Research On Oxide Semiconductor Heterostructures And Their Gas Sensing Properties

Acetone,as one kind of common organic solvents and important raw materials,is widely applied in the industrial production.However,it is quite flammable,explosive and irritant,which makes it important to detect the leakage of acetone in real time for industry safety and human health.In addition,acetone is recognized as an exhaled biomarker of diabetes.Consequently,the effective detection of acetone is of great importance for painless diagnosis of diabetes.In a word,it is imperative to develop acetone sensors with extraordinary sensing performances.Due to the advantages of simple structure,low price and adjustable performance,oxide semiconductor based gas sensor has become the best candidate to detect acetone gas.In this paper,we focused on the?-Fe₂O₃ and ZnO-based sensing materials to improve their sensing properties.Besides the structural optimization,several methods were used to modify the surface of matrix,such as the construction of metal-semiconductor,n-n type and n-p type semiconductor-semiconductor heterostructures.Additionally,the mechanism of the enhancement on sensing performances has been discussed.The main work is summarized as follows:?1?Porous?-Fe₂O₃ microflowers,which were composed of large numbers of nanoparticles,were successfully synthesized through a simple ethanol-mediated method.The results of gas sensing test indicated that the sensor based on porous?-Fe₂O₃ microflowers exhibited a higher response of 14.5 at 210°C,which is 2 times higher than that of?-Fe₂O₃ nanoparticles.Meanwhile,the response and recovery time were 1 s and 39 s for porous?-Fe₂O₃ microflowers,while in terms of?-Fe₂O₃nanoparticles,the times consumed were as long as 7 s and 172 s,respectively.The optimization of the structure of porous?-Fe₂O₃ microflowers improved the receptor function,transducer function and utility efficiency of oxide semiconductor.?2?The Pt nanoparticles were used for modifying the bare?-Fe₂O₃ nanospheres and their impacts on the performances of oxide semiconductors were well studied.First of all,the pure?-Fe₂O₃ porous nanospheres with an average diameter of 300 nm were synthesized by a simple water-bath method.Then,the Pt-loaded?-Fe₂O₃ porous nanospheres were obtained through an impregnation route and the size of Pt nanoparticles was about 5 nm.The results of gas sensing test indicated that the response of the pure?-Fe₂O₃ nanospheres-based sensors was 10.4 at 250°C.After surface modification,the optimal working temperature of the sensor based on Pt-loaded?-Fe₂O₃ was decreased to 220°C.Moreover,the response towards acetone was 27.2,which is 2.6 times higher than that of pristine?-Fe₂O₃.The superior performances of Pt-loaded?-Fe₂O₃ were not only attributed to the porous structure,but also due to the electronic and chemical sensitization of Pt nanoparticles.?3?Through the construction of n-n type heterostructures by replacing the noble metals with other oxide semiconductors,not only the sensing performances were optimized,but also the roduction cost was decreased.On the basis of ZnO flower-like hierarchical structures,the ZnFe₂O₄/ZnO heterostructures were successfully prepared using Fe?NO₃?₃ aqueous solution.Compared with the pure ZnO,the sensor based on Zn Fe₂O₄/ZnO microflowers showed a higher response value and a lower working temperature towards acetone.The optimal working temperature was decreased by100°C,which is favorable for the power consumption.The synergistic effect as well as the formation of the heterojunctions which formed at the interfaces between Zn Fe₂O₄ and ZnO would largely promote the receptor function and transducer function of ZnO-based materials,leading to the enhanced sensing properties eventually.?4?On the basis of ZnO hollow structure,the NiO/ZnO n-p hetero-hollow spheres were obtained through a two-step solution route.The NiO nanoparticles adhered to the surfaces of Zn O with a discrete but not continuous configuration.The results showed that at the temperature of 275°C,the NiO/ZnO composites exhibited a desirable value of 29.8 towards acetone,which was as 4.6-fold high as pure ZnO hollow spheres.Besides that,the response and recovery time were only 1 s and 20 s for NiO/ZnO composites,which was really fast.Specially,under high humidity conditions?90%RH?,the NiO/Zn O hybrids still exhibited a low detection limit,which would meet the practical requirements for diagnosing diabetes.