Controllable Synthesis Of CeO₂ Nanocrystals And Their Room Temperature Gas Sensing Properties

Gas sensors are electronic devices that can transform gas composition and concentration changes into electrical signals for detection,which it has a wide range of applications and a broad development prospect.The core of sensors is sensitive materials,whose size,morphology,and structure directly affect device performance.As a well-known light rare-earth oxide,CeO₂ has a wide rich application prospect due to that the preparation method of CeO₂ material is green and simple,the raw material is economical and available,excellent stability,high redox performance,and extremely abundant oxygen vacancies.The key issues with different CeO₂ materials are poor conductivity and difficulty in recombination of electron holes.Researchers usually use doping other materials to improve performance,while the research on gas sensing applications using pure CeO₂ nanomaterials is not yet mature.In this paper,improvements have been made in controlling the morphology of CeO₂ nanocrystals,controlling their exposed crystal surfaces,and doping precious metals to improve the performance and stability of their room temperature gas sensor materials.The specific results are as follows:1.CeO₂ nanocubes,nanopolyhedra,and nanorods with different morphologies were synthesized with a simple green hydrothermal method by controlling the hydrothermal temperature and the amount of NaOH.The three different morphologies of CeO₂ nanocrystals were used to make gas-sensitive sensors tested and analyzed,respectively.The gas-sensing performance tests revealed that all three of CeO₂ sensors have good gas-sensitive responses to NH₃,and the CeO₂ nanorods have the best sensitivity at room temperature compared to the nanocubes and nanopolyhedra.The excellent gas-sensitive performance of the morphology of CeO₂ nanorods was experimentally demonstrated to be mainly due to the abundant surface defects and oxygen vacancies,as well as the strong active{110}exposure surface.2.In order to improve the room-temperature gas-sensitive response of CeO₂,the CeO₂ nanorods were doped with Pt.After a detailed characterization of CeO₂nanorods doped with different ratios of Pt by a two-step method,room-temperature gas-sensitive tests were carried out,and the mechanism was investigated.It is found that the Pt-doped CeO₂ has a more obvious response to NH₃ at room temperature,and the 4%Pt-CeO₂ material is sensitive to ammonia and has a faster response recovery and higher gas-sensitive response.It is concluded from the analysis that the improved gas-sensitive performance is mainly due to the synergistic effects of material morphology,oxygen vacancies,and Pt-induced chemical sensitization.3.In order to optimize the CeO₂ nanorods gas sensing response,the nanorods obtained by the hydrothermal method were calcined at 400°C,600°C,and 800°C,and then tested for different gases at room temperature;good gas-sensitive performance was found for DMA gas.It was found that the gas-sensitive response of CeO₂ nanorods after calcination at 400°C was the best,showing not only good repeatability but also a fast response recovery time.It is concluded from the discussion that the improved gas-sensitive performance is mainly due to the combined effect of the rod-like structure of CeO₂,oxygen-rich defects,and the formation of surface heterojunctions.