Study On The Sensitive Response Of Nanostructured CeO₂ To Volatile Organic Compounds Gases

Organic volatile gases are harmful to the environment and human health,and metal oxide semiconductor materials have been used in the detection of various volatile gases.As a rare earth N-type semiconductor metal oxide,CeO₂ has a broad prospect in the application of gas sensing materials due to its wide band gap and unique electronic structure.Moreover,many conclusions have confirmed that structural optimization of CeO₂ and doping transition metal modification can improve its sensitive response to organic volatile gases.In this paper,the microstructure,morphology,size,crystal structure and chemical composition of pure and V,Ni doped nanostructured CeO₂ were respectively studied by hydrothermal and coprecipitation methods.The selectivity,temperature,concentration,resistance variation,response and recovery time and stability of the prepared samples to the volatile organic compounds gases were studied through CGS-8 gas sensitive analysis system,this thesis mainly introduced in the followings:1.a polyhedral mesoporous CeO₂ was synthesized by one-step hydrothermal method and used for the detection of volatile organic compounds（VOCs）gases.Scanning electron microscopy（SEM）and transmission electron microscope（TEM）were used to observe the morphology,size and crystallite structure,and X-ray diffraction（XRD）,Raman spectroscopy（Raman）and X-ray photoelectron spectroscopy（XPS）were used to analyze the crystal structure and chemical composition,and automatic gas adsorption analyzer was used to analyze the pore size.CGS-8 gas sensing test system was used to analyze the gas sensing performance.Results show that the as-prepared CeO₂ presents a polyhedral mesoporous structure,and the main pore diameters are less than 4 nm.CeO₂ sensor has the best response temperature at 240℃.In the detection of 100 ppm methanol,formaldehyde,ethanol,ether,acetone,ethylene glycol and xylene,the highest response is 6.5 for acetone gas,and the response and recovery time are 16 s and 4 s,respectively.The sensor has high stability in 60-day period detection,and the relative standard deviation（RSD）is 2.0%.2.Vanadium（V）doped CeO₂ nanomaterials with different molar ratios（1:15,1:11 and 1:7）were prepared by hydrothermal method and applied to detect VOCs.SEM and TEM were used to observe the surface morphology,particle size and crystallite microstructure of the prepared materials,and XRD,Raman and XPS were used to analyze their phase composition and chemical composition.CGS-8 gas sensing test system was used to analyze the gas sensing performance.Results show that the prepared materials exhibit the polyhedral nanostructure.When the molar ratio of V doped CeO₂ is 1:11,the best performance obtained,and its optimal working temperature is 230℃.In the detection of 100 ppm acetone,ethanol,methanol,isopropanol,ethylene glycol,ether,xylene and formaldehyde,the highest response is12 for acetone gas,and the response and recovery time are respectively 15 s and 10 s.The sensor has high stability in the 60-d test period,and the RSD is 0.91%.3.CeO₂ nanoparticles doped with different molar ratios of Ni（0%,1%,2%,3%and 7%）were prepared by coprecipitation method and applied to the sensitive detection of VOCs.SEM and TEM were used to observe the surface morphology,particle size and crystallite microstructure of the prepared materials.XRD,Raman and XPS were used to analyze its phase composition and chemical composition.CGS-8gas sensing test system was used to analyze the gas sensing performance.Results show that the prepared materials present nano particles structure,and the doping of Ni will reduce the particle size of CeO₂.2%Ni doped CeO₂ sensor has the best response performance,the optimum operating temperature is 230℃,the sensitivity to 10 ppm ethanol is up to 28,which is about 20 times higher than the sensitivity（1.43）of pure CeO₂ sensor（at 250℃）,and the response time and recovery time are respectively 16s and 1 s.In addition,in the range of 0.1-2000 ppm,the response shows a good linear relationship（R²=0.9977）.At the same time,the sensor has good cycle stability（RSD=1.42%）in the 60-d test cycle.