Study On Fabrication And Gas Sensing Performance Of Co₃O₄ Based Sensors

With the rapid development of society,metal oxide semiconductor（MOS）gas sensors are widely used in the fields of atmospheric and microenvironment monitoring,industrial and agricultural production,food safety and medical diagnosis because of their advantages of high sensitivity,small size,low power consumption and low price.Among them,the P-type semiconductor oxide cobalt oxide（Co₃O₄）has obvious advantages in the detection of chemically stable gases,such as acetone,benzene,toluene and so on,because of its high surface catalytic activity.However,the sensitivity of P-type semiconductor oxides is generally lower than that of N-type semiconductors.Therefore,surface modification is usually required to regulate the surface energy band,electronic structure and reaction site of oxides to improve the gas-sensitive performance of P-type semiconductor sensors.At present,the conventional surface modification methods of gas sensors include metal ion doping,noble metal loading and heterogeneous structure construction.Among them,there are only 8 optional metal elements carried by precious metals,and the preparation and dispersion process of nano-precious metals particles is complicated,which leads to the increase of the production cost of sensors.Therefore,this paper mainly starts from two aspects of heterogeneous structure and metal ion doping,and carries out surface modification on the catalytic activity and energy band structure of P-type semiconductor metal oxide Co₃O₄.Thus,the gas sensitivity of the sensor to acetone can be improved.The main research contents of this paper are as follows:1.Study on the influence of ZnO/Co₃O₄（n-p）heterogeneous structure on gas sensitive characteristics of Co₃O₄and its sensitization mechanism.Firstly,Co₃O₄hollow flower-like microspheres were successfully prepared by one-step solvothermal reaction using cobalt acetate tetrahydrate as cobalt source,L-lysine as surfactant,deionized water and ethanol as reaction solvents.On this basis,ZnO/Co₃O₄composites with different molar ratios were synthesized by two steps wet impregnation and high-temperature calcination.Morphologic characterization shows that the synthesized ZnO/Co₃O₄composites still maintain the hollow flower structure and have good consistency and dispersion.The gas sensitive test results show that the3 mol%ZnO/Co₃O₄hollow bulb sensor has the best gas sensitive performance to acetone,and the response value to 50 ppm acetone at the optimal operating temperature（150℃）is up to 17.3,and has a low detection limit（100 ppb）.And better moisture resistance.The mechanism study shows that the reason for the improved sensitivity of the composite is that p-n heterogeneous junction is formed between P-type semiconductor Co₃O₄and N-type semiconductor ZnO,which can reduce the surface electron concentration and regulate the width of the surface accumulation layer under different atmospheres,so that the ZnO/Co₃O₄sensor has a higher gas response under the same acetone concentration.2.Study on the influence of Ru doping on gas-sensitive characteristics of Co₃O₄and its sensitization mechanism.In the process of preparation of Co₃O₄hollow flower microspheres experiment,we synthesized pure Co₃O₄and Ru-doped Co₃O₄hollow flower microspheres sensitive materials by adding different proportions of Ruthenium chloride solution,and studied the influence of Ru doping on the gas sensitive performance of Co₃O₄sensor.Among them,1 at%Ru doped Co₃O₄gas sensor shows the best performance for acetone,and the response value for 10 ppm acetone gas is18.8,which is 5.9 times the response value of pure Co₃O₄gas sensor.Notably,the sensor also has an extremely low detection limit,with a response value of 1.5 for 50ppb acetone.Further research found that the sensitization mechanism is that Ru doping can improve the adsorption of oxygen on the surface of the sensitive material,thus improving the oxidation activity of the sensor,and at the same time,Ru doping can improve the resistance value of the sensor.For these reasons,Ru doping can significantly enhance the gas-sensitive performance of Co₃O₄sensor.