An Efficient Solution-processed Synthesis Strategy For Metal Oxides And The Study Of Their Gas Sensing Properties

Metal oxide semiconducting materials have been widely used in various fields due to their portable size,low cost manufacturing and good performance for the applications,especially for gas sensors.As the core functional part of the metal oxide semiconducting gas sensor,it is of great significance to develop metal oxide gas sensing materials.Until now,most metal oxide materials with superior gas-sensitive properties still have several disadvantages such as complicated preparation processes with high energy consumption and expensive raw materials.This means that we need to continuously improve and optimize the synthesis technology and overcome these problems.This thesis mainly use the aqueous solution growing method for synthesizing the metal oxides.Here,water as the only solvent,with a group of environmental,high efficiency and simple strategies to design three metal oxide materials with special microscopic morphology:Co₃O₄,In₂O₃,and MnO₂.Then we do some gas sensitivity research on them and ideal results have been achieved.The main research content is as follows:?1?By using chemical bath deposition?CBD?,a cobalt precursor can be deposited on a glass substrate at 90?.After heat-treating in the air,the precursor can be convert to the nanoflower-like Co₃O₄ material with a grain size in 12 nm.The characterization results show that by changing the cobalt salt species and the water bath heating time,the microstructure morphology,pore size and gas sensitivity of Co₃O₄ products will be different.Gas sensitivity test results show that Co₃O₄ gas sensitive material prepared with cobalt acetate as the cobalt source and heated in a water bath for 9 h has the highest response to ethanol gas,which is1185%?200°C@100ppm?and has a good response-recovery time and stability.?2?First of all,amidoxime PAN nanofiber membranes with-OH were prepared by electrospinning and modified.Then the modified nanofiber membrane as a reaction substrate and immerse it into the chemical water bath?CBD?reaction system,and we can get the precursor product of cobalt,after heat-treating,a double-layered topography structure Co₃O₄material was obtained:the upper layer was made of numerous nanoflowers Coral structure,another layer is composed of hollow nanofiber networks and dispersed nanoflowers.XRD,XPS,and EDS results show that the organics were completely carbonized after heat treatment and the final product was only Co₃O₄.The gas sensitivity test results show that the Co₃O₄material prepared under heat treatment at 500°C has better gas-sensing performance,the response to ethanol can reach 1088%?230°C@100 ppm?,and has ideal response-recovery time and stability.?3?Indium nitrate was used as a raw material to directly obtain a precursor powder of indium by chemical bath deposition,and a cubic-shaped In₂O₃ material was obtained after heat treatment.The material has a large surface area and an ideal mesoporous structure,which is helpful for improving the gas sensing properties.The response to NO₂ gas at a working temperature of 60°C can reach 384?10 ppm?,even at ultra-low concentrations?500 ppb?,a good response can be showed also.?4?The ?-type MnO₂ nanorods were prepared on a large scale by the hydrothermal method.The prepared nanorods with uniform morphology and grew well.The nanorods had a diameter of 50-60 nm and a length of 0.5-1.5?m.Gas sensitivity test results show that the material has better sensing effect on ethanol gas than traditional MnO₂ materials,and the response value can reach 1.53?200°C@100 ppm?.And it has good stability and repeatability.