Structure And Interface Design Of ZnO-based Sensing Material And Its Sensing Performance

The rapid development of industry not only improves people’s living standard,but also destroys the sustainable development of the ecological environment,such as deteriorated indoor and outdoor air quality.Thus,gas sensors arise at the right moment.Chemical-resistance sensors have received extensive attention from scientists due to their advantages of simple operation,portability and good stability.At present,among all sensing materials,ZnO is conspicuous because of its low price,non-toxicity,and high electron mobility.In this paper,ZnO-based sensing materials are rationally designed and synthesized,and the effect of the interface on the sensing performance is studied intensively.The main content can be summarized as follows:Apart from being an important industrial raw material,triethylamine also irritates and corrodes people’s skin and mucous membranes.Therefore,the gas sensors designed in the first three chapters are related to trimethylamine detection.（1）The hierarchical ZnO microspheres modified with Pt particles were prepared initially by hydrothermal and subsequently via sodium borohydride reduction.The results show that the Pt-ZnO gas sensor has excellent sensing characteristics for triethylamine.When the concentration of triethylamine is 100 ppm,the response value of this sensor can be as high as 242.Through analysis,the reasons for its excellent performance are the unique hierarchical structures of ZnO and the modification of Pt particles（Schottky junction and spillover effect）（2）The modification of noble metals can greatly improve the triethylamine sensing performance of ZnO.But noble metals are expensive.Therefore,we prepared CdS/ZnO composite triethylamine sensor by in-situ growth of CdS quantum dots on ultra-thin ZnO nanosheets.The results show that the CdS/ZnO（0.2 at%）gas sensor has a lower operating temperature,a higher response value and a faster response time.The enhanced gas sensitivity is derived from the unique 0D/2D structure and n-n heterojunction.In addition,this research paves the way for the design of sensors with0D/2D structures.（3）The working temperatures of sensors in the above two studies are relatively high,and high energy consumption will severely limit their practical application.Therefore,in the third work,to lower operating temperature,a triethylamine sensor is designed by loading a semiconductor with a narrow bandgap on the surface of ZnO.In this chapter,by decorating Cs Pb Br₃quantum dots on the surface of porous ZnO,a low energy consumption triethylamine sensor is designed.The results show that the operating temperature of the ZnO-Cs Pb Br₃gas sensor is 180℃,which is the lowest among these three works.In addition,for the first time,the existence of vinylamine,an intermediate in the oxidation process of triethylamine was verified via in-situ diffuse scattering Fourier transform infrared spectroscopy.Compared with triethylamine,the harm of formaldehyde is more serious.Long-term exposure to high concentrations of formaldehyde can result in leukemia and even cancer.Therefore,in the last work,we designed and synthesized a ZnO-based high-efficiency formaldehyde sensor.（4）Ag-ZnO/In₂O₃nanofibers were synthesized by electrospinning.The sensor designed based on this composite showed excellent performance against formaldehyde.In particular,at an operating temperature of 260℃,it achieved an ultra-high response value of about 186 to 100 ppm of formaldehyde.The enhanced gas sensitivity is mainly attributed to the multi-level heterojunction（n-n heterojunction and ohmic contact）and the"spillover effect"of Ag.This work suggests that the design of the multi-level heterojunction can significantly improve the sensing performance.The above research achieves significant performance improvement of ZnO-based materials by rationally designing their structurse and interfaces,which provides experimental support and theoretical guidance for the preparation of an efficient ZnO-based gas sensor.