Synthesis And Application Of Double-shelled Metal Oxide Hollow Spheres

At the same time of the development of industry and technology,the harm caused by air pollution and the leakage of toxic and harmful gases is becoming more and more worrying,Gas measurement equipment for real-time monitoring and detection of air quality has become one of the effective means to deal with air pollution.Gas sensors based on semiconductor metal oxides play an important role in the field of gas sensitivity because of their simple structure,low cost and adjustable performance.Intensive research for such sensitive materials plays an important role in the field of gas sensitivity.In recent years,with the rapid development of nanotechnology,semiconductor metal oxide materials with hollow micro-nano structures have been widely used in many fields such as photocatalysis,lithium-ion batteries,supercapacitors,and gas sensors because of their large specific surface area and many surface active sites.Moreover,as the number of shell layers of hollow micro-nano structures increases,their volume mass fraction,vibronic density,and specific surface area also increase,opening up new ways for the performance enhancement of metal oxides.In this thesis,the formation mechanism of single-shelled and double-shelled hollow structures is described by the controlled synthesis of double-shelled hollow micro-nano structures with metal oxides Fe₂O₃ and FeVO₄,and the gas-sensitive properties of composite metal oxides FeVO₄ are explored.The main research contents of this thesis are as follows:(1)Using the method of hydrothermal synthesis and annealing,Fe₂O₃ double-shelled hollow microspheres were prepared,with a diameter of about 0.9-1.0?m and a shell thickness of about 84 nm.The particle is a hierarchical micro-nano structure composed of structural units;the heat loss of precursor during annealing was 94.99%,and the formation of the hollow structure is the thermal decomposition process of the carbonaceous Fe₂O₃ precursor microspheres controlled by the heterogeneous shrinkage mechanism.(2)Based on the synthesis method of hydrothermal reaction and annealing,by adjusting the heating rate in the annealing stage,FeVO₄ single-shelled and double-shelled hollow microsphere structures were synthesized,with a size of about 800-900nm and a shell thickness of about 72 nm.The shell layers are all hierarchical micro-nano structures composed of FeVO₄ nanoparticles;the heating rate of the annealing process has a decisive influence on the shell layer structure.The FeVO₄ single-shelled hollow structure is obtained by the heating rate;the formation of the single-double-shelled hollow structure is a heterogeneous shrinkage mechanism controlling the thermal decomposition process of the carbonaceous FeVO₄ nano-precursor microspheres.(3)The gas sensor based on FeVO₄ single-shelled and double-shelled hollow structure has a sensitivity of 3.53 and 4.03,response time of 42 and 48 s,and recovery time of 200 and 205 s for 200 ppm ethanol,respectively,at an optimal operating temperature of 300?;FeVO₄ single-shelled and double-shelled hollow structures have a good concentration-sensitivity linear relationship in the ethanol concentration range of 1-50 ppm;the gas sensing processes and mechanisms can be explained by the principle of surface depletion layer based on semiconductor oxides.In summary:this thesis makes the design,preparation,characterization,and gas-sensitive testing of double-shelled Fe₂O₃ and FeVO₄ hollow microspheres have been made,which has significance for the development of hollow microspheres in the field of gas sensors.