C H Gas Sensor Based On Ni-Doped Zno Electrospun Nanofibers: Ceramics
C H Gas Sensor Based On Ni-Doped Zno Electrospun Nanofibers: Ceramics
C H Gas Sensor Based On Ni-Doped Zno Electrospun Nanofibers: Ceramics
com
CERAMICS
INTERNATIONAL
Ceramics International 39 (2013) 2883–2887
www.elsevier.com/locate/ceramint
Abstract
Pure and Ni-doped ZnO nanofibers were synthesized using the electrospinning method. The morphology, crystal structure and optical
properties of the nanofibers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photolumine-
scence (PL) spectroscopy, respectively. It is found that Ni doping does not change the morphology and crystal structures of the
nanofibers, and the ultraviolet emissions of ZnO nanofibers present red shift with increasing Ni doping concentration. C2H2 sensing
properties of the sensors based on the nanofibers were investigated. The results show that the C2H2 sensing properties of ZnO nanofibers
are effectively improved by Ni doping, and 5 at% Ni-doped ZnO nanofibers exhibit a maximum sensitivity to C2H2 gas.
& 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
0272-8842/$ - see front matter & 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
http://dx.doi.org/10.1016/j.ceramint.2012.09.062
2884 X. Wang et al. / Ceramics International 39 (2013) 2883–2887
2. Experimental
Intensity (a.u.)
b
Pure ZnO
Intensity (a.u.)
30 40 50 60 70 Wavelength (nm)
2 Theta (deg)
Fig. 3. Room temperature photoluminescence spectrum of Ni-doped
ZnO nanofibers with different doping concentrations after calcinations:
(a) 0; (b) 3; (c) 5 and (d) 8 at%.
12
be attributed to the 1D nanostructures of the nanofibers,
10 which facilitated the fast mass transfer of C2H2 molecules to
and from the interaction region as well as improved the rate
8
for charge carriers to traverse the barriers induced by
6 molecular recognition along the nanofibers [28,29].
It is well accepted that the gas-sensing mechanism of
4
ZnO-based sensors belongs to surface-controlled type,
2
namely, the sensitivity is attributed to the chemisorption
of oxygen on the oxide surface and the subsequent reaction
0 between adsorbed oxygen and test gas, which brings the
180 200 220 240 260 280 300 320 340 360
resistance change. Prior to the test gas (C2H2) injection, the
Temperature (°C)
oxygen molecules in air will absorb on the fiber surface to
Fig. 4. Sensitivity of pure and Ni-doped ZnO nanofibers to 2000 ppm generate chemisorbed oxygen species (O2 , O2 and O )
C2H2 gas at various operating temperatures. by capturing electrons from the ZnO conduction band.
Consequently, ZnO will show a high resistance. Takata
18 et al. found that the chemisorbed oxygen species depend
16
5 at% Ni-doped ZnO strongly on temperature, and the stable oxygen ions were
pure ZnO nanofibers O2 below 100 1C, O between 100 and 300 1C, and O2
14 above 300 1C [30]. Since the sensor was operated at 250 1C,
the O species were more important than other oxygen
Sensitivity (Ra/Rg)
12
adsorbates. When Ni-doped ZnO is exposed to reductive
10
gases (C2H2), the C2H2 molecules will react with adsorbed
O species on the ZnO surface to form CO2 and H2O,
8 which leads to the increase of carrier concentration and the
decrease of the electrical resistance. On the basis of the
6
discussion, the C2H2 sensing mechanism of this ZnO-based
4 gas sensor may be described as follows:
2
O2 ðgasÞ þ 2e -2O
ads
ads -2CO2 þ H2 O þ 5e
C2 H2 ðadsÞþ 5O
0
0 500 1000 1500 2000
Fig. 5. Sensitivities of sensors upon different C2H2 gas concentrations 5 at% Ni-doped ZnO pumping
18
at 250 1C. pure ZnO
16
12
Ni concentration such as 8 at% deteriorate with worse
sensitivity (as shown in Fig. 4). At the optimal Ni doping 10
The high performance of our nanofibers is also up to the [10] D.J. Yang, I. Kamienchick, D.Y. Youn, A. Rothschild, I.D. Kim,
sensing improvement brought by Ni doping. By doping Ni Ultrasensitive and highly selective gas sensors based on electrospun
SnO2 nanofibers modified by Pd loading, Advanced Functional
in ZnO, impurity energy levels will be introduced, and the
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