Synthesis And Gas Sensing Properties Of AB₂O₄-type Composite Oxide Hollow Nanostructures

Under the new era,with the rapid development of society and the gradual improvement of people's living quality,more and more attention has been paid to environmental problems,which puts forward higher requirements for the detection and monitoring of various toxic,harmful,flammable and explosive gases.Semiconductor oxide gas sensors have attracted much attention because of their low cost,simple structure and excellent gas sensitivity.At present,in addition to further improving the structure and gas sensing properties of SnO₂,ZnO and other traditional semiconductor oxide sensitive materials,exploring the application of mixed valence complex oxides in gas sensing field is one of the important development trends in gas sensor field.Gas sensing performance of gas sensors often depends on sensitive materials,and the structure of sensitive materials is an important guarantee to give full play to their performance.Because of its unique structure and micro-morphology,hierarchical hollow nanostructure not only maintain the high specific surface area of hollow structure,but also can rapidly transfer mass on the surface of materials through its micro-porous structure,which has broad application prospects in gas sensors,energy,biomedicine,catalysis and other fields.Therefore,the in-depth exploration of the synthesis,growth process and formation mechanism of hierarchical hollow nanostructures of composite oxides is of great significance for further research and development of new gas sensing materials and improvement of gas sensor performance.In this paper,AB₂O₄-type composite oxides?CoFe₂O₄,NiCo₂O₄?were used as research objects to realize the application of controllable synthesis of hierarchical hollow nanostructures in the field of gas sensing.The hierarchical double-shelled structure of CoFe₂O₄ and NiCo₂O₄ hollow nanospheres were prepared by solvothermal synthesis,and their morphology and structure were characterized in detail.The formation process and structure of the double-layer hollow structure were described.The growth mechanism and the effect of complex hollow structure on the gas sensing properties of materials are explored.The main research contents are as follows:?1?Single-shelled and double-shelled hollow CoFe₂O₄ nanospheres were synthesized by solvothermal synthesis and post-annealing.The effect of ethanol content in solvents on the morphology of the products was investigated.The formation process and growth mechanism of Single-shelled and double-shelled hollow structure of CoFe₂O₄ were described by characterizing the morphology and structure of products at different stages.?2?Solid,single-shelled and double-shelled hollow NiCo₂O₄ porous nanospheres were successfully constructed by controlling the heating rate of annealing process using the combination strategy of solvothermal synthesis and post-annealing.The formation process and growth mechanism of single-shelled and double-shelled hollow structure of NiCo₂O₄ were described by characterizing the crystal structure,morphology and size of the products at different stages.?3?Single-shelled and double-shelled hollow CoFe₂O₄ nanospheres were used as sensitive materials to fabricate side-heating gas sensors,and the gas sensing characteristics of the aged devices were tested.By measuring the gas sensitivity of NH₃,LPG,H₂S and SO₂ in the temperature range of 100 ⁰C-320 ⁰C,240 ⁰C is determined to be the optimum working temperature of the gas sensor.Under this working temperature,the gas sensor has good sensitivity and selectivity to NH₃,especially the sensitivity of double-shelled hollow CoFe₂O₄ nanostructure to NH₃ at 100 ppm concentration reaches 0.697,the response-recovery time of 20 ppmNH₃ gas is 19.6 s and 12.1 s,respectively.Double-shelled hollow CoFe₂O₄ nanomaterials have high sensitivity to NH₃ gas,short response-recovery time,reversibility,recyclability and persistent detection ability.Furthermore,the reasons for the excellent gas sensing performance of the double-layer hollow CoFe2O4 gas sensor are analyzed and discussed.Because of its unique hierarchical hollow multilayer structure,CoFe₂O₄ gas-sensing materials have high specific surface area(121 m²g^-1)and reasonable pore size structure,and high structural stability.While exposing more surface active sites,it ensures that gas molecules can quickly diffuse to the surface of materials,and ultimately improves the sensitivity and response recovery characteristics of materials.In this paper,a lot of basic research work has been done on the controllable synthesis of CoFe₂O₄ and NiCo₂O₄ micro-nanostructures and the gas-sensing properties of CoFe₂O₄,which is of great significance for further exploration of its application in the sensing field.