Gas Sensing Properties Of Noble Metal Loaded Porous Metal Oxides For Organic Toxic Gases

Metal oxide gas sensing materials have many advantages,such as high sensitivity,low cost and long service life.They are widely used in various fields related to production and life.Among them,metal oxides represented by CuO,ZnO,Fe₂O₃,Co₃O₄ and NiO were often utilized as gas sensing materials to construct gas sensors.At present,in the field of gas sensing materials,a highly universal synthesis method and performance improvement method are needed to provide direction for the preparation of gas sensing materials with high performance.According to research at home and abroad,it is believed that the method of building a hierarchically porous structure can maximize the advantages of the material structure,the noble metal load by hydrothermal method can also further enhance the detect ability of toxic gases.Based on this,a hierarchical structure of basic carbonate,hydroxide and hydrate has been prepared by hydrothermal method.Metal oxides with hierarchically porous structure were constructed by calcining at high temperature.Simultaneously,the noble metal loads were carried out by hydrothermal method.The gas sensing properties of unloaded and loaded materials were tested.The effects of hierarchically porous structure,noble metal type,noble metal load method and precursor type on the gas sensing properties of metal oxide materials were systematically studied and the gas sensing mechanism of unloaded and loaded materials were also discussed.The main research work are as follows:?1?Hierarchically porous CuO was prepared by hydrothermal and calcining methods.The Au load experiment of CuO was also carried out.The composition,structure,morphology and porous characteristics of CuO and CuO/Au were studied,all gas detection indexes were tested.The test results show that the hierarchical structure can effectively improve the specific surface area of the material and the porous structure provides more gas channels,which is beneficial to the transmission and contact of the gases to be measured.The experiments show that noble metal loaded materials can greatly enhance the sensitivity for organic toxic gases and reduce the response-recovery time.?2?The ZnO flower-structure composed of porous nanosheets was prepared by hydrothermal and calcining methods.The Au/Pt loaded composites were also prepared by hydrothermal method and light impregnation method.Thermogravimetric Analysis?TGA?results show that the porous structure originated from the thermal decomposition of precursors.After the gas sensing performance test,the materials prepared by hydrothermal method performance better in various gas sensing performance indicators,because the hydrothermal method could provide a constant high temperature and appropriate high pressure for the load reaction.ZnO/Au composite has the better ability to detect organic toxic gases than ZnO/Pt composite.?3?Three kinds of iron metal oxides,Fe₂O₃,Co₃O₄ and NiO with different morphology and similar specific surface area were prepared by hydrothermal and calcining methods.TGA results show that different precursor types lead to different average pore sizes.Because the precursor of Co₃O₄ is alkaline cobalt carbonate and the mass loss of heat is the most,so the average pore size is the largest.The gas sensitivity test showed that the three kinds of iron metal oxides had obvious response to common organic toxic gases,while Co₃O₄ exhibited the best performance.The prepared metal oxide gas sensor can resist the interference of humidity and light,it has the ability of continuous detection.?4?The gas sensing mechanisms of loaded and unloaded materials were compared.The noble metal loaded composites can intensify the physical and chemical reaction between material surface and target gas,it could accelerate the transfer of electrons in the material.As a reaction activation center,noble metal particles reduce the energy required for gas sensing reaction and show better detection performance for organic toxic gases.