ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

Compositional Compositional Dependence of the Dependence of the Structure of TiOStructure of TiO22:Fe :Fe

Nanorods Nanorods A. Kremenovic, B. Antic, E. S. Bozin, J. A. Kremenovic, B. Antic, E. S. Bozin, J.

Blanusa, Blanusa, M. Comor, M. Comor, Ph. Colomban, L. MazzerollesPh. Colomban, L. Mazzerolles

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

TiOTiO22 is a very promising photocatalyst is a very promising photocatalyst:: exhibits higher activity compared to that of exhibits higher activity compared to that of

other semiconductors other semiconductors shows excellent chemical stability shows excellent chemical stability stability in nano higher for anatase than rutilestability in nano higher for anatase than rutile nontoxicnontoxic environmentally friendly environmentally friendly → photocatalytic → photocatalytic

activity against organic waste e.g. herbicidesactivity against organic waste e.g. herbicides

I N T R O D U C T I O I N T R O D U C T I O NN

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

pure TiOpure TiO22 vs. TiO vs. TiO22:Fe :Fe →→ absorption absorption significantly shifts from UV towards VISsignificantly shifts from UV towards VIS

FeFe3+3+ in TiO in TiO22 can reduce the e can reduce the e––-h-h++ recombination raterecombination rate

in nanorods charge carriers are free to in nanorods charge carriers are free to move throughout the length of the crystal move throughout the length of the crystal →→ lower probability of e lower probability of e––-h-h++ recombination recombination

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

C H A R A C T E R I Z A T I O NC H A R A C T E R I Z A T I O N

TEM/HRTEMTEM/HRTEM morphologymorphology crystallographic orientationcrystallographic orientation

XRPDXRPD Rietveld + line broadening analysisRietveld + line broadening analysis PDFPDF

Magnetic measurements – SQUIDMagnetic measurements – SQUID Raman spectroscopyRaman spectroscopy

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

TEM/HRTEMTEM/HRTEM

crystal form and morphology crystal form and morphology ≠ f(%≠ f(%Fe) Fe) → → flowerflower dislocations and stacking faults unobserved dislocations and stacking faults unobserved

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

TEM/HRTEM - TEM/HRTEM - morphologymorphology

rutile nanorods grown from a central rutile nanorods grown from a central nucleusnucleus

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

nanorods 30-100 nm in length and 4-5 nmnanorods 30-100 nm in length and 4-5 nm widthwidth

TEM/HRTEMTEM/HRTEM - morphologymorphology

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

nanorods are grown parallel to the c-axis of nanorods are grown parallel to the c-axis of the rutile structurethe rutile structure

TEM/HRTEM - crystallographic orientationTEM/HRTEM - crystallographic orientation

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

longitudinal sectionlongitudinal section

TEM/HRTEM - crystallographic orientationTEM/HRTEM - crystallographic orientation

Fourier Transform (similar to a local microdiffraction)

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

transverse section - facets corresponding transverse section - facets corresponding to (110) planesto (110) planes → → 110 plane most 110 plane most dense/stabledense/stable

Fourier Transform (similar to a local microdiffraction)

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

XRPDXRPD data collected at 6-ID-D beam-line at data collected at 6-ID-D beam-line at

Argonne National Laboratory Argonne National Laboratory λλ = = 0.125677 0.125677 ÅÅ.. Rietveld + line broadening analysis + Rietveld + line broadening analysis +

PDFPDF

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

?

?

%Fe%Fe

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

Rietveld refinement – rutile + anatase Fe - 1.05%

Rwp~ 3%

A

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

Rietveld refinement – rutile Fe - 0.22%

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

WPPF - rutile Fe - 0.22%

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

Difference between Rietveld and Difference between Rietveld and WPPFWPPF

preferential orientation of crystallites preferential orientation of crystallites no no →→ Ritveld check done Ritveld check done

low crystallite statistics low crystallite statistics no no →→ nano nano specimenspecimen

inadequate line broadening model inadequate line broadening model WPPM in planWPPM in plan

background problem i.e. amorphous like background problem i.e. amorphous like phase phase PDF and RamanPDF and Raman

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

Structure, unit cell and size – strain analysisStructure, unit cell and size – strain analysis needle like size line broadening modelneedle like size line broadening model isotropic strain broadening modelisotropic strain broadening model

degree of anisotropy

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

rutile crystal structure in accord with rutile crystal structure in accord with literature literature

Fe content and distribution unable to refineFe content and distribution unable to refine irregular change of unit cell parameters irregular change of unit cell parameters → no → no

preferential direction for Fe incorporationpreferential direction for Fe incorporation large size broadening anisotropy in accord large size broadening anisotropy in accord

with HRTEMwith HRTEM small strain anisotropy → no dislocations and small strain anisotropy → no dislocations and

stacking faults; probable point defects insidestacking faults; probable point defects inside

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

PDF – spherical particles modelPDF – spherical particles model

Rw~ 15%

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

% Fe/method% Fe/method HRTEMHRTEM RietveldRietveld PDFPDF

1.2 - 4.0 1.2 - 4.0 ÅÅ

1.2 - 20.0 1.2 - 20.0 ÅÅ

00 n.o.n.o. 4.6(7) %4.6(7) % (14(14±±3) %3) % (6(6±±3) %3) %

0.220.22 n.o.n.o. n.o.n.o. (4(4±±3) %3) % (0(0±±3) %3) %

0.470.47 n.o.n.o. n.o.n.o. (3(3±±3) %3) % (0(0±±3) %3) %

1.051.05 n.o.n.o. 6.1(6) %6.1(6) % (11(11±±3) %3) % (5(5±±3) %3) %

HRTEM, Rietveld and PDF – anatase %HRTEM, Rietveld and PDF – anatase %

anatase in a flower centre ???

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

SQUID – magnetic measurementsSQUID – magnetic measurements

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

the origin of ferromagnetism of TiOthe origin of ferromagnetism of TiO22:Fe :Fe still remains a controversial still remains a controversial

here always paramagnetic no matter Fe %here always paramagnetic no matter Fe % no Fe cluster formationsno Fe cluster formations

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

Raman Raman spectroscopyspectroscopy

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

0 200 400 600 800 1000

0% FeR

R

wavenumber / cm-1

R

aman

Int

ensi

ty A

R

B

0 200 400 600 800 1000

R

R

R

A

B

Ram

an I

nten

sity

wavenumber / cm-1

0.22% Fe

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

rutile and anatase confirmedrutile and anatase confirmed no brookiteno brookite more Fe more defects – “boson” peakmore Fe more defects – “boson” peak origin of “boson” peak - Fe (and origin of “boson” peak - Fe (and

vacancy) distribution break the vacancy) distribution break the vibration vibration

most of defects are point defectsmost of defects are point defects

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

HRTEM – anatase unobservedHRTEM – anatase unobserved XRPD – anatase observed in Rietveld but XRPD – anatase observed in Rietveld but

better in PDF better in PDF → low crystallinity→ low crystallinity Raman – best observation of anataseRaman – best observation of anatase Low quantity of anatase, c.c. 5%Low quantity of anatase, c.c. 5% Anatase in a flower centre ???Anatase in a flower centre ??? Anatase first to crystallize then rutile ?Anatase first to crystallize then rutile ?

Where is Where is anatase?anatase?

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

Acknowledgements:Acknowledgements: U.S. Dep. of Energy - DE-AC02-98CH10886 U.S. Dep. of Energy - DE-AC02-98CH10886 MSTRSMSTRS CNRSCNRS FP6 INCO-026401 WBC FP6 INCO-026401 WBC FP7 REGPOT3 - FP7 REGPOT3 - 204374 TERCE-NIPMSS204374 TERCE-NIPMSS

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

Recommendation for Recommendation for further synthesisfurther synthesis

Small amount of Fe stabilize rutile crystal Small amount of Fe stabilize rutile crystal structurestructure

Fe concentration does not influence Fe concentration does not influence significantly on morphology and size of significantly on morphology and size of nanorodsnanorods

Fe concentration influence on vacancy Fe concentration influence on vacancy concentrationconcentration

““Play” with synthesis conditions in order to Play” with synthesis conditions in order to obtain pure rutile with small amount of Feobtain pure rutile with small amount of Fe

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

Supplementary materialSupplementary material

XPS XPS → only Ti→ only Ti4+4+ but Fe but Fe3+3+ (dominantly) and Fe (dominantly) and Fe2+2+

Doping with Fe ions has great influence on Doping with Fe ions has great influence on optical characteristics of the host material optical characteristics of the host material →→ shift of the absorption threshold toward VIS shift of the absorption threshold toward VIS spectral region. spectral region.

No increase of photocatalytic activity after No increase of photocatalytic activity after doping. doping.

The induced photoluminescence as well as the The induced photoluminescence as well as the decrease of photocatalytic activity is probably decrease of photocatalytic activity is probably the consequence of the introduction of the consequence of the introduction of oxygen vacancies through doping procedure. oxygen vacancies through doping procedure.

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

For higher dopant concentrations also For higher dopant concentrations also recombination of photogenerated charge recombination of photogenerated charge carriers occurs with higher probability.carriers occurs with higher probability.

ACA Meeting, Toronto Canada, JuACA Meeting, Toronto Canada, July 25-30, 2009ly 25-30, 2009

PDF – F(Q)PDF – F(Q)