Regulate And Control Of The Surface State Of Semiconducting Metal Oxides And Sensing Properties

With the acceleration of urbanization, the increase of vehicle population and therapid growth of energy consumption, gas sensor technology as devices or systemsaccess to information has already become one of the important pillars of moderntechnology. In practice, chemical sensors have played important roles in militaryengineering, industrial, environmental protection, human life, medical and so on.Sensing material is a core part of the gas sensor, and the design and development ofnovel and efficient synthetic strategies for nanomaterials are playing an importantrole in the enhanced sensing performance of gas sensor. In recent years,development of nanotechnology not only injects new elements for research ofsensing materials and design of sensing materials microstructures but it alsoprovides the motivation and innovation. Metal oxide semiconductor nanomaterialsexhibit the wide application prospects in gas sensor field. For example, hollownanostructure-based sensor exhibits fast response and recovery time,heterostructures-based sensor could enhance the selectivity to target gases and so on.The analysis of the relationship between structure and performance of sensingmaterials and the effect research of the size, component and structure to sensingperformance of sensing materials are of great significance and practical engineeringvalue. Moreover, the analysis of the intrinsic relationship between the surfaceregulation of sensing materials and macroscopic properties of gas sensor break theconventional mechanism for the development of new sensitive devices and expandthe application space. In the project, we have comprehensively investigated the problem of the sensor based on metal oxide semiconductor nanomaterials. It is ofgreat importance to regulate and control the surface structure of semiconductingmetal oxides and explore the relationship between the component, morphology andsensing performances, which are also the research topic of the modification of thegas-sensing properties (such as response, response/recovery time, selectivity andstability) of sensing materials. The main research contents in this thesis aresummarized as follows:(1) Solid SnO2and ZnO nanospheres have been prepared by using a simplehydrothemal method. The gas sensing preformances of the as-prepared solid SnO2and ZnO nanospheres were researched according to the “size effect” discussed inchapter one.(2) For structure of sensing materials, we will propose that the hollow SnO2andZnO nanospheres as sensing material used in gas sensor, and indepth studiedconfinement effects of the loose structure to gas transmission. This structureimproves the speed of the gas go inner and outer surfaces of sensing material, sodecreased the response and recovery time of the sensor.(3) By adding the surfactant composition to regulate the dimension of thestructural unit obtained hierarchical SnO2and ZnO nanostructure with differentstructure unit. The hierarchical SnO2and ZnO nanostructure were obtained by asimple hydrolysis method with subsequent calcination process. It is of greatimportance to regulate and control the surface structure of semiconducting metaloxides and explore the relationship between the loose degree, size, morphology andgas-sensing properties,(4) The core-shell SnO2and ZnO nanostructures with hollow and multiple-shellarchitectures have been successfully synthesized and the first time used in gas sensor.The gas sensing results show the surface state of metal oxide semiconductornanomaterials have moderating effect on sensing performance. We find that thestructure dependence of the gas-sensing characteristics in metal oxidesemiconductor nanomaterials-based sensors, one of the greatest factors in gas-sensorapplications, is managed by various structures. Moreover, we established gas sensing mechanism model for of a metal oxide semiconductor.(5) The surface modification by hierarchical, hollow and core-shell (SnO2andZnO) nanostructure materials would concol the interfaceaction between sensingmaterials and target gases, and enhace the the dispersibility of nanomaterials and theinterfacial bonding with the nanostructure. The structure and content of thesurface-modified compounds would be regulated to balance the dispersingcharacteristic and conductivity of the composite membrane. The enhancement of thedetection precision, selectivity and stablity in gas sensor would be realized, Abovereseach results will provide a scientific basis for devoloping high-quality highhumidity sensing materials and gas sensors.(6) We will develop a new strategy to produce humidity-independent chemicalsensors by combining readily gas-accessible hierarchical sensing layers (n-typesemiconductor nanomaterials) and catalytic surface additives (p-type semiconductornanomaterials). The modified1D nanofibers would be used as the conductivefiller.The loading of p-type Co3O4into n-type1D TiO2nanofibers enhanced thesensing performance remarkably. Moreover, the humidity dependence of all of thesensing characteristics, including the detection precision, selectivity and stablity,was almost removed by the p-type Co3O4nanomaterials loading.In conclusion, in this paper, we have systemically studied the relationshipbetween the composite materials structure/size and the gas sensing properties of thesensors, and in-depth know the sensing mechanism of metal oxide semiconductornanomaterials-based sensor, which establishes the foundation for devolopinghigh-quality high performance sensing materials and gas sensors.