Preparation And Gas Sensitive Properties Of Iron Based Nano-oxides And Composites

Acetone detection sensor plays an important role in the safety production of chemical industry,it can also test the content of acetone exhaled by human body and conduct screening and painless monitoring management for patients with hyperglycemia.Furthermore,it can also be used in food industry fermentation control.Therefore,the preparation of high sensitivity,good selectivity,short response/recovery time,low working temperature and high long-term stability of acetone sensor is of great significance.It is well known that gas-sensitive materials are one of the key factors affecting the performance of gas sensors.Acetone gas sensing materials with excellent properties were prepared by means of structural change,doping and compositing in this thesis on the premise of cheap raw materials and simple synthesis method.And their gas-sensing mechanisms were also systematically discussed for the further development of nanometer iron oxide gas sensitive material to provide experimental foundation and theoretical basis.Zero-dimensional?-Fe₂O₃ nanoparticles,one-dimensional?-Fe₂O₃ nanorods and two-dimensional?-Fe₂O₃ nanosheets were prepared and investigated.The measurement results showed that the smaller size of?-Fe₂O₃ nanoparticles,the higher the specific surface,the greater the adsorption activity and the higher the sensitivity.The one-dimensional?-Fe2O3 nanorods improved the selectivity to acetone gas.Two-dimensional?-Fe₂O₃ nanosheets are assembled by?-Fe₂O₃particles and overlapped with each other in a"sieve"mode.Compared with nanoparticles and nanorods,nanosheets have effectively reduce the agglomeration and improve the response value of target gas acetone.Alpha-Fe₂O₃ prepared by electrospinning was a composite structure,which is composed of integrated particle,one-dimensional linear structure and three-dimensional pore structure assembly.Furthmore,the material utilization rate,conversion rate and response time of?-Fe₂O₃ were effectively enhenced to improve the gas sensing properties.The modification of Ag doped?-Fe₂O₃ was carried on to improve the gas sensitivity and reduce the lower limit of acetone gas detection.The sensor based on 6 at%Ag doped?-Fe₂O₃ nanostructures shows the highest response value among the sensors with different Ag doping content.Also,6%Mn,6%Co and 6%Zn transition metal doped?-Fe₂O₃ were synthesized and its gas sensitivity were analyzed to reduce the cost of gas-sensitive materials.It was found that doping increases the oxygen defect,reduces the crystal size,increases the specific surface area,and has excellent sensing characteristics to acetone gas.Two kinds of ZnFe₂O₄ and NiFe₂O₄ nanomaterials with stable structures were prepared and doping modification of these two materials was carried on.Doping has an impact on the structure of the two materials,such as crystal lattice change,oxygen vacancy change,mesoporous distribution change,so as to affect the surface adsorption energy and activation point.The sensitivity and stability of gas sensor have been improved correspondingly.Two kinds of composite materials,rGO/ZnFe₂O₄ and CNTs/ZnFe₂O₄,were synthesized to reduce the working temperature.The research results showed that ZnFe₂O₄ further decreases particle size and improves the agglomeration of graphene or carbon nanotubes in the application process.The working temperature to acetone vapour came down to 180?and the interference of ethanol gas to acetone was reduced to improve the selectivity to acetone sensor.The structure of CNTs/ZnFe₂O₄ composite material is similar to the linear structure of electrospinning.Because of rich three-dimensional pore formation in low temperature sintering to preparation of gas device,CNTs/ZnFe₂O₄ composite material has faster response/recovery time and higher acetone sensitive performance comparing with sheet structure of rGO/ZnFe₂O₄.