Research On NO₂ Sensing Properties Of Perovskite-structured Metal Oxide Nanomaterials

Nitrogen dioxide?NO₂?is a poisonous gas with red brown color and pungent odor at room temperature.As a major atmospheric pollutant,NO₂ is harmful to human health and environment.Therefore,it is essential to develop high performance sensors for effective detection of NO₂.The current NO₂ sensors based on simple metal oxide have many limitations,such as high working temperature and poor selectivity.Therefore,the research of new material and new morphology is critical.In this work,perovskite-structured metal oxides were chosen as the sensing material.Nanomaterial with different morphologies was prepared by sol-gel method,MOF self-templating method,and electrospinning method.We studied the effect of material and morphology on NO₂ sensing properties of perovskite-structured metal oxides.In Chapter 1,the significance and current status of NO₂ sensors were introduced.Metal oxide semiconductors?MOS?nanomaterials applied to NO₂ sensors were described.The properties and gas sensor applications of perovskite-structured metal oxides were also discussed.In Chapter 2,LaMnO₃ nanoparticles were prepared by sol-gel method.LaMnO₃ thick films were prepared from these nanoparticles by screen-printing technology.The NO₂sensing properties of the thick film were characterized.In addition,the effect of doping was studied.In Chapter 3,Porous hollow microspheres of SmFeO₃ were prepared from a simple process involving a metal organic framework?MOF?compound as the templating precursor.With a diameter of about 2?m,these hollow-centered microspheres are formed by nanoporous thin walls of SmFeO₃.Chemoresistive gas sensors based on these microspheres exhibits excellent sensing performance on NO₂ at 200°C,including high sensitivity?response of 10.2 under 200 ppb?with detection limit as low as 50 ppb,high selectivity,and reasonably short time for response and recovery?369 s/478 s?.The superior sensing response over other SmFeO₃-based NO₂ sensors can be ascribed to the electron-accepting reactions during NO₂ adsorption,which is facilitated by the special morphological features of the microsphere.In Chapter 4,mesoporous SmFeO₃ nanobelts with width of 300 nm were prepared by electrospinning.The nanobelts exhibits obvious response to 5 ppm NO₂ at room temperature,which verified the potential of the mesoporous SmFeO₃ nanobelts for the detection of low concentrations of NO₂ at low temperature.The last chapter gives a summary and outlook of this work.