Discriminable Sensing Response Behavior to Homogeneous Gases Based on n-ZnO/p-NiO Composites.

Wen-Dong Zhou,Jing Li,Davoud Dastan,Qi Wang,Xi-Tao Yin

doi:10.3390/nano10040785

Abstract

Metal oxide semiconductor (MOS) gas sensors have the advantages of high sensitivity, short response-recovery time and long-term stability. However, the shortcoming of poor discriminability of homogeneous gases limits their applications in gas sensors. It is well-known that the MOS materials have similar gas sensing responses to homogeneous gases such as CO and H2, so it is difficult for these gas sensors to distinguish the two gases. In this paper, simple sol–gel method was employed to obtain the ZnO–xNiO composites. Gas sensing performance results illustrated that the gas sensing properties of composites with x > 0.425 showed a p-type response to both CO and H2, while the gas sensing properties of composites with x < 0.425 showed an n-type response to both CO and H2. However, it was interesting that ZnO–0.425NiO showed a p-type response to CO but an discriminable response (n-type) to H2, which indicated that modulating the p-type or n-type semiconductor concentration in p-n composites could be an effective method with which to improve the discriminability of this type of gas sensor regarding CO and H2. The phenomenon of the special gas sensing behavior of ZnO–0.425NiO was explained based on the experimental observations and a range of characterization techniques, including XRD, HRTEM and XPS, in detail.

Highlights

Various gases, including blast furnace gas, coke oven gas, water gas and other secondary gases are used as reducing agents and fuels in metallurgical and chemical production
We illustrated that the poor discriminability of gas sensors based on ZnO against CO and H2 can be enhanced via changing the amounts of the p or n-type oxide materials in p–n composites
ZnO–xNiO composites with different molar ratios of Zn/Ni were prepared using a sol–gel method [48,49] in the following three steps. (a) 1 g of Zn(CH3COO)2·2H2O was dissolved into a mixture of 5 mL distilled water and 10 ml methanol to form a solution; 0.1 g of PVP was added into the above solution and stirred until all PVP were completely dissolved

Summary

Introduction

Various gases, including blast furnace gas, coke oven gas, water gas and other secondary gases are used as reducing agents and fuels in metallurgical and chemical production. Metal oxide semiconductor (MOS) gas sensors have been investigated for gas sensing detection of toxic and flammable gases [6,7,8]. Some strategies have been employed to overcome the low selectivity of this kind of gas sensor, including regulation of the optimal operating temperature [25,26,27]; doping or loading of a noble metal [28,29,30,31,32]; modification of chemical composition, morphology and microstructure of the sensor materials [33,34,35]; and construction of n–n [36,37,38,39] or p–n junction [40,41,42,43,44,45,46,47]. We illustrated that the poor discriminability of gas sensors based on ZnO against CO and H2 can be enhanced via changing the amounts of the p or n-type oxide materials in p–n composites. The phenomenon of the abnormal sensing behavior of ZnO–0.425NiO for H2 and CO is explained in detail

Chemicals

Preparation of Materials

Gas Sensing Measurements

Material Characterizations

Sensing Properties of ZnO–xNiO

Conclusions