Synthesis And Modification Of Rare Earth CeO₂ Nanomaterials And Gas-Sensitive Properties In Acetone

CeO₂ is a kind of cheap rare earth oxide,among which Ce³⁺and Ce⁴⁺have the phenomenon of mutual electron transition.Therefore,CeO₂ has the characteristics of strong oxygen absorption/release capacity,rich oxygen vacancy,easy oxidation and high ion mobility.These unique properties make CeO₂ widely concerned in gas sensing.In this paper,CeO₂ gas sensitive materials were prepared by hydrothermal method,and the influence of calcination temperature on gas sensitive properties was investigated to determine the optimal reaction conditions.On this basis,from the perspective of increasing sensitivity,improving selectivity and stability,CeO₂ was modified to prepare CuO-CeO₂ and NiO/CuO-CeO₂ composite materials.The results show that the composite prepared in this paper is sensitive to acetone gas and has a good application prospect in the analysis and detection of acetone.The specific work is as follows:(1)CeO₂ nanomaterials were prepared by hydrothermal method with cerium nitrate hexahydrate as raw material and sodium hydroxide as precipitant.The effect of calcination temperature on gas sensitive properties of CeO₂nanomaterials was investigated.When the calcination temperature is 700?,the gas sensitive performance of CeO₂ nanomaterials is the best.XRD,SEM,UV-vis,XPS,BET and Mott-Schottky curves were used to characterize the materials.The results showed that the grain size of CeO₂ nanomaterials was 18.3 nm,the band gap width was 3.153 e V,the specific surface area was 19 m²/g,and the carrier density was 5.5×10²⁰cm^-3.At the operating temperature of 250?,The sensitivity of CeO₂ nanomaterials to acetone gas is higher than that of other target gases,and the sensitivity to 100 ppm acetone gas is 2.2,with short response time(14 s)and good stability.(2)In order to enhance the gas-sensitive response of CeO₂ nanometer materials to acetone gas,p-type metal oxide CuO was compounded with it to prepare CuO-CeO₂ composite materials with p-n heterojunction.The influences of hydrothermal temperature,hydrothermal time,calcination temperature and the molar ratio of Ce and Cu on the gas-sensitive properties of CuO-CeO₂ composites were investigated.The optimal process conditions were determined as follows:hydrothermal temperature 160?,hydrothermal time 12 h,calcination temperature 700?,and the molar ratio of Ce and Cu 3:1.XRD,SEM,TEM,UV-vis,XPS,BET and Mott-Schottky curves were used to characterize the materials.The results show that the CuO-CeO₂ composite has a smaller grain size(16.8 nm),a larger specific surface area(38 m²/g),smaller band gap width(1.634 e V)and larger carrier density(3.4×10²¹cm^-3)than pure CeO₂.CuO-CeO₂ composite has a good gas-sensitive property to acetone gas,and its sensitivity to 100 ppm acetonevgas is 95,which is 43 times higher than that of pure CeO₂.The enhancement of gas-sensitive performance was caused by the increase of specific surface area of CuO and CeO₂ and the p-n heterojunction formed on the interface between them.(3)In order to further improve the gas-sensitive response of the material to acetone gas and reduce the working temperature,metal oxide NiO was introduced to prepare NiO/CuO-CeO₂ composite.XRD,SEM,TEM,UV-vis,BET,XPS were used to characterize the materials.The results show that the NiO/CuO-CeO₂composite has a smaller grain size(14.2 nm),a larger specific surface area(47m²/g)and smaller band gap width(1.126 e V)when the molar ratio of Ce,Cu and Ni is 3:1:3.NiO/CuO-CeO₂ composite has a good gas-sensitive performance against acetone gas,and its sensitivity to 100 ppm acetone gas can reach 340 at the operating temperature of 225?,which is 154.5 times higher than that of pure CeO₂ and 3.6 times higher than that of CuO-CeO₂,and the operating temperature is reduced by 25?.The enhanced gas-sensitive properties of NiO/CuO-CeO₂composites can be attributed to the formation of p-n heterojunction between p-type CuO and n-type CeO₂,and the introduction of metal oxide NiO increases the amount of adsorbed oxygen on the surface of the material.