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. 2019 Jun 20;9(6):900.
doi: 10.3390/nano9060900.

Heterostructured NiO/ZnO Nanorod Arrays with Significantly Enhanced H2S Sensing Performance

Dongyi Ao  1 , Zhijie Li  2 , Yongqing Fu  3 , Yongliang Tang  4 , Shengnan Yan  5 , Xiaotao Zu  6
Affiliations

Heterostructured NiO/ZnO Nanorod Arrays with Significantly Enhanced H2S Sensing Performance

Dongyi Ao et al. Nanomaterials (Basel). .

Abstract

H2S gas sensors were fabricated using p-n heterojunctions of NiO/ZnO, in which the ZnO nanorod arrays were wrapped with NiO nanosheets via a hydrothermal synthesis method. When the H2S gas molecules were adsorbed and then oxidized on the ZnO surfaces, the free electrons were released. The increase in the electron concentration on the ZnO boosts the transport speed of the electrons on both sides of the NiO/ZnO p-n junction, which significantly improved the sensing performance and selectivity for H2S detection, if compared with sensors using the pure ZnO nanorod arrays. The response to 20 ppm of H2S was 21.3 at 160 °C for the heterostructured NiO/ZnO sensor, and the limit of detection was 0.1 ppm. We found that when the sensor was exposed to H2S at an operating temperature below 160 °C, the resistance of the sensor significantly decreased, indicating its n-type semiconductor nature, whereas when the operating temperature was above 160 °C, the resistance significantly increased, indicating its p-type semiconductor nature. The sensing mechanism of the NiO/ZnO heterostructured H2S gas sensor was discussed in detail.

Keywords: H2S gas sensor; NiO; ZnO; nanorods; p-n junction.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
SEM images of (a) pure ZnO NRs, (b,c) NiO/ZnO heterostructures and (d) EDS of NiO/ZnO heterostructures.
Figure 2
Figure 2
XRD patterns of ZnO NRs.
Figure 3
Figure 3
(a) TEM bright-field image of NiO/ZnO heterostructures and (b–d) elemental mapping of NiO/ZnO heterostructures.
Figure 4
Figure 4
XPS spectra of (a) full spectrum, (b) Zn 2p, (c) Ni 2p, and (d) O 1s.
Figure 5
Figure 5
(a) UV-visible absorption spectra and (b) plot of (αhυ)2 vs. hυ of ZnO NRs, NiO NSs, and NiO/ZnO heterostructures.
Figure 6
Figure 6
(a) Current density-voltage characteristics at 160 °C and (b) responses of NiO/ZnO-heterostructures-based sensor to 1 ppm of H2S at different operating temperatures.
Figure 7
Figure 7
Dynamic response curves upon exposure to H2S with different concentrations at 160 °C exhibited by sensors based on: (a) pure ZnO NRs and (b) NiO/ZnO, and (c) responses histogram of sensors and (d) pure NiO NSs.
Figure 8
Figure 8
(a) Dynamic response curves of NiO/ZnO-heterostructures-based sensor to H2S and other gases (NH3, C2H6O, NO2, and CO) for the same concentration of 20 ppm was measured at 160 °C; (b) Stability of NiO/ZnO-heterostructures-based sensor to 1 ppm H2S at 160 °C.
Figure 9
Figure 9
Schematic model for sensors exposed to H2S: (a) pure ZnO and (b) NiO/ZnO heterostructures.
Figure 10
Figure 10
Energy band structure of p-NiO/n-ZnO heterostructures.
Figure 11
Figure 11
Dynamic response curves of NiO/ZnO-heterostructures-based sensor to 1 ppm H2S at 160 °C and 240 °C.
See this image and copyright information in PMC

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