Preparation And Gas-sensing Performance Research On Heterojunction Nanofibers With Controlled Shell Thickness

In recent years,due to the advantages of large aspect ratio,high specific surface area,mass preparation,and simple preparation method,various uniaxial metal oxide nanofibers have been widely prepared and used in gas sensing.However,uniaxial metal oxide nanofibers still have some disadvantages such as low sensitivity,poor stability,and slow response and recovery speed.Compared with a pure metal oxide,the preparation of a metal oxide heterostructure material can significantly improve the gas sensitivity of the material.Coaxial electrospinning technology was developed based on uniaxial electrospinning technology,which is a nanofiber material preparation method.The heterojunction core-shell nanofibers can be prepared by coaxial electrospinning technology.In this paper,the p-n heterojunction core-shell nanofibers were taken as the research topic.In order to study the factors affecting the gas sensitivity of core-shell nanofibers,the gas-sensing properties of core-shell nanofibers were compared with that of uniaxial electrospinning nanofibers.The main research content was as follows:(1)Cr₂O₃-TiO₂ core-shell fibers(Cr-Ti CS-NFs)with different shell thicknesses were synthesized by a facile coaxial electrospinning technique.The gas-sensitive performance of Cr-Ti CS-NFs to acetone was enhanced by optimizing the Ti O₂shell thickness.The experimental results show that when the shell thickness of Ti O₂ reaches40 nm,the maximum response of Cr-Ti CS-NFs to 50 ppm acetone is 4.9,and the response and recovery time is 7 s and 13 s,respectively.When the shell thickness of Ti O₂ is relatively thin,the Cr-Ti CS-NFs show a stronger p-type response to acetone than the pure Cr₂O₃ nanofibers(Cr₂O₃-NFs),and the electrons in the Ti O₂ shell are completely depleted.With the increase of the thickness of the Ti O₂ shell,the response of Cr-Ti CS-NFs to acetone showed a transition from p-type to n-type.Besides,the formation of Cr₂O₃-Ti O₂ heterojunction enabled the gas sensors to possess a short response and recovery time to target gas.A possible mechanism of the enhancement of gas-sensitive performance of core-shell Fs was also illustrated.(2)Co₃O₄-TiO₂ core-shell nanofibers,Ti O₂-Co₃O₄ core-shell nanofibers,Ti O₂nanofibers,and Co₃O₄ nanofibers were prepared by coaxial electrospinning.A series of morphology and structure characterization of these four kinds of nanofibers were carried out,and the acetone gas sensitivity of the gas sensor based on these four kinds of nanofibers was tested.The results show that the gas sensor based on core-shell nanofibers has better acetone gas sensitivity than pure nanofibers,and the gas sensor performance of Co₃O₄-Ti O₂ core-shell nanofibers is better than Ti O₂-Co₃O₄ core-shell nanofiber.Finally,the gas-sensing mechanism of these materials was demonstrated.