Study On Gas Sensor Based On WO₃ And ZnO/N3 Semiconductor Materials

In recent decades,with the development of industry,more and more kinds of gases have been used,such as organic volatile gases?benzene,toluene,acetone and formaldehyde etc.?that are often encountered in industrial production and decoration industries,toxic and harmful gases?NOx,NH₃,H₂S,SO₂,etc.?in automobile exhaust emissions,flammable and explosive gases?H₂,CO,CH₄?;these gases not only pollute the environment,but also seriously endanger the safety and health of human.Therefore,there is an increasing demand for detection and alarm of these gas components.In order to cope with the actual gas detection requirements,the gas sensor must have the characteristics of simple material synthesis,high sensitivity,rapid response,wide detection range,and good selectivity.As one of the most widely used gas-sensing materials,semiconductor metal oxides,such as WO₃,ZnO,TiO₂,SnO₂,etc.,have excellent chemical and thermal stability,and gas sensing elements based on semiconductor oxide materials are inexpensive and highly sensitive to target gases,and they can be easily manufactured,all these merits have won the favor of many researchers.Tungsten trioxide?WO₃?,a very typical n-type semiconductor material,has been used to detect gases such as NO₂,NH₃,H₂S and C₂H₅OH.However,it has rarely been reported that tungsten trioxide materials are used to detect chlorine gas.At the same time,the influence of WO₃ morphology on its gas response is rarely mentioned in the literature.In addition,in order to reduce the optimal operating temperature of zinc oxide?ZnO?based gas sensors,many researchers have set their sights on doping different types of semiconductors?SnO₂,CuO,etc.?or noble metals?Pt,Pa,Au,etc.?or adopting photoexcitation methods.However,until now,there has been no report on improving the gas sensing properties of semiconductor materials by doping with dyes such as N3 dyes.The main work of this thesis for constructing high performance WO₃and ZnO gas sensors is as follows:1:By using WCl₆ as the metal salt,three kinds of WO₃ materials with completely different morphologies were prepared by hydrothermal method by changing the kind of solvent used in the material synthesis process.The effect of solvent polarity on the crystallization of WO₃ material was also studied.The WO₃ material prepared above was coated onto a side heat type gas sensor for gas sensing performance analysis.The gas sensing results show that the granular WO₃ material has very high response to chlorine and a very low detection limit compared to WO₃ nanorods and nanosheet materials.X-ray diffraction?XRD?,photoluminescence spectroscopy?PL?and Raman spectroscopy?Raman Spectra?analysis showed that the particulate WO₃ material has better crystalline degree and higher surface oxygen concentration.2:Zn?Ac?₂·2H₂O was used as the metal salt and N3 dye was used as the dopant.The flower-like ZnO material doped with different concentrations of N3 dye was synthesized by one-step hydrothermal method.The N3 doped ZnO material prepared above was coated onto a side heat gas sensor for gas sensing performance analysis.The gas sensing results show that ZnO doped with N3 dye has higher sensitivity,faster response and lower detection limit towards ethanol under the illumination of green light than under dark conditions and ultraviolet light.UV-visible absorption spectroscopy indicates that the doping of N3 dye can significantly increase the absorption intensity of ZnO material in the visible light spectrum.