Khaoula hamdi poster AIRMON 2014 .pdf

Monitoring volatile BTX (benzene, toluene and xylenes)
molecules in workplaces: towards a real-time analyser
Khaoula Hamdi a, b, Mathieu Etienne b , Bruno Galland a, Patrick Martin a, Marc Hebrant b
National de Recherche et de Sécurité (INRS), 54500 Vandœuvre-lès-Nancy, France
b CNRS et Université de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement (LCPME), UMR7564, 54600, Villers-lès-Nancy, France
aInstitut

Introduction

Objectives

Benzene, toluene and xylenes (BTX) are the most abundant among the volatile aromatic
hydrocarbons (VAHs) emitted from petrochemical industry, car emissions and combustion sources
[1]. The various emission sources combined with poorly ventilated confined spaces, like
workplaces, can increase the concentration of VAHs to dangerous levels exceeding the maximum
legal values [2]. The long exposure to VAHs may have a disastrous impact on health due to their
toxicity and carcinogenic properties especially benzene [1], [3].
There is a clear need for knowledge about VAH concentration and monitoring in order to protect
people that might be exposed.
Approved detection methods used in occupational and safety area, based on BTX adsorption on
an activated charcoal followed by a chromatographic analysis in laboratory, can’t provide real time
analysis and quantification of BTX molecules in workplaces.

Detection principle
CH3

The sensing layer

A standard
sampling cycle

X
T
CH3

Sampling workplace atmosphere
for 1, 3 or 5 minutes :

Material regeneration with
purified air flow

Absorbance (au)

Adsorption of BTX molecules on
the sensing layer.
Recording UV spectra

The material synthesis
We used a modified Stöber
process to synthesize a 20 to
50 nm silica nanoparticles.

The sensing layer is a thin film formed by the assembly of
mesoporous silica nanoparticles deposited on a quartz substrate.

CH3

B

The aim of this work is to develop a
sensing layer able to concentrate
volatile BTX in the atmosphere in order
to monitor their concentration in real
time in workplaces.
The developed material should have a
large specific area and an adapted
functionalization to target the BTX
molecules in a very complicated matrix
such as the air.

Spectral analysis to determine
BTX concentration

4,8E-02
4,3E-02
3,8E-02
3,3E-02
2,8E-02
2,3E-02
1,8E-02
1,3E-02
8,0E-03
3,0E-03
-2,0E-03

We grafted functional groups
groups to the surface by cocondensating
a
PhenylTriEthOxy-Silane or a
MethylTriEthOxy-Silane
with
TriEthOxy-Silane.

SEM snapshot of a deposited silica
nanoparticles (500 nm scale bar)

Dual porosity : Inter-and intra-nanoparticles  Large specific area
+ enhanced flow of the gas throughout the material
Controlled thickness:
Functionalization: Functional groups cans be added with the goal to

230

260

enhance the selectivity toward BTX molecules

290

TEA
ΔT
CTACl
H2O
60 minutes
Nanoparticles (20-50 nm)

CetylTrimethylAmmonium
Chloride was used as a
templating agent.
Deposition:
We drop-deposited or dipcoated the
nanoparticles

Too thick = difficult regeneration of the material and limited transmittance.
Too thin = not enough material to concentrate the BTX molecules

200

TEOS Or TEOS: PheTEOS
Or TEOS:MeTEOS

Wavelength (nm)

HCl+EtOH
- CTACl
Mesoporous silica
nanoparticles

solution on a quartz substrate.

RESULTS

450
400
350
300
250
200

90

Methyl
functionnalize
d silica film

80
70
60
50

20

Phenyl
functionnalize
d silica film

10

Pure silica film

40
30

0
150

180

230

280

330

380

Wave length (nm)

100

Specefic surface area of the material = 482,05 m²/g

50
0,0

0,2

0,4

0,6

0,8

1,0

P/P0

Adsorption–desorption isotherms
of nitrogen at 77 K

Optical properties of the
silica film

Specific Surface Area :
Non functionalized silica: nanoparticles : 1014 m²/g
Functionalized silica nanoparticles : (10% of phenyl) : 482 m²/g

Absorbance at 267 nm (OD)

Long cycle :
5 minutes exposition
1 minute regeneration

Medium cycle :
3 minutes exposition
1 minute regeneration

Study of the effect of silica
nanoparticles deposited on the
substrate: Adsorption of 20
ppmv of Toluene

1,4E-2
1,2E-2
1,0E-2
8,0E-3
6,0E-3

Quartz plate with no deposited material

4,0E-3

1 Deposited layer on the quartz substrate

2,0E-3

2 Deposited layers on the quartz substrate

0,0E+0

3 Deposited layers on the quartz substrate
4 Deposited layers on the quartz substrate

-2,0E-3
0

500

1000

1500

2000

8

1,30E-02

7

1,10E-02
Absorbance at 267 nm (OD)

Transmittance of the
material (%)

100

1,6E-2

6
ΔDO *10 -3 (OD)

Typical thickness profile of a the
deposited films, determined by
profilometry

1,8E-2

Adsorption results

TEM snaopshot of the mesoporous
silica nanoparticles (20 nm scale bar)

Volume of N2 adsorbed (cm3/g)

Material characterization

Thickness ≈ 5µm

Short cycle :
1 minute exposition
1 minute regeneration

5
4
3

Time (s)

9,00E-03
7,00E-03
5,00E-03

Pure silica nanoparticle
thin film

3,00E-03

2

1,00E-03

1

-1,00E-03

Phenyl Functionnalized
nanoparticle film
0

500

0
0

10

20
30
40
Concentration of Toluene (ppmv)

50

Material behavior by changing the
concentration of the pollutant (Toluene)

1000
Time (s)

1500

2000

60

Study of the effect of the nature of
functionalization of the material on the
adsorption behavior of the VOC’s (20 ppmv
Toluene here)

CONCLUSIONS
In this work, we have shown the feasibility of using silica nanoparticle films as sensing layer to locally concentrate Toluene molecules. We are
currently exploring different functional groups as well as varying their concentration on the silica surface.
[1]C. P. Ferrari, P. Kaluzny, A. Roche, V. Jacob, and P. Foster, Chemosphere, vol. 37, no. 8, pp. 1587–1601, 1998. [2]EPA An Introduction to IAQ Indoor Air Quality, “An Introduction to IAQ Indoor Air Quality,” 2012.
[3]I. Mögel, S. Baumann, A. Böhme, T. Kohajda, M. von Bergen, J.-C. Simon, and I. Lehmann, Toxicology, vol. 289, no. 1, pp. 28–37, Oct. 2011.