European Network on New Sensing Technologies for Air Pollution
Control and Environmental Sustainability - EuNetAir
COST Action TD1105
2nd International Workshop EuNetAir on
New Sensing Technologies for Indoor and Outdoor Air Quality Control
ENEA - Brindisi Research Center, Brindisi, Italy, 25 - 26 March 2014
Electrophoretic Gold Nanoparticles Depostion On
Carbon Nanotubes For NO2 Sensors
Elena Dilonardo1*, Michele Penza2, Marco Alvisi2, Domenico Suriano2, Riccardo Rossi2,
Cinzia di Franco3, Francesco Palmisano1, Luisa Torsi1, Nicola Cioffi1
1Department of Chemistry, Università degli Studi di Bari ‘Aldo Moro’, Via E. Orabona 4 - 70126, Bari , Italy.
2ENEA, Technical Unit for Materials Technologies - Brindisi Research Center, PO Box 51 Br4; I-72100 Brindisi, Italy.
3Dip. Interuniversitario Fisica “M. Merlin” Università degli Studi Di Bari „Aldo Moro‟ Via Amendola, 173, 70126 Bari , Italy.
*elena.dilonardo@uniba.it
COST is supported
by the EU Framework Programme
ESF provides the COST Office
through a European Commission contract
Source and Effects of NO2: Why NO2 Monitoring?
Industrial/
Commercial/
Residential
19%
Utilities
27%
Ground-level Ozone (Smog)formed when NO2 react in the
presence of sunlight.
Other 9%
Sources
Motor Vehicles
49%
MobileNO2 transported long distances
on prevailing winds
EURO 6 limits NOx emissions:
0.060 g/km
(entry into force in Sept. 2014)
Acid Rain –
NO2 react with other
substances in air to
form acids
Visibility –
NO2 blocks light
reducing visibility
Global Warning –
NO2 is a grrenhouse gas
NO2
Respiratory problems:
inflammation of the lining of
the lungs, and it can reduce
immunity to lung infections.
Particles –
NO2 reacts to form acid
vapor and particles
NO2 useful detection limits*: 10 ppb
(EPA- U. S. Environmental Protection Agency March 2013)
Strict emission standards and the increasing awareness have induced the growth of sensor market.
LIMITATIONS: Current gas sensors address only a minimal set of sensing needs.
 Sensitivity/Detection Limit
 Selectivity
 Kinetic response
 Temperature range
 Stability and Reproducibility
 Life Time
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E. Dilonardo et al.
2nd International Workshop EuNetAir
ENEA - Brindisi Research Center, Brindisi, Italy, 25 - 26 March 2014
Material Selection for Gas Sensing: CNTs
Advantages and Disadvantages of Existing Gas Sensors
SENSOR
SIZE
POWER
SELECTIVITY
SENSITIVITY
STABILITY
Analytical equipment





Electrochemical sensors





Catalytic bead sensors





Metal oxide semiconductors





Conductive polymer sensors





CARBON NANOTUBE as sensing material
 Nanostructured material: high surface area
 High adsorption capacity
 Large change in electrical properties
 High selective
 Stable physically and chemically
FUNCTIONALIZATION WITH METAL NPs TO IMPROVE GAS SENSING PROPERTIES
FUNCTIONALIZED CNTs (p-type): MODEL OF CATALYTICALY-INDUCED CHARGE TRANSFER
Interaction with gas molecules results in an electronic charge transfer between the molecule
and the CNT-NP sensor, which affects the position of the Fermi energy and, hence, the
conductivity of the detection unit.
Electron acceptor gases
(NO2, O2)
-Resistance
-Conductivity
Electron donating gases
(NH3, CO)
-Resistance
-Conductivity
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E. Dilonardo et al.
2nd International Workshop EuNetAir
ENEA - Brindisi Research Center, Brindisi, Italy, 25 - 26 March 2014
Experimental Set-Up
CNTs synthesis
CNTs GROWTH By CVD TECHNOLOGY
Substrate: film cobalt (Co) nanoclusters, 6 nm thick
1st step: H2 plasma pretreatment @ 550°C
2nd step: H2 + C2H4 @ 550°C
M. Penza et al., Sens. Actuators B 144 (2010) 387-394
100 nm
Electrolytic solution :
0.05 M TOAC in THF/ACN=3:1
Electrolysis potential: 1 V
Electrolysis charge: 300 C
Absorbance (a.u.)
Au-NPs electrochemical synthesis Sacrificial Anode Electrolysis (SAE)
Au NP SPR peak @ 526.2 nm
400
500
600
700
Wavelength (nm)
Stabilized spherical Au NPs with diameter of 12 nm
Electrophoretic deposition of Au NPs on CNTs-based gas sensor device
Cathodic process E(V) = -0.5 V (ocp: -0.3 V)
N2
Au NPs
Process parameters:
tdeposition: 90 s
tdeposition: 300 s
tdeposition: 600 s
i = 6.3 10-4 A Q = 5.598 10-2 C
i = 3.4 10-4 A Q = 9.869 10-2 C
i = 3.4 10-4 A Q = 2.069 10-1 C
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CNTs device
Electrophoretic solution:[Au NPs]= 10 mM
[TOAC] = 5 mM
Vsol. = 5 mL in THF/ACN = 3/1
E. Dilonardo et al.
2nd International Workshop EuNetAir
ENEA - Brindisi Research Center, Brindisi, Italy, 25 - 26 March 2014
Characterization
Counts (s)
Surface Chemical Analysis
Au4f
AuNPs/CNTs_t:90s
AuNPs/CNTs_t:300s
AuNPs/CNTs_t:600s
83.4 eV
3200
2800
2400
2000
+
87.1 eV
Au4f7/2
1600
1200
-
400
83.2 eV
0
80
82
Au4f (%)
O1s(%)
CNTs as received
95.0 ± 0.5
/
5.0 ± 0.5
Au NPs/CNTs t:90s
94.4 ± 0.5
0.3 ± 0.2
5.3 ± 0.5
Au NPs/CNTs t:300s
92.0 ± 0.5
0.5 ± 0.2
7.5± 0.5
Au NPs/CNTs t:600s
91.2± 0.5
1.1 ± 0.2
7.8± 0.5
Au4f5/2
t process
800
C1s(%)
 Deposition of Au NPs on CNTs : Au NPs decorate CNTs.
86.9 eV
84
86
88
90
Binding Energy (eV)
Morphology
The content of deposited Au NPs increases increasing the
process time.
Shift of Au4f B.E. to higher eV increasing the deposition process
time (increase of NPs cluster dimension)
AuNPs/CNTs
t:600s
AuNPs/CNTs
t:300s
AuNPs/CNTs
t:90s
200 nm
200 nm
200 nm
100 nm
100 nm
200 nm
100 nm
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E. Dilonardo et al.
2nd International Workshop EuNetAir
ENEA - Brindisi Research Center, Brindisi, Italy, 25 - 26 March 2014
GAS SENSING FUNCTIONAL TESTS
USB-GPIB Card
34401A Multimeter
RS-232
617 Electrometer
MFC Controller Unit
7001 Switch
System
Low-Current Scanner Card
RS-485
RS- MFC
MFC
485
MFC
MFC
MFC
MFC
MFC
Dry air
Check-valve
6644A System DC
Power Supply
Inlet-gas
CHEMIRESISTOR
Exhaust-air
MFC
Sensor-Cell
M. Penza et al., Sens. Actuators B 135 (2008) 289-297
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E. Dilonardo et al.
2nd International Workshop EuNetAir
ENEA - Brindisi Research Center, Brindisi, Italy, 25 - 26 March 2014
NO2 GAS SENSING
T=150°C
3min <tresponse < 5min @ [NO2] ≥5 ppm
tresponse < 8 min @[NO2] ≤5 ppm
0,24
0.24
0.12
0,12
0
0,00
0.1ppm
0.2ppm
0.3ppm
0.4ppm
0.5ppm
-0.12
-0,12
1ppm
-0.24
-0,24
-0.36
-0,36
7pp
10ppm9ppm8ppmm
0
120
240
2ppm
3ppm
4ppm
5ppm
6ppm
360
480
600
CNTs
CNTs_0.3% Au
CNTs_0.5% Au
CNTs_1.1% Au
720
840
960 1080 1200
time (min)
NO2 Mean Sensitivity (%/ppm)
Resistance change (Rf - Ri) (k )
Gas: NO2 - Carrier Gas: Air
texposure: 10 min – trecovery: 60 min (in Air)
 NO2 concentration effect [range: 10-0.1 ppm]
 Tprocess effect [range 100-200°C]
1.1
1,1
1.0
1,0
0.9
0,9
CNTs
CNTs
CNTs_0.3% Au
CNTs/AuNPs_t=90s
CNTs/AuNPs_t=300s
CNTs_0.5% Au
CNTs/AuNPs_t=600s
CNTs_1.1% Au
0.8
0,8
0.7
0,7
0,6
0.6
0.5
0,5
0.4
0,4
0,3
0.3
90 100 110 120 130 140 150 160 170 180 190 200 210
Temperature (°C)
NO2 MEAN SESNITIVITY IS HIGHER FOR Au NPs DECORATED CNTs AT ALL INVESTIGATED T
AuNPs DECORATED CNTs ARE STABLE IN THE INVESTIGATED RANGE OF T
MAXIMUM NO2 MEAN SENSISTIVITY @ T= 150°C
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E. Dilonardo et al.
2nd International Workshop EuNetAir
ENEA - Brindisi Research Center, Brindisi, Italy, 25 - 26 March 2014
INTERFERING GASES
 SO2 (10-0.5ppm) @ T =150°C
VERY LOW RESPONSE: ∆R/Ri (%) < 0.5 %
 CO (1000 – 25 ppm) @ T =150°C
VERY LOW RESPONSE: ∆R/Ri (%) < 0.2 %
 Mix NO2 + [NH3] = 25 ppm @ T=150°C
CNTs
CNTs_0.3% Au
CNTs_0.5% Au
CNTs_1.1% Au
0,2
0,0
-0,2
0.2ppm
0.5ppm
1ppm
-0,4
8ppm 5ppm
60
120
180
240
300
360
420
 NH3 (1000-5ppm) @ T =150°C
VERY LOW RESPONSE: ∆R/Ri (%) < 0.5 %
Resistance change (R f-Ri) (k)
Resistance change (R f-Ri) (k)
 Mix NO2 + [CO] = 1000 ppm @ T=150°C
 CH4 (7000-300ppm) @ T =150°C
VERY LOW RESPONSE: ∆R/Ri (%) < 0.5 %
CNTs
CNTs_0.3% Au
CNTs_0.5% Au
CNTs_1.1% Au
0,0
0.2 ppm
-0,5
0.5 ppm
1 ppm
8 ppm
5 ppm
-1,0
480
60
120
180
240
Resistance change (R f-Ri) (k)
0,25
300
360
420
times (min)
time (min)
 Mix NO2 + [CO] = 25 ppm @ T=150°C
CNTs
CNTs_0.3% Au
CNTs_0.5% Au
CNTs_1.1% Au
 High sensitivity for NO2 also in contemporary
presence of intering gases
0,00
-0,25
0.2ppm
0.5ppm
HIGH SELECTIVITY FOR NO2
1ppm
-0,50
8ppm
60
120
5ppm
180
240
300
360
420
time (min)
E. Dilonardo et al.
2nd International Workshop EuNetAir
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ENEA - Brindisi Research Center, Brindisi, Italy, 25 - 26 March 2014
CONCLUSION
A tunable loading of Au NPs with uniform dimension is efficiently deposited
directly on the surface of CNTs-based sensor device by electrophoretic process.
Au NPs functionalized CNTs-based gas sensor have an higher thermal stability
than un-functionalized one.
Au NPs functionalized CNTs-based gas sensor have an higher NO2 sensitivity
and selectivity than un-functionalized one, revealing [NO2] in sub-ppm range.
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E. Dilonardo et al.
2nd International Workshop EuNetAir
ENEA - Brindisi Research Center, Brindisi, Italy, 25 - 26 March 2014
FUTURE PROSPECTIVES
Investigation of other interfering gases.
Optimization of electrophoretic deposition conditions.
Electrophoretic functionalization of CNTs-based gas sensor devices with
other metals and/or metal oxides nanoparticles.
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E. Dilonardo et al.
2nd International Workshop EuNetAir
ENEA - Brindisi Research Center, Brindisi, Italy, 25 - 26 March 2014
THANK YOU !
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