Synthesis And Gas Sensing Properties Research Of α-Fe₂O₃ Hierarchical Nanostructures And Composites

The rapid development of industrialization has brought many hidden safety hazards to the air environment of human life,which makes the gas sensor as a detection of harmful gas has received extensive attention.Therefore,it is particularly important to develop gas-sensing materials with low cost,fast response,high selectivity,good stability and reproducibility.In this thesis,based on the low-costα-Fe₂O₃ material,two kinds ofα-Fe₂O₃ materials with hierarchical structure were successfully prepared by a simple solvothermal method,and the influence of the preparation process on the product structure and gas sensing performance was explored.Then,α-Fe₂O₃/ZnO composites were prepared,and the effect of different ratios of iron ions and zinc ions in the composites on the structure and properties of the products was investigated,and the mechanism of the composites improving the gas-sensing properties was studied.（1）The cubic morphologicalα-Fe₂O₃ material with particle assembled hierarchical structure was prepared by solvothermal method.The results show that the gas-sensing properties of the product prepared under the process conditions of setting temperature of 160°C,time of14 h,and reactant concentration of 0.25 mol/L are better,and have good selectivity to ethanol gas at 250°C with a concentration of 100 ppm.It has a sensitivity of 11.7 and response/recovery times of 46 s and 61 s.Its hierarchically assembled form provides the material with a loose and porous surface structure with better gas-sensing responsiveness than the aggregated structure of the same material.（2）The flower-like morphologyα-Fe₂O₃ material with nanosheet-assembled hierarchical structure was successfully prepared by solvothermal method.The experimental results show that the products prepared under the conditions of reaction time of 8 h and reactant concentration of 0.02 mol/L have good gas-sensing properties,and have excellent selectivity to NO₂ gas at 120℃,Its sensitivity is 34.5 at a gas concentration of 100 ppm,and the response/recovery times were 24 s and 19 s.The nanosheet assembly hierarchical structure makes the material have a unique loose internal structure,which facilitates the delivery of the target gas into the material and improves the gas-sensing utilization rate of the material.（3）α-Fe₂O₃/ZnO composites with ZnO nanoparticles dispersed and coated on the surface of cubic hierarchicalα-Fe₂O₃ were successfully prepared by solvothermal method.The experimental results confirmed that theα-Fe₂O₃/ZnO composite prepared under the condition of iron-zinc ion ratio of 2:1 had better gas sensing performance,and the sensitivity to 100 ppm ethanol gas at 275℃was 27.6,2.4 times higher than the originalα-Fe₂O₃monomer;the response time is about 7 s,and the recovery time is 19 s,which are 6.5 times and 3.2 times shorter than that ofα-Fe₂O₃ monomer material respectively.The improvement of its gas-sensing performance mainly comes from the n-n-type heterostructure constructed byα-Fe₂O₃ and ZnO,which effectively increases the number of oxygen ions adsorbed on the surface of the material.At the same time,the dispersed coating of ZnO also maintains the gas-sensing properties of the hierarchical structure material.The advantages provide theoretical basis and reliable data for the development of highly sensitive gas sensors.