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the Owner Societies 2014 Phys. Chem. Chem. Phys., 2014, 16, 19327--19332 | 19327
Cite this: Phys. Chem. Chem. Phys.,
2014, 16,19327
Synthesis of porous Co
3
O
4
nanonetworks to
detect toluene at low concentration†
Changhui Zhao, Baoyu Huang, Jinyuan Zhou* and Erqing Xie*
Porous Co
3
O
4
nanonetworks (NNWs), converted from precursor CoOOH nanosheets, have been synthesized
via a controllable chemical reaction route followed by calcination at 400 1Cinair.Themorphologiesand
microstructures of the precursor nanosheets and the final products were characterized by high-resolution
transmission electron microscopy and X-ray diffraction, respectively. The growth mechanism of CoOOH
nanosheets and the structural transformation processes of NNWs were investigated in detail. Significantly, the
porous Co
3
O
4
NNW based sensor showed an enhanced response to toluene gas at low concentration,
which was mainly due to its porous neck-connected networks.
Introduction
As a multifunctional p-type semiconductor, spinel Co
3
O
4
has
attracted much attention in the fields of catalysts, magnets,
electrochromic devices, Li-ion batteries, supercapacitors, and
gas sensors.
1–7
In particular, the gas-sensing properties of
various Co
3
O
4
micro- and nanostructures have been widely
explored, such as nanorods, nanofibers, nanosheets, and
hollow microspheres.
8–14
Among them, porous architectures
are expected and confirmed to play a key role in improving the
sensor performance, due to their high surface area, high gas
transmission abilities, and special grain interconnectivity.
15–17
Up to now, many efforts have been made to convert Co
3
O
4
nanoscale
building blocks into complex hierarchical nanostructures using
hydrothermal, solvothermal, electrospinning, template/template-
free, chemical deposition, and combined methods.
9–10,18–24
But it is still a great challenge to develop a simple, economical
and large-scale synthetic method for the construction of porous
Co
3
O
4
nanostructures.
Previously our group found that porous NiO nanosheets
with neck-connected networks could be prepared by a simpli-
fied chemical bath deposition (CBD) method, and these porous
networks exhibited enhanced ethanol sensing performances.
25
In
this work, ultrathin CoOOH nanosheets have been synthesized
under appropriate chemical reaction conditions, and transformed
into porous Co
3
O
4
nanonetworks (NNWs) after calcination at
400 1C for 2 h. The obtained porous NNWs are constructed
using numerous neck-connected Co
3
O
4
nanoparticles, which
lie between porous nanosheets and nanoparticles. To the best
of authors’ knowledge, this is a new strategy to achieve the
porous Co
3
O
4
NNWs by rebuilding the precursor nanosheets.
The growth mechanism of CoOOH nanosheets and the structural
transformation processes of NNWs were mainly investigated.
Furthermore, the gas-sensing results indicated that the sensor
based on porous NNWs exhibited high performance towards
toluene at a low operating temperature of 150 1C.
Experimental details
Synthesis
All the reagents in our experiment were of analytical grade and
used without any further purification. In brief, 10 mL of 0.1 M
cobalt nitrate hexahydrate (Co(NO
3
)
2
6H
2
O) and 1 mL of aqueous
ammonia (NH
3
H
2
O, 25–28%) were mixed, followed by continuous
stirring for 5 min. Then 5 mL of 0.25 M potassium persulfate
(K
2
S
2
O
8
) was added into the mixture. After stirring for another
20 min, black precipitates were obtained and respectively washed
with deionized water and acetone several times, and dried slowly
to form a type of puffed precursor. All operations were carried out
at room temperature. Finally, the obtained precursors were
calcined at 350, 400, and 500 1C for 2 h in air, respectively.
Characterization and gas-sensing measurements
The microstructures and morphologies of products were char-
acterized by X-ray diffraction (XRD, Rigaku, D/max-2400) and
high-resolution transmission electron microscopy (HRTEM,
FEI, Tecnai G2 F30), respectively. Specific surface area measure-
ments were carried out using the Brunauer–Emmett–Teller (BET,
ASAP 2020) method based on nitrogen (N
2
) gas adsorption.
Key Laboratory of Magnetism and Magnetic Materials of Ministry of Education,
Lanzhou University, Lanzhou, 730000, People’s Republic of China.
E-mail: xieeq@lzu.edu.cn, zhoujy@lzu.edu.cn; Fax: +86 931 8913 554;
Tel: +86 931 8912 616
† Electronic supplementary information (ESI) available: TEM images and XRD
patterns of CoOOH precursors; the EDX spectrum and the STEM image of Co
3
O
4
NNWs; and stability and sensor responses to toluene. See DOI: 10.1039/
c4cp02961e
Received 7th July 2014,
Accepted 28th July 2014
DOI: 10.1039/c4cp02961e
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