Preparation And Gas Sensitivity Studies On ZnFe_O4Composite Films

Air pollution has become an inescapable reality in the world’s urban populationlives. With the rapid development of industry, types and quantities of atmosphericpollutants is increasing. Various air pollutants enter the body through a variety ofways. The impact on the human body is a multifaceted and the harm is extremelyserious. So people urgently need to constantly research and develop the method todetect environmental pollutants.The optical waveguide(OWG) chemical sensors has mechanical strength, highsensitivity, system compactness, fast response, anti-electromagnetic interference, easyto operate at room temperature, easy realization for on-line continuous monitoring andmany other features, has important research prospects in the area of applied chemistry,industrial production and biological monitoring and detection of harmful gases. As animportant part of the OWG, sensitive materials will directly affect the performance ofthe sensor, such as stability, selectivity, sensitivity and response time. Therefore, theselection of appropriate sensitive materials is important. Nano-material is the mostdynamic area of new materials and has a very important influence in the future socialand economic development, it is also the most active part of the nano-technology. Inthis paper, combine with unique properties of nano-materials and superiority of OWG.The first chapter is part of introduction. In this part, the sources and harm ofvolatile organic gases and inorganic pollutant gases, the sensor technology, the opticalchemical sensors and its classification were introduced. The development,classification and the application of optical waveguide chemical sensors, the OWG’ssensing principle, types of sensitive materials and the characteristics of severalsensitive materials used in this paper were mainly introduced. At last, the topicsources and contents of this study work were put forward.The second chapter is mainly about the gas sensitivity study of NiO-ZnFe2O4 composite thin film/tin-diffused glass optical waveguide sensor. In this study, TheNiO doped ZnFe2O4sol was synthesized by a sol-gel method and the sensor wasfabricated by coating a tin-doped glass optical waveguide with a NiO-ZnFe2O4composite film. The optical waveguide sensor was fixed on the gas sensor system todetect VOCs gases. The selective sensing mechanism was explained by changes oforganic gases molar refraction. At the same time poisonous inorganic gases weredetected, the selective sensing mechanism was also explained by changes of theconductivity and refractive index of the sensitive element. The results showed that thesensors have fast response, good repeatability and high sensitivity towards xylene andH2S gases. It can detect1×10-7(volume ratio) of xylene and1×10-9(volume ratio) ofH2S at room temperature.The third chapter is mainly about the gas sensitivity study of SnO2-ZnFe2O4composite thin film/tin-diffused glass optical waveguide sensor. In this part the bestcoating speed, heat treatment temperature and heat treatment time were selected. Different doped composite film were prepared and be used to detect organic andinorganic gases. The selective sensing mechanism was also explained. Among them,SnO2-ZnFe2O4composite thin film/tin-diffused glass optical waveguide sensor dopedwith1%and2%SnO2has high sensitivity towards xylene and H2S. The resultsshowed that, the sensors can detect1×10-9(volume ratio) of xylene and1×10-8(volume ratio) of H2S at room temperature.The forth chapter is mainly about the gas sensitivity study of Al2O3-ZnFe2O4composite thin film/tin-diffused glass optical waveguide sensor. In this study, theAl2O3doped ZnFe2O4sol was synthesized by a sol-gel method and the sensor wasfabricated by coating a tin-doped glass optical waveguide with a Al2O3-ZnFe2O4composite film. Different doped composite film has different response towardsorganic and inorganic gases. The results showed that, the sensors have fast response,good reversible and good selectivity to xylene and H2S gases. Al2O3-ZnFe2O4 composite thin film/tin-diffused glass optical waveguide sensor doped with2%and3%Al2O3has high sensitivity towards xylene and H2S and they can detect1×10-7(volume ratio) of xylene and1×10-8(volume ratio) of H2S at room temperature. Heattreatment temperature and heat treatment time were also selected.The fifth chapter is the concluding part, the main content of our research study wassummarized.