Study On Preparation Of La_1-xSr_xFeO₃with Different Nanostructured Materials And Their Gas-sensing Properties

With the development of economy and improvement of modernization, semicondutor oxide gas sensors have been widely used in the field of industry, agriculture and daily life. As one of the semiconductor metal oxide, ABO3perovskite oxide has excellent properties. In this thesis, gas sensing properties of perovskite oxide La1-xSrxFeO3materials with different nanostructures prepared with different methods were studied. The gas sensing properties of three different nanostrucures were compared. The gas adsorption mechanism of La1-xSrxFeO3to H2O, O2and HCHO were studied with DFT.La1-xSrxFeO3(x=0.0-1.0) nanoparticle materials were prepared by sol-gel method. XRD, TG/DTA, FTIR, SEM and TEM were uesd to characterized. Formaldehyde gas sensing properties of La1-xSrxFeO3(x=0.0-1.0) nanoparticle materials were studied. Both dielectric and humidity properties of La1-xSrxFeO3(x=0.0-0.5) nanoparticle materials were tested. The experimrnts results indicates that La0.7Sr0.3Fe03(x=0.3) shows the highest response to formaldehyde.Lao.7Sro.3Fe03was selected as the object of the research. La0.7Sr0.3FeO3nanoparticle assembled solid nanowires with high length to diameter ratio were prepared by a hydrothermal method. Growth mechanism of nanoparticle assembled nanowires was studied according to the characterization. La0.7Sr0.3FeO3nanowires can detect low concentration of HCHO as low as0.1ppm.Controllable preparation of La0.7Sr0.3FeO3hollow nanofibers were realized by electrospinning. The structural parameters of hollow nanofibers, such as diameters and shell thickness, can be adjusted by controlling the mass ratio of nitrate to PVP. The diameters and grain size can be controlled by adjusting the sintering temperature. Growth mechanism of La0.7Sr0.3FeO3hollow nanofibers were studied according to the characterization. The response of the hollow nanofibers sensors to low formaldehyde was greatly improved.Formaldehyde gas sensing properties of La0.7Sr0.3FeO3with three different morphology and structure indicates that the morphology and structure have great effect on the gas sensing properties. Hollow nanofibers showed the best gas sensing properties due to low sintering temperature, small grain size, large specific area and low operating temperature.Lastly, gas adsorption mechanism of La1-1SrxFeO3were studied by DFT (density functional theory). FeO-terminated La1-xSrxFeO3(010) surface was constructed. H2O adsorption on FeO-terminated LaFeO3(010) surface, O2and HCHO adsorption on La0.75Fe0.25O3(010) surface were studied by DFT, respectively. It shows that Sr doping will change the surface structure and electric properties, and will influence the gas adsorption behavior. La(Sr)O-terminated La0.75Fe0.25O3(010) surface was constructed, HCHO adsorption on La(Sr)O-terminated La0.75Fe0.25O3(010) surface was studied by DFT. C in HCHO will capture O ions on the surface and form H2CO2, H2CO2is easy to decompose into CO2and H2O. The conclusions are consistent with the gas sensing mechanism.