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

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.

Advanced development of metal oxide nanomaterials for H2gas sensing applications

“…It is found that selectivity can be regulated by the modulation of barrier height in heterojunction through the asymmetric gas sensing reactivity of heteromaterials. 48,273 Hu et al 48 Heterostructure can significantly improve the sensor performance and reduce the detection limit of the sensor due to its extremely high chemical reaction activity as well as the presence of a large number of oxygen vacancies at the interface. Scientific researchers can also achieve excellent selective sensor preparation by adjusting the barrier height of heterostructures, but much progress is still needed to reduce the working temperature of gas sensor.…”

Utilization of a Gas-Sensing System to Discriminate Smell and to Monitor Fermentation during the Manufacture of Oolong Tea Leaves

“…Several studies have worked on the improvement for selectivity [ 12 , 13 , 14 ] and electrical property [ 15 , 16 ] of MOS gas sensors. The reliability and limitation issues have also been solved by application of composite material [ 17 , 18 , 19 ]. The resistance of a sensor varies with both the nature of the surrounding gases and their concentration [ 20 ], which can be evaluated by measuring the voltage of the sensors.…”

Recent Advances in ZnO-Based Carbon Monoxide Sensors: Role of Doping

“…Concerning its morphology, ZnO has been obtained as nanostructures, which include nanoneedles, nanosticks, nanocouples, nanoflakes, nanosprings, nanotubes, nanorods, and nanowires [ 31 , 34 , 35 ], as well as porous and dense films [ 36 ]; as gas sensing performance is mainly dependent on the morphology of the material. Significant achievements have been attained in the fabrication of gas sensors based on ZnO structures, including biosensors [ 16 , 30 , 36 , 37 , 38 , 39 , 40 , 41 ]. Nevertheless, further research is needed to improve CO detection at low operating temperatures (e.g., room temperature) and with excellent selectivity to differentiate two gases with similar behaviors, considering the effect of the relative humidity on the gas sensing performance [ 38 , 42 , 43 ].…”

“…Significant achievements have been attained in the fabrication of gas sensors based on ZnO structures, including biosensors [ 16 , 30 , 36 , 37 , 38 , 39 , 40 , 41 ]. Nevertheless, further research is needed to improve CO detection at low operating temperatures (e.g., room temperature) and with excellent selectivity to differentiate two gases with similar behaviors, considering the effect of the relative humidity on the gas sensing performance [ 38 , 42 , 43 ].…”