NO₂ Sensing Properties Of Perovskite-Structured LaFeO₃ Nanomaterials

Nitrogen dioxide?NO₂?is a major air pollutant mainly coming from the emissions of automobile exhaust and industrial waste gas.As the problem of air pollution getting more serious,effective detection of NO₂ has become necessary and urgent.Lanthanum ferrite?LaFeO₃?is a binary metal oxide with ABO₃-type perovskite structure.It has many different applications due to its structural stability and unique physical and chemical properties.As a p-type semiconductor,LaFeO₃ is also one of the most promising materials for gas detection.In the first part of this thesis,the properties and applications of LaFeO₃ were reviewed,followed with an introduction to the gas sensor applications of LaFeO₃ related to its structure,properties,and sensing mechanisms.The main preparation methods for hierarchically structured microspheres were also reviewed.Secondly,LaFeO₃ nanoparticles were prepared through co-precipitation method.XRD and SEM were carried out to study the phase and microstructure of the synthesized samples.NO₂ sensing properties at low temperatures?100?and 150??were characterized.Thirdly,hierarchically structured micro-particles of LaFeO₃ was prepared using spore as a template.The synthesized particles were characterized with XRD and SEM.Using a simple drop-coating technique,a conductometric gas sensor was prepared from the synthesized particles on a FTO glass substrate.Sensing response to NO₂ was studied for the sensor device.As a major effort,we applied a metal organic framework?MOF?self-templating method for the synthesis of shuttle-shaped mesoporous hollow structure of LaFeO₃.The material shows highest responses to NO₂ at 155?,which are 81.4%to 5 ppm and 111.2%to 20 ppm of NO₂.At this temperature the sensor also demonstrates excellent selectivity to NO₂ among other gases.The last chapter gives a summary and outlook of the NO_x gas sensor.