CARBON NANOTUBES-BASED GAS SENSORS FOR POLLUTANTS: ELABORATION METHODS FOR NO2 AND BTX DETECTION NDIAYE Amadou L. (Co-workers : J. Brunet, A. Pauly, C. Varenne, B. Lauron) Institut Pascal (IP) - Axe PHOTON Équipe Microsystèmes Capteurs Chimiques Aubière (France)

Institut de Chimie de Clermont Ferrand (ICCF) – UMR 6296 Équipe Matériaux Inorganiques Aubière (France)

In the Framework of COST- Action TD1105 hosted by the SGS 2012 Workshop 14th September 2012, Cracow , Poland Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

Overview Climat change, Increasing desease (disquieting effects)

Needs for developping Sensors dedicated to pollutants

Source : AIRFOBEP

Pollution: Alteration of air quality induced by the presence of substance (s) or particles which can present toxicologic effect COST – Action TD1105 depending on their concentration Amadou Ndiaye Institut Pascal Université Blaise Pascal (UBP) SGS 2012

Plan 1 - Pollutants: introductory view 2 - CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection
Dispersion route using a surfactant
Characterisation of the CNTs-based sensors
Sensor development and experimental results towards NO2 and O3

3 - CNTs-based sensors: Sensors elaboration for BTX Detection:
Noncovalent functionalisation method
Characterisation of the CNTs-MCs hybrid materials
Sensor development and experimental results towards toluene

4 - Conclusion and perspectives Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

Plan 1 - Pollutants: introductory view 2 - CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection
Dispersion route using a surfactant
Characterisation of the CNTs-based sensors
Sensor development and experimental results towards NO2 and O3

3 - CNTs-based sensors: Sensors elaboration for BTX Detection:
Noncovalent functionalisation method
Characterisation of the CNTs-MCs hybrid materials
Sensor development and experimental results towards toluene

4 - Conclusion and perspectives Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

1- Pollutants: introductory view Major Pollutants: NO2/NOx , O3  NO2 and O3: Similarities
Strong oxidising gases
Alike molecular masses
Chemical reactivities
Similar interactions with materials  NO2 and O3: relationship (in the atmosphere)
These two gases are linked by a chemical reaction:

NO + O3→NO2+ O2+ hνν hν ν

NO2→NO + O O* + O2→O3+ hνν  What about Health?
Carcinogenic, involved in respiratory deseases, etc. Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

1- Pollutants: introductory view What are BTX?
Benzene, Toluene and Xylenes: similar structures, physical properties and reactivities.

Where are the BTX from?
Industries (catalytic reforming, steam cracking etc.), Car exhaust etc.

What about Health?
Carcinogenic, cause problems in the respiratory system, etc. NB: the terminology BTEX can be also found in the litterature: BTX + Ethylbenzene Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

1- Pollutants: introductory view Gas sensors (literature): Sensors based on Metal oxide (MOX) thin films:
SnO2

(Lee et. al, Sens. and Actuators B, 77, 2001, 228)

Sensors based on porous adsorbent material :
Silicate (Yuliarto et. al, Sens. and Actuators B, 138, 2009, 417;

Sensors based on Nanomaterials:
CNTs (Kong and Franklin, et. al, Science 287, 2000, 622; Penza et. al, Sens. and Actuators B, 135, 2008, 289)

Ueno et. al, Sens. and Actuators B, 95, 2003, 282)

Sensors based on conducting polymer :
Polypyrrole (Wallace et. al, Sens. and Actuators B, 84, 2002, 252)

Methodology based on spectroscopic monitoring:
IR, GC-MS (Sanchez et. al, Sens. and Actuators B, 119, 2006, 227; Problems: portability, high cost, space Zampolli et. al, Sens. and Actuators B, 141, 2009, 322; Lahlou et. al, Sens. and Actuators B, 154, 2011, 213)

Amadou Ndiaye

Institut Pascal

Problems:
reproducibility
stability
selectivity
etc.

Université Blaise Pascal (UBP)

SGS 2012

Plan 1 - Pollutants: introductory view 2 - CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection
Dispersion route using a surfactant
Characterisation of the CNTs-based sensors
Sensor development and experimental results towards NO2 and O3

3 - CNTs-based sensors: Sensors elaboration for BTX Detection:
Noncovalent functionalisation method
Characterisation of the CNTs-MCs hybrid materials
Sensor development and experimental results towards toluene

4 - Conclusion and perspectives Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

2- CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection

CNTs for gas sensors! Why the CNTs?

CNTs: Properties - mechanical properties - optical properties - electrical properties (semiconducting, metallic etc.) (SWNTs) - high surface area

Why the dispersion route?

CNTs : Bundling effect - high surface tension
bundling effect - reducing the surface for adsorption

CNTs debundling (surfactant) + Surfactant (

- surface sensitivity towards adsorbed species - high number of adsorption sites Amadou Ndiaye

Institut Pascal

)

debundling Bundle of CNTs

Single CNTs

Surfactant: SDS, NaDDBS, etc. Université Blaise Pascal (UBP)

SGS 2012

2- CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection

CNTs for gas sensors: Dispersion route using a surfactant

Surfactant method (assisted by sonication): How does it work? Hydrophobic and hydrophilic interaction between surfactant + nanotube + water
debundling;  solubilisation / stabilisation in the aqueous phase.

Choice of surfactant? NaDDBS (Natrium dodecylbenzene sulfonate) seems to be advantageous over others ionic and non-ionic surfactants. (*) Benzene ring
additional π−π interaction with the CNTs.

* Islam et. al, Nano Letters, 3, 2003, 269. * Sun and Gao et. al, J. Alloys and Compds, 485, 2009, 456.

Amadou Ndiaye

Institut Pascal

NaDDBs

Université Blaise Pascal (UBP)

SGS 2012

2- CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection

CNTs for gas sensors: Dispersion route using a surfactant

Preparation of the CNTs dispersion using a surfactant: SWNTs + NaDDBS + H2O

Dispersions of SWNTs

- Stirring - Sonication - Centrifugation

Al2O3

sonicated

Pt

{1}

Drop-cast Different dispersions of SWNTs in NaDDBs (after several weeks) Amadou Ndiaye

Institut Pascal

after 1min

{2}

{3}

Drying (110°C) Anneali ng dispersions of SWNTs (150-300° in CHCl3 (MeOH) C) Université Blaise Pascal (UBP)

SGS 2012

2- CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection

CNTs for gas sensors: Dispersion route using a surfactant

Characterisation of the CNTs dispersion : 4.5x10 4.0x10

4

3.5x10

4

3.0x10

4

2.5x10

4

2.0x10

4

1.5x10

4

1.0x10

4

5.0x10

3

I-V Characteristics

without annealing annealing at 150°C annealing at 300°C

3.5x10

- without annealing - after annealing

5

- - after annealing (R2)

-5

2.0x10

-5

I (A)R (Ω)

Intensity (u. a.)

Raman 4

1.0x10 5

3.0x10 0.0 7.5x10

- without annealing (R1)

4

-5

-1.0x104 7.0x10

Resistive Sensor (CNTs on IDE’s)

4

D

0.0 900

1000

1100

1200

1300

1400

6.5x10 -5 -2.0x104 6.0x10

G 1500

1600

-1

Raman shift (cm )

D and G bands, before and after annealing.

4

5.5x10 -1.0 1700

1800

-0.5

300

0.0

0.5

350 V (volts)

1.0

400

T° (K)


Ohmic character (resistive sensors)
Semiconducting behavior (CNTs batch of SC and metallic)


No observable surfactant effect on the Semiconducting behavior Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

2- CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection

CNTs for gas sensors: Dispersion route using a surfactant

Sensor development and experimental results towards NO2 : Sensor response (70°C) 8

1.8x10

NO2 exposure

8

 Resistance decrease under NO2

50 ppb

100 ppb

200 ppb

Resistance (Ω)

8

1.2x10

50 ppb

1.4x10

100 ppb

8

200 ppb

1.6x10


electron withdrawing power of NO2. (p-type semiconducting behaviour of the CNTs)

8

1.0x10

7

8.0x10

5

7.5x10 5 7.0x10 5 6.5x10 5 6.0x10 5 5.5x10 5 5.0x10 5 4.5x10 5 4.0x10 5 3.5x10

Sensor B2a (without annealing) Sensor B2b (after annealing, 150°C)

NB: After annealing at 300 °C: - No valuable responses of the CNTs-based sensors layers?

Air zero (recovery under Air)

500

Amadou Ndiaye

 Annealing improves the responses

1500 3500 2500 Time (minutes)

Institut Pascal

4500

Université Blaise Pascal (UBP)

SGS 2012

2- CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection

SEM characterisation of the sensing layers:

C

O Na S

SEM images of the CNTs layers

CNT + surfactant + H2O

Without annealing Amadou Ndiaye

CNT + surfactant

Annealing at 150 °C Institut Pascal

CNTs layers after annealing

Annealing residu (C,S,Na) CNT

Annealing at 300 °C

Université Blaise Pascal (UBP)

SGS 2012

S

2- CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection

CNTs for gas sensors: Dispersion route using a surfactant

Sensor development and experimental results towards O3 : Test 44 50°C (5h,10h)

180 ppb

160 ppb

140 ppb

120 ppb

100 ppb

2000

80 ppb

1000

60 ppb

40 ppb

40000

20 ppb

180 ppb

50 ppb

180 ppb

50 ppb

180 ppb

50 ppb

180 ppb

50 ppb

46000

180 ppb

41000 47000

45000 39000

R (Ω)

R (Ω)

44000 43000 42000

38000

37000

41000 36000 40000 39000

35000 500

1000

1500

2000

Time (min)

0

3000

4000

5000

6000

7000

8000

9000

Tps (min)

 Resistance decrease under O3
oxidising nature of O3. (p-type semiconducting behaviour of the CNTs)

 Significant baseline up drift (no complete recovery)  Decreasing sensing performance after some exposure cycles Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

Plan 1 - Pollutants: introductory view 2 - CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection
Dispersion route using a surfactant
Characterisation of the CNTs-based sensors
Sensor development and experimental results towards NO2 and O3

3 - CNTs-based sensors: Sensors elaboration for BTX Detection:
Noncovalent functionalisation method
Characterisation of the CNTs-MCs hybrid materials
Sensor development and experimental results towards toluene

4 - Conclusion and perspectives Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

3- CNTs-based sensors: Sensors elaboration for BTX Detection

Functionalisation of Carbon Nanotubes (CNTs) by Macrocycles (MCs) CNTs:

MCs:

R R

N

N M

- mechanical properties (high tensile strenght)

- redox properties

- optical properties

- stability at high temperature

- versatile electrical properties (semiconducting, metallic etc.) (SWNTs) - high surface area

- highly delocalised π-system

R R t

R= Bu; M=Cu

- functionalisation

- changes (conductivity) (due to adsorbed species) - high number of adsorption sites (high sensitivity) Amadou Ndiaye

Institut Pascal

N

N

+

- interaction sites for BTX (π π-system) - functional groups (tailored interaction)

Université Blaise Pascal (UBP)

SGS 2012

3- CNTs-based sensors: Sensors elaboration for BTX Detection

Functionalisation of CNTs: covalent vs. noncovalent route
noncovalent functionalisation :


covalent functionalisation :

based on self-assembling (π π−π interaction)

based on the creation of covalent bonding

- more stable assemblies - irreversible - solubilisation

- instable assemblies - reversible

- alteration of the properties (electrical, optical etc.)

- preserved electrical properties

perylenediimide/SWNT electron donor−acceptor hybrids

Hirsch, Guldi et al. J.A.C.S. 2011, 133, 4580. Campidelli, Torres et al. J.A.C.S. 2008, 130, 11503.

Tassi, Prato et al. Chem. Rev. 2006, 106, 1105.

Amadou Ndiaye

Institut Pascal

Takeuchi et al. J. Phys. Chem. C. 2011, 115, 4533. Yang et al. J. Phys. Chem. C. 2011, 115, 4584. Guldi, Prato et al. J. Mater. Chem. 2006, 16, 62.

Université Blaise Pascal (UBP)

SGS 2012

3- CNTs-based sensors: Sensors elaboration for BTX Detection

Functionalisation of CNTs: choice of the MCs Phthalocyanines derivatives

Porphyrines derivatives

R R N N

N Cu

N N

N N

N R R

R = - tBu - SO3Na


Strong absorption: - functionalisation monitoring
R functional groups: - solubility - modulation of the adsorption
π-system: - π−π interactions (BTX, CNTs) Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

3- CNTs-based sensors: Sensors elaboration for BTX Detection

Functionalisation of CNTs with a Phthalocyanine derivative: UV-Vis Evolution of the 679 nm absorption band (Q band) after addition of CNTs

Adding CNTs + sonication 3.5

3.5

Absorbance (arb. unit)

3.0

679 nm

masse CNTs

4

3.0

1.2 mg

2.5

2.0

5.4 mg

1.5

1.0

0.5

Absorbance (arb. unit)

CuPc(tBu)

2.5 2.0 1.5 1.0 0.5

0.0 300

400

500

600

700

800

0.0 1

2

3

4

5

Mass CNTs (mg)

λ (nm)

UV-Vis absorption spectra of CNTs/CuPc(tBu)4 dispersions [CuPctBu]= 1.785 x 10-5 M 10ml CHCl3

Amadou Ndiaye


Decrease in absorbance highlights the functionalisation Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

3- CNTs-based sensors: Sensors elaboration for BTX Detection

Functionalisation of CNTs with Macrocycles: TEM

CNTs

CNTs +CuPctBu


Adsorbed structures on the CNTs Walls
Noncovalent functionalisation of CNTs ( random way)

CNTs +OEP Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

3- CNTs-based sensors: Sensors elaboration for BTX Detection

Functionalisation of CNTs with a Macrocycle: TGA analysis 0.0

100 98 96

-0.1

94 92

SWNTs+CuPctBu CuPctBu

-0.2

88

Deivative

Weight (%)

90 86 84

SWNTs+CuPctBu CuPctBu SWNTs

82 80

-0.3

-0.4

78 76 74

-0.5

72 70

-0.6

68 100

200

300

400

500

600

700

100

Temperature (°C)

 Considering the weight losses (at 600°C): 2.8 % : CNTs weight loss (mainly impurities) 26 % : MCs weight loss (decomposition)


a real weight loss of 20.7 % in the

200

300

400

500

600

Temperature (°C)

 MCs on the CNTs walls decompose more easily than free MCs:
thermal stability is weaken

CNTs/CuPctBu mainly due to the presence of MC.

Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

3- CNTs-based sensors: Sensors elaboration for BTX Detection

Development of the sensing devices: transduction modes

CNTs-MCs based Materials:

2 transduction modes QCM

IDE’s Al2O3

Interdigitated electrodes (IDE’s)
Resistance variation (∆ ∆R) Pt Amadou Ndiaye

Institut Pascal

Quartz Crystal Microbalance (QCM)
Mass variation ( i.e frequency)

Quartz crystal with Au electrodes

Université Blaise Pascal (UBP)

SGS 2012

3- CNTs-based sensors: Sensors elaboration for BTX Detection

Elaboration of the sensing devices: sensor preparation IDE’s

I

QCM

II

III I: drop-cast deposition II: solvant evaporation III: annealling

Al2O3


Deposition T° Pt Amadou Ndiaye

Institut Pascal

IDE’s coated with CNTs/MCs

Université Blaise Pascal (UBP)

QCM coated with CNTs/MCs SGS 2012

3- CNTs-based sensors: Sensors elaboration for BTX Detection Elaboration of the sensing devices: sensor response towards toluene (RT°) Resistance: IDE’s toluene submission

150000

R (ohms)

145000

140000


Deposition T°

135000

130000

125000

IDE’s coated with CNTs/MCs

air zero 120000 0

200

400

600

800

1000

1200

Time (minutes)


Resistance increases during toluene exposure (reducing gas)
Reversible process
Good repeatability Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

3- CNTs-based sensors: Sensors elaboration for BTX Detection Elaboration of the sensing devices: sensor response under toluene (RT°) air zero

Masse: QCM

4978600

4978400

Frequency (Hz)

4978200

4978000

4977800

4977600

toluene submission

4977400 0

200

400

600

800

1000

1200

QCM coated 1400 with CNTs / MCs

Time (minutes)


Frequency decreases (i.e. Mass increases) under toluene exposure
Reversible process
Good repeatability Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

3- CNTs-based sensors: Sensors elaboration for BTX Detection ∆f= -Cf x ∆m

(Sauerbrey Equation)

∆f: frequency variation (Hz) Cf: sensitivity factor (Hz/ng/cm2) [Cf= 0.056 Hz/ng/cm2 for 5 MHz crystal) ∆m: mass variation per unit area (g/cm2)

Materials

Response

Remarks

SWNTs + CuPctBu CuPctBu

0.009 0.002

Stable, repeatable Moreless stable

SWNTs + OEP OEP

0.008 0.0005

Stable, repeatable Not stable

fA0: frequency value at equilibrium under Air 0 (Hz/ng deposited material)∆f: fA0- fTol
Sensor response fTol: frequency value at equilibrium under Toluene

Better response of CuPctBu compared to OEP:
benzyl moiety
amorphous/crystalline Improvement of the response in the hybrids system (CNTs/MCs) compared to MCs: - CNTs (High SSA) - CNTs-OEP >>> CNTs- CuPctBu (metal) Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

Plan 1 - Pollutants: introductory view 2 - CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection
Dispersion route using a surfactant
Characterisation of the CNTs-based sensors
Sensor development and experimental results towards NO2 and O3

3 - CNTs-based sensors: Sensors elaboration for BTX Detection:
Noncovalent functionalisation method
Characterisation of the CNTs-MCs hybrid materials
Sensor development and experimental results towards toluene

4 - Conclusion and perspectives Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

4- Conclusion and perspectives CNTs-based sensors: Sensors elaboration for NO2 and O3 Detection

∆R/R0

0.35

Without annealing Cycle 1(B2a) (Sensor B2a);

After annealing Cycle 1 (B2b) (Sensor B2b)

Cycle 1 (Sensor B2a); Cycle 2 (Sensor B2a);

Cycle 1 (Sensor B2b) Cycle 2 (Sensor B2b)

0.30

Sensor response

0.25

∆R/R0 = (R0-R) / R0

0.20

- R = R under NO2 - R0 = R under Air zero at equilibrium.

0.15 40

60

80

100

120

140

160

180

200

[NO2] in ppb

 Better response and repeatability given by the annealed layers  No surfactant effect on the sensors responses Conclusion  Low annealing conditions seems to be necessary  For O3, no sensors sensitivity after long time exposure Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

4- Conclusion and perspectives CNTs-based sensors: Sensors elaboration for BTX Detection

Functionalisation: - efficient functionalisation way (noncovalent) leading to a better processing of the CNTs and preserving the properties - choice of the MCs for tailoring the adsorption of BTX:
benzyl moiety
metal free - combination of CNTs and MCs:
higher response (sensitivity increase due to SSA) Sensors responses: - low operating temperature (Room Temperature) - reversible process, good repeatability  Gas sensing experiments for the detection of Benzene and Xylenes are under investigations.  New phthalocyanine derivatives (Metal free) Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

Acknowledgement Institut Pascal (IP) – Axe Photon Équipe Microsystemes capteurs Chimiques Prof. A. Pauly Dr. J. Brunet (MCF) Dr. C. Varenne (MCF-HDR) B. Lauron (Ing.)

Institut de Chimie de Clermont-Ferrand (ICCF) Axe Matériaux Inorganiques Équipe Materiaux Fluorés Prof. M. Dubois Dr. K. Guerin (MCF-HDR) Dr. P. Bonnet (MCF) Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012

Thank you for your attention

Amadou Ndiaye

Institut Pascal

Université Blaise Pascal (UBP)

SGS 2012