Sensors and Actuators B 143 (2009) 278–285
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Sensors and Actuators B: Chemical
journal homepage: www.elsevier.com/locate/snb
Synthesis and gas sensing properties of nanostructured CoSb
2
O
6
microspheres
Carlos R. Michel
∗
, Héctor Guillén-Bonilla, Alma H. Martínez-Preciado, Juan P. Morán-Lázaro
Departamento de Física CUCEI, Universidad de Guadalajara, Blvd. Marcelino García Barragán 1421, Guadalajara, Jalisco 44410, Mexico
article info
Article history:
Received 29 May 2009
Received in revised form 9 September 2009
Accepted 18 September 2009
Available online 30 September 2009
Keywords:
Inorganic colloids
Cobalt oxides
Microspheres
Gas sensors
abstract
Nanostructured CoSb
2
O
6
microspheres were prepared by a colloidal method using cobalt nitrate, anti-
mony trichloride and n-dodecylamine in ethyl alcohol. Microwave radiation, with a power of ∼160 W,
was applied for solvent evaporation. The full evaporation was reached after a non-continuous radiation
for 200 s. The resulting material was then heated at 200
◦
C in static air. At this temperature, a large num-
ber of microspheres with smooth surface were formed. The calcination at 700
◦
C produced single-phase
nanostructured CoSb
2
O
6
hollow microspheres. The surface nanoparticles had an average particle size of
38 nm. The gas sensing properties of CoSb
2
O
6
thick films were investigated at 400
◦
C. The direct current
measurements showed resistance variations (R) of ∼130 in CO
2
and ∼75 in O
2
. In a previous work,
these values were 450 and 180 , respectively, corresponding to CoSb
2
O
6
synthesized by a solution-
polymerization method. Even though a decrease in R was recorded in the present study, more stable
measurements in carbon dioxide were obtained, with lower resistance values. The polarization curves
showed a large non-ohmic behavior, with a significant ability to detect variations in the concentration
of CO
2
and O
2
. Alternating current was also used to characterize the gas sensing properties of CoSb
2
O
6
.
The measurements in AC revealed better repeatability in gas detection and also the capability to detect
variations in the gas concentration.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
Ceramic microspheres have received considerable attention
in the field of functional materials due to their applications in
photoluminescence, anion materials for lithium-ion batteries,
sensors, liquid chromatography and many others [1–5]. For their
preparation, several methods like ultrasonic-assisted aerosol
pyrolysis, microfluidics, hydrothermal, templating, reverse-
emulsion, macroemulsion and ionic liquids have been reported
[6–13].
By the Stöber method, monodisperse silica microspheres have
been synthesized earlier [14]. TiO
2
and Al
2
O
3
microspheres have
also been produced by this method [15–17]. However, a disad-
vantage of this method to prepare microspheres of other inorganic
compounds is that a limited number of metal alcohoxides are com-
mercially available. In the Stöber method, the hydrolysis of metal
alcohoxides plays a key role in the formation of microspheres
[16]. However, Matijevic using colloidal methods has reported the
preparation of microspheres of cobalt phosphate, tin (IV) oxide, zinc
sulfide and other compounds [18–20].
On the other hand, CoSb
2
O
6
is a p-type semiconductor material,
which posses the trirutile-type crystal structure. This struc-
ture derives from the rutile-type lattice by tripling the c-axis.
∗
Corresponding author. Tel.: +52 33 33 45 41 47; fax: +52 33 33 45 41 47.
E-mail address: michelucr@yahoo.es (C.R. Michel).
Long-range ordering of the cations in three dimensions has
been reported in the past for this structure [21]. Moreover, the
electrochemical evaluation of CoSb
2
O
6
as cathode material for
rechargeable lithium-ion batteries revealed limited reversibility
during charge/discharge cycles [22]. The full reduction of CoSb
2
O
6
into a mixture of Li
2
O, Co and Li
3
Sb observed in these experiments
seems to place this oxide out of this application. About gas sen-
sor materials, SnO
2
with the rutile-type structure has been one of
the most studied materials. However, few are known about the
gas sensing properties of oxides having the trirutile-type struc-
ture. Evidently a reduced number of oxides posses this type of
lattice; however, as many other oxides having cobalt, the electrical
properties of CoSb
2
O
6
are interesting to explore with gas sensing
purposes. In a recent work, nanostructured CoSb
2
O
6
prepared by a
solution-polymerization method was tested as a gas sensor mate-
rial [23]. The results indicated that this oxide can detect CO
2
and O
2
,
involving variations in the electrical resistance of 450 and 180 ,
respectively.
Moreover, although CoSb
2
O
6
has been prepared by several
routes, the resulting particle shape was irregular and particle
agglomeration was also present [22,23]. Since the colloidal meth-
ods are effective in controlling the particle shape of inorganic
materials, they can be of interest for the synthesis of this oxide.
Preliminary results indicate that if amines are used in non-aqueous
media, the shape and size of the particles largely depends on the
type of amine used. However, more research is needed to find the
optimal conditions to obtain CoSb
2
O
6
microspheres.
0925-4005/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.snb.2009.09.041