Analisi e caratterizzazione di materiali nanostrutturati per dispositivi e sensori
La sintesi chimica dei materiali porosi nanostrutturati e ... · La sintesi chimica dei materiali...
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La sintesi chimica dei materiali porosi nanostrutturati La sintesi chimica dei materiali porosi nanostrutturati e le applicazioni in catalisi e nella sensoristicae le applicazioni in catalisi e nella sensoristica
Parte 2: applicazioniParte 2: applicazioni
Corso di Laurea in Ingegneria Industriale
Ciclo di Seminari“I nuovi materiali per le tecnologie del futuro”
Parte 2: applicazioniParte 2: applicazioni
Sandra Dirè
Riccardo Ceccato
26 maggio 2008
1Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
MultiMulti--component inorganic oxidescomponent inorganic oxides
•• Hybrid O/I filmsHybrid O/I films
•• SiOC/ZrOSiOC/ZrO22 SiOC/TiOSiOC/TiO22
•• SiOSiO22/SnO/SnO22
•• ZrOZrO TiOTiO VV OO
SolSol--gel Methodgel Method
2
•• ZrOZrO22 TiOTiO22 VV22OO55
•• TiOTiO22/V/V22OO55 NiO/VNiO/V22OO55 BiBi22OO33/V/V22OO55
•• BaO/TiOBaO/TiO22 BaTiOBaTiO33
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Hybrid SolHybrid Sol--Gel materialsGel materials
•Multicomponent materials prepared at low
temperature by sol-gel chemistry
•Alkoxide precursors modified with organic groups
•Presence of organic groups in the inorganic network
(Si-C bond stability towards hydrolysis)
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 3
Obtained materials display chemicalObtained materials display chemical
and surface properties that are intermediateand surface properties that are intermediate
between inorganic networks and organicbetween inorganic networks and organic
polymerspolymers
Hybrid materials:
Class I: Van der Waals interactions between organic and inorganic parts
Class II: covalent bonds between the two counterparts
Hybrid O/I films as chemical sensorsHybrid O/I films as chemical sensorsHybrid O/I films used as sensing elements: Hybrid O/I films used as sensing elements:
•• Porosity, chemical properties of the film surface can be tunedPorosity, chemical properties of the film surface can be tuned
•• Films can operate at ambient temperature Films can operate at ambient temperature
•• Detection of alcohols (vapours) from their electrical responsesDetection of alcohols (vapours) from their electrical responses
•• Detection of aromatic and alkane vapours from their optical propertiesDetection of aromatic and alkane vapours from their optical properties
•• Detection of aromatic molecules from their changes in UVDetection of aromatic molecules from their changes in UV--absorptionabsorption
spectra (molecule and molecule + film)spectra (molecule and molecule + film)
Why aromatic molecules?Why aromatic molecules?
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 4
MoleculeTWA[ppm]
STEL [ppm]
Benzene 0.5 2.5
Chlorobenzene 10 -
Toluene 50 -
O-Xilene 100 150
Why aromatic molecules?Why aromatic molecules?
TWA = Time Weighted AverageSTEL = Short Term Exposure Limit
Directive 2000/69/EC:
TLV for benzene in air: 1.6 ppb
(starting from 2010)
High sensitivity sensorsHigh sensitivity sensors
Synthesis of hybrid filmsSynthesis of hybrid films
TEOS, EtOH, H2O
Pre-hydrolysis, 1h
EtOH/Si = 4/1H2O/Si = 1/1pH = 2, 7
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 5
•• film area: ~ 4 cm2
•• film thickness: ~ 1µm
MTES or GLYMO addition Stirring, 0.5 h
TM 7/3 and 9/1TG 7/3 and 9/1
Dip-coating r = 6 cm/min
Film characterizationFilm characterization
XRD spectra
0 5 10 15 20
Lo
g (
Inte
nsi
ty)
Angle (2θ)(2θ)(2θ)(2θ)
film TM 9/1
0 5 10 15 20
Lo
g (
Inte
nsi
ty)
Angle (2θ)(2θ)(2θ)(2θ)
film TG 9/1 • Intense peak attributable to
silica network (analogous to
mesoporous SiO2)
• Second peak (>d) due to the
O/I phase interaction?
• TM 7/3 film: different situation:
shift to lower d values and
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 6
0 5 10 15 20
Lo
g (
Inte
nsi
ty)
Angle (2θ)(2θ)(2θ)(2θ)
film TG 7/3
0 5 10 15 20
Lo
g (
Inte
nsi
ty)
Angle (2θ)(2θ)(2θ)(2θ)
film TM 7/3
shift to lower d values and
decrease of “inorganic” peak
intensity
• TM and TG 7/3 films: presence
of a halo (~ 6°°°°) due to the higher
network modifier content
(M pure gel)
Instrumental setInstrumental set--upup
line 1 line 1
carrier gascarrier gas
line 2line 2
carrier gas + carrier gas +
moleculemoleculeSampling chamberSampling chamber
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 7
FlowmetersFlowmeters
Sampling chamber: V = 1 dmSampling chamber: V = 1 dm33
Aromatic molecule (liquid) in a bubbler (vapor pressure)Aromatic molecule (liquid) in a bubbler (vapor pressure)
Results: absorbance spectraResults: absorbance spectra
Empty cell
First run
Ab
sorb
ance
•• Film interaction: decrease in absorbanceFilm interaction: decrease in absorbanceof the moleculeof the molecule
•• No peak broadening or fine structureNo peak broadening or fine structurevanishing: surface interaction and novanishing: surface interaction and no
Benzene TG 7/3
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 8
Chlorobenzene TG 9/1
Empty cell
First run
Ab
sorb
ance
vanishing: surface interaction and novanishing: surface interaction and nodiffusion into the filmdiffusion into the film
•• Spectral features of the molecule remains:Spectral features of the molecule remains:different different λλλλλλλλ values of Max absorbance:values of Max absorbance:qualitative analysisqualitative analysis
Chlorobenzene TG 9/1
Results: reversibility of the interactionResults: reversibility of the interaction
Ab
sorb
ance
Benzene recovery TG 7/3
Ab
sorb
ance
o-Xilene recovery TM 9/1
Ab
sorb
ance
Chlorobenzene recovery TG 9/1
Toluene recovery TM 7/3
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 9
Ab
sorb
ance
Ab
sorb
ance
For all film compositions and for all molecules, nitrogen purging allowsFor all film compositions and for all molecules, nitrogen purging allowsthe complete recovering of the film trapping features (Max. 20 min)the complete recovering of the film trapping features (Max. 20 min)
Results: comparison of film performancesResults: comparison of film performances
Ab
sorb
ance
Ab
sorb
ance
Ab
sorb
ance
Ab
sorb
ance
Time (sec)Time (sec)
Benzene
Chlorobenzene
Toluene
o-Xilene
Benzene
Chlorobenzene
Toluene
o-Xilene
TG 7/3TG 7/3
o-Xilene (261 nm)Benzene (254 nm)
TG 7/3 TG 9/1
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 10
Time (sec) Time (sec)
Ab
sorb
ance
Ab
sorb
ance
TG 7/3TM 7/3TG 9/1TM 9/1
TG 7/3TM 7/3TG 9/1TM 9/1
With the same experimental conditions, different film/moleculeWith the same experimental conditions, different film/molecule
interactions interactions �������� different selectivities different selectivities
Benzene: weak interactions with film surfaceBenzene: weak interactions with film surface
OO--Xilene: strong interactions with all filmsXilene: strong interactions with all films
Parametric refinement of kinetic curvesParametric refinement of kinetic curves
ττττττττ00 (sec) is related to the chamber filling time(sec) is related to the chamber filling time
•• In order to characterise different adsorption film capabilities, a simple In order to characterise different adsorption film capabilities, a simple model has been assumed for the kinetic behaviormodel has been assumed for the kinetic behavior
•• When the measurement chamber is empty, the filling rate can be When the measurement chamber is empty, the filling rate can be determined as:determined as:
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 11
ττττττττaa (sec) is related to the adsoprtion(sec) is related to the adsoprtion onto the film surfaceonto the film surface
•• When he film is inserted into the chamber, the whole adsorption When he film is inserted into the chamber, the whole adsorption process can be expressed as:process can be expressed as:
Results: fitting of dataResults: fitting of data
0.1
0.2
0.3
0.4
0.5
0.6
sperimentaliA
ssorb
anza
TM 9/1 Benzene 254nmA
bso
rban
ceExperimental data
Fitting curve
♦♦♦♦Benzene TM 9/1 (254 nm) ( ) ( )-x/397.87-x/81.9672 e-10.05858 e-10.48061 y ∗+∗=
Statistical parameters:
χ2 = 0.00003
R2 = 0.99726
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 12
0 200 400 600 800 1000
0.0
tempo [sec]Time (sec)
ττττττττaa values for benzenevalues for benzene
TM 9/1TM 9/1 398398±±±±±±±±3333
TG 9/1TG 9/1 436436±±±±±±±±3333
TM 7/3TM 7/3 2.72.7±±±±±±±±0.40.4
TG 7/3TG 7/3 6.36.3±±±±±±±±0.60.6
Results: adsorption of benzeneResults: adsorption of benzene
•• Benzene steric hindrance: 6Benzene steric hindrance: 6ÅÅ
•• Adsorption on the film surface (micropores)Adsorption on the film surface (micropores)
•• Reversibility of the interactionReversibility of the interaction
•• ττττττττa a values that depend on electronic effects:values that depend on electronic effects:
•• TM 9/1 and TG 9/1: higher degree of interaction betweenTM 9/1 and TG 9/1: higher degree of interaction between
π π π π π π π π
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 13
SiSi--OH / OH / π π π π π π π π electrons of benzene (hydrogen bond) electrons of benzene (hydrogen bond)
→ high→ high ττττττττaa valuesvalues
•• TG 7/3 and TM 7/3: higher content of “organic” groups TG 7/3 and TM 7/3: higher content of “organic” groups
on the pore surface on the pore surface →→ weaker interaction with weaker interaction with π π π π π π π π electronselectrons
→ low→ low ττττττττaa valuesvalues
Hybrid O/I films for wine characterizationCyclic Voltammetry (CV)
Working electrode: O/I filmCounter electrode: PtReference electrode: Ag/AgCl
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 14
Hybrid O/I films for wine characterization
White and red wines are wellseparated
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 15
TA films show different behaviour:presence of –NH2 groups that areprotonated in acidic solutions
Thermal evolution of SiOC phase in the presence of Thermal evolution of SiOC phase in the presence of the metal oxidethe metal oxide
OSi
O
O
Si
OSi
O
a-SiO2 SiOC glass
SiC
O
O
Si
OSi
O
SiSi
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 16
Metal load influences Si-C bond stability
����Different structural evolution of polysiloxane - titaniagels as a function of metal load
Synthesis of xerogelsSynthesis of xerogels
H2O, HClEtOH
Pre-hydrolysisD
DMexMe, x mol%
PreceramicPolymers
Ceramization Process
Final am./cryst.Nanocomposites
Thermal treatments (Ar)
500 °°°°C↓↓↓↓
800 °°°°C
1000 °°°°C↓↓↓↓
1600 °°°°C
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 17
Characterization of samplesCharacterization of samples
• IR• TGA• N2-sorption
•XRD
GelationNanocomposites 1600 °°°°C
Thermal evolution and porosityThermal evolution and porosity
DTi 10DTi 20DTi 30
S.S
. A.(
m2/g
)
N2-Sorption
-40
-30
-20
-10
0
10
Wei
gh
t lo
ss, %
DTI30
Thermal analysis
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 18
0 400 800 1200 1600Temperature (°C)
-60
-50
200 400 600 800 1000
Temperature, C
DTI10
DTi10: two weight lossesDTi30: one weight lossDTi30 thermal evolution iscompleted at 600 °°°°C, DTi10above 800 °°°°C
DTi30: maximum SSA value at 500 °°°°C (175 m2/g)
DTi10: maximum SSA value at 800 °°°°C(384 m2/g),
high SSA values up to 1000 °°°°C(273 m2/g)
Ceramization processCeramization process
Increase of the metal oxide load:
1. decreases the stability of polysiloxane-oxide network
(due to the increase in phase interaction) ⇒⇒⇒⇒
⇒⇒⇒⇒ Si-C bond cleavage (low temperature)
2. Evolution of methane and Si-based species at low
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 19
2. Evolution of methane and Si-based species at low
temperatures
3. Favours the polymer-to-ceramic conversion
Phase evolutionPhase evolution
Amorphous phasesSiCxO2(1-x) phase (SiOC): stable up to 1600 °°°°C
(except DTi30)
TiOxC1-x phase (TiOC): 800 °°°°C (all DTix)
Evolution SiCxO2(1-x) →→→→ SiO2 (+ SiC for DTi10)
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 20
Crystalline phases TiOxC1-x →→→→ TiC + Ti oxides (DTi20 and DTi30)
TiO2: 1000 °°°°C (all DTix)
SiO2 cristobalite (DTi30 at 1400 and 1600 °°°°C)
SiOC phase evolutionSiOC phase evolution
7,10
7,20
7,30
a (Å
)When the carbon content retained into the phase is higher, the phase density is higher and its a parameter value is lower Si
C
O
O
Si
OSi
O
SiSi
Increasing Ti %: lower C contentIncreasing Ti %: lower C contentand higher a valueand higher a value
All DTix: final amorphous phase isAll DTix: final amorphous phase is
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 21
6,80
6,90
7,00
1000 1200 1400 1600
DTi 10DTi 20DTi 30silica
a (Å
)
Temperature (°C)
All DTix: final amorphous phase isAll DTix: final amorphous phase ispure SiOpure SiO22 (loss of C)(loss of C)
DTi30: crystallization of cristobaliteDTi30: crystallization of cristobalite(tetragonal) starts at (tetragonal) starts at 1400 1400 °°°°°°°°CC
SiOSiO22/SnO/SnO22 SystemsSystems
Homogeneous dispersions of M(IV)-oxide particles in silica matrix
Applications: catalysts, sensors, optical fibers
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 22
Requirements: control on the •thermal stability•particle sizes •porosity•development of suitablephases
SolSol--Gel SynthesisGel Synthesis
DissolutionTHF
Si(OEt)4
[Si(OEt)4] = 1M
Hydrolysis
H2O pH = 2
Molar ratio:H2O/Si = 2
24 h Sol preparation
Sn(OEt)4 in THF
[SnO2] = 0.13 g/ml
≈ 3 daysGelification
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 23
Samples
SiO2/SnO2:
(weight ratios)
95/5
90/10
80/20
70/30
Thermal treatments(Air, O2, He)
Characterization techniques:DTA, N2-physisorption, IR, XRD,
Mössbauer spectroscopy
H2O/Si = 2
Monolithic gels
(dimensions decrease with tin content)
Compositional EffectCompositional EffectIR spectra of the gels
Increasing Sn content:•increase of -OH groups(≈ 3400, 1650 cm-1)
•increase of Si-OH + Si-O-Sn
bands (950 cm-1)
•increase and broadening of
Sn-O band (≈ 650 cm-1)70/30
% T
ran
smit
tan
ce
80/20
% T
ran
smit
tan
ce
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 24
Sn-O band (≈ 650 cm-1)
Increase of the structural disorder of tin species
5001000150020002500300035004000
Wavenumber (cm-1
)
5001000150020002500300035004000
Wavenumber (cm -1 )
5001000150020002500300035004000
% T
ran
smit
tan
ce
Wavenumber (cm-1
)
90/10
5001000150020002500300035004000
% T
ran
smit
tan
ce
Wavenumber (cm -1 )
95/5
Temperature EffectTemperature EffectCrystallization behaviour:
SiO2/SnO2 70/30 samples treated in airXRD spectra
Inte
nsi
ty (
arb
. un
.)
*
* SnO2 cassiterite
+
+ SiO2 cristobalite
SnO2 crystallite sizes (nm):1000 °°°°C →→→→ 10.5(0.3)800 °°°°C →→→→ 3.9(0.3)700 °°°°C →→→→ 2.17(0.06)600 °°°°C →→→→ 1.82(0.06)
•Increasing Sn content,crystallization of SnO2 occursat lower temperature, where the matrix is still amorphous(primary crystallization)
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 25
20 30 40 50 60 70 80
Inte
nsi
ty (
arb
. un
.)
Angle (2Θ)(2Θ)(2Θ)(2Θ)
600 °C
700 °C
800 °C
1000 °C
*
*
*
+ ++
SnO2
cubic phase
600 °°°°C →→→→ 1.82(0.06)
•For 95/5 sample,crystallization occurs at 1160 °°°°C (decomposition of the matrix in SiO2 + SnO2)
Temperature EffectTemperature Effect
Crystallization behaviour:SiO2/SnO2 samples treated in air
DTA curves
Exo
ther
mal
515 °C 895 °C
830 °C
Exo
ther
mal
620 °C
1205 °C
Primary crystallization temperature increaseswhen tin content lowers
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 26
0 200 400 600 800 1000 1200 1400
Temperature (°C)
70/30
0 200 400 600 800 1000 1200 1400
Temperature (°C)
80/20
0 200 400 600 800 1000 1200 1400
Exo
ther
mal
Temperature (°C)
90/10
730 °C
940 °C
0 200 400 600 800 1000 1200 1400
Exo
ther
mal
Temperature (°C)
95/5
1160 °C
Phase evolution by the heat treatmentPhase evolution by the heat treatment
Lo
g(I
nte
nsi
ty)
(arb
. un
.) 95/5
90/10
80/20
70/30
**
**
x
x xx
³
³
x cristobalite
³ tridymite
* cassiterite
Lo
g(I
nte
nsi
ty)
(arb
. un
.)
95/5
90/10
80/20
x
x x x
+ +
*³
x cristobalite
³ tridymite
* cassiterite
+ metal tin
Lo
g(I
nte
nsi
ty)
(arb
. un
.)
95/5
90/10
80/20
x
x x x
+ +
* *
* *
³
³
³³ ³
x cristobalite
³ tridymite
* cassiterite
+ metal tin
XRD spectra of samples heated at 1400 °°°°C
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 27
20 25 30 35 40
Lo
g(I
nte
nsi
ty)
(arb
. un
.)
Angle (2Θ)(2Θ)(2Θ)(2Θ)
70/30
20 25 30 35 40L
og
(In
ten
sity
) (a
rb. u
n.)
Angle (2Θ)(2Θ)(2Θ)(2Θ)
70/30* *
**
³³
³
³
20 25 30 35 40
Lo
g(I
nte
nsi
ty)
(arb
. un
.)
Angle (2Θ)(2Θ)(2Θ)(2Θ)
70/30
* *
Oxygen Air Helium
•Tin content and the heat treatment stabilize different silica polymorphs
•Low tin content and inert atmosphere support the reduction to metal tin by
the decomposition of Sn(II): 2SnO →→→→ Sn + SnO2
Zr(OPr)4
(70% solution in PrOH)
ZrO2 x H2O
Hydrolysis with water excess
(molar ratio: Zr(OPr)4/H2O = 1/160)
ZrO2 sol
Peptization with HCl
(12.5 M; molar ratio: Zr(OPr)4/HCl = 1/1.43)3-4 days at 90°C
30 min. at R.T.
Synthesis of Y-ZrO2 porous films
Organic
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 28
Y(OAc)3.4 H2O (90 mol% ZrO2 / 10 mol%Y2O3)
Organic compound (organic/Σ metal oxides = 20 wt% / 80 wt%)
Casting on PP, drying, xerogels within several days at R.T.
1 h at R.T.
1 h at R.T.
Organic compound
PVA
dextran
sucrose
starch
albumin
CMC
Synthesis of Y-ZrO2 porous films
SURFACE AREA AND MICROPORE AREA BY N2 SORPTION ANALYSIS
Organic compound
PVA
dextran
sucrose
starch
albumin
CMC
Surface area ±±±± SEMa
(m2/g)b
10.08 ± 0.11
6.55 ± 0.23
4.38 ± 0.20
3.68 ± 0.046
3.66 ± 0.047
3.04 ± 0.11
Micropore area(m2/g)c
1.93
3.11
1.59
1.29
1.42
1.29
(1200°C, air, 5°C/min, 1 h isotherm)
� c-YSZ
Inte
nsi
ty (
a.u
.)
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 29
CMC 3.04 ± 0.11 1.29
a SEM: standard error of meanb obtained from BET equationc obtained from t-plot
Angle (2 Θ)20 40 60 80 100
Reverse micelles methodReverse micelles method
Water-in-oil droplets
Formation of a “water pool” → w = [H2O]/[S]
S = surfactant agent
“Reverse micelles”: w < 15; “Microemulsion”: w > 15
Synthesis of TiO2 nanopowders
30
Water
OilAssumption: spherical droplets
Sphere radius:
[ ][ ]S
OH3V R
2aq
W σ=
Vaq = Volume of water molecules
σ = head polar group area
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Ti(OPri)4+
Cyclohexane
TRITON X-100+
Cyclohexane
Molar ratios:
H2O/alkoxides = 10/1
H2O/surfactant =10/1
Surfactant:
TRITON X-100 =polyoxyethylene(10)isooctylphenylether
4-(C8H17)C6H4(OCH2CH2)nOHn ~ 1015
minstirr
Synthesis of TiO2 nanopowders
31Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Reverse micelles
WaterPowder formation
Filtration Drying(T=80°°°°C)
Film Formation
H2O/surfactant =10/1
30 minstirr
3-4 times
100
120
140
160
180
Isotherm Plot
Vo
l. A
dso
rbed
0,005
0,006
0,007
0,008
0,009
0,010
BJH Desorbtion dV/dD Pore Volume
Po
re V
olu
me (
cm3/
c-A
)
Powder characterization
N2-physisorption
Type Iv-a isotherm ���� mesoporous system
0 0,2 0,4 0,6 0,8 1 1,2
0
20
40
60
80
Relative Pressure P/P0
Vo
l. A
dso
rbed
10,0 100,0 1000,0
0,000
0,001
0,002
0,003
0,004
0,005
Pore Diameter (A)
Po
re V
olu
me (
cm3/
c-A
)
32Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Specific Surface Area: 170 m2/g
150
200
250
Inte
nsit
y (
arb
. u
n)
300
400
500
600
700
Inte
nsit
y (
Arb
. U
n.)
Powder characterization
As prepared powder 400 °°°°C-treated powder on glass
10 20 30 40 50 60 70 80
0
50
100
Angle 2Θ
Inte
nsit
y (
arb
. u
n)
5 15 25 35 45 55 65 75 85 95
0
100
200
300
Angle 2Θ
Inte
nsit
y (
Arb
. U
n.)
33Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Quantitative analysis: 75 % anatase25 % brookite
Application: DSSC
34Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
S(adsorbito) + hv→ S°(adsorbito)
S°(adsorbito) → S+(adsorbito) + e-
(iniettato)
S+(adsorbito) + 3/2 I- → 1/2 I-3 + S(adsorbito)
I-3 (catodo) + 2e- → 3I-(catodo)
S°(adsorbito) → S(adsorbito)
S+(adsorbito) + e-
(TiO2) → S(adsorbito)
I-3 (anodo) + 2e-(TiO2) → 3I-(anodo)
DSSC preparation
Experimental measurements
35Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Experimental measurements
-20
0
20
40
60
80
100
120
140
160
180
Mirtillo
Mora
SambucoTen
sio
ne
(V)
Results
0,000 0,050 0,100 0,150 0,200 0,250 0,300 0,350 0,400 0,450 0,500
0
50
100
150
200
250
300
350
400
450
0E+0
1E-2
2E-2
3E-2
4E-2
5E-2
6E-2
7E-2
8E-2
Indoor measurements Outdoor measurements
0 1000 2000 3000 4000 5000 6000
-20
Tempo (s)
36Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
0,000 0,050 0,100 0,150 0,200 0,250 0,300 0,350 0,400 0,450 0,500
Corrente Potenza
Tensione (V)
Synthesis of V2O5 thin films
Sol-gel method: hydrolysis of vanadium alkoxides
a) VO(OPri)3 + i-PrOH → film deposition (in ambient air)
b) VO(OPri)3 + CH3COOH + i-PrOH +H2O → film deposition
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 37
Hydrolysis: water with pH = 0, 1, 2
c) As b) + (Ti, Zr) alkoxides or (Bi, In, Sb) chlorides
(mixed compositions) → film deposition
a), b), c) → gels
V2O5 gels and films
Inte
nsi
ty (
arb
. u
n.)
Alkoxide-derived gels and films = amorphous
XRD spectra on films XRD spectra on gels
V2O5·nH2O
0.5≤ n ≤ 1.8
Inte
nsi
ty (
arb
. u
n.)
pH = 2
d <, n >
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 38
5 10 15 20
Angle (2θ)(2θ)(2θ)(2θ)
pH = 1
pH = 2
no hydr.
pH = 0
•Microstructural order in films depends on the synthesis conditions
(pH of water added during hydrolysis)
•Gels do not show significant changes in unit cell parameters
5 10 15 20 25 30In
ten
sity
(a
rb. u
n.)
Angle (2θ)(2θ)(2θ)(2θ)
pH = 0
pH = 1
Thermal analysis of V2O5 gels
ex
oth
erm
al
pH = 1
pH = 2
* **
d)
c)Inte
nsity
(arb
.un.)
DTA curves Raman Spectra(pH = 2 sample)
°
310 °C
550 °C
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 39
0 100 200 300 400 500 600 700 800
Temperature, °C
pH = 0
200 400 600 800 1000
**
*
* *
x 4
x 4b)
a)
Raman shift (cm-1)
• different thermal behaviour, depending on synthesis conditions
• presence of two exothermal effects
• crystallization of a metastable V2O5-nanotubes (280-310°C)
RT
280 °C
Electrochromic devices
+ _
++
+++++
_________
IonsConductor
Electrode
Electrolyte
Electrode
Conductor
Simultaneous ionic and electronic conductivities
WO3 + xM+ + xe- →→→→ MxWO3 (cathodic)(clear) (blue)FeII[FeII(CN)6]2- →→→→ FeIII[FeII(CN)6]- + e- (anodic)
Inorganic oxides:
40
coloured state
bleached state
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Electrochemical features of VElectrochemical features of V22OO55 thin filmsthin films
Insertion process: xLi+ + V2O5 →→→→ LixV2O5 x ≤ 1
Gels: V2O5·nH2O Layered structure (2D)
•Good cycling reversibility•High insertion levels of Li+
•Simultaneous reduction
41
•Simultaneous reductionV5+ →→→→ V4+
Residual coloration (both anodic and cathodic)
Use of a “bleaching oxide”
(TiO2, NiO, In2O3, Sb2O3, Bi2O3, ZrO2)
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
-0.0
00
20
0.0
00
20
.00
04
Cu
rren
t (A
) 1st cycle
10th cycle
Ti/V oxide systemsElectrochemical behaviour of films
Surfactant effect
-0.0
00
20
0.0
00
2
Cu
rren
t (A
)
1st cycle
10th cycle
-0.0
00
40
0.0
00
4
Cu
rren
t (A
)
1st cycle
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 42
-0.0
00
4
-1 0 1
Voltage (vs. Ag/AgCl)-0
.00
02
-1.5 -1 -0.5 0 0.5 1 1.5
Voltage (vs. Ag/AgCl)
-0.0
00
4
-1.5 -1 -0.5 0 0.5 1 1.5
Voltage (vs. Ag/AgCl)
10th
cycle
Ti/V 1/1 No hydrolysis Ti/V 1/1 + Triton Ti/V 1/1 + Brij
Triton: higher stability, more amorphous systemBrij: lower stability
60
80
100
Film transparency
Ti/V 1/10 400 °C
TI/V oxide systems
43Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
0
20
40
60
300 400 500 600 700 800
First run
Intercalation
Deintercalation
Wavelength (nm)
Electro-optical response in NLC-cells
60,9
Tra
nsm
itte
d lig
th (
a.u
.)
Typical LC cell configuration
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 44
-6
-4
-2
0
2
4
-0,6 -0,4 -0,2 0,0 0,2 0,4 0,60,2
0,3
0,4
0,5
0,6
0,7
0,8
Time (s)
Tra
nsm
itte
d lig
th (
a.u
.)
5V
Ap
plie
d v
olta
ge
(V)
Ti/V 1/1 films
Rectified electro-optical
response
Electrochemical behavior of Ni/V 1/10 filmsElectrochemical behavior of Ni/V 1/10 filmsSol-gel films heated at 400 °C
Ni(acac)2
•Low charge capacity (≈10 mC/cm2)
•Oxidation peak andreduction peaks areunchanged
(70 nm)
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 45
NiCl2
•Low charge capacity(≈10 mC/cm2)
•Oxidation peak decreases (newshoulder at 1.9 V)
•Reduction peakstend to vanish
(60 nm)
Transmittance spectrum of Ni/V 1/10 filmTransmittance spectrum of Ni/V 1/10 film
% T
ransm
itta
nce
first run
intercalation
deintercalation
Sol-gel film from Ni(acac)2 pH = 1
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 46
% T
ransm
itta
nce
deintercalation
•Transmittance > 80 % in all visible region
•No irreversible changes during cycles
-400
-200
0
200
400
600 1Hz
Curr
ent (n
A)
Bi/V 1/10 systems
0
2
4
Ap
plie
d V
oltag
e (
V)
0,085
0,090
0,095
0,100
0,105 Pho
tod
iode
resp
on
se
(arb
.u.)
400 °°°°C treated films
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica 47
-10 -5 0 5 10
-600
Applied Voltage (V)
Low charge capacity
-2 0 2
-4
-2
Time (s)
Ap
plie
d V
oltag
e (
V)
0,075
0,080
Pho
tod
iode
resp
on
se
(arb
.u.)
Similar results than Ti/V systems
Barium TitanateBarium Titanate
Ferroelectric Perovskite ABO3 class:Cubic structure A = mono- or divalent ion (green)B = tri- to hexavalent ion (grey)
48
BaTiO3: high-dielectric constant materialNanocrystalline powders: Multilayer ceramic capacitors (MLCC)(Piezoelectricity)nano-sized powders: amorphous → low dielectric performance
crystalline → ultra thin dielectric layers
Size effect: ferroelectric ceramic lose ferroelectricity at a critical size
Ferroelectricity strongly related to the crystallite size
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Barium TitanateBarium Titanate
Polymorphic transformation: Tetragonal → Cubic
TC = 120 °CTC = 75 °C for 120 nm particle size
49
Grain-size dependenttransformation at R.T(tetragonal → orthorhombic)
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Synthesis and characterization of BaTiO3 nano-powders
Electrical properties that depend on particle size
Effect of synthesis procedure on particle size and phase evolution
BaTiO3 ���� perovskite (cubic) structure ����piezoelectricity
Ti(OPri)4 H2O
50
Mixing Mixing
Hydrolysis
Gelation
2-PrOH
CH3COOH
H2O
Ba(CH3COO)2
Powder80 °°°°C
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
SolSol--Gel synthesis of BaTiOGel synthesis of BaTiO33
1. Barium acetate / Titanium isopropoxide → hydrolysis
2. Barium isopropoxide / Titanium isopropoxide → hydrolysis
3. Addition of acetic acid as a chelating agent
4. Addition of 2-propanol and ethylene glycol (co-solvent)
5. Refluxing of the reagent solutions
51
Results
Phase separation: BaCO3 formation during precipitation
No stoichiometric control of the reaction
TiO2 crystallization (excess of Ti)
Thermal treatment: Transformation to tetragonal BaTiO3
phase above 800 °CNo pure BaTiO3 phase
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Synthesis of BaTiOSynthesis of BaTiO33 powders from RM methodpowders from RM method
Alkoxide precursors
Ba(OPri)2
+
Ti(OPri)4
+
Cyclohexane
TRITON X-100
+
Cyclohexane
Reverse micellesWater
Powder formation
H2O/alkoxides = 10/1
H2O/surfactant =2/1
TRITON X-100 =polyoxyethylene(10)isooctylphenylether4-(C8H17)C6H4(OCH2CH2)nOHn ~ 10
52
Reverse micellesPowder formation
Filtration Drying(T = 80 °C)
Thermal
Treatment
H2O/surfactant =2/1
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Synthesis of BaTiOSynthesis of BaTiO33 powderspowders
Acetate/alkoxide precursors
Ti(OPri)4
+
Cyclohexane
TRITON X-100
+
Cyclohexane
Reverse micellesPowder formation
BaAc2
+
Water
53
Reverse micellesPowder formation
Filtration Drying(T = 80 °C)
Thermal
Treatment
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Powder characterizationPowder characterizationAs-precipitated powders
(pure alkoxide route)
54
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0
0
20
40
60
80
100
120
140
160
180
Relative Pressure (P/P0)V
olu
me
Ads
orb
ed (
cm3
/g S
TP
)
Acicular-shaped aggregates
(tetragonal phase)
Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
N2-physisorption analysis• Type IV-a isotherm• S.S.A. = 200 m2/g
Powder characterizationPowder characterizationAs-precipitated powders
(pure alkoxide route)
10 20 30 40 50 60 70 80
Angle (2θ)
Inte
nsity (
arb
.un
.)
10 20 30 40 50 60 70 80
Angle (2θ)
Inte
nsity (
arb
. u
n.)
550 °C 650 °CBaCO3
decomposition
BaTiO3
crystallization
55
10 20 30 40 50 60 70 80
Angle (2θ)
Inte
nsity (
arb
. u
n.)
10 20 30 40 50 60 70 80
Angle (2θ)
Inte
nsity (
arb
. u
n.)BaTiO3 + BaTi2O5
final production
800 °C 1050 °C
Better control of the stoichiometry (only a slight excess of Ti)
Crystallite size at 1050 °C: ~ 40 nm (BaTiO3)Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
Powder characterizationPowder characterizationAs-precipitated powders
(acetate/alkoxide route)
10 20 30 40 50 60 70 80
Angle (2θ)
Inte
nsity (
arb
. u
n.)
10 20 30 40 50 60 70 80
Angle (2θ)
Inte
nsity (
arb
. un
.)
Static air
450 °°°°C 700 °°°°C
TiO2 separation
10 20 30 40 50 60 70 80
Angle (2θ)
Inte
nsity (
arb
. u
n.)
56Sintesi chimica di materiali porosi nanostrutturati e applicazioni in catalisi e sensoristica
No BaCO3 formation
Air flow
700 °°°°C
Final products:c-BaTiO3BaTi2O5BaTi4O9