icmmm2011 , 8-10 dec 2011, zhengzhou, china

UNIVERSITY OF PATRAS FORTH-ICEHTD. Kouzoudis

ICMMM2011 , 8-10 Dec 2011, Zhengzhou, Chinahttp://www.icmmm.net/ 2012.9.21-23 Beijing


Zeolite thin films as new materials for chemically active layers in

magneto-elastic sensors

D. Kouzoudisa, V. Nikolakisb, Th. Baimposb

a Editor-in-chief, Sensor LettersUniversity of Patras, Greece

b FORTH, Patra Greece

ICMMM2011 , 8-10 Dec 2011, Zhengzhou, China

http://www.icmmm.net/ 2012.9.21-23 Beijing


Outline• Zeolite films – excellent active sensing layers - Review• Magnetoelastic (ME) resonance sensors• Volatile Organic Compounds (VOC)• Detection of VOCs with Zeolite/ME sensors

Zeolite thin films as new materials for chemically active layers in magneto-elastic sensors

ME sensorZeolite film

VOC




Zeolites

(Review on Sensing Applications)




• Inorganic, crystalline, aluminosilicate materials• Chemically and thermally stable • Industry: Excellent catalysts, molecular sieves, ion-exchangers, water softeners •170 different types, about 17 of them commercial interest

Zeolites

ICMMM2011 , 8-10 Dec 2011, Zhengzhou, Chinahttp://www.icmmm.net/

2012.9.21-23 Beijing


• Consist of interconnected SiO2 and AlO2 tetrahedra & Cations+

• Tetrahedra form 3D frameworks with linked channels down to molecular level• High porosity, pores fixed down to nm sizes -> gas sensing• Exceptionally high specific-surface-area

400 m2/gr (two large apartments in one gram !!!)

Zeolites

+ Na++ =



Zeolite Building blocks SiO2 tetrahedra

Chemical formula SiO2?Tetrahedra connected at cornersEach Oxygen is shared by 2 tetrahedra All corners are connected4 × ½ = 2 O atoms →

Schematically, oxygen are shown as straight lines (bonds) and Si at the cornersAll corners are connected → 4 lines from each Si

O SiSi

O Si

Si

O O

Sihttp://www.icmmm.net/

2012.9.21-23 Beijing


Si

SiO

Zeolite - Silicalite (MFI)

1-D channels

All bonds are homopolar → no polarity in the crystal →Extremely hydrophobic



Zeolite - Silicalite (MFI)

(SiO2)

Simplifiedplanar view



Two DifferentBuilding blocks

SiO2

The Al cannot form heteropolar bond with one O =>Local electronegativity =>Extra cation Na+, Ca++ trapped =>Polarity in the crystal

AlO2

BrokenBond

Na+



Zeolite LTA, Si/Al = 1

Na+ [(SiO2) (AlO2)- ]. zH2O

Na


+




Na+ [(SiO2) (AlO2)- ]. zH2O

Na


+

+

+

+

+

++




LTA

Cations cause polarity → attract polar molecules (water, CO2)

+

+



Xm+y/m [(SiO2)x (AlO2)-

y ]. zH2O

(Na+, Ca++)

Zeolite FAU, Si/Al ≠1

FAU

++

+

+



Si x% - Al y%Cations Na, CaPolar3-D entangled channels

FAURing 12

MFISi 100%non-polarHydrophobic1-D channels

Ring 10

LTASi 50% - Al 50%Cations Na, CaPolar3-D straight channels

Ring 8



Useful Zeolite properties for sensing

• Trap selectively gas molecules of the right size• Trap selectively gas molecules of the right

shape• Trap selectively gas molecules of the right

polarity• Highly polar materials, ion conductors and ion

exchangers• Al+3 acidic site: catalyze a number of chemical

reactions • Room temperature operation• High specific surface

Molecular Sieving for octane-isomers LTA



Main Disadvantages:

• Polar Zeolites adsorb humidity, need initial degassing• Slow Diffusion (gas out)



Mass LoadFilm PropertiesFilterGuest/HostComposite

Basically there are 5 different ways on how to use Zeolites for Sensing Applications:



microbalancezeolite

Mass Load: Selective adsorption of certain molecules → Microbalance senses mass load

QCM, SAW, Magneto-elastic,Microcantilever



zeolite

Film: Selective adsorption of certain molecules → Redox interactions with cations → Change of film property

Impedance SpectroscopyResistive SensorsCapacitiveOpticalV



sensor

zeolite

Filter : Selective adsorption of certain molecules → make it to the sensitive layer (+ catalysis )

sens. layer MOS silicon sensors



Guest/Host: Certain molecular complexes pinned at zeolite sites act as sensing centers such as fluorophores, dyes

zeolite

complex

FluorescentOptical sensors



Composite: Zeolite placed inside a matrix in order to improve its sensing properties

matrix

zeolite

Conductive Polymer sensors



Type Sensor Sensed GasMass load QCM

SAWmicrocantilever

NO, SO2, DMMPS. acetonepentane, hexane, H2O, NH3

freon

Film proton conductive zeolitesNa+ ion conducting zeolites

NH3

hydrocarbonsmethanol, 2-propanol and 3-pentanol

Guest/host Ru(II) complex/zeolitemethylene blue/zeoliteLiCl/zeolites

O2, H2O

Filter magnetoelasticoptical fibersurface plasmonresonance

O2, CO, CO2, organics, butylamine

Composites polyaniline/zeolitezirconia/zeoliteplatinum/Y-zeolitesSrTi1-xFexO3/zeoliteTiO2/zeoliteSnO2/zeolite

CONOC4H10, CO and H2

hydrocarbonsalkaneshydrocarbonsmethane, propane, and ethanolXiaowen Xu, Jing Wang, and Yingcai Long, Sensors 2006, 6, 1751-1764



Zeolite based gas sensors

Detection of Sensor type Zeolite

Detection principle

Freon-12 PZT balance MFI Adsorption mass load

A cetone QCM MFI Adsorption mass load

Humidity W ater 500 °CAmmonia

Ohmic HEUH MFIH BEA

Ionic conductivity

Hydrocarbons Electroch. cell NaMFI Ionic conductivityNitric oxide Electroch. cell NaFAU Catalysis

Pentanoic acid Optical fiber MFI adsorption induced reflectivity changeshttp://www.icmmm.net/

2012.9.21-23 Beijing


Electrical resistance of chromium titanium oxide (CTO) sensors overlaid with zeolitesDetection ethanol / isopropanol in dry air operated at 4000C

CTOzeolite

BINIONS et al.: IEEE SENSORS JOURNAL, VOL. 11, NO. 5, MAY 2011

V

ethanol

isopropanol



Typically ethanol / isopropanol react with O-- ions, producing CO2 and releasing electrons => Change of resistanceThey give similar signal because of same functional group

CTO

V

ethanol

isopropanol

BareSensor

O--




The zeolite can make the difference acting as both as a shieve and catalyst enhancing the reaction

CTOzeolite

V

ethanol

isopropanol




ethanol

isopropanol

BareSensor

+LTA zeolite

Sens

or S

igna

l

Time

BareSensor+LTA




Hydrocarbon C3H8 Gas Detection – Impedance sensor

Gunter Hagen and Ralf Moos, SENSOR LETTERS 9, 110–113, 2011Z

The ionic conductivity is measured by impedance spectroscopy



change in color upon protonation /deprotonation of dye molecules intercalated into the zeolite

S. Sohrabnezhad et al. / Materials Letters 61 (2007) 2311–2314

UV–VIS diffuse reflectance spectra

Humidity Detection – Optical Sensor

mordenite zeolite

methylene blue



WWW.wikipedia.com

QCM (Quartz crystal microbalance )

left: Top electrode, right: back electrode



M. Osada, I. Sasaki, M. Nishioka, M. Sadakata, T.Okubo, Microporous and Mesoporous Materials 23 (1998) 287–294

Sensing of SO2 , FAU zeolite

When SO2 is adsorbed on FAU, the mass increase reduces QCM frequency



Micro-Cantilevers: rectangular-shaped bars of Si, less than 1 μm thick. Adsorption results in bending of the cantilever

Cantilever array sensor by Hans Peter Lang1,2*, Martin Hegner1, and Christoph Gerber1

Micro-Cantilevers

Mass Loads as small as ~ 5 ng.



L.Scandella, G. Binder, T. Mezzacasa, J. Gobrecht, R. Berger, H.P. Lang, Microporous & Mesoporous Materials 21 ( 1998) 403

Outgased Zeolite Sensor

Non-Outgased Zeolite Sensor

Humidity sensor using ZSM-5 single crystals



Jian Zhang and Junhang Dong, Langmuir 2005, 21, 8609-8612

SEM image of MFI thin films grown on endface ofan optical fiber

Detection of dissolved organics in water

Adsorption alters zeolite index of refraction → altering the optical reflectivity → reducing

reflected signal power.



Calibration curve of pentanoic acid



Commercial Ludox (Si source)Aluminum foil, Al2O3 (Al source)NaOH: Sodium hydroxide (Na source)

+ organics (catalysts, need removal)TEA: TriethanolamineTPAOH: Tetrapropylamonium hydroxide

(also TEOS:tetraethyl orthosilicate)

Typical Zeolite Synthesis Precursors



Hydrothermal SynthesisQ: Put in autoclave 6 days4.17 Na2O/ Al2O3/ 6 TEA/ 1.87 SiO2/ 460 H2O

T=85 oC(S. Qiu, et al. Microporous Mesoporous Mater., 21, (1998)

245-251)

Create Nucleation site: Dip substrate in solution with FAU crystals (older solution or commercial batch)

Remove organics: Heat treat composite at 300 oC for 12 hrs

Metglas surface before

synthesis

Metglas’ cross section surface after synthesis

Typical Synthesis on Metglas strip



Magnetoelastic Sensors



b)Forced MagnetostrictionMagneto-Elastic ribbons Metglas

Magneto-Elastic materials: Alter their shape under magnetic field H

a) Spontaneous Magnetostriction

Un-magnetized Magnetized-up

H=0

H≠0

H>>0

Length increase



An alternating magnetic field induces vibrations in the sensor

Magneto-Elastic ribbons

A pick up coil detects magnetic flux changes → generates AC voltage

Elastic modulus density

Frequency

EMF V0

0 /f E

The amplitude V0 peaks when excitation frequency equals resonance frequency f0

V = V0 sin(ωt)



[1]Grimes CA, Mungle CS, Zeng ZF, et al., Sensors 2 (7): 294-313 JUL 2002

•Change on the mass molecules adsorbed in the zeolite’s crystal reflects to changes on the sensor’s resonance frequency

mE

LE

Lf

21

21

0

The resonance frequency depends on mass m and elastic (Young) modulus

a) Mass loads decrease frequencyb) E is constant in most solid materials but in magnetoelastic

materials it depends on constant (biasing) fields H and stresses σ

H and σ increase or decrease frequency



0 20 40 60 80 100 120

94,0

94,4

94,8

95,2

95,6

96,0

96,4

96,8N2

CO2

Reso

nanc

e Fr

eque

ncy

[kH

z]

Time [min]

Τ=30οC

Shift in resonance frequency

Cyclic gas changes

ME sensorzeolite

CO2

Frequency (kHz)

EMF

(mV)



Autoclave

Cut of Metglas ribbon (20 mm x 6mm x 30μm)Metglas cleaning i)CH3CCl3 ii)CH3OH

Deposition of FAU crystals on Metglas strip by dip coating

Heat treat 280 oC 12 hrs to remove organics

FAU sensor

MFI sensor

Sensor fabrication

Zeolite20-30 mm 2826 Metglas 30 m

Zeolite20-30 mm

Hydrothermal syntesis19.5 SiO2 + 438 H20 + organics T=185oCHydrothermal syntesis

4.17 Na2O + Al2O3 + 1.87 SiO2 + 460 H2O + organics

T=85 oC

Ozonication to remove organics at 2000 C



Zeolite Composition Time(hr)

Tempe-rature

[0C]Ref

FAU 4.17Na2O:1Al2O3:10TEA:1.87SiO2:460H2O 170 85 [1]

LTA 5SiO2:Al2O3:50Na2O:1000H2O 24 60 [2]

MFI 1.5TPAOH :19.5SiO2 :438H2O 24 185 [3]

[1] S. Qiu, J. Yu, G. Zhu, O. Terasaki, Y. Nozue, W. Pang, R. Xu, Microporous and Mesoporous Mater., 21, 245, (1998)[2] G. J. Myatt, P. M. Budd, C. Price, and S. W. Carr, J. Mater. Chem. 2, 1103, (1992)[3] Tuan, V. A.; Li, S. G.; Falconer, J. L.; Noble, R. D, Journal of Membrane Science, 196, 111, (2002)

Synthesis details



10 15 20 25 30 35

2 theta

IZA

Side B

Side A

10 15 20 25 30

IZA

Side B

2 theta

Side A

FAU

MFI

LTA

10 15 20 25 30

2 theta

IZA

Side B

Side A

020 040 060



MFI

FAU LTA



Volatile Organic Compounds



• Organic liquids with high vapor pressure

• Common by-products in several industrial processes but are also found in everyday life.

• Most of the VOCs vapors are considered harmful and their sensing is a necessity

Volatile Organic Compounds - VOCs

Organic

VOC



Typical VOC Appearance

Formaldehyde Plywood, pressed and particle board, fiberboard, adhesives, smoke and fumes

Benzene Gasoline fumes, rubber and plastic solvents, smoke, stains, paints, varnishes

Xylenes Adhesives, smoke, solvents, enamels, non-lead auto fuels, wall compounds, caulking, clothes and shoe dyes, wall paper, floor coverings, grease cleaner, varnish, pesticides and kerosene vapors

Toluene Same as Xylenes, plus vinyl floor and wall coverings and calcium silicate sheets

Styrene Paints, synthetic rubber, plastics and resins

Toluene diisocyante (TDI) Paints, synthetic rubber, plastics and resins

Trichlorethylene Polyurethane foam aerosols

Ethyl benzene Solvents

Methylene chloride Aerosol finishers and paint strippers

Paradichlorobenzene Room deodorizers & mothballs

Benzyl chloride & benzal chloride

Vinyl tiles covered with Butyl Benzyl Phthalate

2-Butanone (MEK) Same as Xylenes and Toluene

Petroleum distillates Cleaning, solvent, paint thinner & stripper materials

4-Phenylcyclohexene Synthetic carpet and pads

Some common VOCs



n-Hexane C6H14Ethyl-acetate C4H8O2

The VOCs of our work

Propylene C3H6 Propane C3H8



Benzene C6H6

para-Xylene C8H10 ortho-Xylene C8H10

c-Hexane C6H12



VOC Formula Safe <(ppm) Diameter

Vapor Pressure

[kPa]

Propylene C3H6 - 3.9 Å 1152

Propane C3H8 1000 4.3 Å 970

n-hexane C6H14 20 4.3 Å 20Ethyl-Acetate CH3COOCH2CH3 50 5.2 Å 12.6

p-xylene p-C6H4(CH3)2 100 5.8 Å 1.16

Benzene C6H6 1 5.8 Å 13.4

c-hexane (CH2)6 200 6 Å 13

o-xylene o-C6H4(CH3)2 100 6.8 Å 0.88



Detection of VOCs with zeolite/ME sensors



VOC

Experimental Setup



Experimental Setup



0 50 100 150 200 250102,50

102,75

103,00

103,25

103,50

AIR

f [

kHz]

Time [min]

ME sensor

Air

ME sensorZeolite film

VOC



LTAd=4.1 Å

C3H8 (d=4.3 Å)

C3H6 (d=4 Å)

Propylene C3H6 – Propane C3H8, only 4% mass difference, 7% size difference, sensing selectivity problem



0 50 100 150 200 250

Time [min]

0 50 100 150 200 250

Time [min]0 50 100 150 200

98,098,599,099,5

100,0100,5101,0101,5102,0102,5103,0

Time [min]

f [k

Hz]

AIRC3H8

1200C 800C 400C

Baimpos T, Nikolakis V, Kouzoudis D: Science of Advanced Materials Vol. 2, 215–218, 2010

Air – C3H8

0 100 200 300 40098,098,599,099,5

100,0100,5101,0101,5102,0102,5103,0

Time [min]

f [k

Hz]

0 100 200 300 400 500

Time [min]0 50 100 150 200 250 300 350 400

Time [min]

1200C 800C

400C

Air – C3H6



0 20 40 60 80 100 120

94,0

94,4

94,8

95,2

95,6

96,0

96,4

96,8N2

CO2

Reso

nanc

e Fr

eque

ncy

[kH

z]

Time [min]

Τ=30οC

Cyclic gas changes

7.4 Å

Size & shape irrelevant, polar interaction Na+ ion - CO2 quadruple moment

Small Parenthesis:CO2 detection, with FAU, Si/Al = 1.1

-- ++++ -- No net charge

2.3 Å

No dipole moment

quadruple moment ≠ 0



VOC Chemical Formula TLV

(ppm)KineticDiameter

Åo-xylene o-C6H4(CH3)2 100 6.8 c-hexane (CH2)6 200 6 p-xylene p-C6H4(CH3)2 100 5.8 benzene C6H6 1 5.8 ethyl-

acetate CH3COOCH2CH3 50 5.2 n-hexane C6H14 20 4.3

FAU 7.4 Å

MFI 5.5 Å

LTA 4.1 Å



0 100 200 300 400 500 60095,0

95,5

96,0

96,5

97,0

Time [min]

f [k

Hz]

AIR

620052070

30ppm

o-xylene

FAU ME sensorFAU film

VOC

7.4 Å

0 50 100 150 200 250100,4

100,8

101,2

101,6

102,0

102,4f

[kH

z]

Time [min]

AIR

510ppm 1000

2000

c-hexane



0 100 200 300 400

105,5

106,0

106,5

107,0

f [k

Hz]

Time [min]

AIR

530ppm

1100 2300

Benzene

0 100 200 300 400 500

95,5

96,0

96,5

97,0

Time [min]

f [k

Hz]

AIR

20001000

500ppm

EthylAcetate

0 100 200 300 400 500 60099,5

100,0

100,5

101,0

101,5

f [k

Hz]Time [min]

AIR

2000 7700

550

400ppm

p-xylene

FAU

0 50 100 150 200 250 30095,5

96,0

96,5

97,0

97,5f

[kH

z]

Time [min]

AIR

1600800ppm

6200

n-hexane



0 2000 4000 6000 8000

-0,020

-0,015

-0,010

-0,005

0,000

p-xylene

c-hexane

benzeneo-xylene

ethyl-acetate

n-hexane

f/f A

IR

VOC concentration [ppm]

FAU



para-Xylene C8H10 ortho-Xylene C8H10



0 100 200 300 400 500

Time [min]

AIR 4100 ppm

1800095000

c-hexane

MFI ME sensorMFI film

VOC

0 100 200 300105,5

106,0

106,5

107,0

107,5

108,0

f [k

Hz]

AIR

2100 ppm 7500

Time [min]

o-xylene

5.5 Å



0 100 200 300 400105,5

106,0

106,5

107,0

107,5

108,0

f [k

Hz]

Time [min]

AIR

4100 ppm

18000 95000

ethylacetate 0 100 200 300 400

6600028500

4800

Time [min]

AIR

1300 ppm

n-hexane

0 100 200 300 400105,5

106,0

106,5

107,0

107,5

108,0

f [k

Hz]

Time [min]

AIR 4100 ppm

12000 95000

benzene

0 100 200 300 400105,5

106,0

106,5

107,0

107,5

108,0

AIR150 1000

44050 ppm 2300

8200

Time [min]

f [k

Hz]

p-xylene

MFI



0 25000 50000 75000

-0,012

-0,009

-0,006

-0,003

0,000

0,003

0,006

f/f A

IR


p-xylene

o-xylene

c-hexane

benzene

ethyl-acetate

n-hexane

MFI



0 100 200 300 400

Time [min]

AIR

1200 ppm 4000 18000 92000

c-hexane

LTA

ME sensorLTA film

VOC

0 100 200 300 400 500 600101,0

101,5

102,0

102,5

103,0

103,5

104,0

f [k

Hz]

Time [min]

AIR

80 ppm 270 1200

6200

o-xylene

4.1 Å



0 100 200 300 400101,0

101,5

102,0

102,5

103,0

103,5

104,0

85000

f [k

Hz]

Time [min]

AIR

1200 ppm

3900

18000

ethylacetate

0 100 200 300 400 500101,0

101,5

102,0

102,5

103,0

103,5

104,0

f [k

Hz]

AIR

110 ppm

3501600

8200

Time [min]

p-xylene

0 100 200 300 400 500 600

1900 ppm 6200

AIR

28000 142000

Time [min]

n-hexane

LTA

0 100 200 300 400101,0

101,5

102,0

102,5

103,0

103,5

104,0

AIR

1300 ppm

400019000

95000f [k

Hz]

Time [min]

benzene



0 25000 50000 75000

-0,012

-0,009

-0,006

-0,003

0,000

f/f A

IR


p-xylene

c-hexane

benzene

o-xyleneethyl-acetate

n-hexane

LTA



VOC FAU MFI LTA

o-xylene 6 * √ - × 90 * ×

c-hexane 150 √ - × - ×

benzene 30 √ - × - ×

p-xylene 20 √ - × 230 ×

ethyl-acetate 15

√ 770

√ -

×

n-hexane 200 √ 190 * √ 700 ×

Numbers: Measured ppm levels by the three sensors. Dashes: no detection Marks √ and × : whether a VOC molecule fits in pore or not.

Results



0 25000 50000 75000

-0,012

-0,009

-0,006

-0,003

0,000

0,003

0,006

f/f A

IR


p-xylene

o-xylene

c-hexane

benzene

ethyl-acetate

n-hexane

MFIWhy signal reversal? Stress



(a) (b)

(c)(d)

(e) (f)

air n-hexane

c-hexane benzene

o-xylene p-xylene

MFI one side film

Video

MFI 30 m Metglas 30 m



Strain

‰Stress (Mpa)

n-hexane 4,4 131

p-xylane 2,4 73

benzene 1,2 37

Stress calculations based on beam theory




Slow recovery times - Diffusion

0 100 200 300 400 500 60099,5

100,0

100,5

101,0

101,5

f [k

Hz]

Time [min]

AIR

2000 7700

550

400ppm

p-xylene



20 40 60 80 10 0 1 20 14 0

100 .2

100 .4

100 .6

100 .8

101 .0

101 .2f

t

Solution a) Thinner zeolite films than 20 m b) Derivative of Response curve.

Theory + data



0 25000 50000 75000

-0,012

-0,009

-0,006

-0,003

0,000

0,003

0,006

f/f A

IR


p-xylene

o-xylene

c-hexane

benzene

ethyl-acetate

n-hexane

MFI




Effects of stress MFI



Strain

‰Stress (Mpa)

n-hexane 4,4 131

p-xylane 2,4 73

benzene 1,2 37

Stress calculations based on beam theory




(a) (b)

(c)(d)

(e) (f)

air n-hexane

c-hexane benzene

o-xylene p-xylene

MFI one side film



Conclusions

• Zeolite films excellent sensing active layers with nanopores

• High selectively on gas size, shape, polarity

• Room temperature operation• High specific surface • Adsorption stress plays role

• Drawback: Slow recovery time due to diffusion



the 2nd International Conference on Management, Manufacturing and Materials Engineering -ICMMM 2012

Beijing, China Sept. 21-23 2012http://www.icmmm.net/

http://www.icmmm.net/

2012.9.21-23 Beijing

icmmm2011 , 8-10 dec 2011, zhengzhou, china

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