Preparation Of Zinc Ferrite Nanostructures And Its Gas-sensing Properties

The composition and content of exhaled gases from the body can mark certain diseases.And acetone in exhaled breath is widely recognized as one of the markers of diabetes.At present,the detection methods of acetone gas mainly include gas chromatograph and mass spectrometry.However,these methods are not suitable for the preparation of portable acetone sensors due to their large volume and complicated operation.The semiconductor sensor has become one of the means to detect the acetone gas because of its small size,easy operation and good stability.At present,TiO₂,WO₃,ZnO and other gas sensitive materials are used to detect acetone.As a kind of spinel structural materials,ZnFe₂O₄ has the presence of oxygen defects in the crystal cells.In the field of magnetic fluid,photocatalysis and gas sensing,it has attracted extensive attention.The synthesis methods of ZnFe₂O₄ nanomaterials have been reported,which include sol-gel method,solid-phase method,combustion method,etc.The nanostructure of ZnFe₂O₄includes nanosheets,nanorods and hollow nanospheres.However,the hollow hierarchical structure of ZnFe₂O₄ are relatively less reported.In this thesis,ZnFe₂O₄ nanoparticles and nanosheets-assembled ZnFe₂O₄ hollow spheres were prepared by hydrothermal synthesis method.And noble metal was used to activate nanosheets-assembled ZnFe₂O₄ hollow spheres.In this way,the response of the gas sensing materials to acetone had effectively improved.The nanosheets-Assembled ZnFe₂O₄ hollow prepared by hydrothermal method exhibited a better gas sensitivity than that of ZnFe₂O₄ nanospheres.The nanosheets-assembled ZnFe₂O₄ hollow spheres with hierarchical structure had better response to acetone at 150-250?.When the working temperature was 175?,the gas sensor had response to 0.8 ppm acetone gas?determine the characteristic concentration of diabetes?.In this part,we also studied influence of humidity?0%-100%?on the response to acetone.The response of the sensor was not obviously changed when the humidity changed from 0%to 75%whereas it was significantly reduced when the humidity increased from 75%to 100%.In this thesis,we used NaBH₄ at room temperature to activate Pt on the surface of nanosheets-assembled ZnFe₂O₄ hollow spheres.The results showed that the acidic solution destroyed nanostructure of ZnFe₂O₄ during the activation process.With the increase of Pt content,the thickness of ZnFe₂O₄ hollow spheres increased.Gas test results show that Pt-ZnFe₂O₄ had the best response to acetone when the Pt content was 1.5%.Although Pt destroyed the nanostructure of the materials,it still improved the sensing properties of the material to acetone.At the optimal operating temperature of 175?,the effect of different humidity on the sensing performance was studied.In addition,the selectivity of the material is investigated.In the end,the effects of Ag content and activation process on the morphology of the ZnFe₂O₄ hollow spherical were studied by AgNO₃.With the increase of Ag content,the damage to the surface nanostructure was more serious,but the hollow spherical structure was basically preserved.The experimental results showed that the gas sensing performance of 0.25%Ag-ZnFe₂O₄ hollow spheres was the best,and the sensor response to 0.8 ppm acetone was 1.47.0.25%Ag-ZnFe₂O₄ sensor also showed good selectivity and humidity stability.