197 0.197
+0.169 CO2 (g) + 8H+ + 8e- CH4(g) + 2H2O -0.24 -0.65
+0.030 CO2 (g) + 6H+ + 6e- CH3OH(aq) + H2O -0.38 -0.79
0 2H+ + 2e- H2 -0.41 -0.82
-0.071 CO2 (g) + 4H+ + 4e- HCHO(aq) + H2O -0.48 -0.89
-0.103 CO2 (g) + 2H+ + 2e- CO + H2O -0.52 -0.93
-0.199 CO2 (g) + 2H+ + 2e- HCOOH(aq) -0.61 -1.02
-0.475 2CO2 (g) + 2H+ + 2e- H2C2O4 -0.888 -1.29
• Standard potentials for CO2 reduction half-reactions
• Work with Kevin Leung has identified a viable mechanism for CO2 reduction
in aqueous environments.

54. Photoelectrocatalytic CO2 reduction
-0.0250
-0.0200
Current (A)
Ar
-0.0150
CO2
-0.0100
CO2 + Light
-0.0050
0.0000
0.0000 -0.2000 -0.4000 -0.6000 -0.8000 -1.0000 -1.2000 -1.4000 -1.6000 -1.8000
Potential (V)
CoTPP & SnTPP on GDL35BC electrode in KHCO3
room temperature.

55. Solar Conversion of CO2 to CO
Zn Porphyrin Light Harvesting Antenna
• Photocatalytic CO2 reduction
CO
h
H2O CO2
e-
CatOx D h+ e-
O2, H+ Co porphyrin CO2
reduction catalyst
e- e-
(NHE)
Zn/Co CBI photocatalyst-CO2 reduction catalysts
ZnP*/P+ Co(II)/Co(I)P
h CO2/CO H2O/H2
e-
e-
Redox Potential
(pH7)
E = 1.75 eV
H2O/O2
(pH7) e-
ZnP/P+
CBI materials
Energetics of photoassisted
electrochemical reduction of CO2

56. Thank you for your attention.
• Department of Energy, Basic Energy
Sciences, Materials Sciences
• LDRD, Sandia National Laboratories

57. Electron Donor with CO2 Reduction Catalyst
ZnTPPS – light harvesting, photocatalysis
CoT(4-NEtOHPy)P – CO2 reduction catalysis

58. Zn/Co CBI structures
a b c
d e f
• Zn/Co clovers (metals in the porphyrins in Fig. 1) prepared at different temperatures
(a-f): 10 , 20 , 40 , 50 , 60 , and 80 C, respectively.
• ZnTPPS/CoT(NEtOH-4-Py)P.

59. CBI structures with other functionalities:
Nanostars
T(4-NMePy)P (light harvesting) and
FeTPPS (catalysis, electron transport)

60. Dendritic Metal Growth
• Dark field scanning TEM image of a section of a platinum nanowheel.

61. Pt Growth in Soft Lipid Templates
Nanowire
Worm-like
Network
Micellar Network
Pt complex
Ascorbic acid
Bicelle
Nanowheels
• Pt in worm-like micelles give
nanowire networks.
• Pt in bicelles gives nano-wheels. 200 nm

62. Platinum NanoWheels
• Templated dendritic Pt growth in surfactant bicelles—
bilayer lipid disks.

63. Growth of Platinum in Micelles
and Liposomes
Globular
Dendrites
+ Pt complex
10 nm
N Cl N
Sn
N Cl N
+ Ascorbic acid
SnOEP O
CH2 O C CH2(CH2)15CH3
O
Size
CO2H
CO2H
CH2 O C CH2(CH2)15CH3
HO2C control CO2H CH2 O
O
P
-
CH3
+
OCH2CH2N CH3
Dendritic
O
N Cl
Sn
N
DSPC
CH3
Sheets
•Growth of Pt on liposomes gives 2-nm
N Cl N
HO2C CO2H
thick dendritic sheets.
HO2C
CO2H
SnUroP

64. Size Control by Variation of Photocatalyst
Concentration
TEM image
X
1 mM K2PtCl4
23.3 M SnOEP

65. Control of Sheet Size by Porphyrin Concentration
2 mM K2PtCl4
1.6 M SnOEP
TEM HAADF STEM

66. Spherical Shells of Platinum ‘Daisies’
Photocatalytic control of the
number and size of Pt
dendritic sheets leads to
joined small (~10 nm)
dendritic sheets (“Pt daisies”)
to form rigid spherical shells.

67. Platinum Nanosheets
b c
50 nm 30 nm
• Dendritic 1-2-nm thick platinum sheets.
• Diameter can be photocatalytically
controlled by light exposure.

68. Platinum foam-like nanoballs
NanoCoral® (Compass Metals)
• 10 second light exposure
• Dendritic platinum sheets grown on liposomes (1:1 DSPC to cholesterol).
• Song, Y.; Steen, W. A.; Peña, D.; Jiang, Y.-B.; Medforth, C. J.; Huo, Q.; Pincus, J. L.;
Qiu,Y.; Sasaki, D. Y.; Miller, J. E.; Shelnutt, J. A., Chem. Mater. 2006, 18, 2335-2346.

69. Curved Dendritic Pt Nanosheets
High-resolution SEM image
Grown within bilayers of aggregated unilamellar liposomes.

70. Platinized Porphyrin Nanotubes
Platinized porphyrin nanotubes evolve hydrogen in the presence of an electron donor.

71. A Water-splitting Nanodevice?
• A proposed
water-splitting
nanodevice based on
porphyrin nanotubes.
• Energy and electron
transfer in the
nanotubes is necessary
for efficient water
splitting.
• H2 evolution from
platinized porphyrin
nanotubes has been
demonstrated.
Solar hydrogen cell

72. Nanodevice Energetics
• Energetics of the
water-splitting
nanostructure.
• The redox potentials
given are for pH 0.
• Platinized nanotubes
evolve hydrogen at
pH 2 with a sacrificial
electron donor
(ascorbic acid).

73. A Water-splitting Nanodevice
• Can we construct a
water-splitting
nanodevice using
the porphyrin
nanotubes own
photoactivity and
self- assembly?
Solar hydrogen cell

74. Solar Water-Splitting Approaches
Visible light H2
CB e- Pt
Porphyrin nanostructure Visible light
serves as a photocatalyst CB e- Rred H+
(semiconductor). R h+ VB
H2 O h+ VB Electron relay
O2, H+ H2O oxidation H2O reduction
Porphyrin nanostructure
Light
serves as light-harvesting Harvesting
array--bioinspired h
Antenna
approach.
H2 O H2
CatOx D Receptor A CatRed
O2, H+ H+
e- e- e- e-
• Two types of water-splitting nanodevice designs.

75. Porphyrin Nanorod Bundles
SO3-
500 nm
N N
- H
O 3S H
SO3-
N N
Me
+
N SO3-
N N
+
30 nm Me N Sn N+ Me
N N
• SEM and TEM images of porphyrin nanorod bundles prepared
by ionic self-assembly of aqueous solutions of H2TPPS44- and
Sn(OH)2TNMePyP4+ using different solution protocols. N+
Me

76. Photo-initiated Processes Leading to
Platinum Reduction for the Zn/Sn clovers
h
Pt2+
Zn Porphyrin Pt2+
Light-Harvesting h
Donor
Pt2+
Pt2+
e- Pt Pt2+
Pt
Pt2+ h+
e-
D e- h+ e- D
Pt2+
Dox Dox
Sn Porphyrin
Light-Harvesting Acceptor
• Three of the four processes are illustrated.

77. SnTPPS and ZnT(N-EtOHPy)P: Biomorphs
Complex structures like
these microscale
porphyrin ‘four-leaf
clovers’ result from ZnT(N-EtOHPy)P4+
ionic self assembly of Four-leaf micro-
these oppositely clovers are
charged porphyrin complete with
rings. ‘stems’, ‘leaves’,
and ‘veins’.
Sn(OH-)2TPPS-4

78. Ionic Strength Alters Morphology
SnTPPS-ZnT(N-EtOHPy)P Clovers
0 mM 5 mM 10 mM
• Increasing NaCl 15 mM 20 mM
concentration makes
clovers smoother,
• but with increasing
disorder in the clover-like
morphology.
5 mM 10 mM 15 mM 20 mM

79. A New Type of Solid
Cooperative Binary Ionic (CBI) Nanomaterials: SEM
• Composed of two large organic molecular (porphyrin) ions.
• Organic parts of + and - ions have complementary properties
(e.g., donors and acceptors).
• Ionic interactions control composition and crystalline
packing structure.
• Cooperativity and synergism between the organic parts
independently determine their functional properties.
The microscale clovers
are composed of donor
ZnT(N-EtOH-Py)P
and acceptor
porphyrins. Such
structures can lead to
conductors, semiconduc
tors, superconductors, a
Donor SnTPPS nd photochemical
properties that are
Segregated stacking of useful in many
porphyrins, with positive and applications such as
negative charges at the corners of solar energy harvesting
Acceptor
the donor (blue) and acceptor (pink) and utilization.
molecules.

80. Clovers Extended Family
Growth temperatures:
10 C 20 C 40 C 60 C 80 C
Zn/Sn ‘clovers’
Sn/Zn ‘clovers’
20 C 60 C 80 C
• Changing the metals in the porphyrins merely shifts the
temperature at which a particular morphology grows.

81. Altering the porphyrin substituents
changes the morphology.
SnTPPS & SnT(NEtOHPy)P gives microclovers (SEM Changing from the N-ethanol to N-H pyridinium
image). porphyrin derivative (i.e., SnTPPS & SnT(HPy)P at pH 2)
gives a different morphology – nano-raisins (SEM).
• Shape changes from clover to raisin by simply changing the ionic substituent
on one of the porphyrins.
• Charge on the Sn(IV) ion also changes with pH.

82. Solar Conversion of CO2 to CO
• ElectrocatalyticElectrodes 2 reduction
CO Co/TPP
CO
M edium/Low Loadings vs Blanks
2
• Photoelectrocatalytic CO2 reduction
30 0.5M NaHCO3 100
90
CoTPP #1 0.5
(KHCO3) -0.0250
CoTPP #3 0.5
80 mg/CS2 (KHCO3)
CO Conversion
70 CoTPP #3 [CS2]
25 60
(KOH)
Graphite Blank 50
CoTPP #2 5.0
(KOH) -0.0200
Graphite/Py ridine Blank 40 CoTPP #1 [py]
(KOH)
Co/TPP Medium Loading 30
20
Co/TPP Low Loading 20 Ar
10 -0.0150
Current (A)
CO2
I, mAmp s/cm2
0
-0.85 -1.05 -1.25 -1.45
15 E (V)
-0.0100 CO2 + Light
10
-0.0050
5
0.0000
0
0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4 -1.6 -1.8 0.0000 -0.5000 -1.0000 -1.5000 -2.0000
ECO , Volts vs. Ag/AgCl
2 Potential (V)
Comparison of 0.7 mg ( ) CoTPP vs. 0.375 mg ( ) CoTPP & SnTPP on GDL35BC electrode in KHCO3
CoTPP loaded onto 2.5 cm2 electrode. room temperature.
• Photocatalytic CO2 reduction
(NHE) Zn/Co CBI photocatalyst-CO2
reduction catalysts
Nanodevice for solar CO2 conversion to CO
Zn Porphyrin Light Harvesting Antenna
ZnP*/P+ Co(II)/Co(I)P
h CO2/CO H2O/H2 CO
e-
e- h
Redox Potential
(pH7)
E = 1.75 eV H2O CO2
H2O/O2 e-
(pH7) e-
ZnP/P+
CatOx D h+ e-
O2, H+
e- e-
CBI materials Energetics of photoassisted Co porphyrin CO2
electrochemical reduction of CO2 reduction catalyst