Morphology Control Synthesis And Gas Sensing Properties Of Nano-iron Oxide

Due to the rapid development of industrialization,population growth,combustion of vehicle fuels,leakage of toxic chemicals and gases,environmental pollution has increased dramatically,human production and development face enormous security risks.Toxic in the production activities of enterprise factories,the leakage of harmful gases can lead to serious incidents such as physical discomfort,poisoning or fire explosion.Therefore,for toxic purposes,these toxic and hazardous chemicals need to be detected and monitored early.In recent decades,gas sensors based on metal oxide semiconductor materials have attracted considerable attention due to their high sensitivity,low detection limit,large amount of detectable gas,simple manufacturing,stability,and low cost.Among them,iron oxide is an n-type semiconductor?Eg=2.1eV?with good sensitivity,environmental friendliness,high corrosion resistance,low cost and easy manufacturability,and has been widely used in many fields including gas sensors.The gas sensing mechanism of a semiconductor gas sensor is based on the significant conductivity change of an oxide semiconductor,and the change in conductivity is due to the adsorption of oxygen and the chemical reaction between the oxygen species and the target gas molecule.Therefore,composition and structure play a crucial role in its sensing.In addition,single-component iron oxide as a gas-sensitive material still has some shortcomings that cannot be ignored.In recent years,it has been found that composite materials can significantly improve the gas-sensitive properties of iron oxide.In this thesis,iron oxides with different morphologies were prepared by hydrothermal method,and the prepared iron oxide was used as the matrix to improve the gas sensitivity by combining other precious metals,oxides and rGO.The main research of this thesis is as follows:?1?The hydrothermal method was successfully used to synthesize iron oxides in the form of rods,spheres,spindles and cubes by controlling temperature,time,precipitant type and surfactant.SEM and XRD were used to prepare various forms of iron oxide.The structural characterization and analysis were carried out by means of testing methods,and the preparation scheme was determined.It was proved that the prepared sample was pure iron oxide.The obtained sample was then prepared as a gas sensor,and the gas sensitivity test was carried out.The results show that the iron oxides of these four forms have the best selectivity to triethylamine,and the response time is shorter and the stability is better.In view of the dispersibility and sensitivity of the cubic iron oxide,cubic iron oxide is selected as the matrix,which is modified in the next step to improve its gas sensitivity.?2?Sn₂O₃/?-Fe₂O₃ nanocomposites were successfully prepared by hydrothermal method with cubic iron oxide as the matrix.The morphology and structure of Sn₂O₃ nanosheets were characterized by various methods.The results showed that Sn₂O₃ nanosheets were uniformly modified on the surface of iron oxide cube.The synthesis of composite materials preparation of gas sensitive element,the gas sensor test,results showed that the Sn₂O₃/?-Fe₂O₃nanocomposites have better selectivity to ethanol,the best working temperature is 300?,and shorter recovery time response,good stability,in addition,compared with a single component of ferric oxide,composite products for ethanol sensitivity improved.In addition,RuO₂/?-Fe₂O₃nanocomposites with different molar ratios were prepared by simple physical methods,and the prepared samples were analyzed using a series of characterization methods.The results showed that ruthenium oxide nanoparticles were uniformly deposited on the surface of cubic iron oxide,and the composite material had high purity and good crystallinity.Then tested to gas-sensing properties of the preparation of RuO₂/?-Fe₂O₃ nanocomposite,the results show that when the ratio of the ruthenium oxide and the molar volume of iron oxide to 1‰,the product of gas sensitive performance is the most outstanding,it has better selectivity for triethylamine,shorter recovery time and response,good stability,in addition,compared with pure iron oxide,composite products in the best working temperature decreased,sensitivity is improved.?3?Gold?Au?nanoparticles/reduced graphene oxide?rGO?/?-Fe₂O₃ ternary composites were successfully prepared by liquid phase method using cubic iron oxide as the matrix.The prepared samples were analyzed by a series of characterization methods.The results shows that the gold nanoparticles were uniformly deposited on the surface of rGO and cubic iron oxide,and the composite had high purity and good crystallinity.The gas-sensitive properties of the prepared Au/rGO/?-Fe₂O₃ ternary composites were tested.The results show that the Au nanoparticle and rGO nanosheet decoration can enhance the gas sensitivity of Fe₂O₃,Au/rGO/Fe₂O₃ ternary composite.The material responded to 100 ppm of triethylamine by approximately 44?3 times higher than pure iron oxide?.In addition,Au/rGO/?-Fe₂O₃ has a short recovery time and good stability.