Synthesis Of Porous Metal Oxide Materials By Polymer Template Method And Their Application In Gas Sensing

With the rapid development of modern social technology,high-performance gas sensors have attracted widespread attention in fields such as medical diagnosis,environmental protection,and food safety.Among various gas sensors,metal oxide sensors have become one of the most widely studied and used gas sensors due to their advantages such as low cost,high response recovery rate,and easy miniaturization.However,this type of sensor also has some practical problems in the detection process,such as high operating temperature and low sensitivity.Porous metal oxides have unique advantages in the field of gas sensing.Their porous structure is not only conducive to improving the specific surface area and exposing active site,but also can promote the rapid diffusion of gas molecules in materials,thus improving sensitivity and response/recovery speed.In addition,the functionalization of noble metal components can serve both electronic and chemical sensitization,thereby reducing the working temperature and further improving the sensitivity of the material.Based on the above ideas and combined with the practical application of gas sensing,this paper conducts research on the synthesis of porous metal oxide materials using polymer microsphere template method and its application in gas sensing.（1）A simple polymerization induced aggregation strategy has been proposed to synthesize uniformly sized Si doped mesoporous WO₃（Si-m WO₃）microspheres.Firstly,the melamine formaldehyde resin prepolymer（MF prepolymer）was polymerized in the presence of hydrated silicotungstic acid（H₄Si W）to form uniform MF/H₄Si W hybrid microspheres.MF serves as a polymer template,and then the hybrid microspheres are converted into Si-m WO₃ microspheres through a simple thermal decomposition process.In addition,benefiting from the pore confinement effect,monodispersed Pd-decorated Si-m WO₃ microspheres（Pd/Si-m WO₃）were subsequently synthesized and applied as sensitive materials for the sensing and detection of hydrogen.Owing to the oxygen spillover effect of Pd nanoparticles,Pd/Si-mWO₃ enables adsorption of more oxygen anions than pure m WO₃.These Pd nanoparticles dispersed on the surface of Si-m WO₃ can promote charge transfer between Pd nanoparticles and WO₃ grains,thereby improving the sensitivity of H₂sensing.Therefore,the gas sensor based on Pd/Si-m WO₃ microspheres exhibits excellent selectivity and sensitivity to 50 ppm H₂ at relatively low operating temperatures 210℃)（R_a/R_g=33.5）,which is 30 times higher than the pure Si-m WO₃ sensor.To develop intelligent sensors,a portable sensor module based on Pd/Si-m WO₃combined with wireless Bluetooth connection has been designed,achieving real-time monitoring of H₂ concentration and opening up possibilities for the application of intelligent H₂sensors.（2）Three dimensional ordered macroporous LaFeO₃（3DOM-LaFeO₃）and bulk LaFeO₃（Bulk-LaFeO₃）were synthesized by simple polymethyl methacrylate（PMMA）template method and traditional sol-gel method,respectively.PMMA products are arranged in a long range ordered hexagonal shape,forming anti opal nanostructures.The surface area of 3DOM-LaFeO₃ obtained by impregnating metal precursors and calcining is 2.5 times that of Bulk LaFeO₃.The（HCHO）gas sensing performance of 3DOM-LaFeO₃ for formaldehyde was systematically studied.The results indicate that 3DOM-LaFeO₃ has excellent HCHO gas sensing performance,significantly superior to Bulk LaFeO₃.The obtained 3DOM-LaFeO₃ gas sensor has high sensitivity（R_g/R_a=6）to 10 ppm HCHO at 280℃,which is about twice higher than the Bulk-LaFeO₃ sensor.At the same time,the sensor has fast response recovery process,repeatability,and excellent selectivity,which can meet the requirements of practical applications.The enhancement of gas sensing performance is mainly due to its pore structure and large surface area,which can increase the adsorption capacity of gas and promote the diffusion of gaseous reactant molecules,thereby enhancing response and reducing reaction time.（3）This study used polymethyl methacrylate（PMMA）as a template to prepare LaFeO₃ with a three-dimensional ordered macroporous structure（3DOM）through a precursor solution impregnation method.After modifying 3DOM LaFeO₃ with Pt nanoparticles,the obtained Pt/LaFeO₃ composite material is used as a gas sensor for detecting HCHO.Thanks to the ordered macroporous structure and the sensitization of highly dispersed Pt nanoparticles,the prepared macroporous Pt/LaFeO₃ hybrid material has high sensitivity to HCHO at 220℃（R_g/R_a=7 vs 5ppm HCHO）,which is twice that of pure LaFeO₃.In addition,due to the unique catalytic effect of noble metal Pt nanoparticles,the activation energy of the reaction is reduced,so the working temperature of Pt/LaFeO₃（220℃）is also lower than that of LaFeO₃（260℃）.