Research On Acetone Gas Sensor Based On Ternary(AB_mO_n) Semiconductor Oxide

As the pivotal component of gas information collection and acquisition,gas sensors have great application value in the fields of medical and health,atmospheric environment,industry and agriculture,and national security.Among them,the semiconductor metal oxide-based gas sensor devices are all-solid-state sensors,which have the advantages of low cost,simple process,good stability,integration and intelligence,real-time rapid detection,etc.,and have become the focus of academic research and industrial applications.The cornerstone and key to determine the performance of semiconductor gas sensors are sensing materials,the advanced and efficient sensors cannot be separated from the innovation and progress of nanomaterials.Therefore,it is of great scientific significance to design and construct the new sensing materials of gas sensors,and to systematically study the internal relationship between the micro-nano structures of the sensor materials,the composition changes and the gas sensing characteristics of the gas sensors.At the same time,acetone,as one of the important and common flammable and toxic volatile organic compounds（VOCs）,has been widely used in many fields.Long-term exposure to acetone can cause symptoms such as vomiting,coma,and central nervous system anesthesia,and acetone is also an exhalation marker for diabetes.Therefore,in this paper,two systems of spinel and perovskite（ferrite and stannate）sensor materials were synthesized by ultrasonic spray pyrolysis（USP）,and the sensor devices were successfully prepared and applied to detect acetone.This thesis mainly aims at the regulation of the micro-nano structure and the change of a variety of variable valence cations of ternary semiconductor oxides.At the same time,it assists the use of noble metal doping to design sensor-sensitive materials,with the main purpose of improving the utility factor,receptor and transducer functions of gas sensor materials.The main research works of this paper are as follows:1.The sulfonated polystyrene spheres（S-PS）were used as templates to synthesize three-dimensional Zn Fe₂O₄porous microspheres,which were doped with different concentrations of noble metal Pd to further improve the gas sensing performance.Compared with nanoparticles,the three-dimensional Zn Fe₂O₄porous microspheres had stable structure,uniform element distribution,excellent permeability,high utility factor,more reactive sites,and improved adsorption and desorption of gas molecules.Compared with undoped Zn Fe₂O₄porous spheres,the gas sensor based on Pd-doped three-dimensional Zn Fe₂O₄porous microspheres（Pd/Zn atomic ratio of 0.5%）achieved a response of 18.9 to 100 ppm acetone at the optimum operating temperature of 275°C,which was twice than that of the undoped Zn Fe₂O₄.Meanwhile,0.5%Pd-doped Zn Fe₂O₄exhibited the shortest response and recovery times（5 s and 54 s）,as well as the excellent long-term stability to acetone.The improved sensor performance was due to the combined effect of the electronic and chemical sensitization of the noble metal Pd,as well as the porous structure of the material.2.The ZnFe₂O₄ sensitive materials with dense solid,hollow,pleated hollow and nanosheet structures were obtained by adjusting the content of water-soluble green template Na Cl.The gas-sensing response of the pleated hollow Zn Fe₂O₄microsphere sensor to 100 ppm acetone at 200°C reached 95.0,and the response to the same concentration of acetone was higher than 30.0 at high humidity（90%RH）.Meanwhile,there was a response of 3.0 to lower concentrations of acetone（1 ppm）at 200°C,which indicating its great potential for detecting low concentrations of acetone in exhaled breath at high humidity.The gas-sensing performance of the dense solid Zn Fe₂O₄microsphere sensor to acetone（100 ppm）was only 9.7 at 275°C.The ultra-high performance of the pleated hollow Zn Fe₂O₄ microsphere sensor for acetone benefited from the pleated hollow structure,large specific surface area and superior porosity,which effectively increased the reactive sites of the sensor material and utility factor.3.The spinel ferrite AFe₂O₄（A=Zn,Ni,Cu,Co and Mn）with multi-cavity structure was synthesized with Na Cl as template/porogen,and carbonized dextrin as the structural framework.The multi-cavity structure had low density,large specific surface area,and superior porosity,which provided effective channels for the movement of gas molecules and promoted the rapid diffusion of gas molecules.AFe₂O₄ formed normal spinel（Zn Fe₂O₄）,inverse spinel（Ni Fe₂O₄,Cu Fe₂O₄,Co Fe₂O₄）and mixed spinel structures（Mn Fe₂O₄）after the A-site ions changed.At the same time,the gas-sensing properties of AFe₂O₄ for 100 ppm acetone were arranged in descending order:Zn Fe₂O₄>Ni Fe₂O₄>>Cu Fe₂O₄>Co Fe₂O₄>Mn Fe₂O₄.The results showed that the change of metal cations can make the spinel-structured ferrites exhibit distinct different gas-sensing properties.The highest gas-sensing responses of Zn Fe₂O₄ and Ni Fe₂O₄ with multi-cavity structure to 100ppm acetone were 25.0 and 24.3 at 250°C and 175°C,respectively.The reason was that the existence of Zn and Ni ions leaded to the increase of the relative atomic ratio of Fe³⁺/Fe²⁺,the increase of Fe³⁺octahedral sites strongly adsorbed oxygen ions(Fe³⁺-O bonds are stronger than Fe²⁺-O bonds),which improved the chemisorption capacity of oxygen.4.The solid,core-shell,double-shell and single-shell Sn O2/Zn Sn O3 composite microspheres were synthesized by ultrasonic spray pyrolysis and controlling the content of sucrose.Compared with the other structures,the double-shell hollow Sn O2/Zn Sn O3microspheres had a response of 30.0 to 100 ppm acetone at the optimal operating temperature of 290°C.At the same operating temperature and concentration,the response value was twice than that of the dense solid Sn O₂/Zn Sn O₃sensor（S=15.0）.In addition,the sensor with double shell structure exhibited high gas selectivity and long-term stability to acetone.The significant improvement in sensing performance of the double-shell hollow Sn O₂/Zn Sn O₃sensor for acetone can be attributed to the synergistic effect of the double-shell hollow and the mesoporous structure.The material had good porosity,large specific surface area,many reactive sites and high utility factor,which effectively improved the response value of the sensor.This paper systematically studies the relationship between the response values,gas selectivity of the ternary semiconductor oxides（ferrite and stannate）and the micro-nano structure,crystal structure and cation change.It is clear that the changes in the above factors are beneficial to the improvement of sensor performance.At the same time,the gas sensing mechanism of ternary semiconductor oxides is deeply studied,which establish a certain experimental and theoretical foundation for the construction of advanced and efficient semiconductor oxide gas sensors.