Reparation And Gas Sensitive Properties Of Iron-based Spinel Nanomaterials

In people’s production and life,it is unavoidable to contact and produce some toxic,harmful,flammable and explosive organic volatile gases.These gases will pose various threats to our production safety,living environment and personal safety.Faced with various problems caused by toxic and harmful gases,gas sensors have emerged.As an important variety in the field of sensing technology,gas sensors are widely used in various fields and it is a key research field at home and abroad at present.As we all know,sensitive materials are the core of gas sensors,and their performance is extremely important for gas sensors,affecting their selectivity,repeatability,and responsivity.Semiconductor metal oxide has the advantages of low price,simple synthesis method and controllable shape,which is widely used in the field of gas sensors.Studies have shown that the crystal size and surface morphology of semiconductor metal oxide materials have a greater impact on the performance of the gas sensor.Therefore,the gas sensor performance of the material can be improved by changing the morphology,composition and crystal structure of the material.Spinel oxide（AB₂O₄type）materials have received extensive attention as gas sensitive materials in recent years due to their good catalytic performance,unique physical and chemical properties and high reduction sensing ability.However,in practical applications,there are still many shortcomings,such as poor selectivity and low gas response value.In this thesis,iron-based spinel structured nanomaterials are used as the main research object.By controlling its morphology,impurity doping and metal oxide compounding methods,the sensitivity of the pure material is improved,its gas response value and its selectivity are improved.The chemical composition and crystal phase structure of the material were explored,the principle of material sensitization was analyzed and summarized.The details are as follows:（1）In experiment 1,Prussian blue analogues containing iron-nickel were synthesized by a water bath method,and on this basis,different contents of cobalt were doped,and then after a series of operations such as calcination,the materials doped with different amount of cobalt were obtained.All of the NiO/NiFe₂O₄samples showed good response to isopropanol gas.The experimental results show that when the working temperature is 183.5℃,NiO/NiCo_0.03Fe_1.97O₄has the highest response value to isopropyl alcohol.When the concentration of isopropyl alcohol is 100ppm,the gas response reaches 11.2.At the same time,the material has a faster response and recovery speed,and also has better selectivity for isopropanol gas.Compared with pure materials,the improved gas sensitivity of doped materials can be attributed to the difference in the radius of cobalt atom and iron atom,which will lead to lattice defects.The existence of lattice defects can promote the increase of oxygen vacancy and increase oxygen adsorption,and the gas sensitivity response can be further improved.And p-p heterojunction is formed between nickel oxide and nickel ferrite,the existence of heterojunction is also one of the reasons for the improved gas sensitivity response.（2）In the second experiment,zinc ferrite nanospheres were synthesized by hydrothermal method,and on this basis,the pure material was modified with different content of copper oxide and then after a series of work such as centrifugation,washing,calcination,etc.Zinc ferrite modified with different content of copper oxide was prepared.For the copper-modified composite material,all samples showed a good response to xylene gas.The experimental results show that when the working temperature is 206°C,the response value to 100ppm xylene gas reaches 20.7.When the modification amount of copper oxide is 1%.it has good selectivity.The improvement of gas sensitivity of the composites can be attributed to the formation of p-n heterojunction.The existence of p-n junction leads to lattice mismatch,which is beneficial to generate more oxygen vacancies,increase oxygen adsorption and enhance gas sensitivity.