View
94
Download
4
Category
Preview:
DESCRIPTION
Padova University. ISTM-CNR. INSTM. C. Maccato* 2 , D. Barreca 1 , A. P. Ferrucci 2 , A. Gasparotto 2 , C. Maragno 2 , E. Tondello 2 1 ISTM-CNR and INSTM - Padova, Italy 2 Department of Chemistry - Padova University and INSTM - Padova, Italy * chiara.maccato@unipd.it. - PowerPoint PPT Presentation
Citation preview
VI Convegno Nazionale sulla Scienza e Tecnologia dei Materiali – Perugia 12-15 Giugno 2007VI Convegno Nazionale sulla Scienza e Tecnologia dei Materiali – Perugia 12-15 Giugno 2007
CVD SYNTHESIS AND CVD SYNTHESIS AND
PHOTOCATALYTIC ACTIVITY PHOTOCATALYTIC ACTIVITY
OF ZnO NANOPLATELETSOF ZnO NANOPLATELETS
C. Maccato*C. Maccato*22, , D. BarrecaD. Barreca11, A. P. Ferrucci, A. P. Ferrucci22, , A. GasparottoA. Gasparotto22, C. Maragno, C. Maragno22, E. Tondello, E. Tondello22
11 ISTM-CNR and INSTM - Padova, Italy ISTM-CNR and INSTM - Padova, Italy22 Department of Chemistry - Padova University and INSTM - Department of Chemistry - Padova University and INSTM -
Padova, ItalyPadova, Italy
*chiara.maccato@unipd.itchiara.maccato@unipd.it
Padova University
ISTM-CNR
INSTM
Zinc oxide (ZnO)Zinc oxide (ZnO)
WurtziteWurtzite(hexagonal lattice)(hexagonal lattice)
nn-type-typesemiconductorsemiconductor
EEGG3.4 eV3.4 eV
Main interests:Main interests:
Optoelectronics Optoelectronics Gas Gas SensingSensing
Energetics Energetics PhotocatalysisPhotocatalysis
OZn
PHOTOCATALYSIS PHOTOCATALYSIS
AA ˉ̄
Valence Band
++
Conduction Bandhh > E
> Egg
ReductionReduction
AA
OxidationOxidation
DD--
DD
• The aim of semiconductor The aim of semiconductor photocatalysis is to effectivelyphotocatalysis is to effectivelydecompose organic pollutants.decompose organic pollutants.
• Photons are used to createPhotons are used to createelectron – hole pairs in electron – hole pairs in
the semiconductor.the semiconductor.
ee- - + O+ O22 → O→ O22--
hh++ + OH + OH- - → OH→ OH
•The competition between separation and recombination processes ofThe competition between separation and recombination processes ofcharge carriers (echarge carriers (e--, h, h++)).
•Surface catalysts-dye charge transfer and Surface catalysts-dye charge transfer and efficient surface adsorption/desorption processes.efficient surface adsorption/desorption processes.
Photocatalytic Activity depends on:Photocatalytic Activity depends on:
AIM:AIM:Synthesis of nanosystems characterized by a Synthesis of nanosystems characterized by a highhigh surface/volume surface/volume
ratio using a bottom-up ratio using a bottom-up CVDCVD approach approach .
Zn(hfa)Zn(hfa)22TMEDATMEDA
(Hhfa=1,1,1,5,5,5-hexafluoro-2,4-pentanedionate;
TMEDA=N,N,N’,N’-tetramethyilethylendiamine)
Zn(NO)3·xH2O
+
1,1,1,5,5,5-hexafluoro-2,4-pentanedione
+
N,N,N’,N’-tetramethylethylendiamine
Zn(hfa)Zn(hfa)22(TMEDA)(TMEDA)
Yield = 63%Yield = 63%
Tobin J. Marks et al., J. Am. Chem. Soc., (2005) 127, 5613.
Zn
O
H
F
N C
22ndnd Generation precursor Generation precursor
• high volatility high volatility and thermal stabilityand thermal stability
•one-pot synthesisone-pot synthesis
ZnO NANOSYSTEMSZnO NANOSYSTEMS
Zn(hfa)Zn(hfa)22(TMEDA) (TMEDA)
CVD
Si(100)
ZnO(O(O22+H+H22O) = O) = 40 sccm40 sccm
(N(N22) = 40 sccm) = 40 sccm
10 mbar, 60’10 mbar, 60’
TT[[Zn(hfa)Zn(hfa)22(TMEDA)(TMEDA)]] = 60°C = 60°C
TTsub.sub. = 250-500°C = 250-500°C
Thickness [Thickness [ΦΦ(O(O22+H+H22O)O)]]
TTsubsub.. 250250 300300 350350 400400 450450
111111 128128 256256 209209 1281286464 nmnm
500 °C500 °C
100 nm 100 nm
Water effect on morphologyWater effect on morphology
Tsub= 400°C Thin filmThin film
With HWith H22OOTTsubsub= 400°C= 400°C
100 nm100 nm
The obtained systems show very different morphologies
NanoplateletsNanoplatelets(NPTs)(NPTs)
FE-SEMFE-SEM
TTsub sub EFFECT EFFECT
System porosity is System porosity is temperature – dependenttemperature – dependent.
Different Different photocatalyticphotocatalytic
activity is expectedactivity is expected
NPTs mean NPTs mean thickness thickness ~ 5.5 nm~ 5.5 nm
No variationsNo variationsof NPTs morphology of NPTs morphology
afterafterthermal treatment thermal treatment
(600°C, 2h)(600°C, 2h)
100 nm
100 nm100 nm
250°C 250°C
350°C350°C
450°C 450°C
(a)
(c)
(e) (f)
(d)
(b)
100 nm 100 nm
100 nm 100 nm100 nm
100 nm100 nm100 nm100 nm
250°C 250°C
350°C350°C
450°C 450°C
100 nm 100 nm
100 nm100 nm
GIXRD GIXRD The expected intensity ratio The expected intensity ratio
II002002/I/I101101 for ZnO powders is 0.44. for ZnO powders is 0.44.
In the synthesized NPTs the In the synthesized NPTs the
II002002/I/I101 101 ratio depends on Tratio depends on Tsubsub with a with a
maximum value of 3.4 maximum value of 3.4
at Tat Tsubsub= 350°C.= 350°C.
ZnO(001) SurfaceZnO(001) Surface
ZnO(001) surface is polar.
The Lewis acids sites exposed on the surface are very reactive
toward the chemisorption of both H2O and OH- groups.
O Zn504030202 (degrees)
500°C
400°C
450°C
350°C
300°C
250°C
(100
)
(002
)(1
01)
(102
)
XPSXPS
C and F XPS signals disappear after amild sputtering indicating that
they are only surface contaminants.
Auger Parameter Auger Parameter - -
ZnOZnO
Auger Peak: ZnLMMXPS peak: Zn2p3/2
ZnO, literature≈ 2010.1 eV
ZnOZnO ≈ 2010.2 eV≈ 2010.2 eV
BE(XPS) + KE (Auger)BE(XPS) + KE (Auger)
KE = hKE = hυυ - BE - BE
80
60
40
20
0
150100500Sputtering timeSputtering time (min)(min)
Oxygen Zinc
Silicon
%%TTsubsub=350°C=350°C
200400
600800
200400
600
800
nm
4020
nm
(b)
400600
800
126
nm
nm
200
800
200400
600
(c)
200400
600800
200400
600800
nm
30
10
nm(a)
200400
600800
200400
600
800
nm
4020
nm
(b)
200400
600800
200400
600
800
nm
4020
nm
200400
600800
200400
600
800
nm
4020
nm
400600
800
126
nm
nm
200
800
200400
600
(c)
400600
800
126
nm
nm
200
800
200400
600
200400
600800
200400
600800
nm
30
10
nm(a)
200400
600800
200400
600800
nm
30
10
nm
200400
600800
200400
600800
nm
30
10
nm
200400
600800
200400
600800
nm
30
10
nm
AFMAFM
NPTs 350°CNPTs 350°CRMSR = 32 nmRMSR = 32 nm
NPTs 400°CNPTs 400°CRMSR = 6 nmRMSR = 6 nm
Film 400°CFilm 400°CRMSR = 2 nmRMSR = 2 nm
Photocatalytic activityPhotocatalytic activity
ZnO/Si(100)Orange II solution (2.4*10-6 M , pH ~ 6)
UV irradiation (125 W)
Decomposition process shows a pseudo-first order kinetics
K350°C (min-1) = 4.9*10-3
Irradiation time (min)
100
80
60
40
20
0
(Cd
ye/C
dye
,0)*1
00 (
%)
3002001000
ZnO NPTs (350°C) ZnO NPTs(400°C) ZnO thin film (400°C)
CONCLUSIONSCONCLUSIONS
Synthesis of ZnO NPTs on Si(100) starting from
Zn(hfa)2·TMEDA.
Tailoring of nanostructure and morphology as a function
of processing conditions.
Higher photocatalytic efficiency of ZnO NPTs
with respect to continuous films.
PERSPECTIVESPERSPECTIVES
Syntesis of ZnO-TiO2 nanocomposites.
Evaluation of their photocatalytic and gas sensing
performances as a function of synthesis parameters.
Inte
nsi
ty (
a.u
.)536 532 528
BE (eV)
O1s
Zn-OZn-OH
BE (eV)
Inte
nsi
ty (
a.u
.)
1025 1020
Zn 2p3/2
XPSXPS
XPS Signals pertaining to ZnO sample deposited at 350°CXPS Signals pertaining to ZnO sample deposited at 350°C
ZnO
Si
O
Si
OHHH
Si
O
Si
OHHH
ZnLL’
O
O
Si
O
Si
OHHH
ZnLL’
O
O
Si
O
Si
OHH
ZnLL’OH
O
…
(a)
Si
OH
Si
OH
Si
OH
Si
OH
(b)
Si(100)
ZnO
Si
O
Si
OHHH
Si
O
Si
OHHH
ZnLL’
O
O
Si
O
Si
OHHH
ZnLL’
O
O
Si
O
Si
OHH
ZnLL’OH
O
…
(a)
Si
OH
Si
OH
Si
OH
Si
OH
Si
O
Si
OH
Si
OH
Si
OHHHHHH
Si
O
Si
OH
Si
OH
Si
OHHHHHH
ZnLL’
O
O
Si
O
Si
OH
Si
OHHHHH
ZnLL’
O
O
Si
O
Si
OH
Si
OH
Si
OHHHH
ZnLL’OH
O
…
(a)
Si
OH
Si
OH
Si
OHH
Si
OH
Si
OH
Si
OHH
Si
OH
Si
OH
Si
OHH
Si
OH
Si
OH
Si
OHH
(b)
Si(100)
ZnO
(b)(b)
Si(100)
ZnO
Ruolo dei gruppi –OH nella crescita pseudo-
colonnare
RISULTATI ANALISI SEMRISULTATI ANALISI SEM
Alla temperatura del supporto Alla temperatura del supporto di 350°C si ha la deposizione di 350°C si ha la deposizione
miglioremigliore
1.4
1.2
1.0
0.8
0.6
0.4
0.2
ln v
(n
m/m
in)
1.9x10-3
1.71.61.51.41.31/T (K
-1)
CAMPIONI/ T (°C)CAMPIONI/ T (°C) SPESSORE SPESSORE FILM (nm)FILM (nm)
LUNGHEZZA LUNGHEZZA SCAGLIE (nm)SCAGLIE (nm)
SPESSORE MEDIO SPESSORE MEDIO SCAGLIE (nm)SCAGLIE (nm)
ZnO19/250ZnO19/250 111 111 ± 2± 2 5555 5.55.5
ZnO18/300ZnO18/300 128 128 ± 3± 3 6060 5.55.5
ZnO17/350ZnO17/350 256 256 ± 5± 5 6666 5.55.5
ZnO14/400ZnO14/400 209 209 ± 5± 5 7676 5.55.5
ZnO15/450ZnO15/450 128 128 ± 3± 3 5656 5.55.5
ZnO16/500ZnO16/500 64 64 ± 2± 2 3333 5.55.5
Zn(hfa)Zn(hfa)22TMEDA - CARATTERIZZAZIONETMEDA - CARATTERIZZAZIONE
m.p.=104-106°C
analisi elementareC=32,29%, H=2,87%, N=4,64%
analisi 1H- e 13C-NMR
analisi termiche
ln p1 – ln p0 = (H0vap/R)(T0
-1 –T1-1)
H°vap = 102 1 kJ/mol
► singolo processo di sublimazione senza decomposizione
► Perdita in peso = 98%
-8
-7
-6
-5
-4
ln[v
eloc
ità
vap
oriz
zazi
one
(mm
ol/m
in)]
3.0x10-3
2.82.72.6
1/T(K-1
)
sperimentale fit
100
80
60
40
20
0
mas
sa(%
)25020015010050
T(°C)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
derivata massa (%
/°C)
Trasporto di massaTrasporto di massa
Diffusione verso la superficieDiffusione verso la superficie
Reazione superficiale
Desorbimento sottoprodotti
Eliminazione sottoprodottiliminazione sottoprodotti
Nucleazione e crescita
CVD - termico
Centro metallico
R
RRR
R
R
R
Legante
Substrato
R
CVDChemical
Vapor DepositionGas reattivo
1 1
2 2
sourcedetector
GIXRDGIXRD
detector2
1
source
enhancementof surface sensitivity
XRDXRD
detects only reflectionsfor planes parallel
to the sample surface
Ass
orba
nza
(a.u
.)
700600500400300(nm)
0 min15 min45 min75 min
135 min195 min255 min315 min
ORANGE IIORANGE II
Recommended