Structure Design And Sensor Application Of Iron Nano-oxide Semiconductor Materials

With the rapid development of modern social-economic,it emerges more and more environmental issues,interior decoration with high levels of formaldehyde and air pollution have seriously threatened people's healthy life.The appearance of gas sensor has opened up a new way to solve these problems.As the core of the gas sensor,sensing material have been strong drivers of gas sensors growth.Metal oxide semiconductor gas sensors have the advantages of low cost,high sensitivity,simple structure and rapid response,etc.After long-term research,they have been widely used in medical treatment,biotechnology,catalyst and traffic safety.?-Fe₂O₃ as a typical n-type semiconductor has superior stability,corrosion-resistant and environment-benign features.It plays an important role in photocatalytic,lithium batteries and gas sensing.At present,?-Fe₂O₃ with different nanostructures have been fabricated successfully by various synthesis routes.And it's found that gas-sensing performance of oxide semiconductors are closely correlated with their crystalline size,composition,and morphology.Nevertheless,in terms of pure?-Fe₂O₃ still faces many problems such as poor sensitivity and inferior selectivity,which might limit its practical applications.Therefore,to find suitable ways to improve the gas-sensing properties is of particular importance.This paper is taking improving the performance of semiconductor gas sensor as goal,from?-Fe₂O₃ semiconductor nanomaterial's morphology control and doping modification angle embarking,using electrospinning technology to prepare one-dimensional?-Fe₂O₃ materials with different structures and components,and significantly improved the sensitivity,response and recovery behaviors and selectivity.The results obtained in this paper will also provide valuable basis for the development of semiconductor materials.The specific research content is as follows:1.Pure and Eu-doped?-Fe₂O₃ nanotubes and nanowires have been successfully synthesized through the electrospinning techniques.The structures,morphologies and chemical compositions of the as-obtained products were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,thermogravimetric and differential scanning calorimeter analyzer?TGA-DSC?and energy dispersive spectrum?EDS?,respectively.Gas sensors based on the above materials were made and a contrastive gas sensing study between nanotubes and nanowires was performed.It turned out that Eu doping could magnify the impact of morphology on gas sensitivity.At the optimum operating temperature of 240?,the sensitivity of pure?-Fe₂O₃nanotubes and nanowires towards 100 ppm acetone is almost the same?3.59/2.20?,but the sensitivity of 3.0 wt%Eu-doped nanotubes gas sensors can reach 84.05,which is2.7 times as high as that of nanowires sensors at the same doping ratio?31.54?.Moreover,the response and recovery time of the former?11 s and 36 s?is faster than that of the latter?17 s and 40 s?.And 3.0 wt%Eu-doped nanotubes sensors can also detect 0.1 ppm acetone.In addition,the gas sensor based on the two morphologies has a good linearity?0.1-500 ppm?and favorable selectivity in acetone detection.2.Pure and Pd-doped?-Fe₂O₃ porous tubular one-dimensional nanomaterials are synthesized by a facile electrospinning technique.The structure and chemical composition of the materials were analyzed by a series of characterization methods,such as XRD,EDS,SEM,transmission electron microscope?TEM?,X-ray photoelectron spectroscopy?XPS?,nitrogen adsorption/desorption?BET?and so on.Made corresponding gas sensors and meanwhile the influence of noble metal modification on gas sensitivity is analyzed.And the sensing mechanisms of this kind of sensor is discussed.The results reveal that the prepared?-Fe₂O₃ porous nanotubes possess large specific surface area(44.8 m²·g^-1)and the surface is dotted with large number of irregular pores,the average diameter of the pores is 23.4 nm.At the optimum operating temperature of 240?,the 3.0 wt%Pd-doped?-Fe₂O₃ porous nanotubes sensors exhibit superior performance in ethanol detection.The highest sensitivity reaches 65.4 for 50 ppm ethanol,and it present greatest enhancement of 27.2 times in response compared to the pure one?2.4?.Meanwhile,the response time and the recovery time are very short?8 s and 30 s,respectively?.Moreover,the detection limit is as low as 0.1 ppm.Beyond that,the sensors also show excellent selectivity,good long-term stability.The improvement of gas sensing performance is mainly attributed to the dramatic sensitization of the additional Pd components.3.In the present work,the acetone gas sensing material based on pure?-Fe₂O₃nanotubes,pure and Cu-doped?-Fe₂O₃ porous nanotubes were fabricated by electrospinning method.The structure and chemical composition of the product were studied by means of XRD,EDS,SEM and BET.Micro gas sensors based on the above materials were prepared,different Cu dopant concentrations are introduced to investigate the dopant's role in its structure and gas sensing performance.And the acetone sensing results demonstrate that the gas sensitivity of porous nanotubes is better than nanotubes.Moreover,when the doping concentration is low,Cu doping almost does not affect the materials'porous structures but when doping concentration is 5.0wt%,the number of pores on materials'surface decreased significantly.Under the optimum operating temperature of 164?,the micro gas sensor based on 3.0 wt%Cu-doped?-Fe₂O₃ porous nanotubes exhibits higher sensitivity?99.43/100 ppm?towards acetone.The response time is only 5 seconds,the recovery time is 18 s,and the lowest detection limit can be extended to ppb level?2.2/100 ppb?.Besides,the sensor also has good selectivity and repeatability.The enhancement of gas sensitivity is attributed to the porous tubular structure and high catalytic activity of the Cu additive.