Plasmon Sensitized TiO 2 Nanoparticles as a Novel Photocatalyst for Solar Applications

1. e- h+ Plasmon Sensitized TiO2 Nanoparticles as a Novel Photocatalyst for Solar Applications George Chumanov Department of Chemistry, Clemson University, Clemson, SC 29634

2. Reduction e- cb h+ Oxidation vb Titania Photocatalyst ~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 prevent this charge recombination

3. O2- e- e- O2 cb h+ Oxidation vb Role of metal in metal/titania nanocomposites 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

4. E E E H ++   ++ k Plasmon Resonance (PR) in Metal Nanoparticles PR – collective oscillations of conducting electrons in metal nanostructures p = (ne2/0me)1/2 metal (p) = 0 Ag, Au, Cu nanoparticles exhibit PR in the visible spectral range

5. h E quadrupole dipole H Opticaldensity Dipole Quadrupole Hexapole Octapole 200 300 400 500 600 700 800 900 Wavelength (nm) Optical Properties of Silver Nanoparticles Extinction Spectra of Ag Nanoparticles as a Function of Size Local Field is Enhanced Several Orders of Magnitude!

6. Wavelength (nm) Wavelength (nm) Ag Nanoparticles as Efficient Antennae for Capturing of Solar Energy 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)

7. h RuO2 Pt Pt RuO2 RuO2 Pt Pt RuO2 RuO2 Pt ++  Titania Coated Metal Nanoparticles Au Ag Ag/Au 5 ÷ 150 nm TiO2 1 – 5 nm Plasmon Enhanced Electron-Hole Pair Generation

8. 200nm Titania coated Silver Nanoparticles

9. h UV h visible SiO2 TiO2 ++  Metal core shortens the electron-hole pairs generated in titania shell

10. Ag core SiO2/TiO2 Nanoparticles

11. e- Reduction e- cb Migrate to the surface h+ (Visible light) Fe3+/4+ Fe2+/3+ vb Oxidation h+ Metal Ion Doped-Titania Photocatalyst Dopants influences intrinsic properties of titania resulting in lowering the band gap and shifting light absorption into visible spectral range Dopants should be both good electron and hole traps Efficiency of photocatalysis depends on various charge transfer events and migration of charges to the surface

12. Titanium Butoxide/Ethanol Hydrolysis sonicate Fe(III) salt/Ethanol sonicate Condensation Centrifuging Drying at 100°C 12 hours Heating at >450°C Synthesis of Fe3+-doped TiO2

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

14. Electron Microscopy TiO2 as prepared (amorphous) TiO2 after heat treatment (crystalline)

15. Electron Microscopy Fe3+/TiO2 as prepared (amorphous) Fe3+/TiO2 after heat treatment (semi- crystalline)

16. 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

17. O2- e- UV light O2 h+ SRB TiO2 + O2 SRB•+ SRBOO•+ Conduction Band (Eg = 3.2 eV) h+ or •OH Valence Band SO42-, NH4+, CO2, H2O Photocatalysis Using UV light Degradation of chromophore structure (diethylamine, N,N-diethylacetamide, etc)

18. Photosensitization Using Visible light SRB* O2- e- e- O2 Visible light SRB h+ + O2 SRB•+ SRBOO•+ TiO2 Conduction Band Degradation of chromophore structure (diethylamine, N,N-diethylacetamide, etc) (Eg = 3.2 eV) + SO42-, NH4+, CO2, H2O Valence Band G. Liu, L. J. Zhao. New. J. Chem., 2000, 24, 411-417

19. Photocatalysis Experiments

20. e- Reduction e- cb h+ Fe3+/4+ Fe2+/3+ vb Oxidation h+ Role of metal in Metal/Doped-Titania Photocatalyst Silver (Visible light) At the plasmon resonance frequency there would be efficient resonance light absorption. Band-gap excitation wavelength should reasonably match silver plasmon resonance frequency

21. 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.

22. Current Member of the Group David Evanoff, Katrina Daniels, Amar Kumbhar, Steve Hunson, Mark Kinnan, Sravanti Ambati, Kenia Parga EPA