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Compositional Dependence of the Structure of TiO 2 :Fe Nanorods

Compositional Dependence of the Structure of TiO 2 :Fe Nanorods. A. Kremenovic, B. Antic, E. S. Bozin, J. Blanusa, M. Comor, Ph. Colomban, L. Mazzerolles. I N T R O D U C T I O N. TiO 2 is a very promising photocatalyst : exhibits higher activity compared to that of other semiconductors

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Compositional Dependence of the Structure of TiO 2 :Fe Nanorods

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  1. Compositional Dependence of the Structure of TiO2:Fe Nanorods A. Kremenovic, B. Antic, E. S. Bozin, J. Blanusa, M. Comor, Ph. Colomban, L. Mazzerolles ACA Meeting, Toronto Canada, July 25-30, 2009

  2. I N T R O D U C T I O N TiO2 is a very promising photocatalyst: • exhibits higher activity compared to that of other semiconductors • shows excellent chemical stability • stability in nano higher for anatase than rutile • nontoxic • environmentally friendly → photocatalytic activity against organic waste e.g. herbicides ACA Meeting, Toronto Canada, July 25-30, 2009

  3. pure TiO2 vs. TiO2:Fe → absorption significantly shifts from UV towards VIS • Fe3+ in TiO2 can reduce the e–-h+ recombination rate • in nanorods charge carriers are free to move throughout the length of the crystal → lower probability of e–-h+ recombination ACA Meeting, Toronto Canada, July 25-30, 2009

  4. C H A R A C T E R I Z A T I O N • TEM/HRTEM • morphology • crystallographic orientation • XRPD • Rietveld + line broadening analysis • PDF • Magnetic measurements – SQUID • Raman spectroscopy ACA Meeting, Toronto Canada, July 25-30, 2009

  5. TEM/HRTEM • crystal form and morphology ≠ f(%Fe) → flower • dislocations and stacking faults unobserved ACA Meeting, Toronto Canada, July 25-30, 2009

  6. TEM/HRTEM - morphology • rutile nanorods grown from a central nucleus ACA Meeting, Toronto Canada, July 25-30, 2009

  7. TEM/HRTEM - morphology • nanorods 30-100 nm in length and 4-5 nmwidth ACA Meeting, Toronto Canada, July 25-30, 2009

  8. TEM/HRTEM - crystallographic orientation • nanorods are grown parallel to the c-axis of the rutile structure ACA Meeting, Toronto Canada, July 25-30, 2009

  9. TEM/HRTEM - crystallographic orientation • longitudinal section Fourier Transform (similar to a local microdiffraction) ACA Meeting, Toronto Canada, July 25-30, 2009

  10. transverse section - facets corresponding to (110) planes→ 110 plane most dense/stable Fourier Transform (similar to a local microdiffraction) ACA Meeting, Toronto Canada, July 25-30, 2009

  11. XRPD • data collected at 6-ID-D beam-line at Argonne National Laboratory • λ = 0.125677 Å. • Rietveld + line broadening analysis + PDF ACA Meeting, Toronto Canada, July 25-30, 2009

  12. ? %Fe ? ACA Meeting, Toronto Canada, July 25-30, 2009

  13. Rietveld refinement – rutile + anatase Fe - 1.05% Rwp~ 3% A ACA Meeting, Toronto Canada, July 25-30, 2009

  14. Rietveld refinement – rutile Fe - 0.22% ACA Meeting, Toronto Canada, July 25-30, 2009

  15. WPPF - rutile Fe - 0.22% ACA Meeting, Toronto Canada, July 25-30, 2009

  16. Difference between Rietveld and WPPF • preferential orientation of crystallites no → Ritveld check done • low crystallite statistics no → nano specimen • inadequate line broadening model WPPM in plan • background problem i.e. amorphous like phase PDF and Raman ACA Meeting, Toronto Canada, July 25-30, 2009

  17. Structure, unit cell and size – strain analysis • needle like size line broadening model • isotropic strain broadening model ACA Meeting, Toronto Canada, July 25-30, 2009 degree of anisotropy

  18. rutile crystal structure in accord with literature • Fe content and distribution unable to refine • irregular change of unit cell parameters → no preferential direction for Fe incorporation • large size broadening anisotropy in accord with HRTEM • small strain anisotropy → no dislocations and stacking faults; probable point defects inside ACA Meeting, Toronto Canada, July 25-30, 2009

  19. Rw~ 15% PDF – spherical particles model ACA Meeting, Toronto Canada, July 25-30, 2009

  20. HRTEM, Rietveld and PDF – anatase % anatase in a flower centre ??? ACA Meeting, Toronto Canada, July 25-30, 2009

  21. SQUID – magnetic measurements ACA Meeting, Toronto Canada, July 25-30, 2009

  22. the origin of ferromagnetism of TiO2:Fe still remains a controversial • here always paramagnetic no matter Fe % • no Fe cluster formations ACA Meeting, Toronto Canada, July 25-30, 2009

  23. Raman spectroscopy ACA Meeting, Toronto Canada, July 25-30, 2009

  24. ACA Meeting, Toronto Canada, July 25-30, 2009

  25. rutile and anatase confirmed • no brookite • more Fe more defects – “boson” peak • origin of “boson” peak - Fe (and vacancy) distribution break the vibration • most of defects are point defects ACA Meeting, Toronto Canada, July 25-30, 2009

  26. Where is anatase? • HRTEM – anatase unobserved • XRPD – anatase observed in Rietveld but better in PDF → low crystallinity • Raman – best observation of anatase • Low quantity of anatase, c.c. 5% • Anatase in a flower centre ??? • Anatase first to crystallize then rutile ? ACA Meeting, Toronto Canada, July 25-30, 2009

  27. Acknowledgements: • U.S. Dep. of Energy - DE-AC02-98CH10886 • MSTRS • CNRS • FP6 INCO-026401 WBC • FP7 REGPOT3 - 204374 TERCE-NIPMSS ACA Meeting, Toronto Canada, July 25-30, 2009

  28. Recommendation for further synthesis • Small amount of Fe stabilize rutile crystal structure • Fe concentration does not influence significantly on morphology and size of nanorods • Fe concentration influence on vacancy concentration • “Play” with synthesis conditions in order to obtain pure rutile with small amount of Fe ACA Meeting, Toronto Canada, July 25-30, 2009

  29. Supplementary material • XPS → only Ti4+ but Fe3+ (dominantly) and Fe2+ • Doping with Fe ions has great influence on optical characteristics of the host material → shift of the absorption threshold toward VIS spectral region. • No increase of photocatalytic activity after doping. • The induced photoluminescence as well as the decrease of photocatalytic activity is probably the consequence of the introduction of oxygen vacancies through doping procedure. ACA Meeting, Toronto Canada, July 25-30, 2009

  30. For higher dopant concentrations also recombination of photogenerated charge carriers occurs with higher probability. ACA Meeting, Toronto Canada, July 25-30, 2009

  31. PDF – F(Q) ACA Meeting, Toronto Canada, July 25-30, 2009

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