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Artificial photosynthesis cint 0711-2010

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Shelnutt Powerpoint Presentation H generation for KAIST program 06282012

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Artificial photosynthesis cint 0711-2010

  1. 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. 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. 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. 4. Photosynthetic Reaction Center• Light-harvesting complex I & II and the photosynthetic reaction center – site of charge separation.
  5. 5. Photosynthetic Reaction Center OEC• Light-harvesting complex I & II and the photosynthetic reaction center – site of charge separation.
  6. 6. Reaction Center 3 ps e- <1 ps 200 ps <10 s• ~100% efficient charge separation.
  7. 7. Light Harvesting 100-200 fs 35 ps 3-5 ps• Rapid energy transfer among light-harvesting proteins and into reaction center.
  8. 8. Chlorosomes• Chlorosomes of green bacteria are the most efficient light-harvesting structures known. Chlorosomes 100 nm
  9. 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 of100 nm self-assembled bacterio- chlorophyll molecules.• These organisms use bacteriochlorophyll nanostructures light harvesting.• Most efficient biological light-harvesting structures known.
  10. 10. Biomimetic Water-splitting Devices Using Porphyrin Pigments N N X NN 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. 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 NCl 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 PtCl 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. 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. 13. Platinized porphyrin nanospheres 50 nm K2PtCl4 + Ascorbic acid STEM image
  14. 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. 15. Solar Fuels ApproachesArtificial Photosynthesis:Porphyrin nanostructure Lightserves as light-harvesting h Harvesting Antennaarray--bioinspired approach. H2 O H2 CatOx D Receptor A CatRed O2, H+ H+ e- e- e- e- H2Two Optimized Photocatalysts: Visible light CB e- PtPorphyrin nanostructure can CB e- Rred H+serves as one of the Visible lightphotocatalysts (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. 16. Binary Nanostructures from Ionic Self-Assembly of Porphyrins SO3- H + N N N N N + N+- H - IVO 3S H SO3 H N Sn H N N N N - N+ SO3 H H4TPPS4 SnIVTPyP • Porphyrin analogs of chlorophyll
  17. 17. Porphyrin Nanotubes • Formed by ionic self-assembly 70 nmTransmission electron micrograph (TEM) images of porphyrinnanotubes on holey carbon TEM grid.
  18. 18. Small Diameter Porphyrin Nanotubes 5 0 n m x80000 N N N X N N N X NN 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. 19. Optical Properties of Porphyrin Nanotubes Monomer-like Soret bandsA J-aggregate bandsbsorbance 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. 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 nmRaman 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. 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. 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. 23. H2 Generation by Platinized Porphyrin Nanotubes• Platinum catalyzes H2O reduction to H2 using electrons from the SnP anion generated by the photocycle.
  24. 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. 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. 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. 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. 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. 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. 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. 31. Family of Morphologies: Zn/Sn clovers ZnTPPS SnTNEtOHPyP• Zn/Sn clovers at 10 , 20 , 40 , 60 , 80 C.
  32. 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. 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. 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 IntensityIntensity 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. 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. 36. Zn/Co CBI family of structuresa 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. 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-pyridylSEM 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. 38. Energetics: Water Splitting• Sn porphyrin is acceptor; Zn porphyrin is donor.• Sn porphyrin gives reductive cycle; Zn porphyrin gives oxidative cycle.
  39. 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 theacceptor in either the positive or negative channel.
  40. 40. Bulk Heterojunction Solar Cell ITOBulk 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. 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. 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. 43. Nanomanipulator conductivity measurements Clover ZnTPPS • No dark current detected either in- Donor plane or through the clover . • Nanomanipulator is being modifiedSnT(N-EtOHPy)P to provide visible light illumination capability for photoconductivity Acceptor measurements. T. Busani (UNL), B. Swartzentruber, CINT/SNL.
  44. 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. 45. Photo-initiated Processes Leading toMetal 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. 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. 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. 48. Reduction of Platinum Complex Chemical reduction with ascorbic acid OH O Pt2+ + AA Pt0 + AAox O slow OH HO OH by photocatalytic reduction AAN N SnP + h → SnP* SnIVN N SnP* + AA → SnP · + AAox 2SnP · + Pt2+ → 2SnP + Pt0SnOEP by autocatalytic reduction Pt0 Pt2+ + AA Pt0 + AAox fast
  49. 49. Photocatalytic Pt Reduction by Zn/Sn Clovers70 C structure, 3-hr reaction time 1-hr reaction time Dark Light
  50. 50. H2 Generation by Platinized Porphyrin Nanotubes• Platinum catalyzes H2O reduction to H2 using electrons from the SnP anion generated by the photocycle.
  51. 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. 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. 53. CO2 Reduction Reactions o E (Volts vs. NHE) pH 0 pH 7 pH 14 0.197 Ag/AgCl, KCl (satd) 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. 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. 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. 56. Thank you for your attention. • Department of Energy, Basic Energy Sciences, Materials Sciences • LDRD, Sandia National Laboratories
  57. 57. Electron Donor with CO2 Reduction Catalyst ZnTPPS – light harvesting, photocatalysisCoT(4-NEtOHPy)P – CO2 reduction catalysis
  58. 58. Zn/Co CBI structuresa 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. 59. CBI structures with other functionalities: Nanostars T(4-NMePy)P (light harvesting) and FeTPPS (catalysis, electron transport)
  60. 60. Dendritic Metal Growth• Dark field scanning TEM image of a section of a platinum nanowheel.
  61. 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. 62. Platinum NanoWheels• Templated dendritic Pt growth in surfactant bicelles— bilayer lipid disks.
  63. 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 NHO2C CO2H thick dendritic sheets. HO2C CO2H SnUroP
  64. 64. Size Control by Variation of Photocatalyst Concentration TEM image X 1 mM K2PtCl4 23.3 M SnOEP
  65. 65. Control of Sheet Size by Porphyrin Concentration 2 mM K2PtCl4 1.6 M SnOEP TEM HAADF STEM
  66. 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. 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. 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. 69. Curved Dendritic Pt Nanosheets High-resolution SEM imageGrown within bilayers of aggregated unilamellar liposomes.
  70. 70. Platinized Porphyrin NanotubesPlatinized porphyrin nanotubes evolve hydrogen in the presence of an electron donor.
  71. 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. 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. 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. 74. Solar Water-Splitting Approaches Visible light H2 CB e- PtPorphyrin nanostructure Visible lightserves as a photocatalyst CB e- Rred H+(semiconductor). R h+ VB H2 O h+ VB Electron relay O2, H+ H2O oxidation H2O reductionPorphyrin nanostructure Lightserves as light-harvesting Harvestingarray--bioinspired h Antennaapproach. H2 O H2 CatOx D Receptor A CatRed O2, H+ H+ e- e- e- e- • Two types of water-splitting nanodevice designs.
  75. 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. 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. 77. SnTPPS and ZnT(N-EtOHPy)P: BiomorphsComplex structures likethese microscaleporphyrin ‘four-leafclovers’ result from ZnT(N-EtOHPy)P4+ionic self assembly of Four-leaf micro-these oppositely clovers arecharged porphyrin complete withrings. ‘stems’, ‘leaves’, and ‘veins’. Sn(OH-)2TPPS-4
  78. 78. Ionic Strength Alters Morphology SnTPPS-ZnT(N-EtOHPy)P Clovers0 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. 79. A New Type of SolidCooperative 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. 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. 81. Altering the porphyrin substituents changes the morphology.SnTPPS & SnT(NEtOHPy)P gives microclovers (SEM Changing from the N-ethanol to N-H pyridiniumimage). 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. 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- hRedox 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

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