The Preparation Of Zn₂SnO₄??-Fe₂O₃ Hollow Nanostructures And Their Gas Sensing Properties

Gas sensors based on simple binary oxide semiconductor nanostructures have been intensively investigated from synthesis,structural characterizations,property studies to device performances.In comparison to the simple binary oxides sensors,multi-cation metal oxides like perovskite or spinel structures?e.g.,ABO₃,or AB₂O₄,A,B:metal cations?would have more freedom to adjust the performance of the sensors by altering the compositions.Nanomaterials with hollow structures have attracted a great deal of interests due to their low density,large reaction surface area,high porosity and high surface permeability,which would make them have great application potentials in sensors fields.In this paper,we synthesize?-Fe₂O₃ hollow spheres,Zn₂SnO₄ hollow cube,Zn₂SnO₄ hollow spheres and La doped Zn₂SnO₄hollow nanofibers by hydrothermal method and electrospinning respectively.The main work is as following:1.Hematite??-Fe₂O₃?hollow spheres were prepared by a one-step hydrothermal reaction with ethylene glycol?EG?as a solvent and without template and used to fabricate the gas sensors.Structure and morphology of the products were characterized by X-ray diffraction,scanning electron microscopy and transmission electron microscopy.The results indicated that the as-prepared samples were?-Fe₂O₃hollow spheres with an average diameter of 250 nm,which were constructed by small particles with smooth surface and the diameter around 50-70 nm.The sensor based on?-Fe₂O₃ hollow spheres exhibited excellent sensing performance to methanol at280°C,and the response can be reached at 25 when the concentration as low as 10ppm.In addition,sensing mechanism of the sensor towards?-Fe₂O₃ hollow spheres was investigated.2.Uniform Zn₂SnO₄ solid and hollow microcubes are synthesized via hydrothermal method,and followed by an annealing process in air.The morphology and structure are characterized by SEM,TEM and XRD.In addition,a possible formation mechanism of these hollow microcubes is mainly discussed.According to the comparison of experimental results,the hollow Zn₂SnO₄ microcubes exhibit higher response and quicker response-recovery traits than these of solid nanocubes.Under the optimum operating temperature?260^oC?,the response of hollow microcubes sensor to 200 ppm acetone is 141.7,which is 3 times larger than that of solid nanocubes?41.9?.The significant decrease in response-recovery time is attributed not only to the surface accessibility obtained by the hollow architectures,but also to these nanoflowers are constructed by numerous of interweaving petal-like.3.Hollow and porous ZnO,SnO₂ and Zn₂SnO₄ spheres were synthesized by the hydrothermal synthesis using carbonaceous spheres as templates in combination with calcination.The structure,morphology and gas sensing characteristics of the resultant product were investigated by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?,Brunauer–Emmett–Teller?BET?and gas-sensing measurement device,and the results showed that the variety of reaction parameters such as size of the template and different precursor materials have important effects on the formation of the shell structure.Compared with the solid counterparts,the hollow structures of the obtained samples were exploited as gas sensors and exhibited improved sensing performance to a series of gases?especially with regard to acetone?.Moreover,sensitivity and response/recovery time of Zn₂SnO₄ hollow spheres to acetone were both higher than multilayered ZnO and SnO₂ core-shell,and compared the operating temperature?240^oC?of zinc oxide and stannic oxide,zinc stannate had lower operating temperature?200^oC?.The formation mechanism and acetone sensing mechanism of Zn₂SnO₄ hollow spheres were also discussed in detail.4.Hollow porous pure and La doped Zn₂SnO₄ nanofibers were synthesized via single capillary electrospinning technology and successfully used for gas sensors.The structure,morphology and size of nanofibers were characterized by XRD,SEM and TEM.Furthermore,gas sensors were fabricated and an investigation of acetone sensing properties had been conducted.Compared with pure Zn₂SnO₄ hollow nanofibers,the La doped Zn₂SnO₄ hollow nanofibers not only exhibited perfect sensing performance toward acetone with excellent selectivity,high response?131 for200 ppm?and fast response-recovery capability?7 s for adsorption and 9 s for desorption?,but also reduced the operating temperature from 240?to 200?.These results demonstrated that the special hollow porous La doped Zn₂SnO₄ nanofibers structures be used as the sensing material for fabricating high performance acetone sensors.The acetone sensing mechanism of La doped Zn₂SnO₄ hollow nanofibers was discussed too.