Preparation And Performance Of One-Dimensional Semiconductor Oxide Based Methanol Gas Sensors

Methanol?CH₃OH?is a commonly used organic solvent.It is colorless and volatile.It can cause itchy skin,headaches,decreased vision,metabolic acidosis,and formic acidemia.Therefore,it is necessary to detect the methanol gas in the surrounding environment.Semiconductor oxide-based sensors have high sensitivity,low detection temperature,good repeatability,and long-term stability,making them the best choice for methanol gas detection.However,the current methanol gas sensors still have disadvantages such as high operating temperature,low sensitivity,and poor stability.In this thesis,CeO₂ and ZnO nanofibers are prepared by electrospinning,supplemented with hydrogenation annealing treatment or modified with impurity element doping?such as Pd and Ce elements?.The obtained samples were characterized by XRD,Raman,SEM,TEM and XPS,as well as the methanol gas sensitivity tests.With the help of the mechanism analysis,the theoretical basis and experimental methods were explored for improving the detection performance of methanol gas,so as to obtain a high-performance methanol gas sensor.The specific research contents of this thesis are as follows:?1?Hydrogenation of CeO₂ nanofibers and study on their methanol gas sensing performance.CeO₂ nanofibers were synthesized by electrospinning,then annealed in the hydrogen atmosphere at different temperatures.The effects of hydrogenation treatment on the structure,morphology and methanol gas sensitivity were investigated.It is found that the crystalline structure and nanofibre morphology of CeO₂ are not altered by hydrogenation treatment between 180?and 680?.The methanol gas sensitivity tests indicate that the hydrogenation treatment significantly improves the gas sensitivity of the sample,and the detection performance of the sample for methanol increases with the increase of the hydrogenation treatment temperature.When the hydrogenation temperature reaches 680?,the CeO₂-H-680?sample shows the highest response?3.95?to 100 ppm methanol at 200?,which is 2.3 times larger than that of the untreated CeO₂-P sample under the same conditions?1.70?.The origin of improvement of the methanol gas sensitivity of CeO₂ by hydrogenation can be ascribed to the increased content of Ce³⁺ions in CeO₂ and thus the increased concentration of oxygen vacancies after hydrogenation.?2?Preparation of Pd-doped CeO₂ nanofibers by electrospinning and study on their methanol gas sensing performance.It is found that Pd doping does not change the crystal structure and morphology of CeO₂ samples,but enhances the detection ability of CeO₂ for methanol.When the Pd content is 3%,the 3%Pd-CeO₂ sample shows the highest response?6.95?to 100 ppm methanol at 200?,which is 4 times higher than that of the pure CeO₂ samples under the same conditions?1.70?.It also has good repeatability and long-term stability.Therefore,proper Pd doping can not only construct p-n heterojunctions of PdO/CeO₂,but also increase the concentration of oxygen vacancies in the material,which can play a synergistic role between heterojunctions and oxygen vacancies,thus significantly improving its methanol gas sensing performance.?3?Preparation of Ce-doped ZnO nanofibers by electrospinning and study on their methanol gas sensing performance.It is found that Ce doping makes the structure of ZnO nanofibers more compact,but does not alter the wurtzite crystal structure zinc oxide.Gas sensitivity tests show that Ce doping lowers the optimum detection temperature of ZnO for methanol from 250?to 225?.In addition,when the doping amount of Ce element is 1%,the 1%Ce-ZnO sample shows the highest response?9.35?to 100 ppm methanol at 225?,which is 3.3 times larger than that of the pure ZnO sample under the same conditions?2.80?.It also has good repeatability and long-term stability.Therefore,appropriate Ce doping can be used as active sites for gas adsorption,and can also control the concentration of oxygen vacancies in ZnO,thus improving the methanol gas sensing performance of ZnO.