Third Day Poster Session, 17 June 2010 - NanoTR-VI

Poster Session, Thursday, June 17
Theme F686 - N1123
Direct measurement of humidity adsorption kinetics of Calix[4]arene derivative using QCM technique
Omer Mermer 1* , Salih Okur 2 , Fevzi Sümer 1 , Mahmut Ku 3 , eref Ertul 4 , Mevlüt Bayrakç 4 , Mustafa Ylmaz 4
1 Ege University, Department of Electrical and Electronics Engineering Bornova/Izmir/TURKEY
2 Izmir Institute of Technology, Department of Physics Urla/Izmir/TURKEY
3 Selçuk University, Department of Chemical Engineering, Selçuklu/Konya/TURKEY
4 Selçuk University, Department of Chemistry, Selçuklu/Konya/TURKEY
Abstract— This study focuses on the optimization and characterization of calix[4]arene derivative based sensor film coated on
a quartz substrate by drop casting method for use in the detection of humidity. The humidity adsorption and desorption kinetics
calix[4]arene were investigated by Quartz Crystal Microbalance (QCM) technique. The Langmuir model was used to
determine the kinetic parameters such as adsorption, desorption rates and Gibbs free energy between relative humidity between
11% and 97%. Our reproducible experimental results show that calix[4]arene films have a great potential for humidity sensing
applications at room temperature operations.
Monitoring and control of humidity is essential for
industrial progress of the world such as petroleum industry,
medical equipments, food industry and the manufacturer of
moisture sensitive products. Furthermore clean rooms,
greenhouses, research and developments labs are all
environments that are highly effected by moisture levels and
require constant monitoring [1–2].
Quartz crystal microbalances (QCMs) have been widely
used in recently as promising gas sensor applications owing to
their high sensitivity and ease of measurement, since the
measured frequency shift is directly proportional to the mass
change on a quartz crystal [1–2].
Thin films of calix[4]arene derivatives have been widely
used in chemical sensors. Due to their zeolite-like capacity
and selectivity, calix[4]arene became promising materials for
sensor applications. The functional groups at the upper and
lower rims determine their selectivity in host-guest
interactions and physical properties [3]. Calix[4]arene
derivatives have been used in recent times as gas sensors
applications [4,5].
The frequency response curve QCM-based sensor to
cyclic humidity change is depicted in Figure 2 for different
RH levels. The frequency shift of QCM decreases sharply
with increasing humidity concentrations while there is no
change in that of the empty QCM (adsorption process). On the
other hand, during the desorption process, the humidity level
is turned back to the initial value, as a result, QCM recovers
back to its initial resonance frequency value.
Langmuir adsorption isotherm model is frequently
used to describe adsorption and desorption kinetics of gas
vapor molecules onto organic or inorganic films [6-7].
According to this model, the rate of surface reaction for
forming a monolayer on the surface is related to fractional
coverage (), the humidity concentration, and the rate
constants for the adsorption (k a ) and desorption (k d ) processes.
Figure 3 shows the experimental data and the fitting curve for
first adsorption cycle. k a and k d fitting parameters determined
from the fit using Langmuir equation to the experimental data
are given by 62.49 M -1 s -1 and 0.0005 s -1 , respectively [8].
10
8
Figure1 Chemical formula and full name of special design
calix[4]arene.
In this work, special design calix[4]arene molecules were
designed and synthesized for increasing moisture capturing
feature. Chemical structure and full name of this molecule is
given in Figure 1. We have used QCM technique for humidity
detection using a calix[4]arene thin film. We have obtained
very good response and high repeatability characteristics. The
adsorption-desorption kinetics are analyzed and discussed in
details.
f(Hz)
0
-2
-4
-6
-8
-10
-12
-14
11%RH
43%RH
54%RH
75%RH
84%RH
97%RH
0 50 100 150 200 250 300 350
time(s)
Figure2 The frequency response curve QCM-based sensors to
cyclic humidity change
-f(Hz)
6
4
2
K'
8.08
k obs
0.0455
f
( t)
K(1
e
k a
62.49
( kobst)
0
50 100 150 200
time(s)
k d
0.0005
)
G (kJ/mol)
Figure3 The experimental data (blue line) and the fit (red line)
to the Langmuir adsorption isotherm equation
In summary, the QCM results show that calix[4]arene
thin films are very sensitive to humidity and give reproducible
adsorption and desorption kinetic behavior to humidity
changes for short time periods. Our results open a new era to
the high-sensitivity and high-selectivity gas sensor
applications. This work was supported by TUBITAK under
Grant No. TBAG- 109T240.
-29.3
*Corresponding author: omermermer@gmail.com
[1] H. Aizawa, et al., Sens. Actuators B 101 (2004) 150.
[2] H. Zeng, et al., Sens. Actuators B 122 (2007) 1
[3] Koshets I. A., et.al.,Sens. Actuators B 106, (2005), 177
[4] Ohira, Shin-I. , et.al., Talanta 2009, 77, 1814.
[5] S. Okur,et.al., Talanta, Volume 81, Issues 1-2, 2010, Pages 248
[6] D. S. Karpovich and G. J. Blanchard, Langmuir 1994,10, 3315
[7] Y.L. Sun, et. al, Talanta 73, 857-861, 2007.
[8] A. Erol, et.al., Sensors and Actuators B: Chem., 145, 2010, Pages 174-180
6th Nanoscience and Nanotechnology Conference, zmir, 2010 677