Reasearch On The Acetone Sensing Properties And Mechanism Of WO₃ Modified By Noble Metals

As an important component of human exhaled gases,acetone is an important physiological marker of type I diabetes and its content is positively correlated with blood glucose concentration.Therefore,the exhalation analysis of acetone can be used for the rapid screening of diabetes,early prevention and the daily self-diagnosis for patients.The preparation process of tungsten trioxide gas sensing material is simple,and it has a good gas responsive performance to various gases.At present,it has been used for gas sensing of acetone.In this thesis,WO₃ nanoparticles were prepared via an acidification method.Noble metal elements（Pd,Pt and Rh）were loaded on the surface of WO₃ nanoparticles by an impregnation method based on the traditional electron adsorption mechanism.Through XRD,SEM,TEM,XPS and TPR characterization methods,WO₃ nanoparticles and noble metal elements modified WO₃ nanoparticles were characterized and analyzed in detail.The results show that the WO₃ nanoparticles have monoclinic phase,large mesopores and high specific surface area,and the noble metal loading does not change the surface morphology and pore structure of the WO₃ nanoparticles.The dynamic gas distribution test system was used to test the influence of different metal loadings and different working temperatures on the gas sensing performance of acetone,and the stability of the sensor under working temperature was tested for a long time.The results show that the metal loading significantly improves the gas sensing properties of WO₃ to acetone,and the gas sensing response of WO₃ to acetone first increases and then decreases with the increase of the loading amount.Further increasing the load of noble metals,the response of the sensor to acetone decreases due to the Cl elements and the deterioration of noble metal（Pd,Rh）loading or the aggregation of surface noble metal loading（Pt）.The gas sensing ability of WO₃ to acetone increases with the increase of operating temperature,while the gas sensing ability of noble metal-loaded WO₃ to acetone increases first and then decreases with increasing operating temperature.At the same time,noble metal-loaded WO₃ nanoparticles have good repeatability and stability.By analyzing the resistance behavior of oxygen partial pressure and the role of oxygen in the gas sensing response of acetone were analyzed and the gas sensing response mechanism of acetone was explored.The gas sensing response mechanism of WO₃ and noble metal-loaded WO₃ to acetone is not completely the same.The response of WO₃ to acetone is mainly caused by the reaction with adsorbed oxygen;the adsorption of oxygen on the surface and the catalytic action of PdO and WO₃ both affect the sensing properties of PdO-WO₃;the main sensitization of Pt-WO₃ may be caused by redox of Pt nanoparticles;the loading of Rh promotes the electronic interaction between WO₃ and oxygen and the surface activity is greatly enhanced.The main sensitization may be caused by the electron coupling effect of heterojunction between WO₃ and Rh₂O₃.In this thesis,the investigation of gas sensing properties and mechanism of noble metal modified WO₃ nanoparticles to acetone have laid the foundation for the development of high performance acetone gas sensor.In order to develop the acetone sensor that is closer to the actual application of breath analysis,further research should be conducted on improving the sensor’s immunity to humidity and the selectivity of acetone.