Research On Gas Sensor Based On Perovskite-Co₃O₄ Composite Material

With the development of industrial production,a large amount of waste gas has been discharged into the atmosphere,and these air pollutants threaten human health and life safety.Therefore,it is very necessary to monitor toxic and harmful gases in the environment in real time to prevent excessive toxic and harmful gases in people’s working and living environment.In recent years,gas sensor has been developed gradually,which plays an important role in alcohol detector,smoke alarm,gas detection and so on.The working principle of the gas sensor is to present the composition and concentration of a certain amount of target gas into the electrical signal of the sensor through the physical and chemical reaction of the sensing material.The gas sensor can detect and monitor the target gas through these electrical signals in the process of working.When the target gas in the environment exceeds the safe concentration range,it will send an alarm message.Metal oxide semiconductor gas sensor has become a hot research topic because of its advantages such as simple manufacture,sensitive response,high stability and abundant raw materials.In this thesis,the morphologic characteristics,gas sensitive properties and gas sensitive mechanism of the metal oxide semiconductor gas sensitive material composed of perovskite and Co₃O₄were studied.La Mn O₃/Co₃O₄,La Fe O₃/Co₃O₄and Co₃O₄/Gd Fe O₃composites were prepared firstly.The morphological characteristics,elemental composition and chemical state of the materials were analyzed through characterization.The gas sensitive properties of the material such as operating temperature,sensitivity,response/recovery time,selectivity and repeatability were tested,and the gas sensitive mechanism was analyzed.The specific research content of this thesis is as follows:1.LaMnO₃and Co₃O₄nanocomposites were synthesized by simple sol-gel method and hydrothermal method.The gas sensitive properties of the five composite sensors and pure Co₃O₄sensors were tested by experiments,and the gas sensitive properties of the composite sensors based on different proportions were analyzed to find out the best composite ratio of La Mn O₃and Co₃O₄.The results show that the sensitivity of 0.6-LMO/Co₃O₄sensor to 100ppm triethylamine is 9.27 times higher than that of pure Co₃O₄sensor,and the optimal operating temperature is reduced from 150℃to 130℃.Moreover,it has good gas selectivity and repeatability.This experiment provides a new Co₃O₄-based gas-sensitive material for the detection of TEA.The sensor based on 0.6 mol%La Mn O₃and Co₃O₄composite materials has a broad application prospect in the detection of TEA.2.In this experiment,Co₃O₄and LaFeO₃composites containing p-p heterojunction were synthesized by sol-gel and hydrothermal methods.By comparing the gas-sensitive performance of the samples of various composite proportions,the best composite proportion of gas-sensitive performance was found out.The characterization results showed that Co₃O₄nanoparticles were uniformly attached to the surface of La Fe O₃nanoparticles.Performance test results show that the Co₃O₄/La Fe O₃sensors have superior performance over pure Co₃O₄and La Fe O₃sensors in terms of operating temperature,sensitivity,response/recovery time,and selectivity.The 1:1 molar ratio of Co₃O₄and La Fe O₃composites showed the best gas sensitivity of all samples,with a sensitivity of 54.21（R_g/R_a）for 100 ppm n-butanol and 6.54（R_g/R_a）for 1 ppm n-butanol at 150℃.The composite has great development potential in the detection of n-butanol.3.In this experiment,GdFeO₃nanoparticles were prepared by sol-gel method and Co₃O₄nanoparticles by hydrothermal method.The prepared Co₃O₄and Gd Fe O₃powders were mixed by solid mixing.Three samples with different composite ratios of Gd Fe O₃and Co₃O₄were obtained by calcination at 500℃for 3 h,including Co₃O₄/GFO-1:2,Co₃O₄/GFO-1:1 and Co₃O₄/GFO-2:1.The experimental results show that the optimum operating temperature of Co₃O₄/Gd Fe O₃sensor（150℃）is lower than that of pure Co₃O₄sensor（170℃）,and the three composites have good response to n-butanol gas as low as ppb.Co₃O₄/GFO-1:1 has the best gas-sensitive response characteristics.At 150°C,the sensitivity of 0.5 ppm n-butanol can reach 5.01（R_g/R_a）,and the sensitivity of 0.25 ppm n-butanol can also reach 2.68（R_g/R_a）.Moreover,the sensor is good in response recovery time,gas selectivity and stability.