| Ethanol is the most common flammable and explosive gas in daily life,and it also could be used as test gas to measurement of drunk driving.Thus,the need of accurate and rapid detecting environment ethanol is increasing.Semiconductor is a kind of gas sensor materials which could quickly detect and online monitor toxic and harmful environment gases.It is the key to prepare the high performance semiconductor oxide materials and explore the sensing mechanism for ethanol gas in order to improve the gas sensitivity.Metal doped LaFeO3 and ZnO materials were prepared by hydrothermal method,and modified by lattice substitution doping and compound doping.The gas sensing mechanism of doped materials were studied.The response mechanism of the gas sensing material were also speculated by characterization of the morphology,surface state of the material and the electrical and catalytic properties The details are as follows:Sr doped LaFeO3 was successfully prepared by hydrothermal method,and the ethanol sensing properties of doped materials was investigated as well.The calcination temperature and other conditions were optimized by the gas sensing properties as the target.By controlled with the doping amount of Sr to change the microstructure and surface defects,the gas sensing response of the material was adjusted.The surface microstructure and morphology of the sensor materials were analyzed by thermo gravimetric analysis,X-ray diffraction(XRD),scanning electron microscopy(SEM)and high resolution transmission electron microscopy(HRTEM)techniques.Through the characterization of X-ray photoelectron spectroscopy(XPS),UV-vis spectroscopy,the internal structural defects and changes in the surface state and elements content were examined,and the electrical properties were tested by Hall Effect.Besides,the relationship between microstructure with gas-sensitive properties was established by the results of catalytic evaluation of hydrogen temperature-programmed reduction(H2-TPR),CO conversion,thus the gas-sensitive mechanism of Sr doped LaFeO3 was confirmed.The result shows that 10 at%Sr doped material has the best gas sensitivity and its response is 280 to 100 ppm ethanol at the working temperature of 240?,and the response/recovery time was 145/165 s with good stability and selectivity.Moreover,the response can be maintained nearly 75%under the relative humidity of 70%.It could be confirmed that the decrease of working temperatured of Sr doped LaFeO3materials is related to the apparent activation energy according to the results of H2-TPR,CO conversion,XPS.Combined with the resistive of the materials and the carrier concentration,the relationship between the responses with the carrier change rate can be acquired.And the high carrier consumption rate was confirmed to be the reason of the high response of the Sr doped materials.The pinecone-like ZnO material with hierarchical structure was prepared by hydrothermal method.Co element was doped to modify by the surface doping and internal doping way.It was found that the surface doping material had better ethanol gas sensitivity than the interior doped material.The result shows that 1%Co-doped ZnO material with surface doping has the best gas sensitivity,and its response reaches 207 to 100 ppm ethanol at the working temperature of 300? with the good stability and selectivity properties.The XRD and SEM results indicate that the surface doping has little effect on the morphology of ZnO.It was confirmed that the improved gas-sensitive performance of the surface doped ZnO could be attributed to the formation of Co composite structure on the material surface,which resulted in the increase of the initial resistance. |
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