Structure Regulatiom And Gas Sensing Performance Of Co₃O₄ Based Semiconductor Materials

Gas sensor is a device that can convert gas information into usable output signals,which has a wide range of applications in smart home,automotive electronics,environmental monitoring and medical diagnosis.Among them,metal oxide-based gas sensors have always been research focuses in the field of gas sensor because of their low cost,easy portability,simple structure and excellent gas sensitive characteristics.As the core of gas sensor,the choice of sensitive material plays an important role in their performance.Cobalt trioxide（Co₃O₄）is a kind of p-type metal oxide with mixed valence state(Co²⁺/Co³⁺),and its good catalytic activity makes it a potential sensitive material.However,due to the limitations of own conductive mechanism,pure Co₃O₄based sensors often show low sensitivity,slow response/recovery speed and other problems,which greatly limits their practical application.Based on this,this thesis uses Metal-Organic Frameworks（MOFs）as precursors,which have the advantages of large surface area,high porosity and adjustable structure.Co₃O₄is taken as the research object,and its microstructure is reasonably designed.On this basis,the electronic structure of the Co₃O₄based materials is effectively regulated by doping,which significantly improve the sensitivity,response/recovery speed,working temperature and selectivity of the Co₃O₄based gas sensor to triethylamine（TEA）gas.At the same time,the gas sensing mechanism is systematically studied.Specific research contents are as follows:1.The 2D spindle-like Sn-doped Co₃O₄porous nanosheets have been designed and synthesized.And the effects of different Sn ion doping concentrations on the gas sensitive characteristics of Co₃O₄based sensor are systematically analyzed.The response value（70.7）of the 5 at%Sn-Co₃O₄based sensor to 100 ppm TEA gas at a low operating temperature（180^oC）is about 11 times that of the pure Co₃O₄based sensor（6.4）,and the response/recovery time is 1 s/17 s,respectively.In addition,the sensor has good anti-humidity performance,gas selectivity,and long-term stability.The formation of two-dimensional porous nanosheets not only forms abundant active sites on the surface of sensitive materials,but also provides effective channels for gas diffusion and electron transfer.On the basis of this structural sensing,the concentration of charge carriers,oxygen vacancies and chemisorption oxygen in the sensitive material is regulated by Sn doping,thus improving the performance of the sensor.2.The flower-like Sr-doped Co₃O₄hierarchical structure has been designed and synthesized.Gas sensitive test results showed that 2 mol%Sr-Co₃O₄based sensor has better TEA sensing performance than that of pure Co₃O₄based sensor.Specifically,it exhibits a high response value（52）and a short response/recovery time（40/58 s）to 100ppm TEA gas at a low operating temperature（160^oC）.It also has excellent selectivity and long-term stability.Due to the large specific surface area and low agglomeration of flower-like hierarchical structure,abundant active regions are formed on the surface of sensitive materials.On the basis of hierarchical structure sensitization,Sr doping increases the oxygen vacancy concentration in the sensitive material,resulting in the enhancement of sensing performance.3.The bow-like Ga doped Co₃O₄hierarchical structure assembled from ultra-thin porous nanosheets has been designed and prepared.And the gas sensing properties of pure,1%,2%and 5%Ga doped Co₃O₄based sensors have studied systematically.The results show that the sensor based on 2 at%Ga-Co₃O₄shows a high response value（108）to 50 ppm TEA gas at 180^oC,which is about 30 times higher than the pure Co₃O₄based sensor（3.5）.In addition,it has fast response/recovery speed（3 s/15 s）,low detection limit（0.1 ppm）,excellent selectivity,repeatability and long-term stability.The bow-like hierarchically porous structure has the advantages of low agglomeration and strong permeability.On this basis,Ga doping leads to the increase of specific surface area and oxygen vacancy concentration of the sensitive material,which is conducive to the formation of more active sites on the surface of the material,further improving the performance of the sensor.In addition,the good gas selectivity of the sensor is due to the low C-N bond energy and the acid/base interaction between the material surface and TEA molecules.4.One-dimensional Ru/Mo co-doped Co₃O₄hollow microtubes have been designed and prepared.The results show that the Co₃O₄based sensor has the best performance when the doping content of Mo and Ru is 1%and 0.3%,respectively.The0.3%Ru/Mo-Co₃O₄based sensor shows a high response value（126）to 100 ppm TEA gas at 160^oC,which is about 18.5 times that of pure Co₃O₄based sensor.In addition,it has fast response/recovery speed（5 s/7 s）,good selectivity,repeatability and long-term stability.One-dimensional hollow porous structure has the advantages of high carrier mobility and fast diffusion rate of gas molecules.On this basis,Ru/Mo co-doping regulates the concentration of carrier and oxygen vacancy in the sensitive materials,and the strong catalytic activity of Ru/Mo ions promotes the chemical reaction between the chemisorption oxygen and TEA molecules,leading to the improvement of the sensor performance.5.The Al/Mo co-doped porous Co₃O₄hollow tetrahedrons have been designed and synthesized.The results of gas sensitive test show that 0.2 at%Al/Mo-Co₃O₄based sensor shows the best sensing performance.It shows a high response value（132）to 100 ppm TEA at 160^oC,which is 33 times that of pure Co₃O₄based sensor.In addition,the sensor also has fast response recovery speed（4 s/3 6 s）,low detection limit（0.5 ppm）,good selectivity and long-term stability.The construction of hollow porous tetrahedral structure not only forms more active sites on the surface of sensitive materials,but also accelerates the diffusion rate of gas molecules.On this basis,Al/Mo co-doping can effectively regulate the carrier and oxygen vacancy concentration of Co₃O₄material,and promote the oxygen dissociation reaction,and further form more chemisorbed oxygen on the surface of the sensitive material,which is conducive to the enhancement of the sensor performance.