Study On The Surface Regulation Of Semiconductor Oxide And Graphene Composites And Its Room-temperature NO₂ Gas Sensing Properties

Recently,the Internet of things（IoT）is growing fast,gas sensors have great application prospects in the fields of smart home,wearable devices and smart mobile terminals.The researchers focus on the development of practical high-performance gas sensors.Sensitive materials are the key to determine gas sensing properties.The development of sensitive materials with excellent performance is an effective way to improve the gas sensing properties.Graphene has large specific surface area,high carrier mobility at room temperature and low electrical noise,which is suitable for constructing room-temperature gas sensors.Compared with conventional oxide semiconductor gas sensors,graphene based room-temperature gas sensors could decrease power consumption and are easy to be used in flexible and wearable devices.The main objectives of this paper are to develop high-performance room-temperature NO₂ gas sensor and to explore the the relationship between surface microstructure of sensitive materials and gas sensing properties.The purpose of the changing synthesis conditions for sensitive materials is to control the surface and interface of materials,so as to improve the sensitivity,response and recovery speed of the sensors and so on.The main research contents of this paper are summarized as follows:（1）SnO₂-RGO was used as base material.In order to further improve the NO₂sensing performance of SnO₂-RGO at room temperature,the surface microstructure of SnO₂-RGO was controlled to increase the oxygen vacancy concentration.The introduction of high concentration oxygen vacancy,the electrical properties and chemical catalytic activity of sensitive material were changed.Then,the material have a higher adsorption capacity for NO₂,thus the sensing properties were improved.（2）Taking SnO₂-RGO as an example,the interaction between RGO and SnO₂was regulated by controlling the surface oxygen vacancy concentration of sensitive materials.SnO₂-RGO composites were prepared by three methods,for example,in situ hydrothermal growth of GO and Sn⁴⁺,the assembly of GO and SnO₂nanoparticles and the deposition of SnO₂ nanoparticles on RGO surface.SnO₂-RGO prepared by three different synthesis methods have different concentration of oxygen vacancies.The sensing performance is different.The NO₂ sensing performance is proved to be influenced by surface microstructure of the materials.Therefore,it provides a new idea for the development of high-performance RGO gas sensor.（3）Noble metal doping is an effective method for improving the sensing performance of oxide semiconductor.Firstly,the load of Pd nanoparticles on the surface of SnO₂-RGO can improve sensitivity by taking advantage of the electronic sensitization and catalysis of Pd nanoparticles.Subsequently,ZnO nanoparticles were modified on the surface of SnO₂-RGO by wet chemical method.New interface structures and synergistic effects of the three components were introduced to further improve the room-temperature NO₂ sensing performance of SnO₂-RGO binary materials.（4）This part focuses on the influence of environmental humidity on the gas sensing properties of Zn₂SnO₄-RGO based sensor and the reasons for the specific selectivity of oxidizing gases by this sensor.The results showed that Zn₂SnO₄-RGO based sensors have high selectivity to oxidizing gases（NO₂ and O₃）.At the same time,Zn₂SnO₄-RGO has highly response to NO₂ under the condition of high humidity（80%RH）.Finally,in situ DRIFT characterization was used to study the chemical reactions of NO₂ and H₂O molecules on the surface of sensitive materials,and the gas sensing mechanism was analyzed in depth.（5）In order to solve the problem that most of MoS₂ gas sensors can not be completely recovered in air,this part of the research were carried out.MoS₂-RGO hybrids were prepared by hydrothermal synthesis method,which showed a rapid response and recovery behavior,and it can realize the detection of NO₂ with ppb level.The study purpose of this paper is to develop high-performance RGO based room-temperature gas sensor.The relationship between sensitive materials surface microstructure and sensing properties was systematically studied.The sensing properties were improved by surface control and modification of materials.Furthermore,study on adsorption of oxygen and water molecules as well as chemical reactions on the surface of materials offers theoretical and experimental evidence for developing high performance room-temperature gas sensors.