TiO2 nanoparticlesfor CO2 photoreduction: a combined...
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TiO2 nanoparticles for CO2 photoreduction: a
combined experimental and
periodic DFT study of the active sites
Lorenzo MinoC. Deiana, A. M. Ferrari, V. Maurino, G. Martra, G. Spoto
Department of Chemistry, University of Turin
Photocatalysis for energy
Lyon, 15‐17 October 2014
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Background of the study and investigation techniques
Study of the TiO2 exposed surface sites by CO adsorption
CO2 interaction with dehydroxylatedand hydrated TiO2 anatase surfaces
Conclusions and perspectives
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Background of the study and investigationtechniques
Section
Background of the study and investigation techniques
Study of the TiO2 exposed surface sites by CO adsorption
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
Conclusions and perspectives
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4Background of the study and investigation techniques
TiO2 for CO2 photoreductionA long story
surface study atan atomic/molecular level
Already in 1979 Honda and coworkers reported the photoreductionof CO2 to form formic acid, formaldehyde, methyl alcohol andmethane in aqueous suspension of TiO2.
Despite a considerable amount ofsubsequent studies, the conversionefficiency of CO2 into usefulhydrocarbons is still too low for large‐scale technological applications.
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5Background of the study and investigation techniques
The key role of surface sitesShape dependent properties
M.V. Dozzi et al., Catalysts 2013, 3, 455
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6Background of the study and investigation techniques
Nanoparticle morphologyElectron microscopy
TiO2 HT TiO2 T‐SP (Solaronix)TiO2 P25 (Evonik)
50 nm
study at an atomic level
Information on exposed surfaces
more complex morphology:how can we study the surface?
C. Deiana, et al., Phys.
Chem. Chem. Phys., 2013, 15, 307
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7Background of the study and investigation techniques
Nanoparticle morphology and surface propertiesFTIR spectroscopy of adsorbed probe molecules
TiO2 surface
OTi
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8Background of the study and investigation techniques
Nanoparticle morphology and surface propertiesFTIR spectroscopy of adsorbed probe molecules
TiO2 surface
OTi
C
O
OTi
TiO2 surfaceeffect of the interaction with surface sites on the ν of the internal mode
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9Background of the study and investigation techniques
FTIR spectroscopy of adsorbed probe molecules Carbon monoxide
The higher is the blue‐shift, the greater is the Lewis
acidity of the metal cation
Stretching frequency of adsorbed CO is also influenced
by the lateral interactions occuring in the adlayers
Information on surfaceproperties and morphology
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10Background of the study and investigation techniques
FTIR spectroscopy of adsorbed probe moleculesCryostat
G. Spoto et al., Prog. Surf. Sci., 2004, 76, 71
The use of a cryostat allowed us go below the liquid nitrogen
temperature obtaining spectra of considerably
improved quality
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Study of the TiO2exposed surface sites by CO adsorption
Section
Background of the study and investigation techniques
Study of the TiO2 exposed surface sites by CO adsorption
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
Conclusions and perspectives
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2220 2200 2180 2160 2140 2120
Abso
rban
ce 0.5 a.u.
Wavenumbers (cm-1)
12Study of the TiO2 exposed surface sites by CO adsorption
Anatase TiO2 nanocrystalsHRTEM and FTIR of CO adsorbed at 60 K
Ti
L. Mino, G. Spoto, S. Bordiga, A. Zecchina, J. Phys. Chem. C, 2012, 116, 17008
3800 3700 3600 3500
Wavenumbers (cm-1)
need of modeling for full assignment
Physisorbed CO
OH ∙∙ COAnatase extended surfaces Outgassedfor 2 h at 773 K
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8 9 10 11 12 13 14 15 16 17 18 19 200.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
E's
(J/m
2 )
Slab thickness (Å)
(101)
(100)
(103)(110)
(001)
(112)
13
Periodic DFT calculationsAnatase surface energies
Anatase surfaces modeled with bidimensional slabs
characterized by two infinite dimensions (x, y) and a finite
thickness exploiting the CRYSTAL09 code and the PBE0
functional
(001)
(101)
L. Mino et al., J. Phys. Chem. C 2011, 115, 7694
6 Ti‐layers for CO adsorption
Study of the TiO2 exposed surface sites by CO adsorption
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14
Periodic DFT calculationsCO adsorption on the main anatase surfaces
OTi
Study of the TiO2 exposed surface sites by CO adsorption
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15
Periodic DFT calculationsMain computed parameters
OTi
L. Mino et al., J. Phys. Chem. C 2011, 115, 7694
Study of the TiO2 exposed surface sites by CO adsorption
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2220 2200 2180 2160 2140 2120
Abso
rban
ce
0.5 a.u.
Wavenumbers (cm-1)
16Oxide surface properties and particle morphology
CO adsorbed at 60 K on nanoanataseComplete spectral assignment
L. Mino, G. Spoto, S. Bordiga, A. Zecchina, J. Phys. Chem. C, 2012, 116, 17008
Physisorbed CO
(112)
(101)
(001)
OH ∙∙ CO
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17Oxide surface properties and particle morphology
Rutile TiO2Modeling of CO adsorption
(001) (100)
(110)
(011)
L. Mino et al., J. Phys. Chem. C 2013, 117, 11186
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18Oxide surface properties and particle morphology
Rutile TiO2 model systemFESEM and FTIR of CO adsorbed at 60 K
OTi
BET surface area: 2 m2/g
2220 2200 2180 2160 2140 2120
0.3 a.u.
Abso
rban
ce
Wavenumbers (cm-1)
Reconstructed(110)
Rutile Wulffconstruction
(110)
L. Mino et al., J. Phys. Chem. C 2013, 117, 11186
OH ∙∙ CO
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19Oxide surface properties and particle morphology
Mixture of different polymorphsEvonik (Degussa) TiO2 P25
Mixture of about 85% anatase and 15% rutile with a surface area of 60 m2/g prepared by flame hydrolysis of TiCl4.Its outstanding photocatalytic activity makes it a benchmark for testing new synthesized materials.
HRTEM particles in 10‐50 nm range
XRD anatase 26 nm – rutile 42 nm
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20Oxide surface properties and particle morphology
TiO2 P25Ingredients for complete spectral assignment
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21Oxide surface properties and particle morphology
TiO2 P25Complete spectral assignment
L. Mino, G. Spoto, S. Bordiga, A. Zecchina, J. Phys. Chem. C, 2012,
116, 17008
Informatio on face distribution,
surface regularity and crystallinity
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22Oxide surface properties and particle morphology
Anatase TiO2 model systemFTIR of CO adsorbed at 100 K
C. Deiana, M. Minella, G. Tabacchi, V. Maurino, E. Fois, G. Martra, Phys. Chem. Chem. Phys., 2013, 15, 307‐315
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CO2 interaction with dehydroxylated and hydrated TiO2anatase surfaces
Section
Background of the study and investigation techniques
Study of the TiO2 exposed surface sites by CO adsorption
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
Conclusions and perspectives
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Dehydroxylated TiO2 anatase surfacesThe CO surface picture
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
Physisorbed CO
(101)
Low coordinated
Ti sites
OH ∙∙ CO
(001)
Nanoanataseoutgassed for 2h
at 823 K
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Dehydroxylated TiO2 anatase surfacesFTIR of adsorbed CO2 (pressure up to 10 mbar)
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
L. Mino, G. Spoto, A.M. Ferrari, J. Phys. Chem. C, 2014, DOI: 10.1021/jp507443k in press
Nanoanataseoutgassed for 2h
at 823 K
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Dehydroxylated TiO2 anatase surfacesPossible adsorption geometries on the (101) surface
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
ΔEform = ‐9.5 Kcal/mol ‐7.8 Kcal/mol
‐8.5 Kcal/mol2.7 Kcal/mol
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Dehydroxylated TiO2 anatase surfacesPossible adsorption geometries on the (001) surface
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
ΔEform = ‐5.3 Kcal/mol ‐30.1 Kcal/mol
‐3.4 Kcal/mol ‐20.9 Kcal/mol
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Dehydroxylated TiO2 anatase surfacesComputed vibrational frequencies
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
L. Mino, G. Spoto, A.M. Ferrari, J. Phys. Chem. C, 2014, DOI: 10.1021/jp507443k in press
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2400 23001700 1600 1500 1400 1300 1200
Experimental
Abso
rban
ce
Wavenumbers (cm-1)
0.5 a.u.
29
Dehydroxylated TiO2 anatase surfacesExperimental vs simulated FTIR spectra
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
101-L1
001-MC
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2220 2200 2180 2160 2140 2120Wavenumbers (cm-1)
0.5 a.u.
Abso
rban
ce
30
Hydrated TiO2 anatase surfacesThe CO surface picture
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
Physisorbed CO
(101) halved intensity
Low coordinated Ti sites missing
OH ∙∙ COmore intense
(001) missing
Nanoanataseoutgassed for 2h at 823 K and then
partially rehydrated
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Hydrated TiO2 anatase surfacesFTIR of adsorbed CO2 (pressure up to 10 mbar)
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
L. Mino, G. Spoto, A.M. Ferrari, J. Phys. Chem. C, 2014, DOI: 10.1021/jp507443k in press
Nanoanataseoutgassed for 2h at 823 K and then
partially rehydrated
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Hydrated TiO2 anatase surfacesPossible bicarbonates on the (001) surface
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
‐14.6 Kcal/mol
‐4.3 Kcal/mol
‐1.5 Kcal/mol
0.1 Kcal/mol 3.5 Kcal/mol 8.6 Kcal/mol
ΔEform = ‐10.3 Kcal/mol
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Hydrated TiO2 anatase surfacesBicarbonates computed vibrational frequencies
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
L. Mino, G. Spoto, A.M. Ferrari, J. Phys. Chem. C, 2014, DOI: 10.1021/jp507443k in press
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Hydrated TiO2 anatase surfacesExperimental vs simulated FTIR spectra
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
101-L1
001-MB1 001-BB2 001-BB3
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Conclusions and perspectives
Section
‐ The use of adsorbed CO as probe moleculeallowed us to highlight the exposed surface sitesand to determine the average nanoparticlemorphology.
‐ Study of mixtures of different polymorphs ormixtures of different oxides.
- On the most stable anatase (101) surface CO2 isweakly adsorbed and retains its molecularproperties.
‐ On the dehydroxylated anatase (001) surface theformation of monodentate carbonates occurs.
‐ On the partially hydrated (001) surface theformation of bidentate bicarbonates is favored.
‐ Basis for future in situ study under UV irradiation.
Background of the study and investigation techniques
Study of the TiO2 exposed surface sites by CO adsorption
CO2 interaction with dehydroxylated and hydrated TiO2 anatase surfaces
Conclusions and perspectives
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Acknowledgments
A. Zecchina
S. Bordiga
C. Negri
Thank you for the kind attention