Modification And Gas Sensing Properties Of In₂O₃ Nanofiber

Metal oxide semiconductors?MOSs?have been widely used for gas sensing materials due to high response,low cost,and good stability.However,poor selectivity and high operating temperature of MOSs has its practical limitations.Therefore,how to further improve the gas sensing performance of MOSs sensors has been the focus of research in this field.In the past years,structural modification of sensing materials,doping with other metals,loading with other MOSs,have become an effective and widely used method.In this thesis,in order to obtain a high-performance MOSs gas sensing materials,on the one hand,inherent characteristics of electrospun nanofibers with mesh felt structure,such as a large specific area and good electronic conductivity were used to optimize the structure of the sensing materials;on the other hand,metal ion doping and surface modification method were adopted for electrospun In₂O₃ nanofibers?In₂O₃ NFs?.The main research contents are as follows:?1?Synthesis and gas-sensing properties of Sn-doped In₂O₃ nanofibers?Sn-In₂O₃ NFs?.The In₂O₃@C was prepared by the carbon template induced method,and then adsorbed Sn⁴⁺ions on the surface of In₂O₃@C nanofibers by aging in SnCl₄ solution,finally,Sn-In₂O₃ NFs was synthesized through the calcination of it at high temperature.X-ray photoelectron spectroscopy?XPS?and photoluminescence spectroscopy?PL?characterization results indicate that abundant oxygen vacancies were simultaneously introduced on the surface of the Sn-In₂O₃ nanofibers through Sn doping,and the amount of oxygen vacancies was proportional to Sn doping contents.Gas-sensing test results indicate that the sensor based on the Sn-In₂O₃ nanofibers exhibited excellent gas sensing response toward NO₂ compared with the pure In₂O₃ nanofibers.The highest response value of the Sn-In₂O₃ nanofibers reached 44.6 to 1 ppm of NO₂ at 90?,which was 3.4 times higher than that of pure In₂O₃ nanofibers.The superior NO₂ sensing properties were demonstrated to be highly related to the oxygen vacancies on the surface of nanofibers,which could not only enhance the electronic conductivity but also provide active sites for the adsorption of gas molecules.This work might give a deep comprehension of the role of oxygen vacancies in influencing the sensing performance of gas sensors.?2?Synthesis and gas sensing properties of Co₃O₄/In₂O₃ heterojunction hollow nanofibers.Using In₂O₃ hollow nanofibers?In₂O₃ HNFs?as a template material,The ZIF-67/In₂O₃ HNFs was prepared through the reaction between Co²⁺in cobalt nitrate and2-methylimidazole.The Co₃O₄/In₂O₃ HNFs were synthesized by calcinating the ZIF-67/In₂O₃ HNFs at high temperature.The Co₃O₄/In₂O₃ HNFs were characterized by scanning electron microscopy?SEM?,X-ray diffractometer?XRD?,X-ray photoelectron spectroscopy?XPS?.The results show that Co₃O₄ nanoparticles with the polyhedral shape were loaded uniformly on the surface of the In₂O₃ HNFs.Gas-sensing test results indicate that the sensor based on the Co₃O₄/In₂O₃ HNFs exhibited excellent gas sensing response toward NH₃ compared with pure In₂O₃ HNFs and pure Co₃O₄ nanoparticles.The highest response value of the Co₃O₄/In₂O₃ HNFs reached 12.5 to 1 ppm of NH₃ at 80?,which was 1.7 and 2.8 times higher than that of pure In₂O₃ HNFs and pure Co₃O₄ nanoparticles,respectively.The superior NH₃ sensing properties were mainly due to the role of heterojunction between In₂O₃ and Co₃O₄.When two semiconductors contact each other,the space charge layer is formed at the interface because of the difference in the Fermi level.The formation of the space charge region could increase the resistance of sensitive materials in the air,which is beneficial to improve the sensing performance toward reducing gases.In addition,as a derivative of MOF,Co₃O₄ possesses a porous structure which could provide a large specific surface area,and plays an important role in improving the gas sensing performance.