Sensors
and
Actuators
B
193 (2014) 320–
325
Contents
lists
available
at
ScienceDirect
Sensors
and
Actuators
B:
Chemical
journal
h
om
epage:
www.elsevier.com/
locate/snb
Synthesis
of
mesoporous
SnO
2
–SiO
2
composites
and
their
application
as
quartz
crystal
microbalance
humidity
sensor
Ye
Zhu
a
,
Junchen
Chen
b
,
Huimin
Li
a
,
Yongheng
Zhu
a
,
Jiaqiang
Xu
a,∗
a
Department
of
Chemistry,
College
of
Science,
Shanghai
University,
Shanghai
200444,
China
b
Department
of
Chemistry
and
Shanghai
Key
Laboratory
of
Molecular
Catalysis
and
Innovative
Materials,
Laboratory
of
Advanced
Materials,
Fudan
University,
Shanghai
200433,
China
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
2
August
2013
Received
in
revised
form
20
November
2013
Accepted
22
November
2013
Available online 1 December 2013
Keywords:
Humidity
sensor
Mesoporous
QCM
SnO
2
–SiO
2
Sol–gel
a
b
s
t
r
a
c
t
In
this
paper,
chemically
derived
mesoporous
SnO
2
–SiO
2
composite
was
deposited
on
a
transducer
of
quartz
crystal
microbalances
(QCMs)
to
construct
a
humidity
sensor
for
wide
range
humidity
detection.
The
composite
was
synthesized
through
a
facile
one-pot
sol–gel
method
and
characterized
by
XRD,
TEM,
EDX,
ICP
and
nitrogen
adsorption–desorption
test.
The
humidity
sensing
characteristics
of
the
QCMs
coated
with
SnO
2
–SiO
2
composites
thin
film
were
investigated
by
exposing
the
QCMs
to
various
rela-
tive
humidity
(RH)
environments
at
room
temperature,
including
sensitivity
and
linearity,
response
and
recovery,
and
humidity-hysteresis.
The
results
exhibit
that
the
sample
with
a
atomic
ratio
of
Sn/Si
=
1:1
shows
better
humidity
sensing
properties
than
others
within
the
range
of
11–96.1%
relative
humid-
ity
(RH),
and
the
sensor
also
displays
rapid
response
and
recovery
about
14
s
and
16
s,
respectively.
The
nanocomposite
also
shows
suitable
sensitivity
and
low
hysteresis,
revealing
its
great
potential
in
humidity
sensors.
© 2013 Elsevier B.V. All rights reserved.
1.
Introduction
Systems
for
air
quality
humidity
monitoring
are
of
great
impor-
tance
for
quality
control
of
products
in
different
fields,
such
as
electronic
devices
and
precision
instruments
production,
textile
area,
food
storage,
domestic
environments
and
so
on.
There
into
one
of
the
aspects
of
air
quality
is
the
relative
humidity
level,
which
is
very
important
for
human
comfort
and
industrial
processes.
The
requirements
for
practical
application
of
humidity
sensors
can
be
summarized
as
follows:
good
sensitivity
over
a
wide
range
of
humidity
and
temperature,
short
response
time,
good
repro-
ducibility,
very
small
hysteresis,
chemical
and
physical
stability
in
aggressive
atmosphere,
negligible
temperature
dependence,
and
low
cost
[1–3].
The
way
used
to
improve
the
humidity
performance
is
taking
porous
materials
as
the
candidate
sensing
materials,
such
as
zeolites
or
mesoporous
materials
[4–7],
because
these
porous
materials
have
controlled
pore
size,
connected
channel
and
large
surface
area,
which
are
beneficial
to
the
adsorption
and
transfer
of
water
molecules.
Among
these
porous
materials,
mesoporous
silica,
which
was
firstly
synthesized
by
the
researchers
in
Mobil
company
[8],
has
became
a
popular
humidity
sensing
material
in
recent
years
[9,10]
since
it
was
proved
to
have
better
humidity
∗
Corresponding
author.
Tel.:
+86
21
66132701;
fax:
+86
21
66134594.
E-mail
address:
xujiaqiang@shu.edu.cn
(J.
Xu).
response
than
non-porous
silica
[11].
Up
to
now,
a
large
vari-
ety
of
mesoporous
materials
has
been
synthesized
as
humidity
sensing
materials
[12]
.
However,
from
the
viewpoint
of
design-
ing
humidity-sensing
materials,
the
investigation
of
the
humidity
sensing
mechanism
is
of
more
great
importance.
The
design
of
high-performance
sensors
can
be
more
efficient
only
if
the
sensing
mechanism
is
clear.
Generally,
complex
impedance
spectra
tech-
nique
played
an
important
role
in
analyzing
the
sensing
mechanism
of
humidity
sensing
material
[13,14].
Nowadays,
there
are
many
kinds
of
humidity
sensors
in
the
world.
Among
them,
the
mass-sensitive
devices
including
bulk
acoustic
wave
(BAW)
and
surface
acoustic
wave
(SAW)
become
more
and
more
popular
due
to
the
advantages
of
their
high
stability
and
good
sensitivity.
As
a
typical
BAW
device,
quartz
crys-
tal
microbalances
(QCMs)
can
determine
a
small
electrode-mass
change
down
to
the
nano-gram
level
[15–17].
Sauerbrey
has
firstly
derived
the
quantitative
relationship
between
change
of
frequency
of
piezoelectric
crystal
f
(Hz)
and
the
mass
change
caused
by
mass
loading
on
the
piezoelectric
crystal
surface.
f
=
−2.3
×
10
6
×
f
0
A
m
(1)
where
f
0
(10
6
Hz)
is
the
basic
frequency
of
the
unloaded
piezoelec-
tric
crystal,
m
(g)
is
the
change
in
mass
on
the
surface
of
the
crystal,
and
A
(cm
2
)
is
the
surface
area
of
the
electrode.
Since
King
[18]
firstly
introduced
the
QCM
into
analytical
chemistry,
the
QCM
0925-4005/$
–
see
front
matter ©
2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.snb.2013.11.091